Preface
The ngVLA Science Book describes the frontiers of discovery enabled by a next-generation
centimeter-wavelength interferometer with unprecedented sensitivity and angular resolution.
Realizing such a facility will require a substantial financial investment, and the commitment of thesefunds comes with a responsibility upon the project to fulfill this vision within funding and time
constraints. At this stage of the project, it is incumbent upon us to develop our facility concept to adegree where the investment required and the associated risks can be understood by both decision
makers and the project team.
This three-volume compendium describes the ngVLA Reference Design. The reference design is a
low-technical-risk, costed concept that supports the key science goals for the facility, and forms thetechnical and cost basis of the ngVLA Astro2020 Decadal Survey proposal. The compendium includes
a total of 55 technical documents and represents the work of more than 54 engineers and scientists
contributing to the project. While led by the project team at the National Radio Astronomy
Observatory, the author list includes many collaborators from the US and international radio
astronomy community who have contributed their expertise to the project. Many more havecontributed to the definition of the science case and science requirements, or contributed throughcritical review.
This technical compendium describes the system from end to end, and provides a snapshot of thetechnical development of the facility concept as of August, 2019. As the first technical baseline, it has
gaps and minor inconsistencies that will be addressed in advance of the system conceptual design
review, but it presents the clear and substantive progress that has been made in defining a realizable
ngVLA facility concept.
What is most important at this juncture is to have a viable concept for each subsystem that supports
the overall system and science requirements, enabling robust performance and cost estimates, and atechnical baseline for future trade studies. Alternate concepts that improve performance to key
parameters or reduce cost can, and will, be revisited as part of the conceptual design activities.
The volume of this compendium is indicative of the effort invested and the technical maturation of the
project. It is only through the documentation of our ideas that we identify the inconsistencies andgaps in our thinking, and the act of writing forces us to make multiple small decisions that sharpen ourconcepts and produce a realizable design. The development of this reference design gives us
confidence in our performance and cost estimates, the technical readiness of the design, and our ability
to achieve the transformational science described in the ngVLA Science Book.
With the realization of this technical concept, the ngVLA will uniquely tackle a broad range of highpriority scientific questions in modern astronomy, physics, chemistry, and biology, dramaticallyextending the scientific frontiers that are within reach of existing facilities. In doing so, the ngVLA willtransform our understanding of planet formation, the initial conditions for life, galaxy formation andevolution, and the physics of black holes, and will ultimately advance humanity’s understanding of thecosmos and our place within it.
Robert J. Selina
ngVLA Project Engineer
August, 2019For more information and updates, please see the digital version of this book that is available on the
ngVLA website.
Use the QR Code above, or visit us at https://ngvla.nrao.edu/page/projdoc.

Volume II
Preface
R. Selina

Part V: Antennas
Antenna: Preliminary Technical Requirements
020.25.00.00.00-0001-REQ-A
R. Selina
ngVLA Optical Reference Design: Analysis of the ngVLA Antenna Optical Design #6 with Ideal and Actual
Feed020.25.01.00.00-0001-REP-A
L. Baker
ngVLA 18m Antenna: Preliminary Design Document
101-0000-001-PDD-001
D. Chalmers
Short Baseline Array Antenna: Preliminary Technical Requirements
020.47.05.00.00-0001-REQ-A
R. Selina and D. Dunbar
ngVLA 6m Antenna: Concept Design Document
102-0000-001-CDD-001
D. Chalmers

Part VI: Antenna Electronics
Front End: Technical Requirements
020.30.03.01.00-0001-REQ-A
W. Grammer
Front End: Reference Design Description
020.30.03.00.00-0002-DSN-A
W. Grammer
Cryogenic Subsystem: Requirements
020.30.10.00.00-0001-REQ-A
D. Urbain
Cryogenic Subsystem: Reference Design Description
020.30.10.00.00-0002-DSN-A
D. Urbain
Integrated Receiver and Downconverters: Preliminary Technical Requirements
020.30.15.00.00-0001-REQ-A
M. MorganIntegrated Downconverters and Digitizers: Design Description
020.30.15.00.00-0002-DSN-A
M. Morgan
Digital Back End/Data Transmission System: Technical Requirements
020.30.25.00.00-0001-REQ-A
J. Jackson
Digital Back End/Data Transmission System: Reference Design Description
020.30.25.00.00-0002-DSN-AJ. Jackson, M. Luce, A. Erickson, E. Ford, and R. Selina
DC Power Supply: Preliminary Technical Requirements
020.30.50.00.00-0001-REQ-A
P. Lopez
DC Power Supply: Reference Design Description
020.30.50.00.00-0002-DSN-A
P. Lopez
Bins, Modules, and Racks: Preliminary Technical Requirements
020.30.55.00.00-0001-REQ-A
D. Gerrard, S. Sturgis, and J. Allison
Bins, Modules, and Racks: Reference Design Description
020.30.55.00.00-0002-DSN-A
D. Gerard, S. Sturgis, and J. Allison
Antenna Electronics Environmental Control System: Preliminary Technical Requirements
020.30.60.00.00-0001-REQ-A
S. Sturgis and J. Allison
Antenna Electronics Environmental Control System: Reference Design Description
020.30.60.00.00-0002-DSN-A
D. Gerrard, S. Sturgis, and J. Allison
Independent Phase Calibration System: Preliminary Requirements
020.45.00.00.00-0001-REQ-A
A. Erickson
Water Vapor Radiometer: Design Description
020.45.00.00.00-0002-DSN-A
A. Erickson

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

Antenna Preliminary Technical Requirements
020.25.00.00.00-0001-REQ-A-ANTENNA_PRELIM_TECH_REQS

Status: RELEASEDPREPARED BY
R. Selina
D. Dunbar, ngVLA Antenna IPT Lead

ORGANIZATIONElectronics Div., NRAO
ngVLA/NM-Ops, NRAO

DATE
2019-05-29
2019-03-29

APPROVALS
R. Selina,
Project Engineer

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-29

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.29 12:53:03 -06'00'

Asst. Director,
NM-Operations, NRAO

2019-07-29

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.29 12:53:18 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-29

2019.07.29
12:20:42 -06'00'

Page 1 of 45

Title: Antenna Preliminary TechnicalRequirements

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Date: 2019-07-29
Version: A

Change Record
Version

Date

AuthorAffected
Section(s)0.1

04/18/2017

R. Selina

All

0.2

04/24/2017

R. Selina

Appendix

0.3

05/02/2017

R. Selina

All

0.4

05/08/2017

R. Selina

5.3, 5.14,
5.17

0.5

05/09/2017

R. Selina

5.5, 5.6, 9

0.6

06/05/2017

R. Selina

5.9, 5.13,
5.14

0.7

07/07/2017

R. Selina

1.1, 2.1,
2.2, 3.2,
3.3, 5, 9,
10, 11.

0.8

07/24/2017

R. Selina

9, 13

0.9

08/28/2017

R. Selina,
D’Addario

All

0.91

09/06/2017

R. Selina

4.2

0.92

09/11/2017

R. Selina, M.
McKinnonAll

ReasonStarted first draft. Used ngVLA System
Requirements as a template, and pulled in‘Strawman’ requirements by P. Napier. Also
incorporates text and structure from ALMA34.00.00.00-006-C-SPE Version C.
Added coordinate system diagram by S.
Sturgis.
Updated efficiency tables. Added Verification
and Documentation sections. Revisions &elaborations throughout.
Incorporated feedback from T. Beasley.
Updated close packing text. Added
serviceability requirement. Updated lifecycle
text.
Incorporated feedback from W. Grammer.
Revised aperture efficiency requirements.
Added beam subtended half angle
requirement. Updated verification text, etc.
Updated MTBF, maintenance interval, slew
rates and environmental specifications.
Updated post June Workshop. Revised
aperture diameter to 18m. Updated
associated parameters to match. Updated
optical parameters consistent with Granet.
Added Requirements for Design and Safetysections. Added Requirements Summary.
Other minor additions.
Revised EMC requirements. Added EM
performance simulation requirements assuggested by D. Chalmers. Updated
coordinate system narrative to match Granet.
Added representative optical sketch. Other
misc. corrections throughout.
Incorporated input from NRAO-Internal(Napier, Jackson, Grammer, Sturgis, Kern,
Walker, etc.) and TAC (Tetsuo, Lamb,
Kantor, and D’Addario) review. Struck pathlength change requirements. Added focus
stability requirements. Rescoped EM analysis
and requirements.
Struck mount geometry req. ANT0212.
Incorporated comments from McKinnon and
Beasley. Edits to narrative throughout. Added
Design Life to KPP list.

Page 2 of 45

Title: Antenna Preliminary TechnicalRequirements

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Affected
Section(s)Version

Date

Author1

2017-09-12

R. Selina, M.
McKinnon

N/A

1.1

2017-10-12

R. Selina

4.2, 4.5,
4.9, 4.13,
4.15, 4.16,
7.3.2, 10.

2

2018-01-23

R. Selina

N/A

D. Dunbar

Doc
numberand Title,
3.4, 4.14.1,
4.14.2

2.1

2018-11-06

2.2

2018-11-14

D. Dunbar

2.1, 2.2,
4.13, 4.14,
8.1.4, 10

2.3

2019-05-29

R. Selina

3.2

A

2019-07-29

A. LearAll

Date: 2019-07-29
Version: A

ReasonFirst Release for Antenna Reference Design
contract.
Updated to address requested corrections
and questions from GDMS. Clarified MTBF
and M&C requirements. Correctedirregularities in references.
Second Release. Updated for the Antenna
Reference Design Contract.
Updated document number (SPE to REQ) to
conform to System Engineering protocol.
Updated Precision and Normal windvelocities to match System Level Spec.
Added additional reference docs. Updated
Environment Conditions to trace back to
ENV requirements (and not SYS Req).
Updated Electromag table and requirements
to match/point to EMC requirement doc.
Added additional applicable environmental
requirements. Updated Load Case Table(precision) wind loads to match lower
velocity (5 m/s).
Updated introduction materials to reflect
LBA inclusion in project scope.
Prepared PDF for signatures and release.

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Version: A

Table of Contents
1

Introduction ................................................................................................... 7

1.1
1.2

Purpose ................................................................................................................................... 7
Scope ...................................................................................................................................... 7

2

Related Documents and Drawings ............................................................... 8

2.1
2.2

Applicable Documents ........................................................................................................... 8
Reference Documents ............................................................................................................ 83

Overview of Antenna Technical Specifications .......................................... 9

3.1
3.2
3.3
3.4

Document Outline ................................................................................................................. 9
Project Background................................................................................................................ 9
General Antenna Description................................................................................................ 9
Summary of Antenna Requirements ................................................................................... 10

4

4.1
4.2
4.3
4.4
4.5
4.6
4.6.1
4.6.2
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
4.14.14.14.24.14.34.14.44.14.54.14.64.14.74.14.8
4.15
4.16
4.17
4.18

Antenna Functional and Performance Requirements ............................. 11

Operating Frequency Range................................................................................................ 11
Optical and Mounting Geometry ....................................................................................... 11
Allowable Design Volume & Mass ....................................................................................... 13
Number of Antennas ............................................................................................................ 14
Reflector Construction & Accuracy .................................................................................... 14
Pointing Accuracy ................................................................................................................ 14
Pointing Accuracy in Precision Operating Environment ................................................................ 15
Pointing Accuracy in the Normal Operating Environment ........................................................... 15
Focus Stability ...................................................................................................................... 15
Range of Motion .................................................................................................................. 15
Axis Rates ............................................................................................................................. 16
Stow Positions ...................................................................................................................... 16
System Noise Contributions ................................................................................................ 17
Solar Observations ............................................................................................................... 17
Spurious Signals/Radio Frequency Interference Generation ............................................. 17
Environmental Conditions ................................................................................................... 18
Precision Operating Conditions ........................................................................................................... 18
Normal Operating Conditions ............................................................................................................. 18
Limits to Operating Conditions ........................................................................................................... 19
Survival Conditions at Stow Position .................................................................................................. 19
Lightning Protection Requirements ..................................................................................................... 19
Seismic Protection Requirements ........................................................................................................ 20
Site Elevation............................................................................................................................................. 20
Vibration .................................................................................................................................................... 20
Maintenance and Reliability Requirements ....................................................................... 20
Monitor and Control Requirements ................................................................................... 21
Motion Limiting Features .................................................................................................... 22
Lifecycle Requirements ........................................................................................................ 225Interface Requirements .............................................................................. 23

5.1
5.2
5.3
5.4
5.5

Interface to the Foundation/Station ................................................................................... 23
Interface to the Electrical Infrastructure............................................................................ 23
Interface to the Fiber Optic Transmission System ............................................................. 23
Interface to Other External Cables and Piping ................................................................. 24
Interface to the Receiver Enclosure/Front End Electronics ............................................... 24
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5.6
5.7
5.8
5.9

Date: 2019-07-29
Version: A

Interface to the Back End Electronics ................................................................................ 24
Interface to Internal Cables and Piping ............................................................................. 24
Interface to the Cryogenic System ...................................................................................... 25
Interface to the Monitor and Control System ................................................................... 25

6
7

Subsystem Requirements ........................................................................... 26
Safety ............................................................................................................ 26

7.1
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5
7.3
7.3.1
7.3.2
7.3.3
7.3.4
7.3.5
7.3.6
7.3.7
7.4

General ................................................................................................................................. 26
Hazard Analysis .................................................................................................................... 26
Hazard Severity ........................................................................................................................................ 26
Hazard Probability ................................................................................................................................... 27
Hazard Risk Acceptability Matrix......................................................................................................... 27
Requirements on Operational Hazards.............................................................................................. 27
Hazard Analysis ........................................................................................................................................ 28
Safety Design Requirements................................................................................................ 28
Fire Safety .................................................................................................................................................. 28
Mechanical Safety ..................................................................................................................................... 28
Electrical Safety......................................................................................................................................... 29
Hydraulic & Pneumatic Safety ............................................................................................................... 29
Handling, Transport, and Storage Safety ............................................................................................ 29
Toxic Substances ..................................................................................................................................... 29
Confined Space ......................................................................................................................................... 29
Physical Security .................................................................................................................. 29

8

8.1
8.1.1
8.1.2
8.1.3
8.1.4
8.1.5
8.1.6
8.2
8.3
8.3.1
8.3.2
8.3.3
8.3.4
8.3.5
8.3.6
8.3.7
8.3.8
8.3.9
8.3.10Requirements for Design ............................................................................ 30

Analyses and Design Requirements..................................................................................... 30
Finite Element Structural Analyses ...................................................................................................... 30
Thermal Modeling and Analysis ............................................................................................................ 31
Stress Analysis and Load Combination............................................................................................... 31
Antenna EM Analysis Support............................................................................................................... 31
Control loop design and analysis ......................................................................................................... 33
Reliability, Availability, Maintainability Analysis ................................................................................. 33
Electromagnetic Compatibility Requirements ................................................................... 33
Materials, Parts and Processes ............................................................................................ 34
Type of Steel ............................................................................................................................................. 34
Stress relieving.......................................................................................................................................... 34
CFRP ........................................................................................................................................................... 34
Fasteners .................................................................................................................................................... 34
Paints........................................................................................................................................................... 34
Surface Treatment ................................................................................................................................... 34
Thermal Insulation ................................................................................................................................... 34
Rodent Protection ................................................................................................................................... 34
Name Plates and Product Marking ...................................................................................................... 34
Labels .......................................................................................................................................................... 35

9Documentation Requirements ................................................................... 36

9.1
9.2

Technical Documentation ................................................................................................... 36
Software and Software Documentation ............................................................................. 36

10
11
12

Verification and Quality Assurance ........................................................... 37
Key Performance Parameters .................................................................... 40
Appendix....................................................................................................... 41
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12.1
12.2
12.2.212.2.312.2.412.2.512.2.612.3
12.3.112.3.212.3.3

Date: 2019-07-29
Version: A

Abbreviations and Acronyms ............................................................................................... 41
Coordinate System ............................................................................................................... 42
Main Reflector (MR) Coordinate System........................................................................................... 42
Secondary Reflector (SR) Coordinate System.................................................................................. 43
Focal Plane Coordinate system ............................................................................................................ 43
Azimuth of the Antenna ......................................................................................................................... 43
Elevation of the Antenna........................................................................................................................ 44
Maintenance Definitions ..................................................................................................... 44
Maintenance Approach ........................................................................................................................... 44
Periodic Preventive Maintenance ......................................................................................................... 45
Overhaul .................................................................................................................................................... 45

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Title: Antenna Preliminary TechnicalRequirements

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NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

1 Introduction
1.1 Purpose
This document presents a preliminary set of technical specifications for the ngVLA antenna. Manyrequirements flow down from the preliminary ngVLA System Requirements [AD01], which in turn flow
down from the preliminary ngVLA Science Requirements.
The Science Requirements are presently being elaborated by the Science Advisory Council (SAC) and
Science Working Groups (SWGs), and are captured in a series of draft use cases. A preliminary analysisof these use cases, and the flow down recursively to the system and subsystem requirements, is reflectedin this draft.
NRAO desires a cost-effective solution for the antenna that can be manufactured in volume and installed
at remote locations. The optimization for value requires flexibility in key requirements until the cost andtechnical impact of the parameters are understood. These requirements are therefore consideredpreliminary until refined through feedback with the antenna designer.

1.2 Scope
The scope of this document is the ngVLA antenna element. This consists of the foundation, mounting
structure that provides for motion in azimuth and elevation, reflectors and their supporting structures,
drive system, and associated motion control electronics. All other instrumentation, including feed
antennas and receiving electronics, are outside the scope of this element, though interfaces must be
considered. This specification establishes the performance, functional, design, and test requirements
applicable to the ngVLA antennas.

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Title: Antenna Preliminary TechnicalRequirements

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NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of the Technical Specification shall be considered as a superseding requirement.
Ref. No.
AD01
AD02
AD03
AD04
AD05
AD06
AD07
AD08
AD09
AD10
AD11
AD12
AD13

Document Title
ngVLA Preliminary System Requirements
International Standard: Protection Against Lightning
Protection Against Electric Shock: Common Aspects
for Installation and Equipment
Electrical Standards for Industrial Machinery
Safety of Machinery: Electrical Equipment of Machines
Insulation Coordination for Equipment within LowVoltage Systems
Hydraulic and Pneumatic Fluid Power Safety
Occupational Safety and Health Standards for
General Industry
Occupational Safety and Health Standards forConstruction
Military Handbook, Reliability Prediction of Electronic
Equipment
Non-Electronic Parts Reliability Data
Electromagnetic Compatibility
Offset Dual Reflector Antenna

Rev/Doc. No.
020.10.15.10.00-0003-REQ
IEC 62305:2010
IEC 61140:2016
NFPA 79
IEC 60204:2016
IEC 60664
ISO 4413
29 CFR Part 1910
29 CFR Part 1926
MIL-HDBK-217F
NPRD-95
IEC 61000-3-5
Mitsuguch et al., IEEE APS 1976,
DOI 10.1109/APS.1976.1147539

2.2 Reference Documents
The following references provide supporting context:
Ref. No.
RD01

Document Title
Essential Radio Astronomy

RD02

RFI Emission Limits for Equipment at the EVLA Site

RD03

Designing Classical Offset Cassegrain or GregorianDual-Reflector Antennas from Combinations of
Prescribed Geometric Parameters

RD04

USGS Coterminous US Seismic Hazard Map – PGA
2% in 50 Years

RD05

System Electromagnetic Compatibility and Radio
Frequency Interference Mitigation Requirements
System Environmental Specifications

RD06

Page 8 of 45

Rev/Doc. No.
http://www.cv.nrao.edu/course/
astr534/2DApertures.html
EVLA Memo #106. Perley,
Brundage, Mertely.
Christophe Granet, IEEE
Antennas and Propagation
Magazine, Vol. 44, No. 3, June
2002
ftp://hazards.cr.usgs.gov/web/
nshm/conterminous/2014/
2014pga2pct.pdf
020.10.15.10.00-0002-REQ
020.10.15.10.00-0001-SPE

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

3 Overview of Antenna Technical Specifications
3.1 Document Outline
This document presents the technical specifications of the ngVLA antenna element. These parameters
determine the overall form and performance of the antenna.
The functional and performance specifications, along with detailed explanatory notes, are found in Section
4. The notes contain elaborations regarding the meaning, intent, and scope of the requirements. These
notes form an important part of the definition of the requirements and should guide the verification
procedures.
In many cases, the notes contain an explanation or an analysis of how the numeric values of requirements
were derived. Where numbers are not well substantiated, this is also documented in the notes. In thisway, the required analysis and trade-space available is apparent to scientists and engineers who will guidethe evolution of the ngVLA antenna concept.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses.
Safety requirements applicable to both the design phase and the functional antenna are described in Section
7. Additional requirements for the design phase are described in Section 8. Documentation requirements
for both technical design documentation and software are provided in Section 9.
Requirements for the Verification and Test of the antenna, from the conceptual design through toprototype, are described in Section 10.
Section 11 identifies Key Performance Parameters (KPP) that should be estimated and monitored
throughout the design phase. These are metrics to assist in the trade-off analysis of various concepts, andhelp identify and resolve tensions between requirements as the design progresses.

3.2 Project Background
The Next Generation Very Large Array (ngVLA) is a project of the National Radio Astronomy
Observatory (NRAO) to design and build an astronomical observatory that will operate at centimeter
wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116
GHz). The ngVLA will be a synthesis radio telescope composed of approximately 244 reflector antennas
each of 18 meters diameter, and 19 reflector antennas each of 6 meters diameter, operating in a phased
or interferometric mode.
The array’s signal processing center will be located at the Very Large Array site on the Plains of San
Agustin, New Mexico. The array will include stations in other locations throughout New Mexico, west
Texas, eastern Arizona, and northern Mexico. Long baseline stations are located in Hawaii, Washington,
California, Iowa, Massachusetts, New Hampshire, Puerto Rico, the US Virgin Islands, and Canada.

3.3 General Antenna Description
The antennas will operate in free air, during daytime and nighttime, as long as the atmospheric conditions
remain within the specified operating limits. When not in an operating condition, the antenna will be put
in a safe “stow” configuration.

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Version: A

The antennas will be constituted of a shaped paraboloidal reflector with a subtended circular aperture of
18 m diameter. The optical configuration shall be an offset Gregorian feed-low design supported by an
Altitude-Azimuth mount.
The subreflector shall be supported so that neither it nor any of its supporting structure obstructs theaperture of the primary reflector. If necessary to meet the performance requirements, the position of thesubreflector may be remotely adjusted with a controlled mechanism. Space is required near the secondary
focal point for installation of feed antennas, receivers, and other electronics. Additional space is requirednear ground level for electronics and instruments.

3.4 Summary of Antenna Requirements
The following table provides a summary of the major antenna requirements in order to provide the reader
with a high-level view of the desired antenna. Should there be a conflict between the requirements listed
here and the descriptions in Sections 4 through 10, the latter shall take precedence.
Parameter

Summary of Requirement

FrequencyRange

1.2–116 GHz

Diameter
Number of
Antennas
SurfaceAccuracy

18 m
244

Tracking
Range
Movement
Rate

Precision Operating Conditions
160 μm RMS ( /16 @ 116 GHz), primary & subreflector combined
Normal Operating Conditions
300 μm RMS, primary and subreflector combined
Precision Operating Conditions:Absolute pointing: 8 arc sec RMS
Referenced pointing: 3 arc sec RMS (4 deg angle, 15 min time)
Normal Operating Conditions
Absolute pointing: 35 arc sec RMS
Referenced pointing: 5 arc sec RMS (4 deg angle, 15 min time)
Azimuth: ±270 deg
Elevation: 12 deg to 88 deg
Slew: Azimuth 90 deg/min, Elevation 45 deg/min.
Tracking: Azimuth 7.5 deg/min, Elevation 3.5 deg/min

Antenna
Geometry

Offset Gregorian, satisfying Mizuguch-Dragone polarization
condition, with focal point on bottom.

Environment
al Conditions

Survival Conditions at Stow Position: wind PVWHPSHUDWXUH–40 C, 2.5 cm radial ice, 25 cm snow in dish, 2.0 cm
dia hailstones
Precision Operating Conditions: NightWLPHRQO\ZLQG5 m/s,
WHPSHUDWXUH–15 C, no precipitation
Normal Operating Conditions'D\DQGQLJKWZLQG7 m/s,
temperatXUH–15 C, no precipitation

Pointing
Accuracy

Page 10 of 45

Reference
Reqs.
ANT0101
ANT0102
ANT0103
ANT0202
ANT0401
ANT0501
ANT0502
ANT0611
ANT0612
ANT0621
ANT0622
ANT0801
ANT0802
ANT0901
ANT0902
ANT0906
ANT0201
ANT0206
ANT0211
ANT1411through
ANT1447

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

4 Antenna Functional and Performance Requirements
These requirements apply to a properly functioning system, under the normal operating environmental
conditions unless otherwise stated.

4.1 Operating Frequency Range
Parameter
Upper Operating Frequency
Lower Operating Frequency
Optimized Operating Frequencies

Req. #
ANT0101
ANT0102
ANT0103Value
116 GHz
1.2 GHz
8 GHz–50 GHz

Traceability
SYS0801
SYS0801
SYS0801

The upper and lower operating frequencies for the antenna flow down directly from the system
requirements. However, operation above 8 GHz is of higher importance, and the lower operating
frequency should not be permitted to significantly increase the design cost or compromise performanceat higher frequencies.
For example, optimizing performance at 1.2 GHz may necessitate a large subreflector, perhaps 4–5 m indiameter. Such a subreflector may increase the structural requirements on the feed/subreflector arm andmake meeting the pointing specification more difficult due to increased wind loads. Therefore, subreflector
size should be a compromise to provide minimal wind loading at high frequencies, with spillover
temperature optimized for 8 GHz and up.

4.2 Optical and Mounting Geometry
Parameter
Optical Configuration
Type
Primary Aperture
Diameter and Shape
Secondary Reflector
Aperture Diameter
Secondary Angle ofIllumination

Req. #
ANT0201

Value
Offset Gregorian

ANT0202

18m, circular

ANT0203

3.2m minimum

ANT0204

Reflector Offset

ANT0205

Focal Ratio, Primary

ANT0206

Cross Polarization

ANT0207

Reflector Shapes

ANT0208

From the focal point, the aperture of thesecondary reflector shall subtend an angle of
110º
There shall be no overlap of the physicalsecondary reflector with the projected
aperture of the main reflector
The closest paraboloid to the main reflector
shall have a focal ratio of 0.40 ±0.05
The secondary reflector tilt angle ( in Figure 1)
shall be chosen to satisfy the Mizuguch
condition [AD13]
The shapes of the main and secondaryreflectors will deviate no more than 0.25m
from the classical Gregorian conic sections(paraboloid and ellipsoid). For the mainreflector, deviations will be azimuthally
symmetric about the paraboloid axis

Page 11 of 45

Traceability
SYS0701
SYS0601
SYS0501
SYS0601
SYS0501
SYS0701

SYS0501

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQSParameter
Secondary Reflector
Extension

Req. #
ANT0209

Main Reflector
Extensions

ANT0210

Mounting
Configuration

ANT0211

Date: 2019-07-29
Version: A

Value
The secondary reflector shall be extended on
its outside edge by 0.5 m as a shield against
ground radiation. This part of the reflector is
outside its defined aperture and its shape is not
specified; it is not shown in Figure 1. The
extension may be integral with the reflector orconstructed as a separate component.
The main reflector may extend beyond thedefined aperture to facilitate efficient fabrication(e.g., assembly from hexagonal panels).
The focal point shall be closest to the ground at
the minimum elevation angle.

Traceability

The optical configuration for classical conic section reflectors is fully specified by requirements ANT0202
through ANT0207 (except that ANT0205 and ANT0207 specify only minimum values). Figure 1 (nextpage) conforms to these requirements using the minimum secondary reflector size and 10 cm offset(dsr-mr = 10 cm).
The primary aperture diameter is measured in the plane perpendicular to its axis. The physical reflector's
largest dimension, given the offset geometry, is appreciably larger.
The secondary reflector aperture (ANT0203 and ANT0205) is measured in the plane perpendicular to
the geometrical optics ray from focal point to main aperture center. The secondary reflector's physicaledge (not including the extension described in ANT0209) shall be circular when projected into this plane.
The final shapes of the reflectors have not been determined (NRAO responsibility), but they are expected
to deviate from the classical paraboloid and ellipsoid. Whereas the deviation will be small (ANT0208), theclassical shapes should be used for the preliminary design.

Page 12 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

Figure 1 - Cross-section of the optical geometry through the plane of symmetry for unshaped (paraboloid
ellipsoid) reflectors. Values may be refined in the design.

4.3 Allowable Design Volume & Mass
Parameter
Minimum Spacing

Req. #
ANT0301

HeightANT0302

Mass

ANT0303

Value
Antennas whose azimuth axes are separated by 30
m shall not collide for any combination of theirorientations.
At the lower limit of normal elevation motion, no
part of the movable structure shall be closer than
1.0 m to the nearest point on the ground.
Unconstrained.

Page 13 of 45

Traceability

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

If the minimum spacing requirement proves difficult to accommodate, NRAO may evaluate a revision tothis requirement. The height of the pedestal is limited to provide adequate clearance for snow. For service,a low feed arm is desirable, but the design height should also consider equipment and personnel safetyconcerns. The mass is an unconstrained free parameter, but lower mass is preferred in order to minimize
cost. The envelopes of NRAO-supplied equipment will be defined in the ICDs described in Section 5.

4.4 Number of Antennas
Parameter
Number of Antennas

Req. #
ANT0401

Value
244

Traceability
SYS0501

Additional antennas would be desirable. In practice, this requirement is set by construction cost
constraints.

4.5 Reflector Construction & Accuracy
Parameter
Surface Accuracy,
Precision

Req. #
ANT0501

Surface Accuracy,
NormalANT0502

Reflector
Construction

ANT0503

Value
Surface errors shall not exceed 160 m RMS, forthe primary and secondary reflector combined
when operating in the Precision operating
environment.
Surface errors shall not exceed 300 m RMS, forthe primary and secondary reflector combined,
when operating in the Normal operating
environment.
Each reflector shall be a solid metal surface (not amesh or perforated sheet). Each may beconstructed as a single piece or as multiple panels.
If constructed of multiple panels, gaps between
panel edges shall not exceed 1 mm.

Traceability
SYS0501

SYS0501

The surface error at each point is defined to be the deviation of the actual surface from the nominal
surface, measured normal to the nominal surface. The RMS is computed by integrating over the main
aperture (not across the reflector's local surface) with uniform weighting. The limits apply to the RMS of
the sum of the main and secondary reflector errors, but that value may be estimated by taking the rootsum-squared of the main and secondary RMS errors measured separately.
The aim with the reflector construction specification is to ensure high reflector efficiency over theoperating frequencies (Section 4.1) with minimal transmission through gaps from electro-magnetic
interference (EMI) or ground emission. If alternate designs and provisions ensure that the system maintains
aperture efficiency and noise temperature, NRAO may revise this requirement.

4.6 Pointing Accuracy
Pointing error is defined as the difference between the commanded orientation of the antenna and theactual direction of its RF beam. Pointing errors are classified as repeatable and non-repeatable. Pointing
accuracy is specified by the maximum allowable Non-Repeatable Pointing Error and Referenced Pointing
Error. The absolute error may be larger provided it is repeatable over the specified range of environmental
conditions (mainly temperature and wind). Repeatable errors will be calibrated and removed in the control
software.

Page 14 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

Date: 2019-07-29

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Version: A

To further correct the non-repeatable errors, referenced pointing will be used. This involves astronomicalmeasurement of the pointing error using observations of a known object near the desired pointing
direction. The Referenced Pointing Error specifications then limit the difference in pointing error at agiven angular separation from the desired direction and the change in that difference over a given time.
Pointing requirements apply over the full operational range of motion.

4.6.1

Pointing Accuracy in Precision Operating Environment

Parameter
Non-Repeatable Pointing Error
Referenced Pointing Error

Req. #Value
ANT0611 18 arc sec RMS
ANT0612 3 arc sec RMS, within 4º of thetarget position and 15 mins time

Traceability
SYS0801
SYS0701, SYS0801

The non-repeatable pointing specification is equivalent to full width half maximum over ten (FWHM/10)
at 20 GHz, while the referenced pointing requirement is equivalent to the FWHM/10 at 116 GHz. The
control loop used for referenced pointing within 4º should not be unique—performance at larger angles
is expected to degrade in a manner roughly proportional to slew distance. Note that systematic pointing
errors are more damaging than random errors, and this RMS value assumes a random distribution oferrors after application of the pointing model.

4.6.2

Pointing Accuracy in the Normal Operating Environment

Parameter
Non-Repeatable Pointing Error
Referenced Pointing Error

Req. #Value
ANT0621 35 arc sec RMS
ANT0622 5 arc sec RMS within 4°; must
maintain spec for 15 mins time

Traceability
SYS0801
SYS0701, SYS0801

The absolute pointing specification is equivalent to FWHM/10 at 10 GHz, while the referenced pointing
requirement is equivalent to the FWHM/15 at 50 GHz. The latter specification ensures that the array
operates effectively at frequencies below 50 GHz during typical good daytime environmental conditions.

4.7 Focus Stability
Parameter
Req. #
Value
Traceability
Secondary Focus Position Stability in Precision
ANT0701 125 μm over full
Operating Environment
range of elevation
Secondary Focus Position Stability in Normal
ANT0702 300 μm over full
Operating Environment
range of elevation
The focus position stability in the precision environment is equivalent to /20 at 116 GHz, while thespecification in the normal operating environment is equivalent to /20 at 50 GHz. This specification may
be met by active compensation (e.g., moving the subreflector).

4.8 Range of Motion
Parameter
Azimuth Tracking Range
Elevation Tracking Range
Elevation Movement Range

Req. #Value
ANT0801 +/–270º minimum, where zero is towards
true south
ANT0802 12º to 88º minimum from the local
horizon
ANT0803 TBD

Page 15 of 45

Traceability
SYS1201

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

The Azimuth tracking range specified has a zero-degree fiducial vector pointing towards the celestial south
pole. The elevation range is relative to the local horizon. The coordinate system is further explained in
Section 12.2.
The lower elevation permits observations over large portions the southern hemisphere. A lower elevation
limit of 12 degrees allows observations of order –40 declination near the meridian (given the latitude of
the ngVLA Core). However, this limit in particular may prove to be a driving requirement with the feed
low optical design, as the backup and feed support structure may interfere with a pedestal at lower
elevations. Should this requirement prove to be a significant cost or complexity driver, it can be reviewed.
The movement range should be larger than the tracking range. A margin should be provided for the normal
limits of motion before limit switches are reached. The hard mechanical limits should be slightly wider
still. (See Section 4.17 for additional information.) Maintenance and safety stow positions may also beoutside the elevation tracking range.

4.9 Axis Rates
Parameter
Slew: Azimuth
Slew: Elevation
Acceleration: Azimuth
Acceleration: Elevation
Slew + Settle Time

Req. #
ANT0901
ANT0902
ANT0903
ANT0904
ANT0905

Tracking: Azimuth
Tracking: Elevation

ANT0906
ANT0907

Value
90 deg/min. minimum
45 deg/min. minimum
4.5 deg/sec2 minimum
2.25 deg/sec2 minimum
Move 4-deg on sky and settle to within
Referenced Pointing Specification within 10
sec for elevation angles <70º
7.5 deg/min. minimum
3.5 deg/min. minimum

Traceability
SYS1107
SYS1107
SYS1107

The slew speeds and accelerations specified attempt to minimize time spent slewing between targets orcalibrators, without significantly driving the antenna design. They also allow for rapid response to transient
events, reaching anywhere on sky within approximately two minutes. The slew + settle time specification
aims to reduce phase calibration overheads. The 70-degree elevation angle constraint is given so as not
to drive the specification for azimuth slew rates at higher elevation. Should this specification prove to bea driving requirement it may be reviewed, as there are alternative approaches to phase calibration at thesystem level.
The tracking specifications give the rates at which the specified pointing error limits must be maintained.
In general, tracking error that contributes to the pointing error must be included in the pointing error
budget for both Precision and Normal conditions. The azimuth tracking rate corresponds toapproximately ten times sidereal at an elevation of 70 degrees. Tracking at super-sidereal rates will be
important for multiple observation modes, such as on-the-fly mosaicking, or tracking objects that moveacross the celestial sphere, such as planets, asteroids, and satellites.

4.10 Stow Positions
Parameter
Stow Position:
Survival
Stow Position:
Maintenance

Req. #
Value
ANT1001 Survival stow position shall limit wind load on theantenna while ensuring water and snow accumulation
does not exceed safe structural allowances.
ANT1002 Maintenance stow position shall place the receiver
enclosure as close to horizontal as possible.

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Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

Date: 2019-07-29

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Version: A

It shall be possible to stow the antenna in two different positions, one used for occurrence of the survival
atmospheric conditions, the other for specific maintenance to be performed. The Maintenance position
aims to provide a level working platform around the receiver enclosure mounted on the feed arm. In
practice, this may be unattainable in some designs and will be constrained by the lower elevation limit. In
Survival position, the antenna shall withstand the survival conditions described in Section 4.14.4. The
designer shall determine a single survival position that minimizes stress from wind and snow/ice loading.

4.11 System Noise Contributions
Parameter
Resistive Losses

Req. #
ANT1101Value
The primary and secondary reflector shall each havea surface resistive loss of less than 1.0% over theoperating frequency range.

Traceability

Contributions to system noise from the antenna, due to resistive loss of the primary and secondaryreflector surfaces and scattering of ground noise into the feed, shall be minimized as much as possible
without compromising the surface accuracy and pointing requirements. Should this requirement provedifficult to meet at the upper operating frequency, NRAO may review the requirement.

4.12 Solar Observations
Parameter
Solar Observations

Req. #
ANT1201

Value
Direct solar observations allowed. System willmeet specifications for the normal operating
environment.

Traceability
FUN0006

The specifications for pointing and surface accuracy for the Normal operating environment must be met
when pointed directly at the Sun.

4.13 Spurious Signals/Radio Frequency Interference Generation
Parameter
Req. #
Value
Traceability
Spurious
ANT1301 Not to exceed the equivalent isotropic radiated power EMC0310
Signal Level
limits in Table 1
The electronics within the antenna must be shielded to avoid radio frequency interference (RFI) being
received by the Front End electronics, degrading system sensitivity. Table 1 is based on the analysis
presented in RD02, updated for longer integrations consistent with SCI0116.
Freq.
(GHz)
Fh (w/m2)
EIRPh
(W)
EIRPh
(dBm)

1

2

4

6

8

10

20

30

1.5E-19
1.9E-16

1.1E-18
1.4E-15

8.9E-18
1.1E-14

2.9E-17
3.7E-14

6.3E-17
7.9E-14

1.2E-16
1.5E-13

1.2E-15
1.6E-12

4.3E-15
5.4E-12

–127

–119

–110

–104

–101

–98

–88

–83

Table 1 - Allowable radiation power for electronic components.

The table is based on unity gain, assuming the RFI enters through a sidelobe of the antenna. Fh is theharmful power flux density level, and EIRPh is the harmful effective isotropic radiated power. The ratio ofPage 17 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

the emitting device EIRP to the harmful EIRP (EIRPh) is the shielding required. For example, a device with
an EIRP of 1nW @ 2GHz would require of order 59dB of shielding.
Table 1 assumes the radiator is 10 m from the antenna feed. For other distances, the EIRPh can becalculated as follows:4ߨ‫ ݎ‬ଶ ܵ‫ܨ‬௛‫ܩ‬where r is the distance in meters, S is the device shielding ratio, G is equal to 1, and Fh is from Table 1.
‫ܴܲܫܧ‬௛ =Radiated Power shall be computed over a bandwidth that corresponds to a spectral resolution of 100 m/s.
This can be calculated as 333 Hz * ʆG, where ʆG is the RF frequency in GHz.

4.14 Environmental Conditions
Based on historical weather data of the VLA site and other public weather databases, the following
definitions of environmental conditions are adopted. These requirements are verbatim from theenvironmental specification outlined in [AD01].

4.14.1 Precision Operating Conditions
Parameter
Solar Thermal Load

Req. #
ANT1411Wind Speed

ANT1412

Temperature
Temperature Rate of Change
Precipitation

ANT1413
ANT1414
ANT1415

Value
Nighttime only; no solar thermalload within last 2 hours.
:5 m/s average over 10
min time. 7 m/s peak gusts.
–&7&1.8°C/Hr
No precipitation

Traceability
ENV0311
ENV0312
ENV0313
ENV0314
ENV0315

The Precision operating environment defines the conditions under which the system is expected to meetthe most stringent requirements and provide optimal system performance.
The solar thermal load requirement limits this environment to two hours after sunset through sunrise, solong as the other requirements of this section are met. The two-hour restriction is intended to allow
sufficient time for the system to equilibrate.

4.14.2 Normal Operating Conditions
Parameter
Solar Thermal LoadWind Speed
Temperature
Temperature Rate of Change
Precipitation

Req. #Value
ANT1421 Exposed to full sun, 1200W/m2
ANT1422 :7 m/s average over 10
min time; 10 m/s peak gusts
ANT1423 –&735 C
ANT1424 3.6°C/Hr
ANT1425 No precipitation

Traceability
ENV0321
ENV0322
ENV0323
ENV0324
ENV0325

When the environment meets the constraints of normal operating conditions, system performancerequirements are relaxed but still expected to provide adequate performance for operation below 50
GHz.

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Title: Antenna Preliminary TechnicalRequirements

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NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

4.14.3 Limits to Operating Conditions
Parameter
Solar Thermal LoadWind

Req. #
ANT1430
ANT1431

Temperature
Precipitation
Ice

ANT1432
ANT1433
ANT1434

Value
Exposed to full sun, 1200W/m2:PVDYHUDJHRYHU10 mins;:0 m/s gust.
–&7&5 cm/hr over 10 mins
No ice accumulation on structure

Traceability
ENV0330
ENV0331
ENV0332
ENV0333
ENV0334

A third categorization will establish hard limits to the operating conditions. While outside the bounds ofthe normal operating environment but within this regime, no performance guarantees are expected, but
the system shall still be capable of safe operation. Once these limits are exceeded, the antenna will be
moved to its “stow-survival” orientation to prevent damage.

4.14.4 Survival Conditions at Stow Position
Parameter
Wind
Temperature
Radial Ice
Rain Rate
Snow Load—Antenna
Hail Stones
Antenna Orientation

Req. #
ANT1441
ANT1442
ANT1443
ANT1444
ANT1445
ANT1446
ANT1447

Value
PV:PVDYHUDJH–3&7&2.5 cm
16 cm/hr over 10 mins
25 cm
2.0 cmStow-survival, as defined by designer

Traceability
ENV0341
ENV0342
ENV0343
ENV0344
ENV0345
ENV0347
ENV0348

The survival conditions describe the environment that the antenna should be able to withstand without
damage when placed in its least-vulnerable state. The designer must specify the orientation that will resultin minimum stress to the structure at the maximum wind speed and maximum snow and ice loading. Notethat 50 m/s survival wind is not high enough to survive tornadoes in eastern New Mexico and Texas. Thisissue should be considered in the Hazard Analysis described in Section 7.2.
The temperature limits, radial ice, snow load and hail stone requirements are based on experience at the
VLA site and a survey of conditions throughout the extent of the array. Should these requirements prove
onerous or constraining, a risk versus loss analysis may be performed to evaluate the likely cost and time
for repair, and the frequency of expected repairs, compared to the cost impact of meeting the requirement
over the lifetime of the facility. This would be executed as part of the analysis described in Section 7.2.

4.14.5 Lightning Protection Requirements
Parameter
Lightning
Protection:
Structure
Lightning
Protection:
Electronics
Lightning
Protection:
Personnel

Req. #Value
ANT1451 The antenna and housed equipment shall be protectedfrom both direct and nearby lightning strikes, achieving
Protection Level 1 as defined in in IEC 62305-1/3 [AD02]
ANT1452 The antenna electrical and electronics systems shall beprotected against Lightning Electromagnetic Impulse(LEMP) in accordance with IEC 62305-4. [AD02]
ANT1453 A safety hazard analysis shall be performed for
anticipated preventive maintenance tasks that may placepersonnel at risk in the event of direct or nearby
lightning strikes.

Page 19 of 45

Traceability
ENV0511
ENV0512
ENV0513

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

Given the array’s extent and the prevailing environmental conditions, direct and nearby lightning strikes
causing a lightning electromagnetic pulse (LEMP) should be anticipated and mitigated in the antenna design.
The antenna and housed equipment shall be protected in any antenna orientation. The requirements forthe antenna grounding electrode, provided as part of the antenna foundation, shall be documented in therelevant interface control document (ICD) as described in Section 5.1. All bearings shall have bypass
grounding connections. The grounding system shall be designed to minimize ground loops.
The lightning protection system shall be designed to achieve Protection Level I as defined by [AD02] “IEC
62305-1 – Protection against lightning.” This level assures protection against 99% of strikes, with a residual
risk of damage for strikes with parameters outside the defined range.

4.14.6 Seismic Protection Requirements
Parameter
Seismic
Protection

Req. #Value
ANT1461 The antenna and foundation shall be designed towithstand a low probability earthquake with up to 0.2g
peak acceleration in either the vertical or horizontal axis.

Traceability
ENV0521

Low probability has been defined as a 2% probability of an event exceeding this magnitude over a 50-year
period, consistent with data available from the USGS Seismic Hazard Model [RD04]. Equipment shall be
designed to survive this standard in any operational condition and orientation.

4.14.7 Site Elevation
Parameter
Altitude
Range

Req. #Value
ANT1471 The antenna and foundation shall be designed for survival
and operation at altitudes from sea level to 2500 m.

Traceability
ENV0351

4.14.8 Vibration
Parameter
Wind
Vibration

Req. #Value
ANT1481 Exposed equipment, including within the antenna, shall be
designed to withstand persistent wind-induced vibration.

Traceability
ENV0531

The vibration mitigation requirement is especially applicable to all mechanical connectors. All cables shallbe mechanically supported to mitigate vibration loosening of connectors.

4.15 Maintenance and Reliability Requirements
Parameter
Preventive
Maintenance Cycle
Preventive
Maintenance Effort
Mean Time
Between Failures

Req. #Value
ANT1502 Preventive maintenance shall not be required atintervals shorter than 12 months.
ANT1502 Periodic preventive maintenance shall require no
more than a 2-person team and no more than 2
8-hour workdays.
ANT1503 MTBF 35,000 hrs.

Traceability
SYS2301
SYS2301
SYS2302

The maintenance and reliability requirements support high-level requirements that limit total array
operating cost. The preventive maintenance effort is intended to be averaged over the array design lifeand need not be equal on all 12-month cycles.

Page 20 of 45

Title: Antenna Preliminary TechnicalRequirements

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NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

The MTBF requirement corresponds to an annual failure rate of 25% for the antenna electro-mechanicalsystems alone. Monitor points/sensors should be included in the MTBF/MTTR analysis, but sensors andother components that can be reasonably deemed to be ancillary to operation may be removed from thedetermination of compliance with the MTBF requirement (ANT1503).
“Failure” will be defined as a condition which places the system outside of its performance specifications(pointing, slew, tracking, etc.), or into an unsafe state, requiring repair. For example, a malfunction on oneof three redundant anemometers would not meet the standard for failure in the MTBF analysis, and should
not factor into compliance with ANT1503. Similarly, the malfunction of a gearbox temperature sensor
would not be considered a failure for the purposes of ANT1503. However, the malfunction of a metrology
sensor required for pointing model corrections would be considered a failure.

4.16 Monitor and Control Requirements
Parameter
Antenna Control
Unit (ACU)

Req. #
ANT1601

Servo Loops

ANT1602

Self-Monitoring

ANT1603

Weather
Monitoring

ANT1604

Network
Hardening/
Authentication
Remote Reset

ANT1605
ANT1606

Value
The antenna shall be equipped with an electronic
control unit that will drive the azimuth and elevation
axis motions according to commands received fromeither the Monitor and Control system (seeInterfaces) or from a local manual interface(s).
The ACU shall include servos with position and rate
control loops on each axis, and the servo design
shall account for the structure’s dynamic behavior.
The antenna shall measure, report, and monitor a
set of parameters that allow for determination of its
status and may help predict or respond to failures.
The antenna shall be equipped with anemometers
and thermometers to determine when safe
operating conditions have been exceeded and tostow the antenna.
System remote control shall require anauthentication process, and only respond tocommands from authorized sources.
It shall be possible to remotely reset each antenna,
including a reboot of the antenna control unit, andreturn the antenna to operational status.

Traceability

SYS2601
SYS2601

SYS2602

For maintenance purposes, local control of the ACU near the point of service is desirable.
The expectation with self-monitoring (ANT1603) is that the antenna control system will expose lowerlevel sensors to the monitor and control system when queried. The cadence of access is flexible and not
expected at high rates (typical access might be on second to minute scales). Any high-cadence monitoringshould generally be internal to the antenna control system with summary output on the interface.
Exclusions from the remote reset requirement are hardware interconnects for safety, the disconnectionof the power in the case of a fire alarm activation, and recovery from axis in hard stop. Other features of
the ACU interface are to be specified in the Monitor and Control ICD.

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Title: Antenna Preliminary TechnicalRequirements

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NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

4.17 Motion Limiting Features
Parameter
Software
LimitsHardware
LimitsHard Stops
Safety LockOut
Fire Alarm
Fail Safe
BrakesReq. #Value
ANT1701 The antenna shall include logic to prevent motion beyond
programmable limits in azimuth and elevation during
normal operation.
ANT1702 The antenna shall be equipped with mechanically driven
switches to inhibit operation outside its safe operating
limits.
ANT1703 The antenna shall be equipped with hard mechanical stops
that physically prevent the antenna from exceeding
operating limits when damage is imminent.
ANT1704 The antenna shall be equipped with a safety lock-out that
inhibits motion of the antenna during service.
ANT1705 The antenna shall be equipped with fire alarms in any
equipment compartments. The fire alarm shall disconnect
power to the antenna when triggered.
ANT1706 The drive brakes shall engage when the antenna
experiences a loss of power.

Traceability

Fire alarms may be necessary at additional locations as determined by the designer.

4.18 Lifecycle Requirements
Parameter
Design Life

Req. #Value
ANT1801 The antenna shall be designed to require no major
overhaul work for 20 years.
Lifecycle
ANT1802 The antenna design shall minimize its lifecycle cost for 20
Optimization
years of operation.
Country of
ANT1803 The antenna should meet US federal procurement
Originregulations for country of origin content.

Traceability

An exception to the design life is painting, which should not be required for 10 years or more. Lifecycle
costs include manufacturing, transportation, construction/assembly, operation and decommissioning.
The ngVLA will be designed and constructed with a large contribution of federal funds. Provisions to “buyAmerican” are expected, and the design and costing should presume the use of US steel (if steel is includedin the design) and limits on total foreign content.

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Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

5 Interface Requirements
This section provides information about the interfaces of the antenna. ICDs are required between theantenna and all connecting systems. In many cases, specifications for the interfaces are not yet available,
but the broad scope of the ICD can be defined.
These interfaces shall be developed and documented by the antenna designer and approved by ngVLA as
part of the antenna conceptual design effort, then updated throughout the design. Post CoDR, the ICD
shall only be updated through formal project change control processes.

5.1 Interface to the Foundation/Station
The conceptual design of the foundation is within the scope of the antenna element. Final design anddelivery of the foundation will be the responsibility of others.
The foundation refers to all stations where an antenna can be mounted, irrespective of its location.
Antenna stations will be available at the VLA antenna test facility (ATF) site for assembly and testing
purposes.
The ICD between the antenna and foundation shall define the geometry of the attachment and themechanical characteristics of the foundation. Furthermore, it will define the position and geometry of thevaults for the electric power and for the signals routed to the antenna through or adjacent to thefoundation.
Note that contributions from the foundation at the antenna stations shall be taken into account in theperformance of the antenna and included in the error budgets to demonstrate compliance with thespecifications. The antenna designer must ensure that the antenna in conjunction with the foundation
provides the performance required by his/her error budget.
The minimum stiffness and load capability of the foundation shall be defined in the ICD. The finite stiffnessof the combined soil and foundation shall be included in the dynamic analysis of the antenna.

5.2 Interface to the Electrical Infrastructure
Electrical power will be provided to the antenna through a vault adjacent to or integrated into the antennafoundation. Most locations are expected to be connected to the commercial power grid, but some remotesites may use locally generated power. For the preliminary design, it should be assumed that three-phase,
208V, 60 Hz power will be provided at this interface.
Loads shall be protected from brown-out conditions where one or two phases of the distribution system
are lost. Any shunt trip device shall be remotely resettable, and shall have a programmable automatic reset
sequence.
The ICD should describe both the mechanical and electrical specifications of the electrical interfaces.
Circuit sizing and load estimates should include allocations for NRAO-supplied systems housed within theantenna, defined in Sections 5.3 and 5.6. NRAO will provide load estimates for NRAO-supplied equipment.

5.3 Interface to the Fiber Optic Transmission System
A number of fibers will be distributed to each antenna for monitor and control, data transmission, andtime and frequency distribution. The fiber optic cables will be physically routed through a vault adjacent
to or integrated into the antenna foundation and should terminate at a splice box within the baseelectronics enclosure. The conduit or cable wrap may need to be thermally insulated or regulated.

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Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

The ICD should describe the mechanical specifications of the fiber optic interface. Note that the antenna
has no direct optical connection to the Fiber Optic Transmission System. The communications interface
to the antenna shall be considered part of the monitor and control system interface.

5.4 Interface to Other External Cables and Piping
HVAC and cryogenic equipment may be located on or adjacent to the antenna. Other calibrationequipment may also be located in close proximity. The interfaces to all other external systems (excluding
the fiber optic transmission system and electrical infrastructure) will be described in this ICD.

5.5 Interface to the Receiver Enclosure/Front End Electronics
The receiver enclosure will house the complement of feeds, cryogenic receivers and ancillary equipment
necessary for signal recovery at the secondary focus of the antenna. These components will be collectively
referred to as the antenna Front End electronics. The Front End electronics will be connected to theantenna back-end electronics, located in the pedestal room.
Note that the receiver selection mechanism (indexer) and focus adjustment mechanism are theresponsibility of the antenna designer. It is expected that a two-axis stage, providing adjustment in the ZF
and YF axes (see coordinate system in Section 12.2.4), will be required at a minimum. Adjustment in the
XF range may be necessary depending on the degree of gravitational deformation.
The range of adjustment required in each axis is TBD, as it depends on antenna parameters as well as the
Front End electronics. Adjustment ranges of ZF  mm (focus) and YF  mm (translation for band
selection) are expected given the current Front End design. Antenna-based contributions (thermal,
gravitational deformation, etc.) should be added to these allocations. In terms of speed, the YF translation
rate is most important. It should traverse its range of motion in 20 seconds or less (allowing for typicalband switching in a 10-second period).
The receiver enclosure, an NRAO responsibility, will be a shielded enclosure constituted of a durable
continuous metallic surface. Durable RFI shielding will be provided on the access panels and on all otherpenetrations and discontinuities (seams, apertures, vents, cable and pipe penetrations, screws, etc.). The
mounting method between the enclosure and two-axis stage shall ensure proper grounding.
The ICD should define the masses and volumes of the Front End electronics. The requirements in termsof mechanical positioning and stability, electrical loads, and environmental control shall be included.
Requirements for personnel access for maintenance shall also be considered.

5.6 Interface to the Back End Electronics
The Base electronics enclosure shall house the antenna Back End electronics, which provide local timeand frequency references, and a digital Back End that formats the signal collected by the Front End for
distribution back to the central correlator. It also provides an interface to the Monitor and Control
system, described in Section 5.9. The nature of the enclosure and its interface will be dependent on themount design. NRAO will supply volumes, mass, and other interface requirements.

5.7 Interface to Internal Cables and Piping
Fiber optic cables, multi-conductor electrical cables, cryogenic piping and other cooling system piping will
distribute signals and fluids to customer-supplied equipment in the base electronics enclosure, receiver
enclosure and cryogenic platform. While the cables and piping are supplied by other systems, the antenna
must provide suitable routing spaces and wrap protection.

Page 24 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

The ICD will describe the point-to-point connections, cable cross sections, bend radii, and othermechanical parameters necessary for internal cable and piping distribution.
Cable wraps shall be provided in azimuth and elevation that will accommodate all antenna cables as wellas interfacing system cables and hoses. The cable wraps shall permit full angular rotation of the antenna.
The cable wraps shall be such that cables are neither excessively stressed by twisting or bending, nordamaged by pulling over edges of a fixed structure. Specific requirements on bending radii shall be
documented in the ICD. The minimum bending radius of the elevation and azimuth cable wrap shall be in
any case larger than 200 mm.
Possible limitations in amount of torsion which can be sustained by cables and hoses (e.g., helium lines)
shall also be considered. The cable wrap design shall be optimized for durability and reliability taking into
account the lifetime requirements of Section 4.14.7 and 4.18.

5.8 Interface to the Cryogenic System
Space must be available for a cryogenic compressor on the antenna yoke, below the elevation axis but
above the azimuth axis. A combination of rigid and flex lines will provide the supply and return lines
between the compressor and the refrigerators within the receiver enclosure. The ICD should describe
the point-to-point connections, bend radii, platform size, compressor mass and volume, ancillary
connections, and access requirements for maintenance.

5.9 Interface to the Monitor and Control System
The Antenna Control Unit (ACU) will govern the local control of the antenna, processing higher-levelcommands into lower level commands suitable for each axis drive and ancillary mechanisms. Pointing
trajectories will be supplied to the antenna through a series of time-tagged azimuths and elevations.
Suitable interpolation and damping shall be provided in the servo control system to achieve required
tracking accuracy.
The vendor-supplied antenna control unit shall operate in three pointing modes:x Raw or Encoder Mode: The servo system shall be controlled such that the encoder values match thecommanded values.
x Metrology Mode: The servo system shall apply any corrections to the input coordinates based on thevalues of metrology sensors located in the antenna system.
x Active Mode: The servo system may include a pointing model containing the seven classic terms(additional terms may be added through mutual agreement). The antenna must be able to pass a site
acceptance test (SAT) based on the application of this pointing model.
The focus indexer/positioner shall follow a similar design philosophy with three modes of operation(encoder, metrology correction only, full model). Philosophically, any terms or operations which require
modelling of the antenna structure should be corrected for in the metrology mode. Terms that only
depend on sky position can be accommodated in the pointing or focus model.
In all cases, no action or inaction of the monitor and control system can cause incorrect or dangerous
conditions in the covered hardware.
In addition, the ACU shall provide monitor data defining the current condition of key monitor points that
describe the overall health and status of the antenna. The physical interface between the ACU and M&C
system shall be multimode fiber using TCP/IP over Ethernet.

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Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

6 Subsystem Requirements
Derivation of subsystem requirements shall be included as part of the antenna conceptual design effort
and updated throughout the design. Post CDR/FDR, subsystem requirements shall only be updated
through formal project change control processes that will include the designer, manufacturer, and NRAO.
The expected main elements of the antenna include, at a minimum:x Antenna Mountx Reflector Panels
x Panel Adjusters
x Backup Structurex Subreflector
x Subreflector Support Arm/Structure
x Receiver Selection Mechanism
x Cables & Cable Wraps
x Antenna Control System

7 Safety
7.1 General
To achieve protection against all possible hazards, the antenna shall be considered a piece of machinery,
and its design and construction shall comply with the requirements set forth in this section.
Parameter
Code
Compliance
Safety of
Personnel

Req. #
ANT7001
ANT7002Value
The design shall comply with all relevant federal, State
of New Mexico, and State of Texas building codes.
The design shall allow the Observatory to comply withall relevant federal and state occupational health andsafety regulations for personnel servicing the antenna.

Traceability

7.2 Hazard Analysis
7.2.1

Hazard Severity

Hazard severity categories are defined (Table 2) to provide a qualitative measure of the mishap.
Category
I
II
III
IV

Description
Catastrophic
CriticalMarginal
Negligible

Definition
Death, severe injury, or system loss
Major injury, major occupational illness, major system damage
Minor injury, minor occupational illness, minor system damage
Less than minor injury/occupational illness and minor system damage

Table 2 - Hazard severity categories.

System loss: the antenna and/or the housed systems cannot be recovered at reasonable costs.
Major system damage: the antenna and/or the housed systems can be recovered but extensive industrial
support is necessary and/or the system is out of operation for more than three weeks.

Page 26 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

Date: 2019-07-29

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Version: A

Minor system damage: the antenna and/or the housed systems can be repaired by ngVLA without any
support from industry and/or the system is less than three weeks out of operation.

7.2.2

Hazard Probability

Table 3 shows the probability classification of hazards occurring during the 20 years of expected antenna
lifetime.
Level
A
B
C
D
E

Definition
Frequent
Probable
Occasional
RemoteImprobable

Description
Likely to occur frequently (typically once a year)
Will occur several times (6 to 10 times in 20 years)
Likely to occur (2 to 5 times in 20 years)
Unlikely but possible to occur (typically once in 20 years)
So unlikely that occurrence can be assumed not to be experienced (>20 years)

Table 3 - Probability levels.

7.2.3

Hazard Risk Acceptability Matrix

The following two matrices (Table 4 and Table 5) define the degree of acceptability of the various hazard
categories:
Frequency of
Occurrence
Frequent
Probable
Occasional
RemoteImprobable

I
Catastrophic
IA
IB
IC
ID
IE

II
Critical
II A
II B
II C
II D
II E

III
Marginal
III A
III B
III C
III D
III E

IV
Negligible
IV A
IV B
IV C
IV D
IV E

Table 4 - Hazard classification matrix.

Hazard risk index
I A to I D, II A, B; III A
II C, D; III B; IV A
I E; II E; III C; IV B
III D, E; IV C, IV D, IV E

Assessment criteria
Unacceptable
Undesirable (ngVLA decision required)Acceptable with review by ngVLA
Acceptable without review by ngVLA

Table 5 - Hazard acceptability matrix.

7.2.4

Requirements on Operational Hazards

None of the items in the following list (not meant to be exhaustive) shall lead to an unacceptable orundesirable hazard risk for the antenna or human beings:
x One or two independent operator errors;
x One operator error plus one hardware failure;x One or two hardware failures;x One or two software failures;x Partial or complete loss of energy, reference signals, or control communications to the antenna;x Emergency braking of the antenna;x Earthquakes happening for whatever position of the antenna; orx Wind loads.

Page 27 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

7.2.5

Date: 2019-07-29
Version: A

Hazard Analysis

The purpose of a Hazard Analysis is to identify safety critical areas, evaluate hazards, and identify the safetymeasurement to be used. A Hazard Analysis shall list all possible hazards, including an assessment of theirseverity and probability, and shall show that safety considerations are included in all stages of the project
including assembly, training, maintenance, etc.
Safety provisions and alternatives needed to eliminate hazards or reduce their associated risk to a level
acceptable to ngVLA shall be described. As the design of the system progresses, the Hazard Analysis shallbe kept up to date reflecting new considerations, data, and/or information. The following issues shall beconsidered:
1. Safety-related interface considerations among various system elements, e.g., material
compatibility, electromagnetic interference, inadvertent activation, fire initiation and propagation,
hardware and software controls, etc.
2. Environmental hazards including handling and operating environments.
3. All hazards related to operating, testing, maintenance and emergency procedures.
4. Any other identified hazards.
5. A description of any risk reduction methods employed for each hazard like safety-related
equipment, safeguards, interlocks, system redundancy, hardware or software fail-safe design
considerations, etc., taking into account the design requirements noted in Section 4.17.

7.3 Safety Design Requirements
7.3.1

Fire Safety

Smoke detectors are required in any equipment compartment and shall be interlocked to shunt trip allelectric power in the antenna. When smoke is detected the detector shall immediately close a contact
used by ngVLA for a remote fire alarm and will energize a local audible alarm. The shunt trip of all power
shall occur five seconds after smoke detection. Emergency power for the smoke detectors and local alarm
shall utilize “Gel-cells” with a minimal reserve of six hours and less than a 24-hour recharge cycle.

7.3.2

Mechanical Safety

For each component under design, all the possible criteria of mechanical failure relevant to the component
under examination shall be considered (strength, fatigue, buckling, etc.). Unless otherwise required by theStandards applicable to this specification or by any applicable standard the minimum safety margins to be
used are those provided herein.
x A minimum stress safety factor of 1.5 with respect to the yield point shall be used in the design of allmechanical components which in case of a failure lead to an unacceptable or undesirable hazard risk.
x This stress safety factor shall be reduced to 1.1 in case of survival and accidental conditions.
x For metallic materials where the relevant failure criteria is not linked to plasticity (e.g., fatigue), an
equivalent stress safety factor of 1.5 shall be used in the design of all those mechanical components,
which in case of a failure lead to an unacceptable or undesirable hazard risk.
x For CFRP parts, the equivalent stress safety factor shall be applied to the relevant failure mode to beconsidered for the part under examination. All relevant failure criteria shall be considered(delamination, fatigue, cracking, gluing failure, etc.). An equivalent stress safety factor of 1.5 shall be
used in the design of all those components, which in case of a failure lead to an unacceptable orundesirable hazard risk. This value applies also in case of accidental and survival conditions.

Page 28 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

7.3.3

Date: 2019-07-29
Version: A

Electrical Safety

Electrical equipment installed on the antenna shall comply with their relevant international or US productstandard. The Antenna as a whole shall be in conformity with either IEC 60204-1:2016 [AD15] or NFPA
79 [AD14] and with IEC 61140 [AD13].
Electrical installations and equipment shall be specifically built and/or derated in order to safely performtheir intended functions under the applicable environmental conditions. Insulation shall be coordinated inconformity with IEC 60664 [AD17] while taking into account the altitude of up to 2500 m above sea level.
The antenna shall be designed, manufactured and erected to exhibit functional safety with regard toelectromagnetic phenomena. Influence onto the antenna safety of sources of electromagnetic disturbancesinternal to the antenna itself shall be considered in relation with the antenna design.

7.3.4

Hydraulic & Pneumatic Safety

Any hydraulic or pneumatic systems shall be designed in accordance with ISO 4413 [AD18].

7.3.5

Handling, Transport, and Storage Safety

The design of the antenna shall incorporate all means necessary to preclude or limit hazards to personnel
and equipment during assembly, disassembly, test, and operation.

7.3.6

Toxic Substances

No use of toxic substance (asbestos, formaldehyde, lead, etc.) and of their derivatives shall be permitted
in the antenna. Insulation materials and paints specifications shall be reviewed by ngVLA.

7.3.7

Confined SpaceConsiderations of confined space in the sense of OSHA Standards 29 CFR Part 1910 and 1926 shall betaken into account in the design where applicable (e.g., base, yoke, etc.).

7.4 Physical Security
Reasonable protection against unauthorized personnel access and theft shall be provided in the antenna
by means of lockable and caged access ladder, locks on cabinets, doors and similar design provisions.
Sensors shall be installed to monitor the condition “door open” and to relay the information to the ACU
in order to detect unauthorized intrusion.

Page 29 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

8 Requirements for Design
8.1 Analyses and Design Requirements
8.1.1

Finite Element Structural Analyses

All the Finite Element Analyses (FEA) necessary for the verification of the performance of the antenna
must be performed with an internationally recognized numerical code. The structural models used shallbe adapted to the particular analysis for which they are going to be used and shall be accurate enough toprovide a good description of the behavior of the structure under examination in terms of displacements,
stress and frequencies.
The analysis error due to mesh discretization shall be <10% in terms of finite element internal criteria likethe “Percentage error in energy norm.” Alternatively, this type of error can be evaluated by mesh refining.
The analyses which are required to be performed are listed and specified below. In case during the designphase it appears that other analyses are necessary, the list below shall not be considered exhaustive. The
FEA analysis must also support the EM Analysis (by others). Relevant scenarios are described in Table 6
and Table 7 of Section 8.1.4.
8.1.1.1

Static Analysis

Static analyses shall be used in the calculation of the effect of:x Gravity loads (stress and deflection)x Sudden braking (stresses)
x Thermal deformation (input loads derived from the thermal analysis)x Wind under precision and normal operating conditions (deflections)x Wind under survival conditions (stresses).
8.1.1.2

Modal Analysis

A modal analysis shall be performed in order to obtain accurate information concerning the Eigen
frequencies and the Eigen modes of the antenna, when integrated in the antenna station, i.e. the combined
stiffness of the soil and foundation of the antenna stations shall be adequately represented in the dynamic
FE Model. The number of degrees of freedom shall be such as to have a good representation of thefrequency range required. Care must be exerted to correctly represent the boundary conditions of thesystem under examination.
8.1.1.3

Seismic Analysis

The structural model used for the seismic analysis shall adequately represent the distribution of stiffness
and mass so that all significant deformation shapes and inertia forces are properly accounted for under
the seismic action considered. Non-structural elements, 1 which may influence the response of the main
resisting structural system, shall also be accounted for. The response of all vibration modes contributing
significantly to the global response shall be taken into account. This may be demonstrated by either of thefollowing:
x the sum of the effective modal masses for the modes, taking into account at least 80% of the total
mass of the structure, orx all frequencies below 50 Hz are taken into account.

1

An architectural, mechanical or electrical element, system or component which, whether due to lack of strength
or the way it is connected to the structure, is not considered in the seismic design as load carrying element.

Page 30 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

The above conditions have to be verified for each spatial direction. The seismic analysis shall be based on
the modal response spectrum technique, using a linear-elastic model of the structure. It shall be assumed
that the structural damping is 1.5 % of critical damping.
The Square Root Sum of the Square method (SRSS) may be used in order to combine the contribution of
the various modal responses. The three spatial components of the response may also be combined with
the SRSS method. Alternatively, the designer may propose combination rules for the modal and spatial
components consistent with a relevant international earthquake resistance standard.
8.1.1.4

Wind Analysis

The force distribution on the antenna caused by precision and normal operating conditions can be derived
by either of the following:x Adequate Computational Fluid Dynamic (CFD) analysis, orx extrapolated wind tunnel measurement results of similar structure.
The force distribution caused by survival wind loads may be derived from a CFD analysis. These forces
may be applied as quasi-static.

8.1.2

Thermal Modeling and Analysis

A thermal model of the antenna shall be used to compute the temperature distribution in the antennaduring daytime Precision and Normal operating conditions. The model shall also be used to determine theequilibration period duration from sunset. The thermal model shall be able to simulate adequately theeffects of thermal conduction, convection and radiation (solar flux). The calculated temperature
distribution shall be applied as thermal load to the structural finite element model to predict the thermal
error contribution to the pointing and surface error budgets.

8.1.3

Stress Analysis and Load Combination

A detailed stress analysis of the Antenna shall be performed. The stress analysis shall combine theindividual design loads and conditions specified under Section 8.1.1.1. In general, the load combinations tobe verified are given herein, whereby for specific components different load combinations may apply.
Load Combination: Operational Condition
Gravity + Thermal (secondary) + Wind (10 m/sec)
Gravity + Thermal (primary)+ Wind (7 m/sec) + Fast Switching
Load Combination: Accidental Condition
Gravity + Thermal (secondary) + Wind (20 m/sec) + Emergency braking
Load Combination: Survival Condition
Gravity + Wind (50 m/sec)
Gravity + Thermal (–30 qC) + Wind (30 m/sec)
Gravity + Wind (30 m/sec) + Icing + Snow
Gravity + Seismic + Wind (20 m/s)

8.1.4

Antenna EM Analysis Support

Surface deformations shall be computed for the loads shown in Table 6 and Table 7. The set of load cases
is extensive but intended to provide a full representation of antenna performance in the precision
operating environment. The results shall be provided to NRAO for electromagnetic performance analysis(by others).

Page 31 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

Date: 2019-07-29

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Load Case
L.01
L.02
L.03
L.05
L.07
L.08
L.09
L.10
L.11
L.12
L.13
L.14
L.16
L.17
L.18
L.19
L.20

Name
Gravity
Gravity
Gravity
GravityWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/s
Thermal Tu= 10 °C (Uniform over structure)
Thermal gradient Tx= 3.6 °C along XMR axis
Thermal gradient Ty= 3.6 °C along YMR axis
Thermal gradient Tz= 3.6 °C along ZMR axis

Version: A

Az. angle
(deg)
0
0
0
0
0
0
0
0
45
90
135
180
180

El. angle
(deg)
15
30
60
90
15
30
60
90
30
30
30
15
90

Table 6 - Load cases for antenna efficiency analysis.

Combined load cases are shown in Table 7. Combined cases may be calculated from results of theindividual load case analyses. Load combinations L.C.01 through L.C.10 are representative of the precision
operating conditions described in Section 4.14.1, while L.C.11 through L.C14 pertain to the normal
operating conditions of Section 4.14.2. These cases are not fully defined, as they depend on the results of
the analysis of L.C.01 through L.C.10. Only the worst-case gravity and wind scenarios are subject tocombination with the thermal gradients in order to limit the number of load permutations to be analyzed.
Load Case
Combination
L.C. 01
L.C. 02
L.C. 03
L.C. 04
L.C. 05
L.C. 06
L.C. 08
L.C. 09
L.C. 10
L.C. 11
L.C. 12
L.C. 13
L.C. 14Name
L.01+L.07
L.02+L.08
L.03+L.09
L.05+L.10
L.01+L.11
L.01+L.12
L.01+L.13
L.01+L.14
L.05+L.16
L. <worst gravity>+L.<worst wind>+ L.17
L. <worst gravity>+L.<worst wind>+ L.18
L. <worst gravity>+L.<worst wind>+ L.19
L. <worst gravity>+L.<worst wind>+ L.20

Table 7 - Combined load cases for antenna efficiency analysis.

Page 32 of 45

Note
Precision Operating Conditions
Precision Operating Conditions
Precision Operating Conditions
Precision Operating Conditions
Precision Operating Conditions
Precision Operating Conditions
Precision Operating Conditions
Precision Operating Conditions
Precision Operating Conditions
Normal Operating Conditions
Normal Operating Conditions
Normal Operating Conditions
Normal Operating Conditions

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

8.1.5

Date: 2019-07-29
Version: A

Control loop design and analysis

For each function to be controlled, the stability margins shall be computed. Dynamic simulations of thecontrol loops shall be performed, including nonlinear effects like friction, stick-slip, sensor noise, etc.

8.1.6

Reliability, Availability, Maintainability Analysis

A Reliability, Availability, Maintainability analysis shall be performed to locate weak design points anddetermine whether the design meets the Maintenance and Reliability requirements. ngVLA suggests toapply the Parts Count Method for predicting the reliability of the system as described in the MIL-HDBK217F, but the designer may propose to use other methods. For non-electronic parts, the values of NPRD95 [AD22] or data from manufacturers or other databases may be used.
Another, but more time consuming (and considered more accurate) method, the Parts Stress Analysis
Prediction, is also described in MIL-HDBK-217F. This may be used if the result of the Parts Count Method
does not comply with the Maintenance and Reliability requirements.
Some ngVLA antennas will be operated at an elevation up to 2500m above sea level, where temperatureand pressure might decrease the MTBF relative to that at low elevations. These conditions shall be taken
into specific account in the reliability prediction by using the environmental factor given in MIL-HDBK217F. The analysis shall result in estimates of the Mean Time Between Failures (MTBF) and the Mean TimeTo Repair (MTTR), assuming that scheduled preventive maintenance is performed.

8.2 Electromagnetic Compatibility Requirements
The ngVLA antenna element shall exhibit complete electromagnetic compatibility (EMC) among
components (intra-system electromagnetic compatibility). Preventing electromagnetic interference (EMI)between the antenna and other subsystems (inter-system electromagnetic compatibility) is also critical.
The following requirements shall be fulfilled as a minimum to achieve both intra- and inter-system EMC,
but the antenna designer may propose alternatives if quantitative evidence is provided that they are atleast as effective as those specified. Shielding requirements may be computed as described under Radio
Frequency Interference Generation (Section 4.13).
x Control circuits, drive motor amplifiers, and switching devices shall be designed and constructedtaking into account requirements concerning radiated and conducted electromagnetic energy. In
particular, all motor leads, both power and control, shall be filtered.
x All relay contacts and actuators shall be properly bypassed with snubber circuits, shielded, and/or
filtered.
x All amplifiers and oscillators shall be mounted in shielded enclosures that provide effective shieldingof radio frequency energy.
x Silicon-controlled rectifier switching devices shall not be used unless phase-controlled and zerocurrent cross switching techniques are used.
x No gaseous discharge devices, except noise sources for test, shall be employed.
x Means shall be employed to reduce static electricity and the consequent radio frequency noise
generated in any rotating machinery.
x All displays (LCD, plasma, LED, CRT) shall have an RFI shield in front to avoid radiated RFI. Thisrequirement may be waived if the screen is powered off during typical operation and is used formaintenance only. It must be possible to monitor and turn off such emitting devices remotely.
x All digital equipment, whether a simple logic circuit, embedded CPU, or rack-mounted PC, shall beshielded and have its AC power line and communication line(s) filtered at the chassis.

Page 33 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

The frequency range to be covered by these design measures for radiated radio-frequency interference(RFI) suppression shall extend from 50 MHz up to 12 GHz. Demonstration of EMC above 12 GHz is not
required because mitigation at 12 GHz and below is expected to be adequate at higher frequencies.

8.3 Materials, Parts and Processes
8.3.1

Type of SteelThe steel used in the antenna mount shall be a carbon or a low-alloy steel. The selection of the steel shalltake into account the low temperature to be expected during antenna operation and stow, under the
point of view of embrittlement. In particular, the nil-ductility transition temperature of the selected steel
shall not exceed –45ºC. The nil-ductility transition temperature is that at which the material starts to
exhibit cleavage fracture with very little evidence of notch ductility.
When necessary (e.g., gears and pinions, if applicable) materials with suitable hardness or surface hardened
shall be used, in order to ensure the life of the system.

8.3.2

Stress relieving

All structural welded parts shall be stress-relieved by means of an appropriate method to reduce stresses
and ensure dimensional stability (unless proven by the antenna designer to be unnecessary).

8.3.3

CFRP

If Carbon Fiber Reinforced Plastic (CFRP) is used, the material and fabrication processes shall be selected,
examined, and if necessary qualified with respect to strength, fatigue, and life. All CFRP structures shall beprotected against solar radiation and humidity with suitable paints and or sunshades.

8.3.4

Fasteners

All fasteners shall be metric except those on off-the-shelf units. The use of standard metric cross-sections
for construction materials is preferred but not required.

8.3.5

Paints

To limit the effect of solar heating and associated differential expansion of structural members and toprotect the structure against atmospheric corrosion, the antenna structure shall be painted with whitesolar reflecting paint. The paint shall be chosen to last at least 10 years without repainting.

8.3.6

Surface Treatment

Unpainted surfaces shall be treated against corrosion.

8.3.7

Thermal Insulation

Thermal insulation when used in an exterior application by the antenna designer shall be protected witha metal cover.

8.3.8

Rodent Protection

Antennas shall be designed to prevent rodent damage. At a minimum, this may involve protecting all cables
with flexible or rigid conduit or equivalent. Any penetrations within enclosures and raceways shall mitigate
the risk of rodent damage.

8.3.9

Name Plates and Product Marking

As a general rule, the main parts and all exchangeable units shall be equipped with nameplates which arevisible after installation of the part/unit and which contain the following information:

Page 34 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

x Part/unit namex Drawing number including revision
x Serial number
x Manufacturing month and year
x Name of manufacturer
Alternatively, a system of marking based on barcodes or similar system may be used upon approval by
ngVLA. For Line Replaceable Units (LRUs; see Section 12.3), it is highly desirable that the LRU serial
number be ascertainable over the monitor and control interface (see Section 5.9).

8.3.10 Labels
All cables and switches, junction boxes, sensors, and similar equipment shall be labeled. Electrical cabinets,
switch panels, UPS, and all electrical equipment that can be manually operated or is relevant for safety
shall be labeled in English and Spanish.

Page 35 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

9 Documentation Requirements
9.1 Technical Documentation
All documentation related to the antenna shall meet the following requirements:
x The language used for written documentation shall be English.
x Drawings shall be generated according to ISO standards and use metric units.
x Layouts of electronic circuits and printed circuit boards shall also be provided in electronicallyreadable form. The ngVLA preferred formats are Altium Designer files for electronic circuit diagrams
and printed circuit board layouts.
x The electronic document formats are Microsoft Word and Adobe PDF.
x The preferred CADsystem used is AutoDesk Inventor and/or AutoCAD.
x The preferred FEA modeling software is Siemens FeMAP NASTRAN.
Any deviation from the above shall be agreed to by ngVLA.

9.2 Software and Software Documentation
The ACU software and any other specially developed software (SW), are deliverables. The SW shall bedelivered in source and object form, together with all procedures and tests necessary for compilation,
installation, testing, upgrades and maintenance.
x Software must be tagged with suitable version numbers that allow identification (also online remotely)of a Release.
x User manuals of software developed under this specification and of any other commercial software
used (controllers embedded software, special tools, etc.) shall be provided.
x Software maintenance and installation upgrade documentation shall be provided.
x Full Test and Acceptance procedures shall be documented.

Page 36 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

Date: 2019-07-29

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Version: A

10 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A), inspection (I), a factory
acceptance test (FAT), or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which may bechecked by the ngVLA project office during the design phase by review of the design documentation.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which will bechecked by the ngVLA project office during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple inspection
or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item/assembly/unit withthe specified performance shall be demonstrated by tests. A FAT is performed w/o integration withinterfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item/assembly/unit with thespecified performance shall be demonstrated by tests. SAT is performed on-site with the equipment as
installed.
Multiple verification methods are allowed.
Table 8 summarizes the expected verification method for each requirement. This degree of verification
applies to the prototype antenna(s) only. Separate verification procedures should be developed as part ofthe verification plan to ensure all production antennas conform to the design specification (mfg. to print).
Req. #
ANT0101
ANT0102
ANT0103
ANT0201
ANT0202
ANT0203
ANT0204
ANT0205
ANT0206
ANT0207
ANT0208
ANT0209
ANT0210
ANT0211
ANT0301
ANT0302
ANT0303
ANT0401
ANT0501
ANT0502
ANT0503
ANT0611

Parameter/Requirement
Upper Operating Frequency
Lower Operating Frequency
Optimized Operating Frequencies
Optical Configuration TypePrimary Aperture Diameter and Shape
Sub-Reflector Aperture Diameter
Secondary Angle of Illumination
Reflector Offset
Focal Ratio, Primary
Cross Polarization
Reflector Shapes
Secondary Reflector Extension
Main Reflector Extensions
Mounting Configuration
Minimum Spacing
Height
Mass
Number of Antennas
Surface Accuracy, Precision
Surface Accuracy, Normal
Reflector Construction
Non-Repeatable Pointing Error, Precision

Page 37 of 45

D
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*

A

I

FAT

SAT

*
*

*
*

*
*
*
*
*
*
*
*

*

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

Date: 2019-07-29

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Req. #
ANT0612
ANT0621
ANT0622
ANT0701
ANT0702
ANT0801
ANT0802
ANT0803
ANT0901
ANT0902
ANT0903
ANT0904
ANT0905
ANT0906
ANT0907
ANT1001
ANT1002
ANT1101
ANT1201
ANT1301
ANT1411
ANT1412
ANT1413
ANT1414
ANT1415
ANT1421
ANT1422
ANT1423
ANT1424
ANT1425
ANT1430
ANT1431
ANT1432
ANT1433
ANT1434
ANT1441
ANT1442
ANT1443
ANT1444
ANT1445
ANT1446
ANT1447
ANT1451
ANT1452
ANT1453
ANT1461

Parameter/Requirement
Referenced Pointing Error, Precision
Non-Repeatable Pointing Error, Normal
Referenced Pointing Error, Normal
Focus Stability, Precision
Focus Stability, Normal
Azimuth Tracking Range
Elevation Tracking Range
Elevation Movement Range
Slew: Azimuth
Slew: Elevation
Acceleration: Azimuth
Acceleration: Elevation
Slew + Settle Time
Tracking: Azimuth
Tracking: Elevation
Stow Position - Survival
Stow Position - MaintenanceResistive Losses
Solar Observations
Spurious Signal Level
Precision Env.: Solar Thermal Load
Precision Env.: Wind
Precision Env.: Temperature
Precision Env.: Temp. Rate of Change
Precision Env.: Precipitation
Normal Env.: Solar Thermal Load
Normal Env.: Wind
Normal Env.: Temperature
Normal Env.: Temp. Rate of Change
Normal Env.: Precipitation
Ops. Limit: Solar Thermal Load
Ops. Limit: Wind
Ops. Limit: Temperature
Ops. Limit: Precipitation
Ops. Limit: Ice
Survival: Wind
Survival: Temperature
Survival: Radial Ice
Survival: Rain Rate
Survival: Snow Load - Antenna
Survival: Hail Stones
Antenna Orientation
Lightning Protection: StructureLightning Protection: Electronics Systems
Lightning Protection: Personnel
Seismic Protection

Page 38 of 45

D

*
*
*
*
*
*
*

*
*
*
*
*

*

*
*
*
*

Version: A

A
*
*
*
*
*

I

FAT

SAT
*
*
*
*
*

*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*

*
*
*

*

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

Date: 2019-07-29

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Req. #
ANT1471
ANT1481
ANT1501
ANT1502
ANT1503
ANT1601
ANT1602
ANT1603
ANT1604
ANT1605
ANT1606
ANT1701
ANT1702
ANT1703
ANT1704
ANT1705
ANT1706
ANT1801
ANT1802
ANT1803
ANT7001
ANT7002

Parameter/Requirement
Site Elevation
Wind Vibration
Preventive Maintenance Cycle
Preventive Maintenance Effort
Mean Time Between Failure
Antenna Control Unit (ACU)
Servo Loops
Self-Monitoring
Weather Monitoring
Network Hardening/Authentication
Remote Reset
Software Limits
Hardware Limits
Hard Stops
Safety Lock-Out
Fire Alarm
Fail Safe Brakes
Design Life
Lifecycle Optimization
Country of Origin
Code Compliance
Safety of Personnel

Table 8 - Expected requirements verification method.

Page 39 of 45

D**

Version: A

A
*
*
*
*
*

*

I

FAT

*
*

*
*
*
*
*
*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*
*

SAT

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

11 Key Performance Parameters
This section provides Key Performance Parameters that should be estimated by the designer andmonitored by NRAO throughout the design phase of the project. These parameters have a large influenceon the eventual effectiveness of the facility, and are useful high-level metrics for trade-off decisions.
These parameters are of higher importance to NRAO. Improved performance above the requirement isdesirable on these parameters. The impact on system-level performance is often discussed in the narrativein Section 4.
NRAO’s expectation is that the specified technical requirements will not push technical boundaries.
Rather, the key challenge of this antenna design is to deliver a design that can be manufactured in volume
and delivered affordably. A second challenge is reducing the maintenance burden and total lifecycle cost.
Given these expectations, the technical requirements are generally specified as minimum values. The goal
is to give the designer some latitude in optimization for a balanced design. Understanding the anticipatedperformance of the antenna (not just its specified minimum) on these parameters is of value for systemlevel analysis and performance estimation.
These parameters may also be useful for determining the relative priority of the requirements documented
in Section 4 and can assist in the required analysis should tensions be identified between requirements, or
reductions in capability be required to fit within cost constraints.
The Key Performance Parameters that have been identified for monitoring are described in Table 9. Notethat the order in the table reflects the order in the document, and is not indicative of relative importanceor priority.
Key Performance Parameter
Minimum Spacing
Surface Accuracy, Precision Environment
Surface Accuracy, Normal Environment
Non-Repeatable Pointing Error, Precision Environment
Referenced Pointing Error, Precision Environment
Non-Repeatable Pointing Error, Normal Environment
Referenced Pointing Error, Normal Environment
Elevation Range (Lower Elevation Limit)
Slew: Azimuth
Slew: Elevation
Acceleration: Azimuth
Acceleration: Elevation
Slew + Settling Time
Tracking: Azimuth
Tracking: Elevation
Preventive Maintenance Cycle
Preventive Maintenance Effort
Mean Time Between Failures
Design Life
Table 9 - Key performance parameters for monitoring during design.

Page 40 of 45

Req. #
ANT0301
ANT0501
ANT0502
ANT0611
ANT0612
ANT0621
ANT0622
ANT0802
ANT0901
ANT0902
ANT0903
ANT0904
ANT0905
ANT0906
ANT0907
ANT1501
ANT1502
ANT1503
ANT1801

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

12 Appendix
12.1 Abbreviations and Acronyms
Acronym
ACU
AD
ATF
CDR
CoDR
CFD
CFRP
CW
EIRP
EMC
EMI
EMP
FDR
FEA
FOV
FWHM
HVAC
ICD
IF
KPP
LCD
LED
LO
LRU
MTBF
MTTF
MTTR
ngVLA
RD
RFI
RMS
RSS
RTP
SAC
SAT
SNR
SRSS
SWG
TAC
TBD
VLA
WVR

Description
Antenna Control Unit
Applicable Document
Antenna Test Facility (at the VLA Site)
Critical Design Review
Conceptual Design Review
Computational Fluid Dynamics
Carbon Fiber Reinforced Plastic
Continuous Wave (Sine wave of fixed frequency and amplitude)
Equivalent Isotropic Radiated PowerElectro-Magnetic Compatibility
Electro-Magnetic InterferenceElectro-Magnetic Pulse
Final Design Review
Finite Element Analysis
Field of View
Full Width Half Max (of Primary Beam Power)
Heating, Ventilation & Air Conditioning
Interface Control Document
Intermediate Frequency
Key Performance Parameters
Liquid Crystal Display
Light Emitting Diode
Local Oscillator
Line Replaceable Unit
Mean Time Between Failure
Mean Time To Failure
Mean Time To Repair
Next Generation VLA
Reference Document
Radio Frequency Interference
Root Mean Square
Root of Sum of Squares
Round Trip Phase
Science Advisory Council
Site Acceptance Test
Signal to Noise Ratio
Square Root Sum of the Square
Science Working Group
Technical Advisory Council
To Be Determined
Jansky Very Large Array
Water Vapor Radiometer

Page 41 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

12.2 Coordinate System
12.2.1 Antenna Pad Coordinate System
The Antenna Pad Coordinate System (or Foundation Coordinate System) is indicated by Op, Xp, Yp, Zp.
to denote the origin and three Cartesian coordinate vectors, as shown in Figure 2.

Figure 2 - Cartoon of the antenna pad coordinate system and major axes. Separate Cartesian reference frames
define each mirror surface, the focus, and the pad respectively. Antenna design is diagrammatic only.

The Pad Coordinate system is based on the right-hand rule, with the Zp corresponding to the local vertical,
positive direction toward zenith, Xp axis pointing to the geographical North, and the YP axis pointing togeographical West. The origin of the system is in the plane of the embedded flanges at the antenna pad,at the nominal center of the as-built pad, as defined by the kinematic mount of the antenna.

12.2.2 Main Reflector (MR) Coordinate System
The MR coordinate system is a Cartesian coordinate system, based on the right hand rule, fixed to thefocus of the reflector. This system of coordinates is indicated by OMR, XMR, YMR ,ZMR as shown in Figure 3.

Page 42 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

The X–Y plane is perpendicular to the antenna beam, with the XMR axis perpendicular to the elevation
axis, the ZMR axis is parallel to the nominal boresight of the antenna, positive toward the source, and the
YMR axis according to the right hand rule. As such, when the azimuth of the antenna is equal to zero, theYMR axis is parallel, to the Yp axis.

12.2.3 Secondary Reflector (SR) Coordinate System
The SR coordinate system is a Cartesian coordinate system, based on the right hand rule, fixed to thefocus of the main reflector (OSR = OMR). This system of coordinates is indicated by OSR, XSR, YSR ,ZSR as
shown in Figure 3.
The Y-axis is shared with the MR coordinate system. The XSR-axis and ZSR-axis are rotated from the MRaxes by the tilt angle beta ( ).

12.2.4 Focal Plane Coordinate system
The focal plane coordinate system is defined in Figure 3.
This coordinate system is also a Cartesian coordinate system, with coordinates indicated by F0, XF, YF, ZF.
The position of the origin, F0, is the nominal secondary focus of the antenna. ZF is towards the projected
midpoint of the secondary mirror as seen from OF. The YF axis is parallel to YMR and YSR, and the XF axis
according to the right hand rule.

12.2.5 Azimuth of the Antenna
The Azimuth angle shall be zero when the antenna is rotated so that YMR is pointing toward West. The
Azimuth angle origin is then counted from the negative XP (South), positive direction when the antenna
moves in the clockwise direction (Azimuth angle = 90 when YMR is pointing toward North).

Page 43 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

Figure 3 - Antenna optical coordinate system. Separate Cartesian reference frames define each reflector
surface and the secondary focus.

12.2.6 Elevation of the Antenna
The Elevation shall be set to zero when the ZMR axis is pointing to horizon and to +90 when the ZMR axis
is pointing toward zenith.

12.3 Maintenance Definitions
12.3.1 Maintenance Approach
Required maintenance tasks shall be minimized. Maintenance shall be mainly performed at assembly andsubassembly level by exchange of Line Replaceable Units (LRUs). LRUs are defined as units which can beeasily exchanged (without extensive calibration, of sufficient low mass and dimension for easiness ofhandling, etc.) by maintenance staff of technician level.

Page 44 of 45

Title: Antenna Preliminary TechnicalRequirements

Owner: Dunbar

NRAO Doc. #: 020.25.00.00.00-0001-REQ-AANTENNA_PRELIM_TECH_REQS

Date: 2019-07-29
Version: A

LRU exchange shall be possible by 2 trained people within 4 working hours on the installed antenna. It is
desirable that LRU replacement be possible without a boom truck, basket or scissor lift, using only
standard tools and special tools identified in the antenna maintenance manual. A step-by-step procedure
for safe exchange of every LRU shall be provided in the Maintenance Manual. The following equipment
shall be considered an LRU as a minimum:x Subreflector mechanism (if provided)x Elevation encoder(s)x Azimuth encoder(s)x Drive Motors
x Electronic cards and drivesx Stow pin assemblies (if provided)
x End stops
x Elevation cable wrap parts (excluding cables and cable installation)x Locking pins
x Lightning arrestorsx Temperature sensors
x Anemometersx Additional metrology sensors (if provided)
x Limit switches
Other LRUs shall be defined by the antenna designer, depending on the design. The LRUs will bemaintained by the ngVLA project (with or without industrial support).

12.3.2 Periodic Preventive MaintenancePreventive maintenance is performed at planned intervals in order to maintain the antenna operational
and within its specified performance. This includes checking, greasing, substitution of consumables, visualinspection, etc. All maintenance operations shall be planned in a Programmed Check and Intervention List
(PCIL) of the Maintenance Manual, which shall list the tools, the procedures and the time necessary for
their execution and their periodicity.
The antenna design shall enable these maintenance activities to be performed with the antenna stowed in
the “maintenance stow” position as defined in Section 4.10. The normal preventive maintenance shall not
exceed the requirements established in Section 4.14.7. Any greasing operation or lubrication activity thatneeds to be performed at interval shorter than 12 months shall be automatic.

12.3.3 Overhaul
Overhaul is a planned major maintenance operation that is performed at the antenna site. The following
applies:x No overhaul operation shall last longer than three weeks.
x No overhaul operation shall be required at intervals shorter than 20 years.
x Periodic painting and surface protection shall not be necessary more often than every ten years.
x Overhaul activities, including painting and possible exchange of azimuth and elevation bearings, shallbe described in the Maintenance Manual.

Page 45 of 45

Title: ngVLA Optical Reference Design:

Owner: L. Baker

NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

ngVLA Optical Reference Design:
Analysis of the ngVLA Antenna Optical Design #6 with
Ideal and Actual Feed020.25.01.00.00-0001-REP-A-ANTENNA_OPTICAL_REF_DESIGN_REPORT

Status: RELEASEDPREPARED BY

DATE

L. Baker

2018-01-08

APPROVALS (Name and Signature)
R. Selina,
2019.07.29
Project Engineer
14:32:30 -06'00'
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.29 14:41:09 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-29

Asst. Director,
NM-Operations, NRAO

2019-07-29

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.29 14:41:27 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-29

Page 1 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Change Record
Version1
2

Date
2018-01-08
2019-06-14

Author
L. Baker
R. Carver

ReasonFirst distributed version of the document.
Formatting and applying template.

3

2019-06-19

A. LearCopyediting and preparation for approvals.

4

2019-06-23

R. Selina

Minor corrections for release as part of the reference design.

A

2019-07-29

A. LearPrepared PDF for signatures and release.

Page 2 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Table of Contents
1
2
3
4
5
6
7
8

Introduction ................................................................................................... 4
High-Efficiency Mapping Function................................................................ 4
Optical Design and Reflector Geometry ..................................................... 6
Physical Optics Analysis with an Ideal Feed ................................................ 7
Tipping Curve with an Ideal Feed .............................................................. 12
Physical Optics Analysis with an Actual Feed ........................................... 14
Tipping Curve with an Actual Feed ........................................................... 21
Conclusions .................................................................................................. 22

Page 3 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

1 Introduction
This document presents a reference design targeting high-efficiency optics for the ngVLA. A new aperture
illumination function and its corresponding mapping function underlies this shaped design. The ngVLA
specifications allow for higher than typical near-in sidelobes, which allows for a nearly uniform, highefficiency aperture illumination. However, a high-efficiency design still must have very low spillover so thatnoise temperature is minimized. The design presented here achieves both of those goals along with very
low intrinsic cross polarization and excellent beam symmetry.

2 High-Efficiency Mapping Function
A new mapping function that provides very high illumination efficiency has been developed andimplemented in the dual reflector shaping software. This function gives a uniform aperture illumination
over almost all of the aperture, with a sharp roll-off near the edge. The function is a scaled and translated
version of a hyperbolic tangent function.
The equation for this function is displayed in Figure 1, where it is plotted for the parameters used in thisdesign. The parameter t sets the steepness of the roll-off and x0 is chosen indirectly to give the desirededge taper at scaled radius = 1. Figure 1 is for t = 10 and x0 is chosen to give an edge taper of .1, –10 dB.
The calculated efficiency of this illumination is .95. It is to be expected that an illumination this uniform
will result in higher than typical near-in sidelobes.

Figure 1 - Aperture illumination relative amplitude.

This function has several useful features besides its general shape of being flat over most of the aperture.
It is continuous with continuous derivatives and is composed of a single function over the whole span. It
is integrable in closed form on the unit disk (by Mathematica), which facilitates manipulations to obtainthe mapping function. It does not go negative for scale radii above one, which allows shaping of thereflectors with extension points beyond the nominal physical edges.
The desired mapping from the feed to the aperture is provided by the transformation given by the shaped
optics. The feed pattern function here is taken as a cosine raised to a noninteger power. The power ischosen to give the desired edge taper on the rim of the subreflector. This function also integrates in closed
form in spherical coordinates. In this design, the edge angle is 55° and the chosen edge taper is –16 dB.

Page 4 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Transforming this deeply tapered feed pattern to the aperture illumination shown in Figure 1 requires
significant redistribution of power, which is described by the mapping function shown in Figure 2. This
curve is obtained by equating the integral power inside a given elevation angle at the feed to the same
integral power inside the corresponding radius in the aperture. The plot is scaled by the maximum
elevation angle and aperture radius so the curve goes from the point 0,0, which is the central ray, out tothe point 1,1, which is a ray on the edges of the subreflector and primary. The plot extends beyond thepoint 1,1 so the reflector shapes can have extension points beyond the physical edges. The dashed straightline passes through the points 0,0 to 1,1 and is close to what a conic section design produces.

Figure 2 - Scaled mapping function.

The effect of the mapping function can be described as follows. Near the center of the reflectors, theslope of the map is greater than the straight line, which gives a larger increment in radius for a given
increment in elevation. This results in the intense central peak of the feed pattern being spread out overa larger area in the aperture plane, reducing its intensity.
Near the middle of the map, the slope is the same as the line and the spreading is moderated. In this area,
the feed pattern is lower and less spreading gives an aperture intensity which is the same as near thecenter. Beyond the middle, the slope of the map is less than the line and this corresponds to the feed
intensity being squeezed to raise the intensity in the aperture. The feed pattern is even smaller in thisregion and the squeezing keeps the aperture intensity uniform. At the very end, the slope starts to increaseagain, which along with the very low feed intensity provides the sharp roll-off in intensity at the very edgeof the aperture. The resultant intensity in the aperture is quite sensitive to small changes in the mapping
function because of this derivative behavior. This requires a lot of attention to the calculation and software
implementation of any mapping function.

Page 5 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

3 Optical Design and Reflector Geometry
Figure 3 shows the cross section of the optical design implementing the mapping function. The geometricparameters are the ngVLA antenna specifications: an 18-meter diameter aperture, a 3.5-meter diameter
subreflector, and a 55° half opening angle. This design has the subreflector spaced a longer distance fromthe lower, left edge of the primary. This has the beneficial effect of reducing the tilt angle of the primaryand making it somewhat smaller at the expense of a longer feed arm. This choice of the geometry was
made in collaboration with the structural design team. The tilt angle of the central ray from the focus is
optimized to give low cross polarization, analogous to the Mizugutch condition in conic sections.
The numbers above the secondary and below the primary are the rim-to-rim distance, the area of thesurface, and the area of the surface as a fraction of the aperture area.
The behavior described in the mapping section can be seen in the cross section of the optics shown in
Figure 3. The rays emanating from the focus are equally spaced in elevation angle. The spacing of the raysin the aperture is larger near the center and get progressively closer together moving outward. The lastradial increment at the edge is slightly bigger, which contributes to the deep roll-off in intensity there.
For reference when discussing the physical optics analysis, note the distance from the focus to the surfaceof the secondary varies by roughly a 2:1 ratio across the span of elevation angles. At lower frequencies,
this places the left part of the secondary in the near field of the feed. Another effect is that the area on
the secondary inside a quadrilateral formed by four adjacent rays varies by the same 2:1 ratio. These
effects combine to blur the illumination of the secondary towards the primary in the vicinity of the ray
going to the far right edge of the primary. This gives a progressively larger spillover over the right edge ofthe primary at lower frequencies.

Figure 3 - ngVLA_6 Optics: Cross-section in the symmetry plane.

Page 6 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

4 Physical Optics Analysis with an Ideal Feed
The geometry shown in Figure 3 was imported into GRASP for analysis. The first analysis is done with an
ideal Gaussian feed pattern having a –16 dB edge taper at 55°. This differs slightly from the cosine functionused to develop the mapping function but is the best available choice in GRASP.
This first analysis was performed at 5 GHz, which is a good compromise between fast runs and avoiding
most low-frequency diffraction effects. Analyzing the optics with a perfect feed establishes a baseline
performance so the effects of a real feed can be seen separate from the optics performance.
The copolar aperture illumination on the plane at z = 0 is shown in Figure 4. The illumination is nearly
uniform across the aperture with a steep roll-off at the edge. This confirms that the design mapping
function was successfully achieved. Although obscured by the wide logarithmic scale, there is somediffraction ripple across the aperture plane, which is expected since the z = 0 plane is some distance fromthe primary reflector. The left side of the plot shows the interference effects of the feed spilloverinteracting with the aperture illumination. This does not affect the main beam performance since thespillover and aperture project to different angles in the far field.

Figure 4 - Copolar aperture illumination on the plane at z = 0.

Page 7 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Figure 5 shows the close-in far-field pattern in three azimuth cuts at 0°, 45°, and 90°. The vertical scale isgain over isotropic in dB. The peak gain is 59.0 dB, which corresponds to an overall efficiency of .89. The
illumination efficiency is .95 and the feed spillover past the secondary is a factor of .98.
Other small factors combine to give the final overall efficiency. The first sidelobe level is –19 dB below
peak. The second sidelobe level about –27 dB. These values are higher than typical designs with conics
and result from the nearly uniform aperture illumination. The maximum cross-polar level is about –45 dB
below the main beam peak. The cross polarization is everywhere zero in the symmetry plane and peaksin the plane perpendicular to the symmetry plane. The intrinsic cross polarization of the optics is verysmall, smaller than the cross polarization introduced by any realistic feed. The rotational symmetry of themain beam is essentially perfect.

Figure 5 - Close-in far-field pattern using azimuth cuts at 0°, 45°, and 90°.

Page 8 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

To better understand the wide-angle pattern and especially the tipping curve, it is useful to visualize theentire far-field sphere to see the general features. Figure 6 and Figure 7 show the far-field sphere in two
halves, the north and south hemispheres. Each hemisphere is projected and plotted on a unit disk, which
distorts the view slightly but still gives a good sense of the features. The color bar gives the scaling in dBi.

Figure 6 - Unit disk projection of the far-field response, north hemisphere.

There are two main features outside of the main beam at the North Pole. In the north hemisphere, thefeed spillover past the secondary is very clear. The feed tilt angle is about –25° with an opening angle of+/–55°. In the symmetry plane, the spillover is just past the geometric edges at –80° and 30°. Perpendicular
to the symmetry plane, the spillover is just past +/–55°.
On the right side of the north hemisphere, there is a small part of the secondary spillover past the primary.
This area corresponds to the ray that goes from the left edge of the secondary to the right edge of the
primary and is slightly above the horizon.

Page 9 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Looking at the arc of the secondary spillover above the horizon shows it is slightly more intense than therest of the secondary spillover seen in the south hemisphere. As discussed above, this is due to that partof the secondary being closer to the focus. The effect is very minor at 5 GHz and will get smaller at higher
frequencies and larger at lower frequencies.

Figure 7 - Unit disk projection of far-field response, south hemisphere.

Page 10 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Figure 8 shows the far-field pattern over the entire range of elevation angles and the same three azimuth
cuts. The main features here are the very low wide-angle sidelobes. The peaks of the wide pattern are atleast –6 dB below isotropic except the small peak at 85° which is the spillover past the primary discussed
above. The other peaks correspond to various parts of the feed spillover as shown above.

Figure 8 - Plot of far-field pattern over the entire range of elevation angles and azimuth cuts of 0°, 45°, and 90°.

One effect might slightly disturb the far-field main beam: The edge diffraction past the rim of the secondaryfans out in a range of angles, some of which are essentially parallel to the main beam. This small
contribution to the main beam has a different path length and goes in and out of phase with varying
frequency. This produces a small gain ripple versus frequency on boresight. This effect was first
documented by the South African MeerKAT/SKA team. In this case, it is mitigated by the very deep edge
taper on the secondary. A future calculation could quantify its effect here.

Page 11 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

5 Tipping Curve with an Ideal Feed
A key parameter of the antenna design is the contribution to system noise temperature from spillover
outside of the main beam area at all pointing angles. To calculate this, a model of the noise environment
surrounding the antenna is required. Figure 9 shows the SKA standard noise model at 5 GHz. Comparison
with site specific data at the VLA site shows this model to be slightly pessimistic in the upper hemisphere.
The contribution of the receiver is not included in these plots.
To compute the tipping curve, the noise model is multiplied by the antenna pattern at various tilt angles
and integrated over the sphere. To simplify the calculation the simple noise model is tilted instead of thecomplicated antenna pattern, but the result is the same.

Figure 9 - SKA noise model of brightness temperature at 5 GHz.

The result of the calculation is shown in Figure 10 for both feed arm up and feed arm down pointing. The
noise model is also shown so that the effect of spillover can be directly seen. If the antenna pattern was adelta function, then the tipping curve would be the same as the noise model. Any difference is due to thesmall wide-angle spillover illuminating various parts of the noise model.

Figure 10 - ngVLA Design #6, tipping curve at 5 GHz with ideal feed and SKA noise model.

Page 12 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

There is only a small difference between feed up and feed down pointing. Feed arm down pointing steadilyrotates the feed spillover on to the warm ground while the spillover past the primary rotates up on to
the cold sky. In this case the feed spillover is a bit larger so the net effect is a slightly larger noise increase.
The converse happens for feed up pointing. The feed spillover stays on the sky until at larger zenith angles
where the part at +30° crosses the horizon. The smaller spillover past the primary rotates completely on
the ground and stays there.
The MeerKAT and SKA antenna designs from the South African design team have an extension on thelower edge of the subreflector, which redirects part of the feed spillover to over the far edge of the
primary. For feed arm down pointing, this mitigates the effect of the feed spillover striking the ground andgives a better result. Such an extension could be investigated as an addition to this design.
Another possible way to improve the tipping curve would be increasing the edge taper on the secondary
to a level below –16 dB, capturing more of the feed energy in the optics.
Reiterating a point discussed before, the slightly larger spillover due to diffraction effects on the secondary
will get larger as the frequency goes lower. In the SKA case, where the operating frequency goes well
below 1 GHz, it gets very large and dominates the tipping behavior. Conversely, at frequencies higher than
the 5 GHz here, it will get even smaller.
For comparison to other designs and reports, Figure 11 plots the difference between the noise model andtipping curves in Figure 10. Leaving the details aside, the spillover noise contribution is very small overall.
At the higher-frequency bands of the ngVLA, the sky and receiver temperatures will dominate over thissmall contribution.

Figure 11 - ngVLA Design# 6, spillover curve at 5 GHz with ideal feed and SKA noise model.

Page 13 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

6 Physical Optics Analysis with an Actual Feed
The optics are next analyzed with the corrugated horn feed shown in Figure 12, with the pattern plot in
Figure 13. This axial ring design was developed for the DVA1 project at L-band. It has excellent
performance over an octave bandwidth and is compact, an important trait at L-band. The original L-band
design was scaled to the frequency range of 4 to 8 GHz, which places the 5 GHz analysis frequency in thelower part of the frequency coverage.
The performance with this feed is very close to the performance with a perfect feed. The commentary in
the previous sections applies, with small changes, so only the differences in the two cases will be discussed.

Figure 12 - Cross-section of corrugated feed horn used for analyzing the ngVLA_6 optics performance.

Page 14 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

The feed pattern in Figure 13 has an edge taper slightly deeper than –16 dB. However, when placed in the
optics, it has a slightly larger spillover than the perfect Gaussian feed. This may be due to a difference inoverall shape and possibly small phase errors in outer edges of the feed illumination.
Otherwise, the pattern is almost perfectly rotationally symmetric and has small cross polarization, whichis zero in the principle planes and peaks in the diagonal planes.

Figure 13 - ngVLA_6 feed pattern plot, using the corrugated horn feed shown in Figure 12.

Page 15 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

The illumination in the z = 0 aperture plane (Figure 14) is very similar to before. The diffraction ripple isa little more evident, which may be due to this plot being generated with quadruple the number of data
points. The deep cutoff at the edge is still the same. The interference effect on the left side is a little more
extensive, evidence that the spillover from this horn feed is slightly larger than the perfect feed.

Figure 14 - Illumination pattern of ngVLA_6 in z = 0 aperture plane using the corrugated feed horn.

Page 16 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

The close-in beam pattern is shown is Figure 15. The peak gain is 58.9 dBi, which is slightly lower andcorresponds to an overall efficiency of 0.87. The small drop in efficiency is partly caused by small phaseerrors in the real feed. Any realistic feed will have some phase errors in the low level parts of the pattern.
Another difference is the increased cross polar level in the diagonal plane. Corrugated horns have a “fourleaf clover” cross polar pattern, and this is what causes the increased cross polar level. It is still quite small
at about –32 dB below peak and the peak is outside the –3 dB level on the main beam. There is also a tiny
asymmetry in the sidelobes.

Figure 15 - Plot of close-in beam pattern for ngVLA_6 using the corrugated feed horn.

Page 17 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Figure 16 and Figure 17 show the pattern on the far-field sphere. The slightly larger spillover of the feed
past the secondary is evident. This will have a small effect on the tipping curve, especially feed down.
Otherwise, all of the previous commentary holds.

Figure 16 - Unit disk projection of far-field illumination pattern using corrugated feed horn, north hemisphere.

Page 18 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Figure 17 - Unit disk projection of far-field illumination pattern using corrugated feed horn, north hemisphere.

Page 19 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

Figure 18 shows the wide-angle far-field pattern. All of the general features are the same with the peaksof the feed spillover being approximately 1 dB larger.

Figure 18 - Plot of wide-angle far-field illumination pattern using corrugated feed horn.

Page 20 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

7 Tipping Curve with an Actual Feed
Figure 19 shows the tipping curve, which is mostly similar to before with an extra .5 Kelvin at zenith andthe feed down curve being somewhat worse. Again, for feed down, a subreflector extension would likely
improve the performance.

Figure 19 - ngVLA_6 tipping curve at 5 GHz with corrugated feed horn and SKA noise model.

Figure 20 shows spillover performance. The spillover temperature differs notably between feed arm up
and feed arm down.

Figure 20 - ngVLA_6 spillover curve at 5 GHz with corrugated feed horn and SKA noise model.

Page 21 of 22

Title: Analysis of the ngVLA Antenna
Owner: L. Baker
Optical Design #6 with Ideal andActual Feed
NRAO Doc. #: 020.25.01.00.00-0001-REP-AANTENNA_OPTICAL_REF_DESIGN_REPORT

Date: 2019-07-29
Version: A

8 Conclusions
This first design for the ngVLA antenna optics is very successful, achieving both high efficiency and very
low antenna temperature. The performance with a realistic feed horn is very close to the performancewith a mathematically perfect feed at 5 GHz.
It should be emphasized that the performance is dominated by the choice of feed. Other possible feeds
should be analyzed in the optics to compare performance results. This first design could be modified withan extension on the subreflector or a modification to the optics to improve the feed-down tipping. Reviewof the overall geometry from a structural perspective might also suggest changes.

Page 22 of 22

101-0000-001-PDD-001
Revision: 1

ngVLA 18m Antenna Preliminary Design Document
Document Number...................................................................................... 101-0000-001-PDD-001
Revision: ......................................................................................................................................... 1
Author ...................................................................................................................... Dean Chalmers
Date ................................................................................................................................ 2019-07-25
Status ................................................................................................................................ Released
Classification..................................................................................................................Unrestricted

Prepared By
Reviewed By

Approved By
Issued By

Name
Organisation
Name
Organisation
Name
Organisation
Name
Organisation
Name
Organisation
Name
Organisation

Dean Chalmers
NRC
Gordon Lacy
NRC

Signature
Signature
Signature
Signature

Scott Roberts
NRC
Donna Morgan
NRC

Signature
Signature[This document describes preliminary design for the ngVLA 18m Antenna Design project.]2019-07-25

Page 1 of 99

101-0000-001-PDD-001
Revision: 1

DOCUMENT HISTORY
Revision

Date

Change Request

Change Description

A

17Sep2018

Initial draft for comment

B

24Jan2019

Post PDR Update

1

25July2019

Approved for release

DOCUMENT SOFTWARE
Application

Wordprocessing

VersionFilename

101-0000-001-PDD001_PreDesignDoc_1_2019-07-25

MSWordORGANISATION DETAILSDesignation

Primary Author and Responsible Organisation
Contributors

2019-07-25

Name

Dean Chalmers
G. Lacy
M. Islam
M. Fleming
M. Wessel
R. Osterried
R. Hellyer
J. Fitzsimmons
L. Baker
B. Veidt

Organisation

NRC
NRC
NRC
Minex
SED Systems
SED Systems
NRC
NRC
Consultant
NRC

Page 2 of 99

101-0000-001-PDD-001
Revision: 1

TABLE OF CONTENT
1INTRODUCTION............................................................................................................... 10
1.1
Purpose of Document ............................................................................................ 10
1.2
Scope of Document ............................................................................................... 10
1.3
Intended Audience................................................................................................. 10
1.4
Project WBS .......................................................................................................... 112

APPLICABLE AND REFERENCE DOCUMENTS ............................................................ 12
2.1
Applicable Documents ........................................................................................... 12
2.2
Reference Documents ........................................................................................... 12

3

OPERATIONAL CONTEXT .............................................................................................. 14
3.1
Operational Environment ....................................................................................... 14

4

ASSUMPTIONS AND RISKS............................................................................................ 17
4.1
Assumptions .......................................................................................................... 17
4.1.1
SRC Transportation to Antenna Locations .............................................. 17
4.2
Risks...................................................................................................................... 17

5

PRELIMINARY DESIGN ................................................................................................... 21
5.1
Design Background................................................................................................ 22
5.2
Design Overview.................................................................................................... 25
5.2.1
Elevation Rotating Assembly .................................................................. 25
5.2.2
Mount ..................................................................................................... 39

6

PERFORMANCE .............................................................................................................. 54
6.1
System Noise Contribution..................................................................................... 54
6.2
Integrated Model Finite Element and Electromagnetic Analysis ............................. 55
6.3
Aperture Efficiency................................................................................................. 56
6.3.1
Simulated Efficiencies............................................................................. 57
6.3.2
Calculated Efficiencies............................................................................ 82
6.3.3
Total Efficiency ....................................................................................... 85
6.4
Pointing.................................................................................................................. 87
6.5
Survivability ........................................................................................................... 92
6.6
Potential Areas of Improvement ............................................................................. 92

7

MAINTENANCE, RELIABILITY AND LIFETIME .............................................................. 95
7.1
Maintenance and Reliability ................................................................................... 95

2019-07-25

Page 3 of 99

101-0000-001-PDD-001
Revision: 1
7.2
8

Design Life............................................................................................................. 96

FUTURE WORK ............................................................................................................... 97
8.1
Design and Analysis .............................................................................................. 97
8.1.1
Drive System Trade Study ...................................................................... 97
8.1.2
iBUS to oBUS Connection ...................................................................... 97
8.1.3
Surface Adjusters ................................................................................... 97
8.1.4
Feed/Secondary Support Structure......................................................... 97
8.1.5
Feed Indexer........................................................................................... 97
8.1.6
Complete Integrated FEA Model ............................................................. 97
8.1.7
Yoke Structure Optimization ................................................................... 98
8.1.8
Multi-piece Primary Reflector Concept .................................................... 98
8.2
Logistics................................................................................................................. 98
8.3
Prototyping and Testing ......................................................................................... 98
8.3.1
Surface Adjusters ................................................................................... 98
8.3.2
Process Induced Distortion Study ........................................................... 98
8.3.3
Multi-piece Concepts .............................................................................. 98
8.4
Materials Analysis and Testing .............................................................................. 98

2019-07-25

Page 4 of 99

101-0000-001-PDD-001
Revision: 1

LIST OF TABLES
Table 1 Applicable Documents...................................................................................................... 12
Table 2 Reference Documents...................................................................................................... 12
Table 3 Precision Operating Conditions ........................................................................................ 14
Table 4 Normal Operating Conditions ........................................................................................... 15
Table 5 Limit to Operating Conditions ........................................................................................... 15
Table 6 Survival Conditions .......................................................................................................... 16
Table 7 Project Risks .................................................................................................................... 18
Table 8 Product Risks................................................................................................................... 19
Table 9 Elevation Drive Loads (based on average wind speeds) .................................................. 41
Table 10 Elevation Drive Performance Matrix ............................................................................... 43
Table 11 Azimuth Rotating Structure Components........................................................................ 46
Table 12 Azimuth Drive Loads (based on average wind speeds) .................................................. 48
Table 13 Direct Drive Azimuth Motor Performance Matrix............................................................. 50
Table 14 Azimuth Direct Pinion Drive Performance Matrix ............................................................ 52
Table 15 System Noise Contributions Requirement ...................................................................... 54
Table 16 Aperture Efficiency Related Requirements ..................................................................... 56
Table 17 Proposed Antenna Efficiency Specification ................................................................... 57
Table 18 Gain for Undistorted Surfaces ........................................................................................ 61
Table 19 Gain and Efficiency, Gravity Load Cases ....................................................................... 67
Table 20 Gain and Efficiency, Wind Load Cases........................................................................... 74
Table 21 Primary Reflector Component CTEs .............................................................................. 75
Table 22 Gain and Efficiency, Thermal Load Cases...................................................................... 81
Table 23 Precision Operating Target Surface Accuracy Error Budget .......................................... 82
Table 24 Normal Operating Target Surface Accuracy Error Budget ............................................. 82
Table 25 Secondary Surface Accuracy Precision.......................................................................... 83
Table 26 Secondary Surface Accuracy Normal............................................................................. 83
Table 27 Secondary Reflector Efficiency Precision ....................................................................... 84
Table 28 Secondary Reflector Efficiency Normal .......................................................................... 84
Table 29 Primary Surface Accuracy Precision .............................................................................. 84

2019-07-25

Page 5 of 99

101-0000-001-PDD-001
Revision: 1
Table 30 Primary Surface Accuracy, Normal................................................................................. 85
Table 31 Primary Reflector Efficiency Precision ............................................................................ 85
Table 32 Primary Reflector Efficiency Normal ............................................................................... 85
Table 33 Efficiency Calculation Cases .......................................................................................... 86
Table 34 Aperture Efficiency, Precision Operating Condition ........................................................ 86
Table 35 Aperture Efficiency, Normal Operating Condition ........................................................... 87
Table 36 Estimated Efficiency for All Frequency Bands, Precision................................................ 87
Table 37 Estimated Efficiency for All Frequency Bands, Normal ................................................... 87
Table 38 Precision Pointing Requirements.................................................................................... 88
Table 39 Normal Pointing Requirements....................................................................................... 88
Table 40 Reference Pointing Model Compensation ...................................................................... 89
Table 41 Pointing Errors; Precision, Uncompensated (except SPEM)........................................... 90
Table 42 Pointing Errors; Normal, Uncompensated (except SPEM).............................................. 91
Table 43 Maintenance Requirements............................................................................................ 95
Table 44 Design Life Requirements .............................................................................................. 96

LIST OF FIGURES
Figure 1 NRC ngVLA 18m Antenna Design Concept .................................................................... 21
Figure 2 NRC Mk1 Dish ................................................................................................................ 22
Figure 3 NRC Mk2 Dish ................................................................................................................ 23
Figure 4 Allen Telescope Array 6m Antenna ................................................................................. 23
Figure 5 DVA1 Antenna ................................................................................................................ 24
Figure 6 NRC 15m Antenna Study................................................................................................ 25
Figure 7 Primary surface edge adjuster tab concept ..................................................................... 26
Figure 8 Primary surface edge adjuster with oBUS ....................................................................... 27
Figure 9 Surface Reinforcement Patches...................................................................................... 27
Figure 10 Assembled oBUS structure ........................................................................................... 28
Figure 11 oBUS assembly details ................................................................................................. 29
Figure 12 Cross Section of Antenna at Low (12º) Elevation Angle ................................................ 30
Figure 13 iBUS with its 11 Discrete Connection Points to the oBUS ............................................. 30

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Figure 14 iBUS structure............................................................................................................... 31
Figure 15 Secondary Support Structure. ....................................................................................... 32
Figure 16 Stiffening Ribs on Primary Reflector to Support Secondary Support Structure .............. 33
Figure 17 Secondary and Feed Support Structure. ....................................................................... 33
Figure 18 Primary Surface cut Panel Dimensions [ft] .................................................................... 34
Figure 19 Proposed multi-piece primary surface connection detail................................................ 35
Figure 20 Cross section through one of the primary surface joining bolts showing the inserts ...... 35
Figure 21 Lifting points added to one of the 4 primary surface panels........................................... 36
Figure 22 Assembly jig for the primary surface parts..................................................................... 37
Figure 23 One of the four primary surface parts on its transport jig and flat deck trailer ................ 37
Figure 24 Nesting multiple instances of primary surface pieces for transport to remote sites ........ 38
Figure 25 Four primary surface parts being added to the assembly jig.......................................... 38
Figure 26 Elevation Drive Stator Pylon Structure .......................................................................... 40
Figure 27 Elevation Drive Load Path and Drive Components........................................................ 41
Figure 28 Elevation Drive Configuration........................................................................................ 42
Figure 29 Azimuth Rotating Structure ........................................................................................... 45
Figure 30 Yoke and Elevation Drive Structure............................................................................... 45
Figure 31 Azimuth Bearing Detail.................................................................................................. 46
Figure 32 Azimuth Pinion/Gear Drive ............................................................................................ 47
Figure 33 Azimuth Drive Options .................................................................................................. 48
Figure 34 Inside Cylindrical Rotor Direct Drive .............................................................................. 49
Figure 35 Direct Drive Azimuth Motor X-section............................................................................ 49
Figure 36 Direct Pinion/Gear Drive ............................................................................................... 51
Figure 37 Reflector Surface Noise Measurement Results ............................................................. 54
Figure 38 (a) Integrated FE model (15° elevation angle), (b) example FEA results ....................... 55
Figure 39 Undistorted Surfaces Beam Pattern 10 GHz ................................................................. 58
Figure 40 Undistorted Surfaces Beam Pattern 30 GHz ................................................................. 59
Figure 41 Undistorted Surfaces Beam Pattern 50 GHz ................................................................. 60
Figure 42 15° Elevation Angle Gravity Loading Case Beam Pattern 10 GHz ................................ 62
Figure 43 15° Elevation Angle Gravity Loading Case Beam Pattern 30 GHz ................................ 63
Figure 44 15° Elevation Angle Gravity Loading Case Beam Pattern 50 GHz ................................ 64
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Figure 45 90° Elevation Angle Gravity Load Case Beam Pattern 10 GHz ..................................... 65
Figure 46 90° Elevation Angle Gravity Load Case Beam Pattern 30 GHz ..................................... 66
Figure 47 90° Elevation Angle Gravity Load Case Beam Pattern 50 GHz ..................................... 67
Figure 48 Wind load cases: (a) & (c) are pressure coefficient contour plots at Az: 0 El: 16 and
Az: 90 El: 66 ........................................................................................................ 68
Figure 49 Wind Load Case 1 Beam Pattern 10 GHz ..................................................................... 69
Figure 50 Wind Load Case 1 Beam Pattern 30 GHz ..................................................................... 70
Figure 51 Wind Load Case 1 Beam Pattern 50 GHz ..................................................................... 71
Figure 52 Wind Load Case 2 Beam Pattern 10 GHz ..................................................................... 72
Figure 53 Wind Load Case 2 Beam Pattern 30 GHz ..................................................................... 73
Figure 54 Wind Load Case 2 Beam Pattern 50 GHz ..................................................................... 74
Figure 55 Beam Pattern, Thermal Bath 10 GHZ ........................................................................... 76
Figure 56 Beam Pattern, Thermal Bath 30 GHZ ........................................................................... 77
Figure 57 Beam Pattern, Thermal Bath 50 GHZ ........................................................................... 78
Figure 58 Beam Pattern, Thermal Gradient, 10 GHz..................................................................... 79
Figure 59 Beam Pattern, Thermal Gradient, 30 GHz..................................................................... 80
Figure 60 Beam Pattern, Thermal Gradient, 50 GHz..................................................................... 81
Figure 61 Deforms at the secondary support locations ................................................................. 94

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LIST OF ACRONYMS AND ABBREVIATIONS
ALMAAtacama Large Millimeter ArrayATA

Allen Telescope Array

BUS

BackUp Structure

CFD

Computational Fluid Dynamics

CFRP

Carbon Fibre Reinforced Polymer

COTS

Commercial-off-the-shelf

CTE

Coefficient of Thermal Expansion

DVA

Dish Verification Antenna

EM

ElectroMagnetic

ERA

Elevation Rotating Assembly

FEA

Finite Element Analysis

iBUS

Inner Backup Structure

MRC

Multi-piece Rim-supported Composite

ngVLA

next generation Very Large Array

NRAO

National Radio Astronomy Observatory (USA)NRC

National Research Council (Canada)oBUS

Outer Backup Structure

PDR

Preliminary Design Review

PE

Pointing Error

PID

Process Induced Distortions

RMS

Root Mean Square

RTM

Resin Transfer Moulding

SPEM

Systematic Pointing Error correction Model

SRC

Single-piece Rim-supported Composite

TDP

Technology Development Program

VLA

Very Large Array

VLT

Very Large Telescope

WBS

Work Breakdown Structure

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1

INTRODUCTION

1.1

Purpose of Document

The purpose of this document is to describe the Preliminary Design of the National Research Councilof Canada (NRC) Next Generation Very Large Array (ngVLA) 18m Antenna Design as called out inStatement of Work NRC ngVLA 18m Antenna Study, AD03.

1.2

Scope of Document

This document describes the operational context of the design and the operating conditions as definedin the ngVLA Antenna: Preliminary Technical Specifications, AD01.
The project assumptions and risks are presented with their status and mitigation plans.
A descriptive overview of the NRC antenna design is provided.
Error budgets are presented along with methods of deriving allocations and current status of theanalysis results for key performance requirements are presented.
Finally, a summary of the key future tasks is provided.

1.3

Intended Audience

This document is expected to be used by the NRC ngVLA Antenna Design Team, National Radio
Astronomy Observatory (NRAO) Antenna Integrated Product Team and Management Teams, and thengVLA System Engineering and Management Team. This document is expected to be read by review
panel members of the Preliminary Design Review (PDR).
The project Work Breakdown Structure (WBS) follows in the next section.

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1.4

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2

APPLICABLE AND REFERENCE DOCUMENTS

2.1

Applicable Documents

The following documents at their indicated revision form part of this document to the extent specified
herein.
Table 1 Applicable Documents
Document/Drawing
Number

Ref NoDocument Title

AD01020.25.00.00.00-0001-SPE ngVLA Antenna: Preliminary Technical Specifications

AD02

ngVLA Memo # 17

ngVLA Reference Design Development & Performance
Estimates

AD03

020.05.40.05.01-0002SOW

Statement of Work, NRC ngVLA 18m Antenna Study

AD04

101-0000-004-PLN

ngVLA 18m Antenna Preliminary Production Plan

2.2

Revision
B

A

Reference Documents

The following documents provide useful reference information associated with this document. These
documents are to be used for information only. Changes to the date and/or revision number do notmake this document out of date.
Table 2 Reference Documents
Ref NoDocument/Drawing Number

Document Title

RD01“Fabry-Perot Resonator Design for the Measurementof Surface Reflectivity,” D. Henke et al. in 9th Global
Symp. on Millimeter-Waves., Espoo, Finland, Jun. 6–8, 2016.

RD02“Measurements of Composite Reflectors across QBand (33–50 GHz) and W-Band (75–115 GHz),” D.
Henke et al. [accepted] in 18th Int. Symp. Antenna
Technol. Appl. Electromagn. (ANTEM), Aug. 19–22,
2018.

RD03

ngVLA Memo # 26

ngVLA Technical Study Offset Gregorian Antenna

RD04

ngVLA Memo # 27

Various Suitable Mounts for 18m AntennaRD05

101-0000-001-REG-001

ngVLA 18m Antenna Risk Register2019-07-25

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RD06

101-0200-001-RPT-001

ngVLA 18m Antenna Elevation Rotating Assembly
Analysis Report

B

RD07

101-0100-000-RPT-001

ngVLA 18m Antenna Antenna Mount Analysis Report

B

RD08

9P033REP01

ngVLA Report, Main Drive Axes, Phase USA

RD09

TBD

ngVLA AIV Timeline

01

RD10

Spring-back Analysis of Telescope Dish: Final Report

RD11

DVA-1 Optics Design and Analysis

5

RD12

DVA-1 Dish Mechanical and Thermal Design

1

RD13

Long-term properties of fibre reinforced epoxy
resins(composites)

RD13

LTR-AL-2010-0017 Final Report Wind Tunnel Investigations of Symmetric- andOffset-Reflector Radio-Telescope Antennas
for the Square Kilometre Array (SKA):
Mean Winds Loads and Surface Pressures

RD14

101-0000-001-RPT

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3

OPERATIONAL CONTEXT

The ngVLA array will consist of 244 x 18m antennas and 19 x 6m antennas. The 18m antennas will be
deployed on and off of the Plains of San Agustin in New Mexico with baselines up to 1000 km, AD02.
The array will be centred at the current Very Large Array (VLA) site, approximately 170 of theantennas will be located on the plains with the remainder being located in single antenna stations
around New Mexico, Texas and Mexico. All antennas will be fixed position, the array will not bereconfigurable.
The project has defined four functional regimes:
1. Precision Operating: low wind speed, at night, low temperature rate of change, no precipitation.
2. Normal Operating: moderate wind speed, day/night, moderate temperature rate of change,noprecipitation.
3. Limit to Operations: higher wind speed, low and high temperature limits and precipitation
resulting in ice build-up.
4. Survival Conditions: high winds, extreme temperatures, snow and/or ice accumulation and hail.
Additionally, requirements are identified for seismic and lightning strike events.

3.1

Operational Environment

The antennas will be located primarily in desert and semi-desert locations at altitudes up to 2500 m.
Many antennas will be located at remote sites and all will be operated remotely. The defined operating
conditions are shown in Table 3, Table 4, Table 5 and Table 6.
Table 3 Precision Operating Conditions
Parameter

Req. #

Solar Thermal Load

ANT1411 Night time only; no solar
thermal load within last 2
hours.

SYS2411Wind Speed

ANT1412

SYS2412

Temperature

ANT1413 -SYS2413

Temperature Rate of Change

ANT1414 1.8°C/Hr.

SYS2414

Precipitation

ANT1415 No precipitation.

SYS24152019-07-25

Value

5 m/s average over
10 min time. 7 m/s peakgusts.

Traceability

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Table 4 Normal Operating Conditions
Parameter

Req. #

Value

Traceability

Solar Thermal Load

ANT1421 Exposed to full sun.

SYS2421Wind Speed

ANT1422

SYS2422

Temperature

ANT1423 -15

SYS2423

Temperature Rate of Change

ANT1424 3.6°C/Hr.

SYS2424

Precipitation

ANT1425 No precipitation.

SYS2425

7 m/s average over 10
min time. 10 m/s peak gusts.

Table 5 Limit to Operating Conditions
Parameter

Req. #

Wind

ANT1431

Temperature

ANT1432-

SYS2433

Precipitation

ANT1433

Any precipitation rate that does
not result in accumulation of ice
on the antenna structure.

SYS2434

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Traceability
SYS2432

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Table 6 Survival Conditions
Parameter

Req. #

Value

Wind

ANT14410 m/s

W

50 m/s average.

SYS2441

Temperature

ANT1442

-30 C

T

50 C

SYS2442

Radial Ice

ANT1443

2.5 cmSYS2443

Snow Load

ANT1444

25 cm

SYS2444

Hail Stones

ANT1445

2.0 cmSYS2445

Antenna Orientation

ANT1446

Stow-survival, as defined by designer

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4

ASSUMPTIONS AND RISKS

4.1

Assumptions

4.1.1

SRC Transportation to Antenna Locations

It was initially assumed that it would be possible to transport 18m Single-piece Rim-supported
Composite (SRC) reflector assemblies from a central production facility to all 244 antenna locations(see Risk 101-R5). A site survey with a qualified contractor (Precision Heavy Haul who moved the
Atacama Large Millimeter Array (ALMA) prototype antenna from the Very Large Array (VLA) to Kitt
Peak) was conducted and it was confirmed that this will be possible only for the 175 antennas locatedon the Plains of San Agustin. For the remaining antennas an alternate solution is proposed.
NRC has carried out development under the following assumptions:
The SRC design will be used for the on-plains antennas.
A multi-piece version of the SRC primary reflector, Multi-piece Rim-supported Composite(MRC) will be used for the remaining antennas.
Development of the MRC will continue in parallel with the SRC.

4.2

Risks

Risks have been categorized into either Project or Product risks. Project risks are those that might
impact the completion of the design work within the defined budget and schedule, while product risks
are those that might impact the ability of the design to meet the requirements. Both project andproduct risks are further categorized as to the nature of their impact; Budget, Schedule, Logistical orTechnical. All identified risks are tracked in the project risk register, RD05.

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Table 7 Project Risks

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Table 8 Product Risks

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5

PRELIMINARY DESIGN

The preliminary design for the ngVLA 18m antennas is a Single-piece Rim-supported Composite(SRC) Reflector on a steel yoke and pedestal mount, Figure 1.

Figure 1 NRC ngVLA 18m Antenna Design Concept

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5.1

Design Background

The proposed design is an evolution of work that has been carried out at NRC and Minex Engineeringover the past 12 years. The concept of a single-piece composite reflector was first explored at NRC in2006 with the fabrication of the Mark 1 (Mk1) reflector, Figure 2.

Figure 2 NRC Mk1 Dish
Based on the results of the Mk1 design, changes were incorporated in order to improve the surface
accuracy and manufacturability and were implemented in the Mk2 in 2008, Figure 3.

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Figure 3 NRC Mk2 DishThe single-piece rim-supported reflector concept was used by Minex Engineering in construction of
the Allen Telescope Array (ATA) 6m antennas, Figure 4, using a hydro-formed aluminium reflector
surface.

Figure 4 Allen Telescope Array 6m Antenna

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Figure 5 DVA1 Antenna
The collaboration of the NRC’s Square Kilometre Array (SKA) effort and the US Technology
Development Program (TDP) SKA program brought the two concepts together and resulted in the
Dish Verification Antenna 1 (DVA1), Figure 5. The composite reflector surface allowed a larger, more
thermally stable surface to be manufactured and the rim-support concept provided uniform support tothe surface without any hard points on the reflecting surface. Despite a catastrophic transport incident
the repaired DVA1 met the design requirements of high efficiency performance at frequencies up to 10
GHz. It has since been used to make record breaking antenna noise measurements and is currently
being used for a polarization survey.
With the increased interest in higher frequency observing in radio astronomy and the desire to
upgrade the VLA, the DVA2 project was undertaken to push the SRC technology to higher
frequencies. The DVA1 mould had limitations in terms of stability and so an interim frequency of
50GHz was selected as the target for the DVA2. The mould was reworked to achieve a higher surface
accuracy, a new reflecting material was developed and modifications were made to the BackUp
Structure (BUS) design to increase the stiffness. Additional improvements were made to thesecondary reflector structure and mount to improve the overall performance. At this time the DVA2
primary reflector has been fabricated, installed on the BUS, and measured to confirm that it meets therequirements to achieve high efficiency at 50 GHz.
In 2017 NRC conducted a Community Design Study for an ngVLA capable antenna based on the
DVA1/2 reflector design, Figure 6. The feed-low reflector configuration and tight pointing requirements

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drove the team to consider a wheel & track design. Details of this design can be found in RD03 and
RD04.

Figure 6 NRC 15m Antenna Study

5.2

Design Overview

5.2.1

Elevation Rotating Assembly

The Elevation Rotating Assembly (ERA) design features a SRC primary reflector surface supported by
a composite shell outer BackUp Structure (oBUS) which attaches to a fabricated steel inner BUS(iBUS). Incorporated into the iBUS is the elevation axis tube and elevation drive arc. A composite
space frame secondary support structure attaches to the oBUS at the rim of the primary reflector andsupports the feed package and secondary reflector.

5.2.1.1

Primary Reflector Surface

The primary reflector surface manufacturing technique is based on the vacuum infused carbon
fibre/epoxy resin layup process used in the fabrication of the DVA antennas. The surface is ~5mmthick and consists of 5 layers of quasi-isotropic carbon fibre fabric, a copper reflective layer andprotective layers of thin fibreglass veil. The primary surface infusion is of uniform thickness and does

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not include a rim or other features that may result in process induced distortions. The exception is thesurface adjuster tabs which will be infused with the surface. These will be designed to result in minimal
distortions and are located around the perimeter in a small band of the surface outside of the opticalsurface. Figure 7 shows a concept sketch for the adjuster tabs. The metal spool would be added at theedge of the layup, then overwrapped around its perimeter with a pre-cured carbon-fibre ‘fan’ as
illustrated in the figure. The green zone in the figure represents the 100mm wide extension to theprimary surface which is outside of the aperture. The carbon fibre ‘fan’ would be incorporated into thecentre of the layup (through-thickness) during the primary layup and in this way would form an integral
part of the structure.

Figure 7 Primary surface edge adjuster tab concept
Figure 8 shows the primary surface edge adjuster concept in context with the oBUS edge structure.
The primary surface (left hand panel) is suspended from the oBUS by the primary surface edge
adjuster tabs shown in Figure 7 together with a clevis and stud arrangement. Nuts and washers
located on each side of the oBUS flange on the studs will allow for the adjustment of the perimeter
tension loads on the surface and, in turn, the shape of the surface.

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Figure 8 Primary surface edge adjuster with oBUS
Two surface reinforcement patches are added adjacent to where the forward feed legs attach to the
oBUS to further reduce distortions in the primary surface. To avoid process induced distortions due tochanges in the laminate thickness these will be fabricated separately and bonded on after the primary
infusion, Figure 9.

Figure 9 Surface Reinforcement Patches

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5.2.1.2

Outer Backup Structure

The oBUS is comprised of 22 panels, 15 ribs and 11 rim beam sections. The complete oBUS structureis depicted in Figure 10.

Figure 10 Assembled oBUS structure
The component dimensions are designed to enable standard transport to site. The panels and ribs arecarbon fibre/epoxy composite layup similar to that used in the surface (without the reflective layer).
The ribs provide stiffening at the panel joints and load paths from the feed/secondary support structure
connections to the iBUS. The structure is stiffened by the circumferential rim beam. Figure 11 depicts
a partially assembled oBUS and illustrates some of the components that make up the structure. The
22 surface panels will be added to the oBUS assembly jig and bonded along their long edges via abond lap joint. Once this is accomplished the 11 segments of the rim beam will be bonded on (seeFigure 11, the blue beams). Finally the 11 radial beams and the extra four angled beams that directly
support the secondary structure will be bonded on. Finally, there will be a steel frame added to thelower elliptical edge of the oBUS that will provide stiffness to this open end of the oBUS during
shipping and handling, and ultimately comprise the connection between the oBUS and the iBUS.

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Figure 11 oBUS assembly details
The resulting structure is very stiff in shear between the reflector surface and iBUS. This is ofparticular importance for the feed-down configuration because the reflector will spend most of its timeoriented in a vertical or near vertical orientation where the shear stiffness of the oBUS will provide thelarger portion of necessary support for the primary surface (imagine the reflector surface being
dragged downward by gravity) in Figure 12.
The oBUS is connected to the iBUS through bolted connections between the metal ring defining thebottom edge termination of the oBUS and the metal ring defining the same location on the iBUS. The
connection points will be at 11 discrete points directly over the 11 corners defining the 11 sided
connecting polygon. When the iBUS and oBUS are combined, they will provide the stiffness required
to achieve the pointing and surface accuracy.

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Figure 12 Cross Section of Antenna at Low (12º) Elevation Angle

Figure 13 iBUS with its 11 Discrete Connection Points to the oBUS

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5.2.1.3

Inner Backup Structure

The iBUS provides the interface and transfers drive loads between the reflector assembly and theyoke. It is an assembly of machined and fabricated steel components. The iBUS connects to the
oBUS through the metal frame that defines the lower edge of the opening near the centre of theoBUS.

Figure 14 iBUS structure
In Figure 14 the red part of the iBUS, together with the two members the oBUS form a stiff tetrahedral
structure between the elevation axle and the top rail of the truss attached to the elevation drive arc.
The white steel members represents a second level of structure in the iBUS which carries the loads forthe eleven discrete attachment points that connect the iBUS to the oBUS around the perimeter of theellipse which defines the interface between the two. The iBUS will be assembled on-site from large,
but shippable sub-assemblies. Once assembled, the iBUS will be lifted into position onto the yoketower assembly. The primary reflector assembly will be lifted by crane and the connection between
the oBUS and iBUS made once in position.

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5.2.1.4

Secondary Support

The secondary support structure is a carbon fibre truss to minimize weight and coefficient of thermal
expansion (CTE), and maximize stiffness. Figure 15 shows the general arrangement.

Figure 15 Secondary Support Structure.
The primary truss structures (orange) support the secondary reflector (black) and attach to the rim of
the primary reflector at two points. A carbon tube on each side (blue in Figure 15) connects to the rimof the primary reflector as far around the rim as practical while still staying out of the optical path andkeeping the tube length down to practical limits. An additional small brace added to each of thesecarbon tubes increases their buckling strength and natural frequency thus minimizing the dynamic
coupling with the vibration caused by vortex shedding. The feed package and indexer (white box) is
supported by an intermediate truss structure (green).
Stiffening ribs integrated into the oBUS transfer the loads from the secondary legs to the iBUS, Figure
16.

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Figure 16 Stiffening Ribs on Primary Reflector to Support Secondary Support Structure
Figure 17 shows a close-up view of the feed and secondary support structure. The different colours
indicate separate shippable parts. On-site assembly would occur, with a combination of glue-bonded
and bolted connections.

Figure 17 Secondary and Feed Support Structure.

5.2.1.5

Multi-piece Reflector for Remote Site Antennas

For those reflectors that will be transported off the plain that surrounds the Socorro VLA site a multipiece reflector concept has been developed. The underlying structural principles are the same: a rim
supported monocoque primary surface with a carbon-cone outer back structure supported by a steel
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inner back structure. The principle difference is that the primary surface will be cut into 4 sections fortransport after it is fabricated. Figure 18 shows the surface panel cut line concept. In consulting with atrucking firm about width, length, and height restrictions on US roads it was determined that parts over
18 feet wide were quite expensive to move, splitting the reflector into 4 pieces will keep the width to~16 feet. While 68 feet is quite a long load, it shouldn’t exceed the 90 foot overall truck and trailer
length which represents another (albeit softer) dimensional boundary. For height, 10 feet off the deckof the flat deck trailer is the number given, the 4 pieces will easily remain below that.

Figure 18 Primary Surface cut Panel Dimensions [ft]The concept is to fabricate the reflector in one piece on the mould using the identical process as would
be used for the ~170 one-piece reflectors. Once the reflector has been fabricated (vacuum infused),
and while it is still on the mould, the connectors will be bonded on. Figure 19 shows the connector
concept.

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Figure 19 Proposed multi-piece primary surface connection detailThe upper (red) piece would be vacuum infused in carbon fibre, and would require a separate mouldfor each of the three joints required. The lower (green) piece would also be moulded separately, butwould benefit from being built using the RTM (Resin Transfer Moulding) process which allows both the
top and bottom surfaces to be moulded. Since the three joints are all close to 70 feet long, it would be
more practical to fabricate the upper piece in at least two pieces (which could be joined with aseparate overlapping piece), and the lower piece most likely should be built in 4 pieces (but needn’t bejoined).
The upper and lower pieces would be assembled on a jig and match drilled for the bolts and inserts.
Figure 20 shows a cross section through one of the bolts.

Figure 20 Cross section through one of the primary surface joining bolts showing the inserts
Once assembled on the jig a special drill would be used to drill and counter bore the required holes.
Once drilled the parts are again removed from the jig and the metal inserts are pressed in, and finallythe upper and lower parts are again placed on the jig and the connecting bolts added. In this way the

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upper and lower parts of the joint connector are pre-aligned before being added to the primarysurface.
The pre-assembled primary surface connector units are positioned on the back of the primary reflector
surface, aligned using alignment jigs attached to the edges of the mould and laser projected lines, andbonded on.
Next, lifting tabs (also built from carbon fibre) would be bonded onto the back of each of the 4 primarysurface parts. Figure 21 shows the arrangement typical for one of the pieces. These lifting points are
made from carbon fibre to insure a matched CTE with the surface material, and would be placed suchthat each panel could be safely lifted (with appropriate spreader bars). Initially the whole primarysurface would be lifted in one piece using some of the lifting points situated on each panel, and using
different spreader bars designed for the purpose.

Figure 21 Lifting points added to one of the 4 primary surface panels
This first lift would be to move the (currently one piece) primary surface from the mould onto a cutting
jig, Figure 22. The one piece primary surface would be aligned to the cutting jig using pre-definedalignment tabs built into the ends of the joint connectors. A circular saw equipped with a diamondblade would be pulled through a guide situated under each of the three desired cut lines, and in thisway the cuts would be accomplished at the correct locations. Once all the cuts were completed, thebolts between each part would be removed and the parts lifted off the cutting jig in a specific orderfrom one side to the other in the direction that the overlapping joint flanges overlapped.
Note that lifting points have only been detailed on the right hand primary surface part in Figure 22, butsimilar lifting points would be bonded to the other 3 primary surface parts as well.

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Figure 22 Assembly jig for the primary surface parts
Each of the 4 primary surface parts must be supported for transport once they are removed from thecutting jig. Figure 23 shows a typical arrangement. The transport trailer shown is 70 feet long toaccommodate the middle two pieces, the side pieces being a bit shorter. The transport jig is notional.

Figure 23 One of the four primary surface parts on its transport jig and flat deck trailer
For remote sites where more than one antenna will be located or where multiple antenna stations lie
along a given route, it is possible to nest like pieces for transport, Figure 24,

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Figure 24 Nesting multiple instances of primary surface pieces for transport to remote sites
Once at the antenna station the four primary surface parts would be assembled to the assembly jig
Figure 23. The assembly jig would be key to predetermined alignment tabs located along the edge ofeach of the primary surface parts. As each piece of the primary surface was added, the bolts
connecting the parts together would also be added.

Figure 25 Four primary surface parts being added to the assembly jig

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Once the primary surface has been bolted together, the same assembly jig would be used toassembly the oBUS to the primary surface. The oBUS would first be preassembled on a jig at theantenna station using the same methodology as for the single piece reflectors. Once assembled theoBUS would be lifted onto the primary surface assembly jig and connected. This step would require
some more structure around the rim of the primary surface jig, a structure that is not shown in Figure
25.
The primary assembly jig would break down into flat transportable pieces. Each of these pieces would
be made up as weldments, but would require some precision machined surfaces and would beconnected using taper pins and bolts. Pre-alignment between parts would be insured by the taper
pins, but a stable foundation would be required at the building site, and a final check using a laser
tracker would be required on some predefined targets because such a large structure would need tobe supported at multiple points where adjustable feet would be supplied for the final alignment. This jig
would need to be made by a company such as Janicki Industries that understands the complexities ofaligning large metal structures and has the capability to machine large complex (non-planer) surfaces(even though the complex surfaces in this case need only be narrow support strips where the jig
touches the surface of the part).

5.2.2

Mount

As mentioned for the 15m design study a wheel and track style of mount was chosen driven by thefeed-low configuration and tight pointing requirement. The wheel and track mount has been applied tomany radio telescopes in the past but there also have been some issues associated with it in terms of
maintenance and reliability. A pedestal mount with the feed-low offset reflector requires an offset
between the elevation and azimuth axes which compromises the structural stiffness. However the
reliability and low maintenance requirements make it an attractive option especially for an array ofmany antennas. With a potential wheel and track mount design concept already in hand it was
decided to explore the potential of the pedestal mount for this study. The challenge will be in achieving
the required stiffness at a reasonable cost.

5.2.2.1

Elevation Drive Configuration

The elevation drive configuration was tied to the yoke vs. turnhead decision; once the decision wasmade to go with the yoke, the task that remained was to determine a location for the drive arc anddrive stator sectors. A large drive arc radius is clearly desirable because it will reduce the physicalsize and power requirement for the drive motors. Conversely, a large drive arc radius means long
yoke arms which then reduce the stiffness of the yoke structure which negatively impacts the pointing.
A compromise that was arrived at was to move the drive arc to a high position. This enabled the yokearms to be shorter and stiffer while maintaining a larger drive sector radius. Additionally the lower endof the drive arc must penetrate through a hole in the yoke central structure just above the azimuth
bearing. Also this required the drive stator sectors to be mounted on a structure mounted high up on
top of the yoke, Figure 26. Because of the drive stator sector position (and lack of lateral stiffness),
elevation axial loads from the reflector must be taken at the elevation bearings and not on the drive
sector; however, it is thought that this is a workable solution.
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Figure 26 Elevation Drive Stator Pylon Structure

5.2.2.2

Elevation Drive

For the elevation drive, the direct drive appears attractive because of the large radius available. If one
examines the loading path between two opposed gear drives as shown in Figure 27, it is clear thatchanges in gear tooth pressure will result in inconsistent deflections across the large structure. No
inconsistent deflections occur with the direct drive. The sector gear itself is expensive and could beconsidered analogous to the armature magnet plates. Good alignment or gap control is required forboth systems. Drive carriages that track the sector can reduce the alignment requirement but it
generally results in more deflection parts and maintenance parts. Lubrication of a sector gear andpinion set is a maintenance issue and difficult to keep clean. The direct drive armature magnets may
have magnetic dirt issues. The cost of gear and direct drive are more comparable.

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Figure 27 Elevation Drive Load Path and Drive Components
A preliminary elevation drive design has been performed by Phase USA [RD08] based on themechanical configuration and loading scenarios provided by NRC. Drive loads, based on the NRC
wind tunnel data scaled for the reflector size and average wind speeds of the ngVLA, are shown in
Table 9.
Table 9 Elevation Drive Loads (based on average wind speeds)

Max Elevation Drive Loads [kNm]
Precision
35

Normal
71

Limit
284

Survival
1774

The initial drive sizing is performed based on the Limit condition (with a 20% oversizing margin) underwhich the antenna must be driven to the stow position where brakes and/or stow pins are deployed.
The drive configuration is shown in Figure 28.

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Figure 28 Elevation Drive Configuration

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Table 10 Elevation Drive Performance Matrix

The elevation drive performance matrix is shown in Table 10. Tracking the power required is 1.6 kW
for Precision and 6.9 kW for Normal wind conditions. Power required to move from slew to stow isabout 23 kW.

5.2.2.3

Azimuth Rotating Structure

In the 15m design study performed by NRC in 2017 a wheel and track mount was selected in order toachieve the pointing requirement. In scaling the design to 18m it was found that it was not possible tomeet the surface accuracy requirements with the steel tube BUS with discrete attachment points to thereflector surface. Instead a composite cone outer BUS (oBUS) with continuous attachment to thesurface was selected, see section 5.2.1. With the cone BUS the necessary structure to attach theelevation axis at the rim, as had been proposed in the 15m concept, no longer existed. The placementof the elevation axis was moved to the back of the oBUS where it connected to a steel fabrication

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inner BUS (iBUS). This also reduced the width of the elevation axis structure and so a wheel and track
mount no longer was applicable and so a pedestal structure design was selected for the design study.
Both the ATA and DVA antennas have used a turnhead type of azimuth rotating structure where thestructure is contiguous between the elevation bearings and is located inside the primary reflector BUS.
This allowed a compact, stiff structure to be used. In both cases the elevation drive was by a ballbearing jackscrew which could be mounted on the back of the turnhead.
For the ngVLA due to the tight pointing requirement and the desire for low maintenance it was
attractive to investigate the use of a direct drive system similar to that used on the European andJapanese ALMA antennas. This requires a large drive arc sector to be mounted on the BUS; use of aturnhead would have necessitated mounting of the drive off to one side, creating offset loads or having
two drive arcs one on each side of the turnhead. This would have incurred greater cost andcomplexity.
A yoke type azimuth rotating structure, Figure 29, allows the drive arc to be mounted centred on the
BUS between the yoke arms. In addition the interface to the BUS at the elevation axis can be wider
potentially providing more stiffness. A challenge for the yoke will be in achieving the pointing
requirement (stiffness of yoke arms). The desired direct drive system requires a large radius to bepractical. In general this forces long yoke arms, near 5.9m, causing serious stiffness problems.
Additionally it is important to have solid support above and below the azimuth bearing for a distance ofat least half the bearing diameter or about 2m. These requirements combine to force the azimuth
bearing lower down the pedestal, reducing stiffness. An offset design offers the opportunity to shift thedrive sector onto the high side of the BUS. By cantilevering the lower portion of the drive sector it can
project through the front face of the yoke centre, Figure 30. This is extremely useful, because it allows
a short beam across the front part of the yoke arms shortening the cantilever by about 35%. The shortbeam also stiffens an important area of the yoke centre above the Azimuth bearing. Now the drive arc
can pass just above the Azimuth bearing.
With this type of mount, the yoke arms are often responsible for nearly 50% of the bending deflection.
With the encoders mounted on the ends of the yoke arms this is the largest amount of non-repeatable
pointing error for the entire mount. It is quite difficult to stiffen these structures and it may benecessary to consider internal reference structures similar to what has been done with ALMA andother high performance antennas.

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Figure 29 Azimuth Rotating Structure

Figure 30 Yoke and Elevation Drive Structure

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Table 11 Azimuth Rotating Structure Components
Support Section

26770 lbs = 12140 kg

Plate 1” = 25mm at 150”
=3.81mYoke Centre Section

24410 lbs = 11070 kg

Plate 5/8 = 16mm

Yoke Arm

16650 lbs = 7550 kg

Plate 5/8 = 16mm

Drive Column

6070 lbs = 2750 kg

Plate 5/8 = 16mm

Azimuth Bearing

11070 lbs = 5020 kg

3.80m, 4130 x 3500 x 235mm

Support & Centre Transport

62350 lbs = 28280 kg nomotors4.32 max dia. x 7.40m long

The azimuth bearing will most likely be a 3 row roller type design, Figure 31. It has good stiffness andthe best chance of precision manufacturing at a nominal 3.8 m diameter.

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5.2.2.4

Azimuth Drive

For the azimuth drive system, a direct or geared system could be added either outboard of theazimuth bearing or inboard. Inboard has the advantage of not adding to the transport size of theassembly and an opportunity to do factory assembly and a clean environment for operation andmaintenance. It has the disadvantage of acting at a small radius of 1.6m requiring many stators at
significant cost and cooling may be a problem. Outboard mounting increases the acting radius toabout 2.00m or about 26% more than internal mounting. Cost would be reduced, cooling will be lessof a problem but the advantages of interior mounting will be lost. For azimuth using a ring gear andpinion set may have a far less penalty than the elevation case. The loading path between two
opposed gear drives as shown in Figure 32 is quite short. The cost for a quality gear material isreasonable, because the high quality bearing steel is already present. The inboard and outboard
question is less extreme, with only an 18% difference, allowing us to favour the inboard application.
Lubrication is needed, but it can be shared with the azimuth bearing requirement. Applying the directdrive concept to pinions would allow between 14:1 to 18:1 reduction and could be the mosteconomical solution while still avoiding many of the troubles associated with further gear reduction.

Figure 32 Azimuth Pinion/Gear Drive
Two preliminary azimuth drive designs has been performed by Phase USA [RD08] based on themechanical configuration and loading scenarios provided by NRC. Drive loads, based on the NRC
wind tunnel data scaled for the reflector size and average wind speeds of the ngVLA, are shown in
Table 12.

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Table 12 Azimuth Drive Loads (based on average wind speeds)

Max Azimuth Drive Loads [kNm]
Precision
33

Normal
67

Limit
266

Survival
1665

The two drive concepts under consideration are shown in Figure 33; direct drive (left) and direct pinion
and gear drive (right).

Figure 33 Azimuth Drive Options

5.2.2.4.1.1 Azimuth Direct Drive
The direct drive, similar to that used in the European ALMA antennas, consists of a rotor of magnets
and several drive segments as used for the elevation drive.
Azimuth motor is composed of 12 stator sections, Figure 34 distributed within a 3.75m diameter
having an active stack length of 210mm and 4mm air gap. Each section can be individually assembled
and is suitable for volume production which is ideal when considering the quantity of antennas in the
ngVLA. The location of the sectors is as close to the main Azimuth bearing as possible.

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Figure 34 Inside Cylindrical Rotor Direct Drive
The rotor can be comprised of magnetic sectors or a continuous ring, whichever is deemed mostfeasible during final design. Each magnet is protected with an individual stainless steel protection
cover sealed and retained with four stainless steel side screws.
Each motor section is equipped with dedicated holes on the top mounting plane to be used to fix an
extraction tool which can be used to pull out radially the section against the magnetic attraction formaintenance purpose. In the same way it is possible to slowly let the section slide in the magnetic
plates during the assembly procedure. Additionally, the design is conceived to have a motor subassembly which integrates the main Azimuth bearing and stator housing, Figure 35, allowing the unit
to be pre-assembled and tested during manufacturing. The total unit can then be transported bystandard truck and further integrated into the main structure.

Figure 35 Direct Drive Azimuth Motor X-section

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Care is to be taken during maintenance or assembly procedures, as each segment has a magnetic
attraction force close to 45,000 N. This force is balanced once the full ring is assembled.
Each stator unit, or forcer, is equipped with an embedded power drive which is fed through a 600 Vdc
bus line.
The interface with the control system is through an Ethernet bus with EtherCat Protocol.
For simplicity, from the torque capability point of view, in the following data the Azimuth motor isconsidered as a single unit even if in practice the total torque is generated by the sum of each single
drive section.
Table 13 Direct Drive Azimuth Motor Performance Matrix

The direct drive azimuth performance matrix is shown in Table 13. Tracking the power required is 2.5
kW for Precision and 11.2 kW for Normal wind conditions. Power required the slew to stow is about 38
kW.

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5.2.2.4.1.2 Azimuth Direct Drive Pinion
More traditional solutions for Azimuth drives consider a rack and pinion mechanical transmission,
Figure 36. This solution considers Phase Motion Control’s standard TK series of frameless, brushless
motors in a packaged configuration containing a pinion output shaft. This arrangement transfers thetorque generated by the rotor magnets to the pinion gear and plays a role in the overall stiffness of theantenna structure. In this gear train, the bending of the gear teeth, attachment flanges, and torsion of
the shaft influence the stiffness. From a thermal sizing perspective, the motors are typically designed
to minimize the temperature rise. This causes motor sizing to lend preference to oversizing of the units
to satisfy operation. When compared to Direct Drive solutions the additional cost the costs of the rack,
pinion and lubrication system must be considered.

Figure 36 Direct Pinion/Gear Drive

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Table 14 Azimuth Direct Pinion Drive Performance Matrix

The direct pinion azimuth performance matrix is shown in Table 13 (note values are per motor).
Tracking the power required is 2.2 kW for Precision and 12.6 kW for Normal wind conditions. Powerrequired the slew to stow is about 72 kW.

5.2.2.4.1.3 Azimuth Drive Comparison
As antennas become larger, the need and challenge to control their movement becomes ever moresignificant. A critical point includes not altering the antenna or antenna performance achieved throughoptimal mechanical and thermal design allowing fast switching drive systems operating in harshconditions. This introduces very high torque requirements in acceleration (pointing) due to the verylarge mass of the structure. Additionally, radio antennas must reach survival torque conditions instorms and can easily reach million Nm. Overall a servo system is realized with high resolution andwide control bandwidth.
To achieve the desired performance, many factors must be considered. Both Direct Drive and Direct
Pinion Drive solutions are considered. These large structures are heavy, so friction is also important.
The use of geared motor drives, including rack and pinion introduces:
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A resonance between motor inertia and structure distributed inertia, limiting the achievable
control bandwidth.
A high spatial frequency error due to gear inaccuracies, which may fall outside the control loop
bandwidth and thus affect the antenna motion.
A nonlinearity due to stick-slip friction or gear backlash; in either case this would generate an
instability at low speed, typically seen in the Elevation axis at meridian crossing.
Potentially, lower up-front cost with additional cost of ownership.
Maintenance Requirements, Lubrication, Additional power requirements, Wear components,
etc.
Utilizing direct drives, the control system comprises a number of electromagnetic thrusters, or forcers,
integrated within the structure and can apply the required force to obtain motion directly to the stiffest
parts, or nodes, of the actuated structure. These thrusters do not add inertia to the system and canbrace the system. The force is generated electromagnetically and can be integrated into the structure.
In further comparison, switching and tracking motions require high pulse power to accelerate andbrake the large antenna inertia. This requires a high control bandwidth and clean linear response,
which tend to very long settling times in gear solutions. The resulting effect is not meeting specification
or introducing pointing errors, whereas direct drives settle in a fraction of a second. Additionally, thegeared solutions add the motors inertia multiplied by the square of the transmission ratio to theantenna inertia. Direct drives do not add inertia relative to the structure. The motion energy can also
be stored in pre-charged capacitors to minimize the power requirement from the grid to be minimal.
From a performance standpoint the direct drives are very attractive. Future work will include a fulllifecycle trade study in order to make a final selection.

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6

PERFORMANCE

6.1

System Noise Contribution
Table 15 System Noise Contributions Requirement

Parameter

Req. #

Value

Resistive Losses

ANT1101

The primary and secondary reflector shalleach have a surface resistive loss of lessthan 1.0% over the operating frequency
range.

Traceability

NRC has conducted tests of its reflecting materials to determine the system noise contributions. The
test method is detailed in RD01 and the latest results are detailed in RD02 and presented in Figure 37.
Samples A1/2 are the materials developed for DVA1, B1/2 material developed for DVA2 and the mostrecent material developed for the ngVLA project is C1/2. Gains were made between DVA1 and 2 byswitching from aluminium to copper and further gains to the most recent material were due to material
configuration changes.

Figure 37 Reflector Surface Noise Measurement Results
The worst case noise temperature contribution from the surface for the C materials is ~0.75 K @ 115
GHz. The resistive loss is calculated as follows;

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6.2

Integrated Model Finite Element and Electromagnetic Analysis

Post PDR an integrated finite element analysis (FEA) model of the entire antenna assembly wascreated, Figure 38. Analysis results presented here are from that integrated model. See [RD06] formore details.

Figure 38 (a) Integrated FE model (15° elevation angle), (b) example FEA results
The following procedure is used:
1. A particular load case is applied to the integrated FEA model.
2. Primary surface distortions, and secondary reflector and focal point solid body motions(translations and rotations) are calculated.
3. Node data of the distorted primary surface is exported, re-gridded to a regular grid andimported into GRASP.
4. Secondary reflector and feed position solid body motions are applied to the GRASP model (atthis time secondary surface distortions are not modelled).
5. The GRASP simulation is run to calculate the antenna gain and pointing error.

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6. The aperture efficiency is calculated by comparing the distorted model gain to the un-distorted
model gain.

6.3

Aperture Efficiency

The key requirements for aperture efficiency relate to surface accuracy and reflector surface
continuity, Table 16. Operating conditions requirements are reproduced in Table 3 and Table 4.
Table 16 Aperture Efficiency Related Requirements
Parameter

Req. #

Value

Traceability

Surface Accuracy, Precision

ANT0501

Surface errors shall not exceed 160 m
RMS, for the primary and secondaryreflector combined when operating in thePrecision operating environment.

SYS0501

Surface Accuracy, Normal

ANT0502

Surface errors shall not exceed 300 m
RMS, for the primary and secondaryreflector combined, when operating in
the Normal operating environment.

SYS0501

Reflector Construction

ANT0503

Each reflector shall be a solid metal
surface (not a mesh or perforated sheet).
Each may be constructed as a single
piece or as multiple panels. If
constructed of multiple panels, gaps
between panel edges shall not exceed 1
mm.

Strictly speaking the NRC SRC does not meet the requirement for Reflector Construction (ANT0503)
as the surface reflecting material does have perforations, however as demonstrated by the low systemtemperature contributions in the previous section this will not prevent the reflectors from achieving therequired aperture efficiency.
The results of the analysis method outlined in 6.2 are antenna efficiency but the ngVLA antenna
specification [AD01] specifies surface accuracy in microns root mean square (RMS). NRC hassuggested a change to the way the efficiency is specified and NRAO has proposed the method shownin Table 17. The values listed in the “Structure” column are the applicable to the analysis resultspresented here.

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Table 17 Proposed Antenna Efficiency Specification

For an SRC reflector the following factors contribute to the surface error; mould accuracy, process
induced distortions (PID), aging, wind, gravity and thermal loads. The efficiency loss due to the last
three of these are estimated by simulation while losses for the first three have been estimated fromexperience and engineering judgement.

6.3.1

Simulated Efficiencies

In order to calculate the efficiency under loading the undistorted surfaces must first be modelled in
GRASP to determine the ideal gain. The beam patterns for the undistorted surfaces are shown in
Figure 39 (10 GHz), Figure 40 (30 GHz), Figure 41 (50 GHz).

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Figure 39 Undistorted Surfaces Beam Pattern 10 GHz

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Figure 40 Undistorted Surfaces Beam Pattern 30 GHz

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Figure 41 Undistorted Surfaces Beam Pattern 50 GHz

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The peak gain is shown in Table 18.
Table 18 Gain for Undistorted Surfaces

Frequency [GHz]Gain [dB]1064.75830
74.33650
78.756The efficiency for the load cases presented from here on will be calculated as;

Where;

6.3.1.1

Gravitational Loading

Two gravitational loading cases were analysed; 15° and 90° elevation angles. Details of the analysis
can be found in [RD06]. The results of the GRASP simulations are shown in Figure 42, Figure 43 andFigure 44 for 15° elevation angles at 10, 30 and 50 GHz respectively. Note pointing corrections havebeen applied to all gravity load case plots.

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Figure 42 15° Elevation Angle Gravity Loading Case Beam Pattern 10 GHz

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Figure 43 15° Elevation Angle Gravity Loading Case Beam Pattern 30 GHz

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Figure 44 15° Elevation Angle Gravity Loading Case Beam Pattern 50 GHz
The results of the GRASP simulations are shown in Figure 45, Figure 46 and Figure 47 for 90°
elevation angles at 10, 30 and 50 GHz respectively.

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Figure 45 90° Elevation Angle Gravity Load Case Beam Pattern 10 GHz

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Figure 46 90° Elevation Angle Gravity Load Case Beam Pattern 30 GHz

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Figure 47 90° Elevation Angle Gravity Load Case Beam Pattern 50 GHz
The peak gain and calculated efficiency for the two gravity load cases is shown in Table 19. Notegravity load cases are the same for precision and normal operating conditions.
Table 19 Gain and Efficiency, Gravity Load Cases
Gravity 15deg
Gravity 90deg

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Frequency [GHZ]
Gain [dB]
Efficiency
Gain [dB]
Efficiency

1064.75299.9%
64.75499.9%

30
74.27798.7%
74.31999.6%

50
78.59896.4%
78.72999.4%
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6.3.1.2

Wind Load Deformations

In order to analyse the surface deformations due to wind loading it is necessary to understand what
the load on the reflector due to wind will be. In 2010 NRC performed a series of wind loading tests on
an offset reflector in the NRC wind tunnel facility at the Institute for Aerospace Research, details of thistesting can be found in [RD13]. The output from these tests was a series of wind pressure and windload coefficients for various reflector configurations at a range of elevation and azimuth angles. The
pressure coefficient field results for a feed-low configuration were used for wind load modelling on the
ngVLA 18m dish. Two of the worst wind load cases were analysed: 1) 0º Azimuth angle and 16ºelevation angle and 2) 90º azimuth angle and 66º elevation angle. The pressure field contour maps forboth the cases are shown in Figure 48.

Figure 48 Wind load cases: (a) & (c) are pressure coefficient contour plots at Az: 0 El: 16 and
Az: 90 El: 66 .
The two cases were analysed with a wind speed of 5 m/s (precision conditions), details of this analysis
can be found in [RD06]. The results of the GRASP simulations for the 15° elevation angle are shownin Figure 49, Figure 50 and Figure 51 at 10 GHz, 30 GHz and 50 GHz respectively.

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Figure 49 Wind Load Case 1 Beam Pattern 10 GHz

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Figure 50 Wind Load Case 1 Beam Pattern 30 GHz

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Figure 51 Wind Load Case 1 Beam Pattern 50 GHz
The results of the GRASP simulations for the 90° elevation angle case are shown in Figure 52, Figure
53 and Figure 54 at 10 GHz, 30 GHz and 50 GHz respectively.

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Figure 52 Wind Load Case 2 Beam Pattern 10 GHz

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Figure 53 Wind Load Case 2 Beam Pattern 30 GHz

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Figure 54 Wind Load Case 2 Beam Pattern 50 GHz
The peak gain and calculated efficiency for the two wind load cases are shown in Table 20.
Table 20 Gain and Efficiency, Wind Load Cases
W01
W07

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Frequency [GHZ]
Gain [dB]
Efficiency
Gain [dB]
Efficiency

1064.758100.0%
64.758100.0%

30
74.334100.0%
74.334100.0%

50
78.75199.9%
78.752
99.9%

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The reflector models used for the wind tunnel testing have a different BUS configuration than the
ngVLA design and therefore in future design phases computational fluid dynamics (CFD) analysis will
be performed to refine wind load data.

6.3.1.3

Thermal Deformation

Two key thermal loading cases have so far been considered; thermal bath and thermal gradient.

6.3.1.3.1

Thermal BathIn Precision operating conditions the requirement is for night time operation so only thermal bathneeds consideration however the temperature operating range is large, that is assembled at 15 C but operated at -15 C must therefore maintain performance over atemperature range of 30 C.
20 C but results can belinearly scaled to other temperature ranges.
During night operation the reflector is assumed to be at thermal equilibrium and so distortions due tothermal expansion/contractions will be caused by differences in CTE in different parts of the structure.
The CTEs of the major components of the primary reflector structure are shown in Table 21. It is clear
from the table that the thermal expansion coefficients vary across the structure.
Table 21 Primary Reflector Component CTEs
Components

Material

CTE [µm/m/ºC]

Reflector Surface

Carbon fibre/epoxy/ reflective material

7.8

Composite materials

Carbon fibre/epoxy

6.1

oBUS

Foam Cored carbon fibre/epoxy

9.2

iBUS

Steel

12

The results of the GRASP simulations are shown in Figure 55, Figure 56 and Figure 57 at 10 GHz, 30
GHz and 50 GHz respectively.

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Figure 55 Beam Pattern, Thermal Bath 10 GHZ

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Figure 56 Beam Pattern, Thermal Bath 30 GHZ

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Figure 57 Beam Pattern, Thermal Bath 50 GHZ

6.3.1.3.2

Thermal Gradient

Thermal gradient was also studied with the same FEA model where a 5C temperature variation
was introduced on the long axis of the dish. The results of the GRASP simulations are shownin Figure 58, Figure 59 and Figure 60 at 10 GHz, 30 GHz and 50 GHz respectively.

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Figure 58 Beam Pattern, Thermal Gradient, 10 GHz

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Figure 59 Beam Pattern, Thermal Gradient, 30 GHz

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Figure 60 Beam Pattern, Thermal Gradient, 50 GHz
The peak gain and calculated efficiency for the two thermal load cases is shown in Table 22.
Table 22 Gain and Efficiency, Thermal Load Cases
Thermal BathThermal Gradient2019-07-25

Frequency [GHZ]
Gain [dB]
Efficiency
Gain [dB]
Efficiency

103064.748 74.277
99.8% 98.7%
64.757 74.333
100.0% 99.9%50
78.62897.1%
78.752
99.9%

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6.3.2

Calculated Efficiencies

At this time efficiency losses due to mould accuracy, process induced distortions (PID), aging for bothreflectors and the load induced distortions on the secondary are not included in the electromagnetic(EM) simulations. Therefore these must be estimated through use of the Ruze equation and then usedin the final overall efficiency calculation. The values assigned to these error sources in surface
accuracy error budgets developed for the PDR, Table 23 for precision operating conditions and Table
24 for normal operating conditions, are used to estimate the corresponding efficiencies.
Table 23 Precision Operating Target Surface Accuracy Error Budget
Value
Primary
Mould
Process
Gravitational
Wind
ThermalAgeing
Total

Value

100 Mould
86 Process
53 Gravitational
20 Wind45 Thermal
7 Ageing
149 Total

50
18
20
4
10
2
58

160
160
Table 24 Normal Operating Target Surface Accuracy Error Budget
Value
Primary
Mould
Process
Gravitational
Wind
ThermalAgeing
Total

Value

100 Mould
86 Process
53 Gravitational
41 Wind
68 Thermal
16 Ageing
158 Total

50
18
20
9
15
3
59

169
300
6.3.2.1.1

Secondary Reflector Efficiency

Using the values from Table 23 and Table 24 the surface accuracies of the secondary reflector are
calculated, Table 25 and Table 26.
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Table 25 Secondary Surface Accuracy Precision
Value
Primary
Mould
Process
Gravitational
Wind
ThermalAgeing
Total

Value
Mould
Process
Gravitational
Wind
ThermalAgeing
Total

50
18
20
4
10
2
58

58
Table 26 Secondary Surface Accuracy Normal
Value
Primary
Mould
Process
Gravitational
Wind
ThermalAgeingTotal

Value
0 Mould
0 Process
0 Gravitation
0 WindThermalAgeing
Total

50
18
20
9
15
3
59

59
The Basis Of Estimates (BOE) for values in the budgets are:a. Mould accuracy is based on experience with the DVA and MeerKat moulds.
b. Process induced distortion is based on experimental measurements, modelling andexperience.
c. Gravity, thermal and wind induced distortions based on FEA modelling.
d. Aging is based on study conducted for the ALMA antennas [RD13] that suggested a 10%
reduction on elastic modulus (stiffness) for carbon fibre reinforced polymer (CFRP) structures
over time. The value used is: the sum of deformations related to stiffness; gravity, thermal andwind, multiplied by 0.1.

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From these values using the Ruze equation the efficiency is calculated, Table 27 and Table 28.
Table 27 Secondary Reflector Efficiency Precision
Frequency(GHz)

Surface eff

10

30

50

80

100

120

99.9%

99.5%

98.5%

96.3%

94.3%

91.9%

Table 28 Secondary Reflector Efficiency Normal
Frequency(GHz)

Surface eff

6.3.2.1.2

10

30

50

80

100

120

99.9%

99.5%

98.5%

96.2%

94.1%

91.6%

Calculated Primary Reflector Efficiency Due To Mould, Process and Aging

Using the values from Table 23 and Table 24 the surface accuracies of the primary reflector due tomould, process and aging are calculated.
Table 29 Primary Surface Accuracy Precision
Value
Primary
Mould
Process
Gravitational
Wind
ThermalAgeing
Total

Value

100 Mould
86 Process
Gravitational
Wind
Thermal
7 Ageing
132 Total

132

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Table 30 Primary Surface Accuracy, Normal
Value
Primary
Mould
Process
Gravitational
Wind
ThermalAgeing
Total

Value

100 Mould
86 Process
Gravitational
Wind
Thermal16 Ageing
133 Total

133
The Basis Of Estimates (BOE) for values in the budgets are;a. Primary mould accuracy is an engineering estimate based on NRC experience anddiscussions with the mould vendor.
b. Process induced distortion is based on experimental measurements, modelling andexperience.
c. Aging is based on study conducted for the ALMA antennas [RD13] that suggested a 10%
reduction on elastic modulus (stiffness) for CFRP structures over time. The value used is: thesum of deformations related to stiffness; gravity, thermal and wind, multiplied by 0.1.
From these values using the Ruze equation the efficiency is calculated, Table 31 and Table 32.
Table 31 Primary Reflector Efficiency Precision
Frequency(GHz)

Surface eff

10

30

50

80

100

120

99.7%

97.3%

92.6%

82.2%

73.6%

64.3%

Table 32 Primary Reflector Efficiency Normal
Frequency(GHz)

Surface eff

6.3.3

10

30

50

80

100

120

99.7%

97.2%

92.5%

82.0%

73.3%

64.0%

Total Efficiency

The total aperture efficiency is calculated by taking the product of the efficiencies of all contributing
cases. Cases considered are shown in Table 33.

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Table 33 Efficiency Calculation Cases
Operating Condition
Load Cases

Precision

NormalWorst case

Worst case

Thermal Bath

Yes

Yes*

Thermal Gradient

No

Yes

Wind

Yes

Yes*

Secondary Reflector

Yes

Yes

Mould, process and aging

Yes

Yes

Gravity* Scaled to Normal operating conditions.
The considered load case efficiencies and total aperture efficiencies are shown in Table 34 (precisionconditions) and Table 35 (normal conditions).
Table 34 Aperture Efficiency, Precision Operating Condition

Gravity
ThermalWind
Secondary
Mould, Process & Aging

2019-07-25

10
100%
99.3%
99.9%
99.8%
100.0%
99.9%
99.7%

30
95%
94.3%
98.7%
98.7%
100.0%
99.5%
97.3%

50
88%
85.3%
96.4%
97.1%
99.9%
98.5%
92.6%

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Table 35 Aperture Efficiency, Normal Operating Condition
10
98%
98.0%
99.9%
99.0%
99.5%
99.9%
99.7%

Total Normal
Gravity
ThermalWind
Secondary
Mould, Process & Aging

30
86%
85.7%
98.7%
94.1%
95.4%
99.5%
97.2%

50
66%
67.6%
96.4%
87.6%
87.9%
98.5%
92.5%

Currently GRASP simulation has only been performed up to 50 GHz due to computational timerequired. The efficiency at higher frequencies can be estimated by back-calculating an equivalentsurface accuracy from the efficiencies in Table 34 and Table 35 and using that to calculate theefficiency. The results of this exercise are shown in Table 36 and Table 37.
Table 36 Estimated Efficiency for All Frequency Bands, Precision
Frequency
(GHz)

10

30

50

80

100

120

Surface eff
Requirement

99.3%
100%

93.7%
95%

83.5%
88%

63.0%
73%

48.6%
61%

35.3%
49%

Table 37 Estimated Efficiency for All Frequency Bands, Normal
Frequency
(GHz)

10

30

50

80

100

120

Surface eff
Requirement

98.2%
98%

85.1%
86%

63.8%
66%

31.6%
35%

16.5%
20%

7.5%
9%

It can be seen that at this time the design is very close to meeting the requirement. Paths to meeting
the requirement are discussed in the Section 6.6.

6.4

Pointing

The pointing error (PE) requirements for the ngVLA 18m antenna are shown in Table 38 andTable 39.

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Table 38 Precision Pointing Requirements
Parameter

Req. #

Value

Traceability

Non-repeatable Pointing Error

ANT0611 18 arc sec RMS.

SYS0801

Referenced Pointing Error

ANT0612 3 arc sec RMS, within 4º of
the target position and 15
minutes of time.

SYS0701,
SYS0801

Table 39 Normal Pointing Requirements
Parameter

Req. #

Value

Traceability

Non-repeatable Pointing Error

ANT062135 arc sec RMS.

SYS0801

Referenced Pointing Error

ANT06225 arc sec RMS, within 4°.
Must maintain spec for aminimum of 15 minutes.

SYS0701,
SYS0801

Preliminary pointing analysis has been performed, the results are presented for Precision and Normal
conditions. With the development of the integrated FEA model all of the structural PEs are now
expressed in a single term (as opposed to one for elevation assembly, one for pedestal, etc.) for a
specific load case.
The BOEs of the errors are;a. Estimate based on experience and other antennas. Typically only used for errors that are fullycompensated anyways.
b. From GRASP electromagnetic (EM) analysis of FEA structural analysis results.
c. Gust contributions scaled from constant wind case. Based on method used in ALMA where an
equivalent wind that accounts for gusts is used for the constant wind cases and the gustcomponent is then calculated as;. Where;,based on ALMA values.
d. Servo modelling results [RD14].

,,. Assumed

The assumptions made for the level of compensation provided by the Reference pointing model
are shown in Table 40.

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Table 40 Reference Pointing Model Compensation
Reference Pointing Compensation
Thermal Soak
Thermal Gradient
Constant Wind
Wind Gusts

90%
50%
50%
0%

The Absolute and Reference pointing errors with only Systematic Pointing Error correction Model(SPEM) compensation are shown in Table 41 (Precision) and Table 42 (Normal).

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Table 41 Pointing Errors; Precision, Uncompensated (except SPEM)

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Table 42 Pointing Errors; Normal, Uncompensated (except SPEM)

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The pointing requirements under precision conditions have been met and almost met under normal
conditions. Having said that there are still many items that are estimated and will need to be confirmed
by modelling, example or testing. In addition the method of calculating the PE due to wind gustcomponents should be discussed and an agreed upon method adopted for future design work.

6.5

Survivability

At this time the elevation rotating assembly has been analysed for one survival wind load case; wind
angles Az = 90°, El = 66°, wind velocity = 50m/s. The analysis included linear buckling analysis of thecomposite surfaces. The results indicate that the elevation assembly will survive under these
conditions, for details see [RD06].
Further analysis of the complete structure will be required in the next phases.

6.6
6.6.1.1

Potential Areas of Improvement
Structural Improvements

The yoke structure is currently one of the biggest contributors to PE and has an effect on the surface
accuracy of the primary reflector. An initial optimization of this structure shows there is some potential
for improvement, see [RD06] for further details.
The current secondary/feed support structure attaches to the primary reflector BUS at four points andcauses distortions in the primary surface around these locations. A new secondary/feed support
structure is being considered that attaches to the primary BUS at six points in order to spread the loadand decrease the resulting distortions in the primary surface.

6.6.1.2

Manufacturing Errors

The SRC reflectors are manufactured as the name implies in one piece on a mould. The asmanufactured surface accuracy depends on: materials selection, mould accuracy, composite layup
design, process design and process control.
Unlike small machined or formed panels it is nearly impossible to actually measure just the asmanufactured surface accuracy on a large single piece reflector surface. As soon as the part isremoved from the mould it is subject to gravitational and thermal effects, it cannot be put in atemperature controlled room, supported ideally and measured on a coordinate measuring machine(CMM) as can be done with panels.
Attainable mould accuracy has increased considerably over time with new machines and methods
developed by industrial entities such as Janicki Industries. The 15m DVA2 mould was reworked to 210
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micron RMS from the DVA1 mould that had been designed to meet the 500 micron RMS requirementsof a 10 GHz reflector. The structure was a steel back structure with a fibreglass faceplate and putty
surface which is not very thermally stable and suffered from differential thermal expansion effects
between the face structure (putty and fibreglass) and the back structure. A 100 micron RMS accuracy
for machined all carbon mould on an isothermal steel base in a thermally stable environment isbelieved to be achievable.
NRC has conducted extensive research into minimizing process induced distortion with large gains
being made through laminate design, material selection and process control to the point where small
length scale surface process induced distortion has been minimized. In fact extremely fine surface
features present in the mould are reproduced on the part.
For the DVA1 project NRC contracted Convergent Technology to conduct a study of the process
induced distortions (PID) in the 15m reflector infusion process. The study [RD10] involved a
combination of test, measurement and finite element modelling and resulted in several significant
design changes to reduce PID. The modelling predicted a 69 micron RMS surface accuracy due to
PID [RD11], [RD12]. Unfortunately it is extremely difficult to verify this as any measurement of the
produced surface includes gravity, thermal and adjustment effects. In addition no measurement was
conducted on the DVA1 before it suffered damage in transport. The primary source of PID is thevolumetric shrinkage of the resin during cure. In an effort to further decrease PID in the DVA2 theresin was changed from vinyl ester (~8%-11% shrinkage) to epoxy resin (~2% shrinkage). The
budgeted value of 86 microns for PID in the ngVLA 18m reflector is based on the DVA1 modelledvalue of 69 microns reduced by 15% (estimated) to account for resin change and then scaled by thesquares of reflector diameters (182/152). A study of the proposed 18m primary surface will becommissioned with Convergent to confirm this number.
The DVA1 reflector surface was removed from the mould, flipped over, mounted on the steel backup
structure, and then adjusted. For DVA2 the moulded reflector surface was released but not removed
from the mould before installation of the steel tube BUS. The surface and BUS assembly was thenremoved from the mould and adjustment of the BUS performed to reach the final surface accuracy. In
both cases it is unknown how much of the deformation being adjusted out was process induced, howmuch was gravitational and how much was due to manufacturing tolerances in the BUS. Efforts areunderway to attempt to extract a value from the measurement data of the DVA antennas.
For the ngVLA the plan is to attempt to “capture” the surface shape by installing the oBUS on to thesurface before it is released from the mould. For serial production it is easy to justify a jig to accuratelyalign the oBUS to the moulded part during installation. Final adjustments can then be made if
necessary to reach the final accuracy requirement once the complete assembly is removed from themould.

6.6.1.3

Surface Adjustment

The nature of the SRC reflector is such that the surface deformations are generally large scale andgreater around the rim of the reflector. Small scale deformations are governed by the mouldsmoothness. Experience with the DVA1 and 2 reflectors has shown that adjustment at the rim of the
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reflector is very effective in smoothing large scale deformations. The adjustment scheme outlined in
section 5.2.1 provides radial adjustment tangential to the reflector surface at many points aroundperimeter of the surface. Initial modelling [RD06] shows that this is effective at reducing large scale
deformations due to gravity or to compensate for manufacturing tolerances in the oBUS. Simply
applying adjustments at four locations shown in Figure 61 was shown to reduce the surface error by~5microns.

Figure 61 Deforms at the secondary support locations
No optimization of the adjustment was applied at this point so further reduction can be expected.
Using this model NRC is developing a method of determining required adjustment from a given
deformed shape. The goal is to be able to determine adjustments from a measured surface and feedthem into a semi-automated adjustment tool similar to that used for the ALMA antennas.

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7

MAINTENANCE, RELIABILITY AND LIFETIMEAt this early stage of the design cycle it is difficult to provide definitive information regarding themaintenance, reliability and life cycle of the final product. It is possible to speak to the concepts thatwill be applied in order to minimize required maintenance and to maximize reliability and lifetime.

7.1

Maintenance and Reliability

The maintenance requirements for the ngVLA antennas are given in Table 43 [AD01]. At this point in
the design cycle it is premature to assign numbers to the maintenance intervals and efforts required.
However it is possible to illustrate the approach being taken to satisfy these requirements.
Table 43 Maintenance Requirements
Parameter

Req. #

Value

Traceability

Preventive Maintenance Cycle

ANT1502 Preventive maintenanceshall not be required atintervals shorter than 12
months.

SYS2301

Preventive Maintenance Effort

ANT1502 Periodic preventive
maintenance shall require
no more than a 2-person
team and no more than 2 8hour workdays.

SYS2301

Mean Time Between Failures

ANT1503

SYS2302

With the very large number and the wide geographical locations of antennas in the ngVLA themaintenance requirements of the antennas are a major concern. In the design of bespoke andselection of commercial-off-the-shelf (COTS) components for the NRC ngVLA antenna both low
preventative maintenance and high reliability have been considered. As the design matures
maintenance requirements will be analysed in greater depth to ensure maintenance costs are kept toa minimum. Examples of components and design elements being considered include:
Direct drives
Modular design
Azimuth bearing oil bath
Appropriate consideration will be given to implementation of condition-based maintenance byincorporating sensors and self-test procedures that will allow remote monitoring of the condition of theantenna. Condition-based maintenance reduces cost by reducing unnecessary time-based

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preventative maintenance while allowing necessary maintenance to be planned and scheduled as achange in a component or system’s condition is identified.
Particular attention will be paid to auxiliary mechanisms such as stow pins and cable wraps which if
not well designed can “nickel and dime” a project. Where possible and appropriate, accelerated life
testing of components and systems will be carried out early in the development.

7.2

Design LifeThe design life requirements of the ngVLA antennas are shown in Table 44 [AD01].
Table 44 Design Life Requirements
Parameter

Req. #

Value

Design Life

ANT1801 The antenna shall be
designed to require no
major overhaul work for 20
years.

Life Cycle Optimization

ANT1802 The antenna design shallminimize its life-cycle costfor 20 years of operation.

Traceability

The 20 year design life and life cycle optimization requirements for the ngVLA antennas should not bedifficult to achieve. A large portion of the mount is based on mature technology (steel fabrications,rolling element bearings, etc.) for which the life cycles are well understood. Two areas that will require
greater attention in future phases are the direct drives and the composite structures.
Direct drives have been in use in optical telescopes for 20 years for almost 10 years; for example, inthe Very Large Telescope (VLT) and in radio telescopes such as ALMA. The drives have no moving
parts to wear out and no limited lifetime electrolytic capacitors so achieving 20 years life should easily
be possible. A part of the planned trade study between direct drives and traditional gear train drives
will include both lifecycle and maintenance aspects.
Composite structures have been employed in the marine and other industries for over 50 years andsome have been in service for that entire time. The key to making them last is to provide protection
from the sun’s ultra violet (UV) and from moisture ingress, both of which can be achieved with wellapplied, high quality paint, and high quality material choices and structural design. However for thecomposite structures employed in the ngVLA antenna design, a key aspect is long-term shapestability. Although this is not unique to radio telescopes the degree to which it is required is; so it is notpossible to satisfy this by example. Recognizing this NRC has initiated a series of studies involving
both test and analysis to investigate the long-term shape stability of the structures in question.

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8

FUTURE WORK

8.1

Design and Analysis

The following design and analysis tasks will be performed in the next phase.

8.1.1

Drive System Trade Study

Direct drive vs direct pinion/gear drive will be studied for both azimuth and elevation drives withconsideration of performance and cost, both capital and maintenance.

8.1.2

iBUS to oBUS Connection

The connection between the inner and outer BUS structures will be detailed. Emphasis will be on
providing a stiff connection while providing accommodation for reasonable manufacturing tolerances
for the large structures.

8.1.3

Surface Adjusters

Detail design of surface adjusters.

8.1.4

Feed/Secondary Support Structure

The new Feed/Secondary Support Structure concept requires detailed analysis to ensure adequate
performance and further design detailing for volume manufacture.

8.1.5

Feed Indexer

Little attention has been paid to the feed indexer at this time due to resource limitations as it is seen as
low risk. Design and analysis effort will be required in the next phase.

8.1.6

Complete Integrated FEA Model

The secondary reflector surface will be incorporated into the integrated antenna FEA in the next phaseto allow EM modelling of the complete optical system under various load cases.

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8.1.7

Yoke Structure Optimization

An initial topology optimization has been performed on the yoke structure and shows promise to
reduce PE and improve surface accuracy. The rationalization of the optimized shape has been started
and will be completed and integrated into the FEA model for future analysis.

8.1.8

Multi-piece Primary Reflector Concept

Development of the MRC design will continue including development of a cost model.

8.2

Logistics

Work will continue on the production planning and transport aspects of the project.

8.3

Prototyping and Testing

Several aspects of the design will be prototyped in order to retire associated risks.

8.3.1

Surface Adjusters

Surface adjusters can be prototyped in isolation and/or on a small diameter reflector.

8.3.2

Process Induced Distortion Study

A contract for an updated analysis of the process induced distortion for the design presented here will
be issued. The new analysis will consider the 18m diameter design and incorporate changes inmaterials and other design elements (i.e. no rim in dish surface infusion).

8.3.3

Multi-piece Concepts

Several aspects of the proposed MRC design can be prototyped on a smaller scale. In particular thejoint connections to determine ease of manufacture and accuracy after reassembly.

8.4

Materials Analysis and Testing

A feature of composite materials is the ability to vary the properties by changing the type of fibres,
resin and process used. The down side of this is that the only way to precisely know the properties of

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a particular material is through testing. As part of the ngVLA antenna design project NRC will becarrying out the following analysis and testing of materials;
Coefficient of Thermal Expansion – the layup of the reflector surface proposed for the ngVLA
has changed somewhat from that of the DVA dishes. The reflective material, resin and some of
the fibre materials have changed. All of these changes should result in a slightly reduced CTE
so samples of the proposed dish surface layup along with layups representing other parts ofthe structure such as the OBUS will be measured in-house and/or sent out to an external
testing lab for CTE measurement.
Weathering – in order to address risk 101-R6 the long term stability of the surface accelerated
aging tests will be conducted on the proposed materials well as modelling of the materials andaging mechanisms.
Peel test – peel tests will be conducted to address 101-R3 the bond strength of the reflective
material to the structural laminate analysis.
A comprehensive new set of coupon testing for mechanical properties of laminates intended
for the ng-VLA telescope. Initial design work is typically done with existing material property
values from earlier work as well as estimates done with micromechanics where test results
don’t exist, but as the design progresses confirmation of material properties for each proposed
laminate in each separate orthogonal direction must be measured.
Small scale structural tests – structural testing on the scale of fabricated sub-components suchas the rim connector to dish edge connection would be tested. Other structural components
such as the glue joints between the oBUS components, and the strength of the oBUS to iBUS
point load strap-type connectors would also be tested.

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Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

Short Baseline Array Antenna: Preliminary TechnicalRequirements
020.47.05.00.00-0001-REQ-A-SBA_ANTENNA_TECH_REQS

Status: RELEASEDPREPARED BY
R. Selina''XQEDUORGANIZATIONElectronics Div., NRAO
ngVLA/NM-Ops, NRAO

DATE
201--
2019-0

APPROVALS
R. Selina,
Project Engineer

ORGANIZATIONElectronics Division,
NRAO

DATE
2019-07-23

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.23 14:04:17 -06'00'

Asst. Director,
NM-Operations, NRAO

2019-07-23

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.23 14:04:32 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-23

2019.07.23
10:36:25 -06'00'

Page 1 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

Change Record
Date

AuthorAffected
Section(s)01

2017-09-25

R. Selina

All02

2017-09-26

R. Selina

3, 4, 7

Version03

2018-11-06

D. Dunbar

Doc no.,Doc Title,
3.3, 4.14.1,
4.14.204

2018-11-14

D. Dunbar

2.1, 2.2,
4.13, 4.14,
8.1.4, 1005

2019-04-15

D. Dunbar

AllA

2019-07-23

A. LearAll

ReasonStarted first draft. Used ngVLA Antenna
Preliminary Technical Specifications
020.25.00.00.00-0001-SPE as a base.
Updated requirement IDs, changed language
to SBA0503. Minor title and text changes forclarity.
Updated document number (SPE to REQ) to
conform to System Engineering protocol.
Updated Precision and Normal windvelocities to match System Level Spec.
Added new reference documents. Updated
Environment Conditions to trace back to
ENV requirements (and not SYS Req).
Updated Electromag table and requirements
to match/point to EMC requirement doc.
Added additional applicable environmental
requirements. Updated Load Case Table(precision) wind loads to match lower
velocity (5 m/s)
Updated antenna count to 244 18m and 19
6m
Incorporated edits by M. McKinnon and R.
Selina. Prepared PDF for signatures andrelease.

Page 2 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

Table of Contents
1

Introduction ................................................................................................... 6

1.1
1.2

Purpose ................................................................................................................................... 6
Scope ...................................................................................................................................... 6

2

Related Documents and Drawings ............................................................... 6

2.1
2.2

Applicable Documents ........................................................................................................... 6
Reference Documents ............................................................................................................ 7

3

Overview of SBA Antenna Technical Specifications .................................. 8

3.1
3.2
3.3
3.4

Document Outline ................................................................................................................. 8
Project Background................................................................................................................ 8
General SBA Antenna Description ........................................................................................ 8
Summary of SBA Antenna Requirements ............................................................................. 9

4

4.1
4.2
4.3
4.4
4.5
4.6
4.6.1
4.6.2
4.7
4.8
4.9
4.10
4.11
4.12
4.13
4.14
4.14.14.14.24.14.34.14.44.14.54.14.64.14.74.14.8
4.15
4.16
4.17
4.18

SBA Antenna Functional and Performance Requirements..................... 10

Operating Frequency Range................................................................................................ 10
Optical and Mounting Geometry ....................................................................................... 10
Allowable Design Volume and Mass ................................................................................... 12
Number of Antennas ............................................................................................................ 12
Reflector Construction and Accuracy ................................................................................. 12
Pointing Accuracy ................................................................................................................ 13
Pointing Accuracy in Precision Operating Environment ................................................................ 13
Pointing Accuracy in the Normal Operating Environment ........................................................... 13
Focus Stability ...................................................................................................................... 14
Range of Motion .................................................................................................................. 14
Axis Rates ............................................................................................................................. 14
Stow Positions ...................................................................................................................... 15
System Noise Contributions ................................................................................................ 15
Solar Observations ............................................................................................................... 16
Spurious Signals/Radio Frequency Interference Generation ............................................. 16
Environmental Conditions ................................................................................................... 16
Precision Operating Conditions ........................................................................................................... 17
Normal Operating Conditions ............................................................................................................. 17
Limits to Operating Conditions ........................................................................................................... 17
Survival Conditions at Stow Position .................................................................................................. 18
Lightning Protection Requirements ..................................................................................................... 18
Seismic Protection Requirements ........................................................................................................ 19
Site Elevation............................................................................................................................................. 19
Vibration .................................................................................................................................................... 19
Maintenance and Reliability Requirements ....................................................................... 19
Monitor and Control Requirements ................................................................................... 20
Motion Limiting Features .................................................................................................... 21
Lifecycle Requirements ........................................................................................................ 21

5Interface Requirements .............................................................................. 22

5.1
5.2
5.3
5.4

Interface to the Foundation/Station ................................................................................... 22
Interface to the Electrical Infrastructure............................................................................ 22
Interface to the Fiber Optic Transmission System ............................................................. 23
Interface to Other External Cables and Piping ................................................................. 23

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5.5
5.6
5.7
5.8
5.9

Date: 2019-07-23
Version: A

Interface to the Receiver Enclosure/Front-End Electronics ............................................... 23
Interface to the Back-End Electronics ................................................................................ 24
Interface to Internal Cables and Piping ............................................................................. 24
Interface to the Cryogenic System...................................................................................... 24
Interface to the Monitor and Control System ................................................................... 24

6
7

Subsystem Requirements ........................................................................... 25
Safety ............................................................................................................ 26

7.1
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5
7.3
7.3.1
7.3.2
7.3.3
7.3.4
7.3.5
7.3.6
7.3.7
7.4

General ................................................................................................................................. 26
Hazard Analysis .................................................................................................................... 26
Hazard Severity ........................................................................................................................................ 26
Hazard Probability ................................................................................................................................... 26
Hazard Risk Acceptability Matrix......................................................................................................... 27
Requirements on Operational Hazards.............................................................................................. 27
Hazard Analysis ........................................................................................................................................ 27
Safety Design Requirements................................................................................................ 28
Fire Safety .................................................................................................................................................. 28
Mechanical Safety ..................................................................................................................................... 28
Electrical Safety......................................................................................................................................... 28
Hydraulic and Pneumatic Safety ........................................................................................................... 29
Handling, Transport, and Storage Safety ............................................................................................ 29
Toxic Substances ..................................................................................................................................... 29
Confined Space ......................................................................................................................................... 29
Physical Security .................................................................................................................. 29

8

8.1
8.1.1
8.1.2
8.1.3
8.1.4
8.1.5
8.1.6
8.2
8.3
8.3.1
8.3.2
8.3.3
8.3.4
8.3.5
8.3.6
8.3.7
8.3.8
8.3.9
8.3.10Requirements for Design ............................................................................ 30

Analyses and Design Requirements..................................................................................... 30
Finite Element Structural Analyses ...................................................................................................... 30
Thermal Modeling and Analysis ............................................................................................................ 31
Stress Analysis and Load Combination............................................................................................... 31
Antenna EM Analysis Support............................................................................................................... 31
Control Loop Design and Analysis ...................................................................................................... 33
Reliability, Availability, Maintainability Analysis ................................................................................. 33
Electromagnetic Compatibility Requirements ................................................................... 33
Materials, Parts, and Processes ........................................................................................... 34
Type of Steel ............................................................................................................................................. 34
Stress Relieving......................................................................................................................................... 34
CFRP ........................................................................................................................................................... 34
Fasteners .................................................................................................................................................... 34
Paints........................................................................................................................................................... 34
Surface Treatment ................................................................................................................................... 34
Thermal Insulation ................................................................................................................................... 34
Rodent Protection ................................................................................................................................... 34
Name Plates and Product Marking ...................................................................................................... 34
Labels .......................................................................................................................................................... 35

9Documentation Requirements ................................................................... 36

9.1
9.2

Technical Documentation ................................................................................................... 36
Software and Software Documentation ............................................................................. 36

10

Verification and Quality Assurance ........................................................... 37

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Date: 2019-07-23
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11
12

Key Performance Parameters .................................................................... 39
Appendix....................................................................................................... 41

12.1
12.2
12.2.212.2.312.2.412.2.512.2.612.3
12.3.112.3.212.3.3Abbreviations and Acronyms ............................................................................................... 41
Coordinate System ............................................................................................................... 42
Main Reflector (MR) Coordinate System........................................................................................... 42
Secondary Reflector (SR) Coordinate System.................................................................................. 43
Focal Plane Coordinate system ............................................................................................................ 44
Antenna Azimuth ..................................................................................................................................... 44
Antenna Elevation .................................................................................................................................... 44
Maintenance Definitions ..................................................................................................... 45
Maintenance Approach ........................................................................................................................... 45
Periodic Preventive Maintenance ......................................................................................................... 45
Overhaul .................................................................................................................................................... 45

Page 5 of 45

Title: Short Baseline Array Antenna:
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NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

1 Introduction
1.1 Purpose
This document presents a preliminary set of technical specifications for the ngVLA Short Baseline Array(SBA) antenna. Many requirements flow down from the preliminary ngVLA System Requirements [AD01],
which in turn flow down from the preliminary ngVLA Science Requirements.
The Science Requirements are presently being elaborated by the Science Advisory Council (SAC) and
Science Working Groups (SWGs), and are captured in a series of draft use cases. This document reflects
a preliminary analysis of these use cases, and the flow down recursively to the system and subsystem
requirements.
NRAO desires a cost-effective solution for the antenna that can be manufactured in volume and operated
affordably. The optimization for value requires flexibility in key requirements until the cost and technicalimpact of the parameters are understood. These requirements are therefore considered preliminary, until
refined through feedback with the antenna designer.

1.2 Scope
The scope of this document is the ngVLA SBA Antenna element. This consists of the foundation, mounting
structure that provides for motion in azimuth and elevation, reflectors and their supporting structures,
drive system, and associated motion control electronics. All other instrumentation, including feed
antennas and receiving electronics, are outside the scope of this element, though interfaces must be
considered. This specification establishes the performance, functional, design, and test requirements
applicable to the ngVLA SBA antennas.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of the Technical Specification shall be considered as a superseding requirement.
ReferenceNo.
AD01

Document Title

Rev/Doc. No.

ngVLA Preliminary System Requirements

AD02
AD03

International Standard: Protection Against Lightning
Protection Against Electric Shock: Common
Aspects for Installation and Equipment
Electrical Standards for Industrial Machinery
Safety of Machinery: Electrical Equipment of
Machines
Insulation Coordination for Equipment Within
Low-Voltage Systems
Hydraulic and Pneumatic Fluid Power Safety

V1.0, 3/30/2017
Doc: 020.10.15.10.00-0003-REQ
IEC 62305:2010
IEC 61140:2016

AD04
AD05
AD06
AD07

Page 6 of 45

NFPA 79
IEC 60204:2016
IEC 60664
ISO 4413

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Reference
No.
AD08
AD09
AD10
AD11
AD12
AD13

Date: 2019-07-23
Version: A

Document Title

Rev/Doc. No.

Occupational Safety and Health Standards for
General Industry
Occupational Safety and Health Standards forConstruction
Military Handbook, Reliability Prediction ofElectronic Equipment
Non-Electronic Parts Reliability Data
Electromagnetic Compatibility
Offset Dual Reflector Antenna

29 CFR Part 1910
29 CFR Part 1926
MIL-HDBK-217F
NPRD-95
IEC 61000-3-5
Mitsuguch et al., IEEE APS 1976,
DOI 10.1109/APS.1976.1147539

2.2 Reference Documents
The following references provide supporting context:
Reference
No.
RD01
RD02
RD03

RD04
RD05
RD06

Document Title

Rev/Doc. No.

Essential Radio Astronomy

http://www.cv.nrao.edu/course/
astr534/2DApertures.html
EVLA Memo #106, Perley,
Brundage, Mertely.
Christophe Granet, IEEE Antennas
and Propagation Magazine, Vol. 44,
No. 3, June 2002

RFI Emission Limits for Equipment at the
EVLA Site
Designing Classical Offset Cassegrain or
Gregorian Dual-Reflector Antennas from
Combinations of Prescribed GeometricParameters
USGS Coterminous US Seismic Hazard Map:
PGA 2% in 50 Years
ngVLA System Electromagnetic Compatibility
and Radio Frequency Interference Mitigation
Requirements
ngVLA System Environmental Specifications

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ftp://hazards.cr.usgs.gov/web/nshm/
conterminous/2014/2014pga2pct.pdf
Doc: 020.10.15.10.00-0002-REQ
Doc: 020.10.15.10.00-0001-SPE

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Date: 2019-07-23
Version: A

3 Overview of SBA Antenna Technical Specifications
3.1 Document Outline
This document presents the technical specifications of the ngVLA SBA antenna element. These parameters
determine the antenna’s overall form and performance.
The functional and performance specifications, along with detailed explanatory notes, are found in Section
4. The notes elaborate on the meaning, intent, and scope of the requirements. These notes form an
important part of the definition of the requirements and should guide the verification procedures.
In many cases, the notes explain or analyze how the numeric values of requirements were derived. Where
numbers are not well substantiated, this is also documented in the notes. In this way, the required analysis
and trade-space available is apparent to scientists and engineers who will guide the evolution of the ngVLA
SBA antenna concept.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses.
Safety requirements applicable to both the design phase and the functional antenna are described in Section
7. Additional requirements for the design phase are described in Section 8. Documentation requirements
for both technical design documentation and software are provided in Section 9.
Requirements for the Verification and Test of the antenna, from the conceptual design through toprototype, are described in Section 10. Section 11 identifies Key Performance Parameters (KPP) thatshould be estimated and monitored throughout the design phase. These metrics assist in the trade-off
analysis of various concepts, and help identify and resolve tensions between requirements as the design
progresses.

3.2 Project Background
The Next Generation Very Large Array (ngVLA) is a project of the National Radio Astronomy
Observatory (NRAO) to design and build an astronomical observatory that will operate at centimeter
wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116
GHz). The observatory will be a synthesis radio telescope constituted of approximately 244 reflector
antennas each of 18 meters diameter, operating in a phased or interferometric mode.
The design will also include a compact Short Baseline Array (SBA) composed of approximately 19 reflector
antennas each of 6 meters diameter. These antennas will be spaced randomly but closely, providing
information necessary to recover large-scale source structure. The SBA may be operated in conjunction
with the 18m array in an interferometric mode, or independently.
The array signal processing center will be located at the Very Large Array site, on the plains of San Agustin,
New Mexico. The array will include stations in other locations throughout New Mexico, west Texas,
eastern Arizona, and northern Mexico. Operations will be conducted from both the VLA Control Building
and the Domenici Science Operations Center in Socorro, NM.

3.3 General SBA Antenna Description
The SBA antennas will operate in free air, during daytime and nighttime, as long as the atmosphericconditions remain within the specified operating limits. When not in an operating condition, the antenna
will be put in a safe “stow” configuration.

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Date: 2019-07-23
Version: A

The SBA antennas will be constituted of a shaped paraboloidal reflector, with a subtended circular
aperture of 6 m diameter. The optical configuration shall be an offset Gregorian feed-low design supported
by an Altitude-Azimuth mount.
The subreflector shall be supported so that neither it nor any of its supporting structure obstructs theaperture of the primary reflector. If necessary to meet the performance requirements, the position of thesubreflector may be remotely adjusted with a controlled mechanism. Space is required near the secondary
focal point for installation of feed antennas, receivers, and other electronics. Additional space is requirednear ground level for electronics and instruments.

3.4 Summary of SBA Antenna Requirements
The following table summarizes the major SBA antenna requirements to give the reader a high-level viewof the desired antenna. Should a conflict exist between the requirements listed here and the descriptionsin Sections 4 through 10, the latter shall take precedence.
Parameter
Frequency Range

Summary of Requirement
1.2–116 GHz

DiameterNo. of Antennas
Surface Accuracy

6m
19Precision Operating Conditions:
160 μm RMS ( /16 @ 116 GHz), primary andsubreflector combined.
Normal Operating Conditions:
300 μm RMS, primary and subreflector combined.
Precision Operating Conditions:Absolute pointing: 54 arc sec RMS
Referenced pointing: 9 arc sec RMS(4 deg angle, 15 min time)
Normal Operating Conditions:Absolute pointing: 105 arc sec RMS
Referenced pointing: 15 arc sec RMS(4 deg angle, 15 min time)
Azimuth: ±270 deg
Elevation: 12 deg to 88 deg
Slew: Azimuth 90 deg/min, Elevation 45 deg/min.
Tracking: Azimuth 7.5 deg/min, Elevation 3.5 deg/min.
Offset Gregorian, satisfying Mizuguch-Dragone
polarization condition, with focal point on bottom.
Survival Conditions at Stow Position: Wind PV
tHPS–40°C, 2.5 cm radial ice, 25 cm snow in dish,2.0 cm dia hailstones
Precision Operating Conditions: Nighttime only,
ZLQG5 PVWHPSHUDWXUH–15°C, no precipitation.
Normal Operating Conditions: Day and night, wind
7 PVWHPSHUDWXUH–15°C, no precipitation.

Pointing Accuracy

Tracking Range
Movement Rate
Antenna Geometry
Environmental
Conditions

Page 9 of 45

Reference Reqs.
SBA0101, SBA0102,
SBA0103
SBA0202
SBA0401
SBA0501, SBA0502

SBA0611, SBA0612,
SBA0621, SBA0622

SBA0801, SBA0802
SBA0901, SBA0902,
SBA0906
SBA0201, SBA0206,
SBA0211
SBA1411 through
SBA1446

Title: Short Baseline Array Antenna:
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Date: 2019-07-23
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4 SBA Antenna Functional and Performance Requirements
These requirements apply to a properly functioning system, under the normal operating environmental
conditions unless otherwise stated.

4.1 Operating Frequency Range
Parameter
Upper Operating Frequency
Lower Operating Frequency
Optimized Operating Frequencies

Req. #
SBA0101
SBA0102
SBA0103Value
116 GHz
1.2 GHz
8 GHz–50 GHz

Traceability
SYS0801
SYS0801
SYS0801

The upper and lower operating frequencies for the antenna flow down directly from the system
requirements. However, operation above 8 GHz is of higher importance, and the lower operating
frequency should not be permitted to significantly increase the cost of the design or compromise theperformance at higher frequencies.
For example, optimizing performance at 1.2 GHz may necessitate a large subreflector, perhaps 4–5m indiameter. Such a subreflector may increase the structural requirements on the feed/subreflector arm andmay make meeting the pointing specification more difficult due to increased wind loads. Therefore,
subreflector size should be a compromise to provide minimal wind loading at high frequencies, withspillover temperature optimized for 8GHz and up.

4.2 Optical and Mounting Geometry
Parameter
Optical Configuration
Type
Primary Aperture
Diameter and Shape
Secondary Reflector
Aperture Diameter
Secondary Angle ofIllumination
Reflector Offset
Focal Ratio, Primary
Cross Polarization
Reflector Shapes

Req. #Value
SBA0201 Offset Gregorian
SBA0202 6m, circular
SBA0203 2.5m minimum
SBA0204 From the focal point, secondary reflector
aperture shall subtend an angle of 110º.
SBA0205 There shall be no overlap of the physicalsecondary reflector with the projected apertureof the main reflector.
SBA0206 The closest paraboloid to the main reflector shallhave a focal ratio of 0.40 ±0.05.
SBA0207 The secondary reflector tilt angle (ȕ inFigure 1) shall be chosen to satisfy the Mizuguch
condition [AD13].
SBA0208 The shapes of the main and secondary reflectors
will deviate no more than 0.25m from theclassical Gregorian conic sections (paraboloid andhyperboloid). For the main reflector, deviations
will be azimuthally symmetric about theparaboloid axis.

Page 10 of 45

Traceability
SYS0701,
SYS0601
SYS0501,
SYS0601
SYS0501,
SYS0701

SYS0501

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Secondary Reflector
Extension

Main Reflector
Extensions
Mounting
Configuration

Date: 2019-07-23
Version: A

Req. #Value
SBA0209 The secondary reflector shall be extended on its
outside edge by 0.5 m as a shield against groundradiation. This part of the reflector is outside its
defined aperture and its shape is not specified; it
is not shown in Figure 1. The extension may be
integral with the reflector or constructed as aseparate component.
SBA0210 The main reflector may extend beyond thedefined aperture if that facilitates efficientfabrication (e.g., assembly from hexagonal panels).
SBA0211 The focal point shall be closest to the ground at
the minimum elevation angle.

Traceability

The optical configuration for classical conic section reflectors is fully specified by requirements SBA0202
through SBA0207 (except that SBA0205 and SBA0207 specify only minimum values), and Figure 1
conforms to these requirements using the minimum secondary reflector size and 10 cm offset.

Figure 1 - Cross-section of the optical geometry through the plane of symmetry for unshaped (paraboloid
ellipsoid) reflectors. Values may be refined in the design.

Page 11 of 45

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Date: 2019-07-23
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The primary aperture diameter is measured in the plane perpendicular to its axis. The physical reflector's
largest dimension, given the offset geometry, is appreciably larger.
The secondary reflector aperture (SBA0203 and SBA0205) is measured in the plane perpendicular to thegeometrical optics ray from the focal point to the center of the main aperture. The secondary reflector's
physical edge (not including the extension described in SBA0208) shall be circular when projected into
this plane.
The final shapes of the reflectors have not been determined (NRAO responsibility), but they are expected
to deviate from the classical paraboloid and ellipsoid. Whereas the deviation will be small (SBA0208), theclassical shapes should be used for the preliminary design.

4.3 Allowable Design Volume and Mass
Parameter
Minimum
Spacing
HeightReq. #
SBA0301

Mass

SBA0303

SBA0302

Value
Antennas whose azimuth axes are separated by 11m shallnot collide for any combination of their orientations.
At the lower limit of normal elevation motion, no part ofthe movable structure shall be closer than 1.0 m to thenearest point on the ground.
Unconstrained

Traceability

If the minimum spacing requirement proves difficult to accommodate, NRAO may evaluate a revision tothis requirement. The height of the pedestal is limited to provide adequate clearance for snow. For service,a low feed arm is desirable, but the design height should also consider equipment and personnel safetyconcerns. The mass is an unconstrained free parameter, but lower mass is preferred in order to minimize
cost. The envelopes of NRAO-supplied equipment will be defined in the ICDs described in Section 5.

4.4 Number of Antennas
Parameter
No. of Antennas

Req. #Value
SBA0401 19

Traceability
SYS0501

The final number of antennas will depend on the configuration design for both the 18m main array andthe SBA. Values of 16–20 have been adequate in preliminary studies but should be revisited as theconfiguration design matures.

4.5 Reflector Construction and Accuracy
Parameter
Surface Accuracy,
Precision
Surface Accuracy,
NormalReflector
Construction

Req. #Value
SBA0501 Surface errors shall not exceed 160 ȝm RMS for the
primary and secondary reflector combined when
operating in the Precision operating environment.
SBA0502 Surface errors shall not exceed 300 ȝm RMS, forthe primary and secondary reflector combined,
when in the Normal operating environment.
SBA0503 Each reflector may be constructed as a single pieceor multiple panels. If constructed of multiple panels,
gaps between panel edges shall not exceed 1 mm.

Page 12 of 45

Traceability
SYS0501
SYS0501

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The surface error at each point is defined to be the deviation of the actual surface from the nominal
surface, measured normal to the nominal surface. The RMS is computed by integrating over the main
aperture (not across the reflector’s local surface) with uniform weighting. The limits apply to the RMS of
the sum of the main and secondary reflector errors, but that value may be estimated by taking the rootsum-squared of the main and secondary RMS errors measured separately. The reflector construction
method is not intended to preclude innovative composite layups. The goal is that the reflector surface
provide high reflectivity and minimal transmission over the operating frequency range.

4.6 Pointing Accuracy
Pointing error is defined as the difference between the commanded orientation of the antenna and theactual direction of its RF beam. Pointing errors are classified as repeatable and non-repeatable. Pointing
accuracy is specified by the maximum allowable Non-Repeatable Pointing Error and Referenced Pointing
Error. The absolute error may be larger provided that it is repeatable over the specified range ofenvironmental conditions (mainly temperature and wind). Repeatable errors will be calibrated andremoved in the control software.
To further correct the non-repeatable errors, referenced pointing will be used. This involves astronomicalmeasurement of the pointing error using observations of a known object near the desired pointing
direction. The Referenced Pointing Error specifications then limit the difference in pointing error at agiven angular separation from the desired direction and the change in that difference over a given time.
Pointing requirements apply over the full operational range of motion.

4.6.1

Pointing Accuracy in Precision Operating Environment

Parameter
Non-Repeatable Pointing Error
Referenced Pointing Error

Req. #
SBA0611
SBA0612Value
54 arc sec RMS
9 arc sec RMS, within 4º of target
position and 15 minutes of time

Traceability
SYS0801
SYS0701, SYS0801

The non-repeatable pointing specification is equivalent to full width half maximum over ten (FWHM/10)
at 20 GHz, while the referenced pointing requirement is equivalent to the FWHM/10 at 116 GHz. The
control loop used for referenced pointing within 4º should not be unique; performance at larger angles is
expected to degrade in a manner roughly proportional to slew distance.
Note that systematic pointing errors are more damaging than random errors, and this RMS value assumes
a random distribution of errors after application of the pointing model.

4.6.2

Pointing Accuracy in the Normal Operating Environment

Parameter
Non-repeatable Pointing Error
Referenced Pointing Error

Req. #
SBA0621
SBA0622Value
105 arc sec RMS.
15 arc sec RMS, within 4º. Must
maintain spec for 15 mins minimum.

Traceability
SYS0801
SYS0701,
SYS0801

The absolute pointing specification is equivalent to FWHM/10 at 10 GHz, while the referenced pointing
requirement is equivalent to the FWHM/15 at 50 GHz. The latter specification ensures that the array
operates effectively at frequencies below 50 GHz during typical good daytime environmental conditions.

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Date: 2019-07-23
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4.7 Focus Stability
Parameter
Secondary Focus Position Stability in
Precision Operating Environment
Secondary Focus Position Stability inNormal Operating Environment

Req. #Value
SBA0701 125 μm over full elevation range

Traceability

SBA0702 300 μm over full elevation range

The focus position stability in the precision environment is equivalent to /20 at 116 GHz, while thespecification in the normal operating environment is equivalent to /20 at 50 GHz.
This specification may be met by active compensation (e.g., moving the subreflector).

4.8 Range of Motion
Parameter
Azimuth Tracking Range
Elevation Tracking Range
Elevation Movement
Range

Req. #Value
SBA0801 +/– 270º minimum, where zero is towards
true South.
SBA0802 12º to 88º minimum from local horizon.
SBA0803 As required to support operation over theelevation tracking range. (TBC)

Traceability
SYS1201

The Azimuth tracking range has a zero-degree fiducial vector pointing towards the celestial south pole.
The elevation range is relative to the local horizon. Section 12.2 details the coordinate system.
The lower elevation permits observations over large portions of the southern hemisphere. A lower
elevation limit of 12 degrees allows observations of order –40 declination near the meridian (given thelatitude of the ngVLA SBA). However, this lower elevation limit in particular may prove to be a driving
requirement with the feed low optical design, as the backup and feed support structure may interfere witha pedestal at lower elevations. Should this requirement prove to be a significant cost or complexity driver,it can be reviewed.
The movement range should be larger than the tracking range. A margin should be provided for the normal
limits of motion before limit switches are reached. The hard mechanical limits should be slightly wider still(see Section 4.17 for additional information). At the discretion of the designer, maintenance and safety
stow positions may be outside the elevation tracking range.

4.9 Axis Rates
Parameter
Slew: Azimuth
Slew: Elevation
Acceleration: Azimuth
Acceleration: Elevation
Slew + Settle Time

Req. #
SBA0901
SBA0902
SBA0903
SBA0904
SBA0905

Tracking: Azimuth
Tracking: Elevation

SBA0906
SBA0907

Value
90 deg/mins minimum
45 deg/mins minimum
4.5 deg2/sec minimum
2.25 deg2/sec minimum
Move 4-deg on sky and settle to within
Referenced Pointing Specification within 10
seconds for elevation angles <70º.
7.5 deg/mins minimum
3.5 deg/mins minimum

Page 14 of 45

Traceability
SYS1107
SYS1107
SYS1107

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

The slew speeds and accelerations specified attempt to minimize time spent slewing between targets orcalibrators, without significantly driving the antenna design. They also allow for rapid response to transient
events, reaching anywhere on sky within approximately two minutes.
The slew + settle time specification aims to reduce phase calibration overheads. The 70-degree elevation
angle constraint is given so as not to drive the specification for azimuth slew rates at higher elevation.
Should this specification prove to be a driving requirement, it may be reviewed, as alternative approaches
to phase calibration exist at the system level.
The tracking specifications give the rates at which the specified pointing error limits must be maintained.
In general, there is a tracking error that contributes to the pointing error and must be included in the
pointing error budget for both Precision and Normal conditions. The azimuth tracking rate corresponds
to approximately 10 times sidereal at an elevation of 70 degrees. Tracking at super-sidereal rates will be
important for multiple observation modes, such as on-the-fly mosaicking, or tracking objects that moveacross the celestial sphere, such as planets, asteroids and satellites.

4.10 Stow Positions
Parameter
Stow Position:
Survival

Req. #
SBA1001

Stow Position:
Maintenance

SBA1002Value
The survival stow position shall limit the wind load on
antenna while ensuring water and snow accumulation
does not exceed safe structural allowances.
The maintenance stow position shall place the receiver
enclosure as close to horizontal as possible.

Traceability

It shall be possible to stow the antenna in two different positions, one used for occurrence of the survival
atmospheric conditions, and the other for specific maintenance to be performed on the antenna.
The maintenance position aims to provide a level working platform around the receiver enclosure
mounted on the feed arm. In practice, this may be unattainable in some designs and will be constrained by
the lower elevation limit. In the survival position, the antenna shall withstand the survival conditions
described in Section 4.14.4. The designer shall determine a single survival position that minimizes stressfrom wind and snow/ice loading.

4.11 System Noise Contributions
Parameter
Resistive
LossesReq. #Value
SBA1101 The primary and secondary reflector shall each have asurface resistive loss of <1.0% over the operating
frequency range.

Traceability

Contributions to system noise from the antenna, due to resistive loss of the primary and secondaryreflector surfaces and scattering of ground noise into the feed, shall be minimized as much as possible
without compromising the surface accuracy and pointing requirements.
Should this requirement prove difficult to meet at the upper operating frequency, NRAO may review therequirement.

Page 15 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

4.12 Solar Observations
Parameter
Solar
Observations

Req. #
SBA1201

Value
Direct solar observations allowed. System will meet
specifications for the normal operating environment.

Traceability
FUN0006

The specifications for pointing and surface accuracy for the Normal operating environment must be met
when pointed directly at the Sun.

4.13 Spurious Signals/Radio Frequency Interference Generation
Parameter
Spurious Signal Level

Req. #Value
SBA1301 Not to exceed the equivalent isotropic radiatedpower limits in Table 1.

Traceability
EMC0310The electronics within the antenna must be shielded to avoid radio frequency interference (RFI) being
received by the front-end electronics, degrading system sensitivity. Table 1 lists the allowable radiation forelectronic components as a function of frequency, and is based on the analysis presented in RD02, updated
for longer integrations consistent with SCI0116.
Freq.
(GHz)
Fh (w/m2)
EIRPh
(W)
EIRPh
(dBm)

1

2

4

6

8

10

20

30

1.5E-19
1.9E-16

1.1E-18
1.4E-15

8.9E-18
1.1E-14

2.9E-17
3.7E-14

6.3E-17
7.9E-14

1.2E-16
1.5E-13

1.2E-15
1.6E-12

4.3E-15
5.4E-12

–127

–119

–110

–104

–101

–98

–88

–83

Table 1 - Allowable radiation power for electronic components.

The table is based on unity gain, assuming the RFI enters through a sidelobe of the antenna. Fh is theharmful power flux density level, and EIRPh is the harmful effective isotropic radiated power. The ratio of
the emitting device EIRP to the harmful EIRP (EIRPh) is the shielding required. For example, a device with
an EIRP of 1nW @ 2GHz would require of order 59dB of shielding.
Table 1 assumes the radiator is 10 m from the antenna feed. For other distances, the EIRPh can becalculated as follows:4ߨ‫ ݎ‬ଶ ܵ‫ܨ‬௛‫ܩ‬where r is the distance in meters, S is the device shielding ratio, G is equal to 1, and Fh is from Table 1.
Radiated power shall be computed over a bandwidth that corresponds to a spectral resolution of 100 m/s.
This can be calculated as 333 Hz * G, where G is the RF frequency in GHz.
‫ܴܲܫܧ‬௛ =4.14 Environmental Conditions
Based on historical weather data of the VLA site and other public weather databases, the following
definitions of environmental conditions are adopted. These requirements are verbatim from theenvironmental specification outlined in [AD01].

Page 16 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

4.14.1 Precision Operating Conditions
Parameter
Solar Thermal Load

Req. #
SBA1411Wind Speed

SBA1412

Temperature
Temperature Rate of Change
Precipitation

SBA1413
SBA1414
SBA1415

Value
Nighttime only; no solar thermal load
within last 2 hours.
0  W 5 m/s average over 10 min
time. 7 m/s peak gusts.
–15°C  T  25°C
1.8°C/Hr.
No precipitation.

Traceability
ENV0311
ENV0312
ENV0313
ENV0314
ENV0315

The Precision operating environment defines the conditions under which the system is expected to meetthe most stringent requirements and provide optimal system performance.
The solar thermal load requirement limits this environment to two hours after sunset through sunrise, solong as the other requirements of this section are met. The two-hour restriction is intended to allow
sufficient time for the system to equilibrate.

4.14.2 Normal Operating Conditions
Parameter
Solar Thermal LoadWind Speed

Req. #
SBA1421
SBA1422

Temperature
Temperature Rate of Change
Precipitation

SBA1423
SBA1424
SBA1425

Value
Exposed to full sun, 1200W/m2: m/s average over 10
min time. 10 m/s peak gusts.
–15°C  T 35°C
3.6°C/Hr.
No precipitation.

Traceability
ENV0321
ENV0322
ENV0323
ENV0324
ENV0325

When the environment meets the constraints of the normal operating conditions, system performancerequirements are relaxed but are still expected to provide adequate performance for operation below 50
GHz.

4.14.3 Limits to Operating Conditions
Parameter
Solar Thermal LoadWind

Req. #
SBA1430
SBA1431

Temperature
Precipitation
Ice

SBA1432
SBA1433
SBA1434

Value
Exposed to full sun, 1200W/m2:PVDYHUDJHRYHUPLQs.
:PVJXVW
–20°C  T 45°C
5 cm/hr over 10 min
No ice accumulation on structure.

Traceability
ENV0330
ENV0331
ENV0332
ENV0333
ENV0334

A third categorization will establish hard limits to the operating conditions. While outside the bounds ofthe normal operating environment but within this regime, no performance guarantees are expected, but
the system shall still be capable of safe operation.
If these limits are exceeded, the antenna will be moved to "stow-survival" orientation to prevent damage.

Page 17 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

4.14.4 Survival Conditions at Stow Position
Parameter
Wind
Temperature
Radial Ice
Rain Rate
Snow Load – Antenna
Hail Stones
Antenna Orientation

Req. #
SBA1441
SBA1442
SBA1443
SBA1444
SBA1445
SBA1446
SBA1447Value
0 m/s  W 50 m/s average.
–30°C  T 50°C
2.5 cm
16 cm/hr. over 10 min
25 cm
2.0 cmStow-survival, as defined by designer

Traceability
ENV0341
ENV0342
ENV0343
ENV0344
ENV0345
ENV0347
ENV0348

The survival conditions describe the environment that the antenna should be able to withstand without
damage when placed in its least-vulnerable state. The designer must specify the orientation that will resultin minimum stress to the structure at the maximum wind speed and maximum snow and ice loading.
Note that 50 m/s survival wind is not high enough to survive tornadoes in eastern New Mexico and Texas.
This issue should be considered in the Hazard Analysis described in Section 7.2.
The temperature limits, radial ice, snow load and hail stone requirements are based on experience at the
VLA site and a survey of conditions throughout the extent of the array.
Should these requirements prove onerous or constraining, a risk versus loss analysis may be performed
to evaluate the likely cost and time for repair, and the frequency of expected repairs, compared to thecost impact of meeting the requirement over the lifetime of the facility. This would be executed as partof the analysis described in Section 7.2.

4.14.5 Lightning Protection Requirements
Parameter
Lightning Protection:
Structure
Lightning Protection:
Electronics Systems
Lightning Protection:
Personnel

Req. #Value
SBA1451 The antenna and housed equipment shall beprotected from both direct and nearby lightning
strikes, achieving Protection Level 1 as definedin IEC 62305-1/3. [AD02]
SBA1452 The antenna electrical and electronics systems
shall be protected against Lightning
Electromagnetic Impulse (LEMP) in accordancewith IEC 62305-4. [AD02]
SBA1453 A safety hazard analysis shall be performed for
anticipated preventive maintenance tasks thatmay place personnel at risk in the event of
direct or nearby lightning strikes.

Traceability
ENV0511

ENV0512

ENV0513Given the extent of the array and the prevailing environmental conditions, direct and nearby lightning
strikes, causing a lightning electromagnetic pulse (LEMP), should be anticipated and mitigated in theantenna design.
The antenna and housed equipment shall be protected in any antenna orientation. The requirements forthe antenna grounding electrode, provided as part of the antenna foundation, shall be documented in therelevant ICD as described in Section 5.1.
All bearings shall have bypass grounding connections. The grounding system shall be designed to minimize
ground loops.

Page 18 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

The lightning protection system shall be designed to achieve Protection Level I as defined by [AD02] “IEC
62305-1, Protection Against Lightning.” This level assures protection against 99% of strikes, with a residual
risk of damage for strikes with parameters outside the defined range.

4.14.6 Seismic Protection Requirements
Parameter
Seismic
Protection

Req. #
SBA1461Value
The antenna and foundation shall be designed towithstand a low probability earthquake with up to 0.2g
peak acceleration in either the vertical or horizontal axis.

Traceability
ENV0521

Low-probability has been defined as a 2% probability of an event exceeding this magnitude over a 50-year
period, consistent with data available from the USGS Seismic Hazard Model [RD04]. Equipment shall be
designed to survive this standard in any operational condition and orientation.

4.14.7 Site Elevation
Parameter
Altitude Range

Req. #
SBA1471

Value
The antenna and foundation shall be designed for
operation and survival at altitudes ranging from sea
level to 2200 m.

Traceability
ENV0531

Req. #
SBA1481

Value
Exposed equipment, including all equipment within theantenna, shall be designed to withstand persistentwind-induced vibration.

Traceability
ENV05314.14.8 Vibration
Parameter
Wind Vibration

The vibration mitigation requirement is especially applicable to all mechanical connectors. All cables shallbe mechanically supported to mitigate vibration loosening of connectors.

4.15 Maintenance and Reliability Requirements
Parameter
Preventive
Maintenance Cycle
Preventive
Maintenance Effort

Req. #
SBA1502

Mean Time
Between Failures

SBA1503

SBA1502

Value
Preventive maintenance shall not be required atintervals shorter than 12 months.
Periodic preventive maintenance shall require no
more than a two-person team and no more than
two 8-hour workdays.
MTBF 35,000 hrs

Traceability
SYS2301
SYS2301
SYS2302

The maintenance and reliability requirements support high-level requirements that limit total operating
cost of the array. The preventive maintenance effort is intended to be averaged over the design life of thearray, and needn’t be equal on all 12-month cycles.
The MTBF requirement corresponds to an annual failure rate of 25% for the antenna electro-mechanicalsystems alone. Monitor points/sensors should be included in the MTBF/MTTR analysis, but sensors andother components that can be reasonably deemed to be ancillary to operation may be removed from thedetermination of compliance with the MTBF requirement (ANT1503).

Page 19 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A“Failure” will be defined as a condition which places the system outside of its performance specifications(pointing, slew, tracking, etc.), or into an unsafe state, requiring repair. For example, a malfunction on oneof three redundant anemometers would not meet the standard for “failure” in the MTBF analysis, andshould not factor into compliance with ANT1503. Similarly, the malfunction of a gearbox temperature
sensor would not be considered a “failure” for the purposes of ANT1503. However, the malfunction of a
metrology sensor required for pointing model corrections would be considered a “failure.”

4.16 Monitor and Control Requirements
Parameter
Antenna Control
Unit (ACU)

Req. #
SBA1601

Servo Loops

SBA1602

Self-Monitoring

SBA1603

Weather
Monitoring

SBA1604

Network
Hardening/
Authentication
Remote Reset

SBA1605
SBA1606

Value
The antenna shall be equipped with an electronic
control unit that will drive the azimuth and elevation
axis motions according to commands received fromeither the Monitor and Control system (seeInterfaces) or from a local manual interface(s).
The ACU shall include servos with position and rate
control loops on each axis, and the design of these
servos shall account for the dynamic behavior of thestructure.
The antenna shall measure, report and monitor a setof parameters that allow for determination of its
status and may help predict or respond to failures.
The antenna shall be equipped with anemometers
and thermometers to determine when safe
operating conditions have been exceeded and tostow the antenna.
System remote control shall require anauthentication process, and only respond tocommands from authorized sources.
It shall be possible to remotely reset each antenna,
including a reboot of the antenna control unit, andreturn the antenna to operational status.

Traceability

SYS2601

SYS2601

SYS2602

For maintenance purposes, local control of the ACU near the point of service is required. Exclusions fromthe remote reset requirement are hardware interconnects for safety, the disconnection of the power inthe case of a fire alarm activation, and recovery from axis in hard stop.
The weather-monitoring requirement can be met centrally if preferred by the designer. The SBA antennas
are expected to be located within a geographically compact area (less than a square km in extent) so
uniform weather may be assumed. Other features of the ACU interface are specified in the M&C ICD.

Page 20 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

4.17 Motion Limiting Features
Parameter
Software
LimitsHardware
LimitsHard Stops
SafetyLock-OutFire Alarm
Fail Safe
BrakesReq. #Value
SBA1701 The antenna shall include logic to prevent motion beyond
programmable limits in azimuth and elevation during
normal operation.
SBA1702 The antenna shall be equipped with mechanically driven
switches to inhibit operation outside its safe operating
limits.
SBA1703 The antenna shall be equipped with hard mechanical stops
that physically prevent the antenna from exceeding
operating limits when damage is imminent.
SBA1704 The antenna shall be equipped with a safety lock-out that
inhibits motion of the antenna during service.
SBA1705 The antenna shall be equipped with fire alarms in any
equipment compartments. The fire alarm shall disconnect
power to the antenna when triggered.
SBA1706 The drive brakes shall engage when the antenna
experiences a loss of power.

Traceability

Fire alarms may be necessary at additional locations as determined by the designer.

4.18 Lifecycle Requirements
Parameter
Design Life
Lifecycle
Optimization

Req. #Value
SBA1801 The antenna shall be designed to require no major
overhaul work for 20 years.
SBA1802 The antenna design shall minimize its lifecycle cost for 20
years of operation.

Traceability

An exception to the design life is painting, which should not be required for ten years or more. Lifecycle
costs include manufacturing, transportation, construction/assembly, operation and decommissioning.

Page 21 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

5 Interface Requirements
This section provides information about the antenna interfaces. Interface Control Documents (ICDs) are
required between the antenna and all connecting systems. In many cases, interface specifications are not
yet available, but the broad scope of the ICD can be defined.
These interfaces shall be developed and documented by the SBA antenna designer and approved by ngVLA
as part of the antenna conceptual design effort, and updated throughout the design. Post CoDR, the ICD
shall only be updated through formal project change control processes.
Note that some consistency between the SBA antenna interfaces and 18m antenna interfaces is desirable,
in order to promote reuse of equipment.

5.1 Interface to the Foundation/Station
The conceptual design of the foundation is within the scope of the antenna element. Final design anddelivery of the foundation will be the responsibility of others.
The foundation refers to all stations where an antenna can be mounted, irrespective of its location.
Antenna stations will be available at the VLA antenna test facility (ATF) site for assembly and testing
purposes.
The ICD between antenna and foundation shall define the geometry of the attachment and the mechanicalcharacteristics of the foundation. Furthermore, it will define the position and geometry of the vaults forthe electric power and for the signals routed to the antenna through or adjacent to the foundation.
Note that contributions from the foundation at the antenna stations shall be taken into account in theperformance of the antenna and included in the error budgets in order to demonstrate compliance withthe specifications.
The antenna designer must ensure that the antenna in conjunction with the foundation provides theperformance required by his/her error budget.
The minimum stiffness and load capability of the foundation shall be defined in the ICD. The finite stiffnessof the combined soil and foundation shall be included in the dynamic analysis of the antenna.

5.2 Interface to the Electrical Infrastructure
Electrical power will be provided to the antenna through a vault adjacent to or integrated into the antennafoundation. Most locations are expected to be connected to the commercial power grid, but some remotesites may use locally generated power. For the preliminary design, it should be assumed that three-phase,
208V, 60 Hz power will be provided at this interface.
Loads shall be protected from brown-out conditions where one or two phases of the distribution system
are lost. Any shunt trip device shall be remotely resettable and have a programmable automatic reset
sequence.
The ICD should describe both the mechanical and electrical specifications of the electrical interfaces.
Circuit sizing and load estimates should include allocations for NRAO-supplied systems housed within theantenna, defined in Sections 5.3 and 5.6. NRAO will provide load estimates for NRAO-supplied equipment.

Page 22 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

5.3 Interface to the Fiber Optic Transmission System
A number of fibers will be distributed to each antenna for monitor and control, data transmission, andtime and frequency distribution.
The fiber optic cables will be physically routed through a vault adjacent to or integrated into the antennafoundation and should terminate at a splice box within the base electronics enclosure. The conduit orcable wrap may need to be thermally insulated or regulated.
The ICD should describe the mechanical specifications of the fiber optic interface. Note that the antenna
has no direct optical connection to the fiber optic transmission system. The communications interface tothe antenna shall be considered part of the monitor and control system interface.

5.4 Interface to Other External Cables and Piping
HVAC and cryogenic equipment may be located on or adjacent to the antenna. Other calibrationequipment may also be located in close proximity to the antenna.
The interfaces to all other external systems (excluding the fiber optic transmission system and electricalinfrastructure) will be described in this ICD.

5.5 Interface to the Receiver Enclosure/Front-End Electronics
The receiver enclosure will house the complement of feeds, cryogenic receivers and ancillary equipment
necessary for signal recovery at the secondary focus of the antenna. These components will be collectively
referred to as the antenna front end electronics.
The front end electronics will be connected to the antenna back-end electronics, located in the pedestal
room.
Note that the receiver selection mechanism (indexer) and focus adjustment mechanism are theresponsibility of the antenna designer. It is expected that a two-axis stage, providing adjustment in the ZF
and YF axes (see coordinate system in Section 12.2.4) will be required at a minimum. Adjustment in the
XF range may be necessary depending on the degree of gravitational deformation.
The range of adjustment required in each axis is TBD, as it depends on antenna parameters as well as thefront-end electronics. Adjustment range of ZF 20mm (focus) and YF PP (translation for band
selection) are expected given the current front-end design. Antenna-based contributions (thermal,
gravitational deformation, etc.) should be added to these allocations.
In terms of speed, the YF translation rate is most important. It should traverse its range of motion in 20
seconds (allowing for typical band switching in a 10-second period).
The receiver enclosure, an NRAO responsibility, will be a shielded enclosure constituted of a durable
continuous metallic surface. Durable RFI shielding will be provided on the access panels and on all otherpenetrations and discontinuities (seams, apertures, vents, cable and pipe penetrations, screws, etc.). The
mounting method between the enclosure and two-axis stage shall ensure proper grounding.
The ICD should define the masses and volumes of the front-end electronics. The requirements in termsof mechanical positioning and stability, electrical loads, and environmental control shall be included.
Requirements for personnel access for maintenance shall also be considered.

Page 23 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

5.6 Interface to the Back-End Electronics
The Base electronics enclosure shall house the antenna back-end electronics, which provide local timeand frequency references and a digital back-end that formats the signal collected by the front end for
distribution back to the central correlator. It also provides an interface to the monitor and control system,
described in Section 5.7.
The nature of the enclosure and its interface will be dependent on the mount design. NRAO will supply
volumes, mass and other interface requirements.

5.7 Interface to Internal Cables and Piping
Fiber optic cables, multi-conductor electrical cables, cryogenic piping and other cooling system piping will
distribute signals and fluids to customer-supplied equipment in the base electronics enclosure, receiver
enclosure and cryogenic platform. While the cables and piping are supplied by other systems, the antenna
must provide suitable routing spaces and wrap protection.
The ICD will describe the point-to-point connections, cable cross sections, bend radii, and othermechanical parameters necessary for internal cable and piping distribution.
Cable wraps shall be provided in azimuth and elevation which will accommodate all antenna cables as wellas interfacing system cables and hoses. The cable wraps shall permit full angular rotation of the antenna.
The cable wraps shall be such that cables are neither excessively stressed by twisting or bending, nordamaged by pulling over edges of a fixed structure. Specific requirements on bending radii shall be
documented in the ICD. The minimum bending radius of the elevation and azimuth cable wrap shall be in
any case larger than 200 mm.
Possible limitations in the amount of torsion that can be sustained by cables and hoses (e.g., helium lines)
shall also be considered. The design of the cable wrap shall be optimized for durability and reliability taking
into account the lifetime requirements of Sections 4.17 and 4.18.

5.8 Interface to the Cryogenic System
Space must be available for one (1) cryogenic compressor on the antenna yoke, below the elevation axis
but above the azimuth axis. A combination of rigid and flex lines will provide the supply and return lines
between the compressor and the refrigerators within the receiver enclosure.
The ICD should describe the point-to-point connections, bend radii, platform size, compressor mass andvolume, ancillary connections, and access requirements for maintenance.

5.9 Interface to the Monitor and Control System
The Antenna Control Unit (ACU) will govern the local control of the antenna, processing higher-levelcommands into lower level commands suitable for each axis drive and ancillary mechanisms.
Pointing trajectories will be supplied to the antenna through a series of time-tagged azimuths andelevations. Suitable interpolation and damping shall be provided in the servo control system to achieve
the required tracking accuracy. The vendor supplied antenna control unit shall operate in three pointing
modes:
x Raw or Encoder mode: In this mode, the servo system shall be controlled such that the encoder
values match the commanded values.
x Metrology mode: In this mode, the servo system shall apply any corrections to the input coordinates
based on the values of any metrology sensors located in the antenna system (if included in the design).

Page 24 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

x Active mode: In this mode, the servo system may include a pointing model containing the seven classic
terms (additional terms may be added through mutual agreement). The antenna must be able to pass
SAT based on the application of this pointing model.
The focus indexer/positioner shall follow a similar design philosophy with three modes of operation(encoder, metrology correction only, full model). Philosophically, any terms or operations which require
modeling of the antenna structure should be corrected for in the metrology mode. Terms that only
depend on sky position can be accommodated in the pointing or focus model.
In all cases, no action or inaction of the monitor and control system can cause incorrect or dangerous
conditions in the covered hardware. In addition, the ACU shall provide monitor data defining the current
condition of key monitor points that describe the overall health and status of the antenna.
The physical interface between the ACU and M&C system shall be multimode fiber using TCP/IP over
Ethernet.

6 Subsystem Requirements
Derivation of subsystem requirements shall be included as part of the antenna conceptual design effort,
and updated throughout the design. Post CDR/FDR, the subsystem requirements shall only be updated
through formal project change control processes that will include the designer, manufacturer, and NRAO.
The expected main elements of the antenna include, at a minimum:x Antenna mountx Reflector panels
x Panel adjusters
x Backup structurex Subreflector
x Subreflector support arm/structure
x Receiver selection mechanism
x Cables and cable wraps
x Antenna control system

Page 25 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

7 Safety
7.1 General
To achieve protection against all possible hazards, the antenna shall be considered a piece of machineryand its design and construction shall comply with the requirements set forth in this section.
Parameter
Code
ComplianceReq. #
SBA7001

Safety of
Personnel

SBA7002Value
The design shall comply with all relevant Federal and statebuilding codes. When in conflict, the most stringent codeshall apply.
The design shall allow the Observatory to comply with all
relevant federal and state occupational health and safety
regulations for personnel servicing the antenna.

Traceability

7.2 Hazard Analysis
7.2.1

Hazard Severity

Hazard severity categories are defined to provide a qualitative measure of the mishap.
Category
I
II
III
IV

Description
Catastrophic
CriticalMarginal
Negligible

Definition
Death, severe injury, or system loss
Major injury, major occupational illness, major system damage
Minor injury, minor occupational illness, minor system damage
Less than minor injury/occupational illness and minor system damage

Table 2 - Hazard severity categories.

System loss: the antenna and/or the housed systems cannot be recovered at reasonable costs.
Major system damage: the antenna and/or the housed systems can be recovered but extensive
industrial support is necessary and/or the system is out of operation for more than three weeks.
Minor system damage: the antenna and/or the housed systems can be repaired by ngVLA without any
support from industry and/or the system is less than three weeks out of operation.

7.2.2

Hazard Probability

Table 3 defines classification of the probability of hazards occurring during the 20 years of expected
antenna lifetime.
Level
A
B
C
D
E

Definition
Frequent
Probable
Occasional
RemoteImprobable

Description
Likely to occur frequently (typically once a year).
Will occur several times (6 to 10 times in 20 years).
Likely to occur (2 to 5 times in 20 years).
Unlikely but possible to occur (typically once in 20 years).
So unlikely that the occurrence can be assumed not to occur (>20 years)

Table 3 - Probability levels.

Page 26 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

7.2.3

Date: 2019-07-23
Version: A

Hazard Risk Acceptability Matrix

Table 4 and Table 5 define the degree of acceptability of the various hazard categories.
Frequency of
Occurrence
Frequent
Probable
Occasional
RemoteImprobable

I
Catastrophic
IA
IB
IC
ID
IE

II
Critical
II A
II B
II C
II D
II E

III
Marginal
III A
III B
III C
III D
III E

IV
Negligible
IV A
IV B
IV C
IV D
IV E

Table 4 - Hazard classification matrix.

Hazard risk index
I A to I D, II A, B; III A
II C, D; III B; IV A
I E; II E; III C; IV B
III D, E; IV C, IV D, IV E

Assessment criteria
Unacceptable
Undesirable (ngVLA decision required)Acceptable with review by ngVLA
Acceptable without review by ngVLA

Table 5 - Hazard acceptability matrix.

7.2.4

Requirements on Operational Hazards

None of the items in the following list (not meant to be exhaustive) shall lead to an unacceptable orundesirable hazard risk for the antenna or human beings:
x One or two independent operator errors
x One operator error plus one hardware failure
x One or two hardware failuresx One or two software failuresx Partial or complete loss of energy, reference signals, or control communications supplied to theantennax Emergency braking of the antennax Earthquakes happening for whatever position of the antenna
x Wind loads

7.2.5

Hazard Analysis

The purpose of a hazard analysis is to identify safety critical areas, evaluate hazards, and identify the safetymeasurement to be used.
A hazard analysis shall list all possible hazards, including an assessment of their severity and probability,
and shall show that safety considerations are included in all stages of the project including assembly,
training, maintenance, etc.
Safety provisions and alternatives needed to eliminate hazards or reduce their associated risk to a level
acceptable to ngVLA shall be described. As the design of the system progresses, the hazard analysis shallbe kept up to date reflecting new considerations, data and/or information. The following issues shall beconsidered:Page 27 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

1. Safety-related interface considerations among various elements of the system, e.g. material
compatibility, electromagnetic interference, inadvertent activation, fire initiation and propagation,
hardware and software controls, etc.
2. Environmental hazards including handling and operating environments.
3. All hazards related to operating, testing, maintenance and emergency procedures.
4. Any other identified hazards.
5. A description of any risk reduction methods employed for each hazard like safety-related
equipment, safeguards, interlocks, system redundancy, hardware or software fail-safe design
considerations, etc., taking into account the design requirements noted in Section 4.17.

7.3 Safety Design Requirements
7.3.1

Fire Safety

Smoke detectors are required in any equipment compartment and shall be interlocked to shunt trip allelectric power in the antenna. When smoke is detected the detector shall immediately close a contact
which ngVLA will use for a remote fire alarm and will energize a local audible alarm. The shunt trip of all
power shall occur 5 seconds after smoke detection. Emergency power for the smoke detectors and local
alarm shall utilize “Gel-cells” with a minimal reserve of six hours, and less than a 24-hour recharge cycle.

7.3.2

Mechanical Safety

For each component under design all the possible criteria of mechanical failure relevant to the component
under examination shall be considered (strength, fatigue, buckling, etc.).
Unless otherwise required by the standards applicable to this specification or by any applicable standard,
the minimum safety margins to be used are those provided herein.
A minimum stress safety margin of 1.5 with respect to the yield point shall be used in design of allmechanical components which in case of a failure lead to an unacceptable or undesirable hazard risk.
This stress safety factor shall be reduced to 1.1 in case of survival and accidental conditions.
For metallic materials where the relevant failure criteria is not linked to plasticity (example fatigue), an
equivalent stress safety factor of 1.5 shall be used in the design of all mechanical components which incase of a failure lead to an unacceptable or undesirable hazard risk.
For CFRP parts, the equivalent stress safety factor shall be applied to the relevant failure mode to beconsidered for the part under examination. All relevant failure criteria shall be considered (delamination,
fatigue, cracking, gluing failure, etc.). An equivalent stress safety factor of 1.5 shall be used in the design of
all components which in case of a failure lead to an unacceptable or undesirable hazard risk. This value
applies also in case of accidental and survival conditions.

7.3.3

Electrical Safety

Electrical equipment installed on the antenna shall comply with their relevant international or US productstandard.
The Antenna as a whole shall be in conformity with either IEC 60204-1:2016 [AD15] or NFPA 79 [AD14]
and with IEC 61140 [AD13].
Electrical installations and equipment shall be specifically built and/or derated in order to safely performtheir intended functions under the applicable environmental conditions. Insulation shall be coordinated inconformity with IEC 60664 [AD17] while taking into account the altitude of up to 2500 m above sea level.

Page 28 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

The antenna shall be designed, manufactured and erected to exhibit functional safety with regard toelectromagnetic phenomena. Influence onto the antenna safety of sources of electromagnetic disturbancesinternal to the antenna itself shall be considered in relation with the antenna design.

7.3.4

Hydraulic and Pneumatic Safety

Any hydraulic or pneumatic systems shall be designed in accordance with ISO 4413 [AD18].

7.3.5

Handling, Transport, and Storage Safety

The design of the antenna shall incorporate all means necessary to preclude or limit hazards to personnel
and equipment during assembly, disassembly, test, and operation.

7.3.6

Toxic Substances

No use of toxic substance (asbestos, formaldehyde, lead, etc.) and of their derivatives shall be permitted
in the antenna. Insulation materials and paint specifications shall be reviewed by ngVLA.

7.3.7

Confined SpaceConsiderations of confined space in the sense of OSHA Standards 29 CFR Part 1910 and 1926 shall betaken into account in the design where applicable (e.g., base, yoke, etc.).

7.4 Physical Security
Reasonable protection against unauthorized personnel access and theft shall be provided in the antenna
by means of lockable and caged access ladder, locks on cabinets, doors and similar design provisions.
Sensors shall be installed to monitor the condition “door open” and to relay the information to the ACU
in order to detect unauthorized intrusion.

Page 29 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

8 Requirements for Design
8.1 Analyses and Design Requirements
8.1.1

Finite Element Structural Analyses

All the Finite Element Analyses (FEA) necessary for the verification of the performance of the antenna
must be performed with an internationally recognized numerical code. The structural models used shallbe adapted to the particular analysis for which they are going to be used and shall be accurate enough toprovide a good description of the behavior of the structure under examination in terms of displacements,
stress and frequencies.
The analysis error due to mesh discretization shall be <10% in terms of FE internal criteria like the“Percentage error in energy norm.” Alternatively, this type of error can be evaluated by mesh refining.
The required analyses are listed and specified below. If during the design phase it appears that otheranalyses are necessary, the list below shall not be considered exhaustive.
The FEA analysis must also support the EM Analysis (by others). Table 6 and Table 7 of Section 8.1.4
describe relevant scenarios.
8.1.1.1

Static Analysis

Static analyses shall be used in the calculation of the effect of:x Gravity loads (stress and deflection)x Sudden braking (stresses)
x Thermal deformation (input loads derived from the thermal analysis)x Wind under precision and normal operating conditions (deflections)x Wind under survival conditions (stresses)
8.1.1.2

Modal Analysis

A modal analysis shall be performed to obtain accurate information concerning the Eigen frequencies andthe Eigen modes of the antenna when integrated in the antenna station, i.e. the combined stiffness of thesoil and foundation of the antenna stations shall be adequately represented in the dynamic FE model.
The number of degrees of freedom shall have a good representation of the frequency range required.
Care must be exerted to correctly represent the boundary conditions of the system under examination.
8.1.1.3

Seismic Analysis

The structural model used for the seismic analysis shall adequately represent the distribution of stiffness
and mass so that all significant deformation shapes and inertia forces are properly accounted for under
the seismic action considered. Non-structural elements 1, which may influence the response of the main
resisting structural system, shall also be accounted for. The response of all vibration modes contributing
significantly to the global response shall be taken into account. This may be demonstrated by either of thefollowing:x The sum of the effective modal masses for the modes taking into account at least 80% of the total
mass of the structurex All frequencies below 50 Hz are taken into account.
1

Architectural, mechanical or electrical element, system, or component which, whether due to lack of strength or
how it is connected to the structure, is not considered in the seismic design as load carrying element.

Page 30 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

The above conditions must be verified for each spatial direction.
The seismic analysis shall be based on the modal response spectrum technique, using a linear-elastic modelof the structure. It shall be assumed that the structural damping is 1.5% of critical damping.
The Square Root Sum of the Square method (SRSS) may be used in order to combine the contribution of
the various modal responses. The three spatial components of the response may also be combined with
the SRSS method. Alternatively, the designer may propose combination rules for the modal and spatial
components consistent with a relevant international earthquake resistance standard.
8.1.1.4

Wind Analysis

The force distribution on the antenna caused by precision and normal operating conditions can be derived
by either of the following:x Adequate Computational Fluid Dynamic (CFD) analysis
x Extrapolated wind tunnel measurement results of similar structure
The force distribution caused by survival wind loads may be derived from a CFD analysis. These forces
may be applied as quasi-static.

8.1.2

Thermal Modeling and Analysis

A thermal model of the antenna shall be used to compute the temperature distribution in the antennaduring daytime Precision and Normal operating conditions. The model shall also be used to determine theequilibration period duration from sunset.
The thermal model shall be able to simulate adequately the effects of thermal conduction, convection andradiation (solar flux). The calculated temperature distribution shall be applied as thermal load to thestructural FE model to predict the thermal error contribution to the pointing and surface error budgets.

8.1.3

Stress Analysis and Load Combination

A detailed stress analysis of the Antenna shall be performed. The stress analysis shall combine theindividual design loads and conditions specified under Section 8.1.1.1. In general, the load combinations tobe verified are given herein, whereby for specific components different load combinations may apply.
Load Combination Operational Conditions
Gravity + Thermal (secondary) + Wind (10 m/sec)
Gravity + Thermal (primary)+ Wind (7 m/sec) + Slew
Load Combination Accidental Conditions
Gravity + Thermal (secondary) + Wind (20 m/sec) + Emergency braking
Load Combination Survival Conditions
Gravity + Wind (50m/sec)
Gravity + Thermal (-30 qC) + Wind (30 m/sec)
Gravity + Wind (30 m/sec) + Icing + Snow
Gravity + Seismic + Wind (20 m/s)

8.1.4

Antenna EM Analysis Support

Surface deformations shall be computed for the loads shown in Table 6 and Table 7. The set of load cases
is extensive, but intended to provide a full representation of the antenna performance in the precision
operating environment. The results shall be provided to NRAO for electromagnetic performance analysis(by others).

Page 31 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Load
Case
L.01
L.02
L.03
L.05
L.07
L.08
L.09
L.10
L.11
L.12
L.13
L.14
L.16
L.17
L.18

Name

L.19

Gravity
Gravity
Gravity
GravityWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/sWind 5 m/s
Thermal Tu = 10°C (Uniform over structure)
Thermal gradient Tx = 3.6°C along XMR axis
Thermal gradient Ty = 3.6°C along YMR axis

L.20

Thermal gradient Tz= 3.6°C along ZMR axis

Date: 2019-07-23
Version: A

Azimuthangle (deg)
0
0
0
0
0
0
0
0
45
90
135
180
180

Elevation
angle (deg)
15
30
60
90
15
30
60
90
30
30
30
15
90

Table 6 - Load cases for antenna efficiency analysis.

Table 7 shows combined load cases. Combined cases may be calculated from results of the individual loadcase analyses. Load combinations L.C.01 through L.C.10 represent the precision operating conditions
described in section 4.14.1, while L.C.11 through L.C14 pertain to the normal operating conditions ofSection 4.14.2. These cases are not fully defined, as they depend on the analysis results for L.C.01 throughL.C.10. Only the worst-case gravity and wind scenarios are subject to combination with the thermal
gradients to limit the number of load permutations to be analyzed.
Load casecombination
L.C.01
L.C.02
L.C.03L.C.04
L.C.05
L.C.06
L.C.08L.C.09L.C.10
L.C.11
L.C.12
L.C.13
L.C.14Name

Note

L.01+L.07
L.02+L.08
L.03+L.09
L.05+L.10
L.01+L.11
L.01+L.12
L.01+L.13
L.01+L.14
L.05+L.16
L. <worst gravity>+L.<worst wind>+ L.17
L. <worst gravity>+L.<worst wind>+ L.18
L. <worst gravity>+L.<worst wind>+ L.19
L. <worst gravity>+L.<worst wind>+ L.20

Precision operating conditions
Precision operating conditions
Precision operating conditions
Precision operating conditions
Precision operating conditions
Precision operating conditions
Precision operating conditions
Precision operating conditions
Precision operating conditions
Normal operating conditions
Normal operating conditions
Normal operating conditions
Normal operating conditions

Table 7 - Combined load cases for antenna efficiency analysis.

Page 32 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

8.1.5

Date: 2019-07-23
Version: A

Control Loop Design and Analysis

For each of function to be controlled, the stability margins shall be computed. Dynamic simulations of thecontrol loops shall be performed, including non-linear effects like friction, stick-slip, sensor noise, etc.

8.1.6

Reliability, Availability, Maintainability Analysis

A Reliability, Availability, Maintainability analysis shall be performed to locate weak design points anddetermine whether the design meets the Maintenance and Reliability requirements. ngVLA suggests theParts Count Method for predicting system reliability as described in MIL-HDBK-217F, but the designer
may propose other methods. For non-electronic parts, the values of NPRD-95 [AD22] or data frommanufacturers or other databases may be used.
Another but more time-consuming (and considered more accurate) method, the Parts Stress Analysis
Prediction, is also described in MIL-HDBK-217F. This may be used if the result of the Parts Count Method
does not comply with the Maintenance and Reliability requirements.
ngVLA SBA antennas will operate at an elevation of 2200m above sea level, where temperature andpressure might decrease the MTBF relative to that at low elevations. These conditions shall be taken into
specific account in the reliability prediction by using the environmental factor given in MIL-HDBK-217F.
The analysis shall result in estimates of the Mean Time Between Failures (MTBF) and the Mean Time to
Repair (MTTR), assuming that scheduled preventive maintenance is performed.

8.2 Electromagnetic Compatibility Requirements
The ngVLA SBA antenna element shall exhibit complete electromagnetic compatibility (EMC) among
components (intra-system electromagnetic compatibility). Preventing electromagnetic interference (EMI)between the antenna and other subsystems (inter-system electromagnetic compatibility) is also critical.
The following requirements shall be fulfilled as a minimum to achieve both intra- and inter-system EMC,
but the antenna designer may propose alternatives if quantitative evidence is provided that they are atleast as effective as those specified. Shielding requirements may be computed as described under Radio
Frequency Interference Generation (Section 4.13).
x Control circuits, drive motors amplifiers, and switching devices shall be designed and constructedtaking into account the requirements concerning radiated and conducted electromagnetic energy. In
particular, all motor leads, both power and control, shall be filtered.
x All relay contacts and actuators shall be properly bypassed with snubber circuits, shielded, and/or
filtered.
x All amplifiers and oscillators shall be mounted in shielded enclosures that will provide effective
shielding of radio frequency energy.
x Silicon-controlled rectifier switching devices shall not be used unless phase controlled and zerocurrent crossing switching techniques are used.
x No gaseous discharge devices, except noise sources for test, shall be employed.
x Means shall be employed to reduce static electricity and the consequent radio frequency noise
generated in any rotating machinery.
x All displays (LCD, plasma, LED, CRT) shall have a RFI shield in front of the display to avoid radiated
RFI. This requirement may be waived if the screen is powered off during typical operation, and is used
for maintenance purposes only. It must be possible to monitor and turn off such emitting devices
remotely.
x All digital equipment, whether a simple logic circuit, embedded CPU, or rack mounted PC shall beshielded and have its AC power line and communication line(s) filtered at the chassis.
Page 33 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

The frequency range to be covered by these design measures for radiated radio-frequency interference(RFI) suppression shall extend from 50 MHz up to 12 GHz. Demonstration of EMC above 12 GHz is not
required because mitigation at 12 GHz and below is expected to be adequate at higher frequencies.

8.3 Materials, Parts, and Processes
8.3.1

Type of SteelThe steel used in the antenna mount shall be a carbon or a low-alloy steel. The selection shall account for
the lowest temperature to be expected during antenna operation and stow to minimize embrittlement.
In particular, the nil-ductility transition temperature (at which the material starts to exhibit cleavage
fracture with very little evidence of notch ductility) of the selected steel shall not exceed –45ºC. Whennecessary (e.g., gears and pinions, if applicable), materials with suitable hardness or surface hardened shallbe used to ensure system life.

8.3.2

Stress Relieving

All structural welded parts shall be stress relieved using an appropriate method to reduce stresses andensure dimensional stability (unless proven by the antenna designer to be unnecessary).

8.3.3

CFRP

If carbon fiber reinforced plastic (CFRP) is used, the material and fabrication processes shall be selected,
examined, and if necessary qualified with respect to strength, fatigue and life. All CFRP structures shall beprotected against solar radiation and humidity with suitable paints and/or sunshades.

8.3.4

Fasteners

All fasteners shall be metric except those on off-the-shelf units. The use of standard metric cross-sections
for construction materials is preferred but not required.

8.3.5

Paints

To limit the effect of solar heating and associated differential expansion of structural members and toprotect the structure against atmospheric corrosion, the antenna structure shall be painted with whitesolar reflecting paint. The paint shall be chosen to last at least ten years without repainting.

8.3.6

Surface Treatment

Unpainted surfaces shall be treated against corrosion.

8.3.7

Thermal Insulation

Thermal insulation used in an exterior antenna application shall be protected with a metal cover.

8.3.8

Rodent Protection

Antennas shall be designed to prevent rodent damage. At a minimum, this may involve protecting all cables
with flexible or rigid conduit or equivalent. Any penetrations within enclosures and raceways shall mitigate
the risk of rodent damage.

8.3.9

Name Plates and Product Marking

As a general rule, the main parts and all exchangeable units shall be equipped with nameplates which arevisible after installation of the part/unit and contain the following information:x Part/unit namex Drawing number including revision
Page 34 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

x Serial number
x Manufacturing month and year
x Name of manufacturer
Alternatively, a marking system based on barcodes or similar system may be used upon ngVLA approval.
For Line Replaceable Units (LRUs, Section 12.3), it is highly desirable that the LRU serial number be
ascertainable over the monitor and control interface (Section 5.9)

8.3.10 Labels
All cables and switches, junction boxes, sensors, and similar equipment shall be labeled. Electrical cabinets,
switch panels, UPS, and all electrical equipment which can be manually operated or is relevant for safety
shall be labeled in English and Spanish.

Page 35 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

9 Documentation Requirements
9.1 Technical Documentation
All documentation related to the antenna shall meet the following requirements:
x The language used for written documentation shall be English.
x Drawings shall be generated according to ISO standards and use metric units.
x Layouts of electronic circuits and printed circuit boards shall also be provided in electronicallyreadable form. Altium Designer files are the ngVLA preferred formats for electronic circuit diagrams
and printed circuit board layouts.
x The electronic document formats are Microsoft Word and Adobe PDF.
x The preferred CADsystem used is AutoDesk Inventor and/or AutoCAD.
x The preferred FEA modeling software is Siemens FeMAP NASTRAN.
Any deviation from the above shall be agreed to by ngVLA.

9.2 Software and Software Documentation
Deliverables include ACU software and any other specially developed software. The software shall bedelivered in source and object form, together with all procedures and tests necessary for compilation,
installation, testing, upgrades, and maintenance.
x Software must be tagged with suitable version numbers that allow identification (also online remotely)of a release.
x User manuals of software developed under this specification and of any other commercial software
used (controllers embedded software, special tools, etc.) shall be provided.
x Software maintenance and installation upgrade documentation shall be provided.
x Full Test and Acceptance procedures shall be documented.

Page 36 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

10 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A), inspection (I), a factory
acceptance test (FAT), or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which the ngVLA
project office may check during the design phase by design documentation review.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which the ngVLA
project office may check during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple inspection
or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item/assembly/unit withthe specified performance shall be demonstrated by tests. A FAT is performed without integration withinterfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item/assembly/unit with thespecified performance shall be demonstrated by tests. SAT is performed on-site with the equipment as
installed.
Multiple verification methods are allowed.
Table 8 summarizes the expected verification method for each requirement. This degree of verification
applies to the prototype antenna(s) only. Separate verification procedures should be developed as part ofthe verification plan to ensure all production antennas conform to the design specification (mfg. to print).
Req. #
SBA0101
SBA0102
SBA0103
SBA0201
SBA0202
SBA0203
SBA0204
SBA0205
SBA0206
SBA0207
SBA0208
SBA0209
SBA0210
SBA0211
SBA0301
SBA0302
SBA0303
SBA0401
SBA0501
SBA0502
SBA0503
SBA0611

Parameter/Requirement
Upper operating frequency
Lower operating frequency
Optimized operating frequencies
Optical configuration typePrimary aperture diameter and shape
Sub-reflector aperture diameter
Secondary angle of illumination
Reflector offset
Focal ratio, primary
Cross polarization
Reflector shapes
Secondary reflector extension
Main reflector extensions
Mounting configuration
Minimum spacing
Height
Mass
Number of antennas
Surface accuracy, precision
Surface accuracy, normal
Reflector construction
Non-repeatable pointing error, precision

Page 37 of 45

D
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*

A

I

FAT

SAT

*
*

*
*

*
*
*
*
*
*
*
*

*

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Req. #
SBA0612
SBA0621
SBA0622
SBA0701
SBA0702
SBA0801
SBA0802
SBA0803
SBA0901
SBA0902
SBA0903
SBA0904
SBA0905
SBA0906
SBA0907
SBA1001
SBA1002
SBA1101
SBA1000
SBA1001
SBA1411
SBA1412
SBA1413
SBA1414
SBA1415
SBA1421
SBA1422
SBA1423
SBA1424
SBA1425
SBA1430
SBA1431
SBA1432
SBA1433
SBA1434
SBA1441
SBA1442
SBA1443
SBA1444
SBA1445
SBA1446
SBA1447
SBA1451
SBA1452
SBA1453
SBA1461

Parameter/Requirement
Referenced pointing error, precisionNon-repeatable pointing error, normal
Referenced pointing error, normal
Focus stability, precision
Focus stability, normal
Azimuth tracking range
Elevation tracking range
Elevation movement range
Slew: Azimuth
Slew: Elevation
Acceleration: Azimuth
Acceleration: Elevation
Slew + settle time
Tracking: Azimuth
Tracking: Elevation
Stow position, survival
Stow position, maintenanceResistive losses
Solar observations
Spurious signal level
Precision env.: Solar thermal load
Precision env.: Wind
Precision env.: Temperature
Precision env.: Temp. rate of change
Precision env.: Precipitation
Normal env.: Solar thermal load
Normal env.: Wind
Normal env.: Temperature
Normal Env.: Temp. rate of change
Normal env.: Precipitation
Ops. limit: Solar thermal load
Ops. limit: Wind
Ops. limit: Temperature
Ops. limit: Precipitation
Ops. limit: Ice
Survival: Wind
Survival: Temperature
Survival: Radial ice
Survival: Rain rate
Survival: Snow load, antenna
Survival: Hail stones
Survival: Antenna orientation
Lightning protection: StructureLightning protection: Electronics systems
Lightning protection: Personnel
Seismic protection

Page 38 of 45

D

*
*
*
*
*
*
*

*
*
*
*
*

*

*
*
*
*

A
*
*
*
*
*

Date: 2019-07-23
Version: A

I

FAT

SAT
*
*
*
*
*

*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*

*
*
*

*

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Req. #
SBA1471
SBA1481
SBA1501
SBA1502
SBA1503
SBA1701
SBA1702
SBA1703
SBA1704
SBA1705
SBA1706
SBA1701
SBA1702
SBA1703
SBA1704
SBA1705
SBA1706
SBA1801
SBA1802
SBA7001
SBA7002

Parameter/Requirement
Site elevation
Wind vibration
Preventive maintenance cycle
Preventive maintenance effort
Mean time between failure
Antenna control unit (ACU)
Servo loops
Self-monitoring
Weather monitoring
Network hardening/authentication
Remote reset
Software limits
Hardware limits
Hard stops
Safety lock-out
Fire alarm
Fail safe brakes
Design life
Lifecycle optimization
Code compliance
Safety of personnel

D
*
*

A
*
*
*
*
*

*

Date: 2019-07-23
Version: A

I

FAT

SAT

*
*

*
*
*
*
*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*

Table 8 - Expected requirements verification method.

11 Key Performance Parameters
This section provides key performance parameters that the designer should estimate and NRAO should
monitor throughout the project design phase. These parameters have a large influence on the eventual
facility effectiveness and are useful high-level metrics for trade-off decisions. These parameters are ofhigher importance to NRAO, making improved performance above the requirement desirable. The impact
on system-level performance is discussed in depth in Section 4.
NRAO’s expectation is that the specified technical requirements will not push technical boundaries.
Rather, the key challenge is to deliver a design that can be manufactured in volume and delivered
affordably. A second challenge is reducing the maintenance burden and total lifecycle cost.
Given these expectations, the technical requirements are generally specified as minimum values. The goal
is to give the designer some latitude in optimization for a balanced design. Understanding the anticipatedantenna performance (not just its specified minimum) on these parameters facilitates system-level analysis
and performance estimation.
These parameters may also be useful for determining the relative priority of the requirements documented
in Section 4 and can assist in the required analysis should tensions be identified between requirements orcapability reductions be required to fit within cost constraints.
Table 9 lists key performance parameters identified for monitoring. Note that their order reflects theorder in the document, and is not indicative of relative importance or priority.

Page 39 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Req. #
SBA0301
SBA0501
SBA0502
SBA0611
SBA0612
SBA0621
SBA0622
SBA0802
SBA0901
SBA0902
SBA0903
SBA0904
SBA0905
SBA0906
SBA0907
SBA1501
SBA1502
SBA1503
SBA1801

Key Performance Parameter
Minimum spacing
Surface accuracy, precision environment
Surface accuracy, normal environment
Non-repeatable pointing error, precision environment
Referenced pointing error, precision environment
Non-repeatable pointing error, normal environment
Referenced pointing error, normal environment
Elevation range (lower elevation limit)
Slew: Azimuth
Slew: Elevation
Acceleration: Azimuth
Acceleration: Elevation
Slew + settling time
Tracking: Azimuth
Tracking: Elevation
Preventive maintenance cycle
Preventive maintenance effort
Mean time between failures
Design life

Table 9 - Key performance parameters for monitoring during design.

Page 40 of 45

Date: 2019-07-23
Version: ATitle: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

12 Appendix
12.1 Abbreviations and Acronyms
Acronym
ACU
AD
ATF
CDR
CoDR
CFD
CFRP
CW
EIRP
EM
EMC
EMP
FDR
FEA
FOV
FWHM
HVAC
ICD
IF
KPP
LCD
LED
LO
LRU
MTBF
MTTF
MTTR
ngVLA
RD
RFI
RMS
RSS
RTP
SAC
SNR
SRSS
SWG
TAC
TBD
VLA
WVR

Description
Antenna Control Unit
Applicable Document
Antenna Test Facility (at the VLA Site)
Critical Design Review
Conceptual Design Review
Computational Fluid Dynamics
Carbon Fiber Reinforced Plastic
Continuous Wave (Sine wave of fixed frequency and amplitude)
Equivalent Isotropic Radiated PowerElectro-Magnetic
Electro-Magnetic Compatibility
Electro-Magnetic Pulse
Final Design Review
Finite Element Analysis
Field of View
Full Width Half Max (of Primary Beam Power)
Heating, Ventilation, and Air Conditioning
Interface Control Document
Intermediate Frequency
Key Performance Parameters
Liquid Crystal Display
Light Emitting Diode
Local Oscillator
Line Replaceable Unit
Mean Time Between Failure
Mean Time To Failure
Mean Time To Repair
Next Generation VLA
Reference Document
Radio Frequency Interference
Root Mean Square
Root of Sum of Squares
Round Trip Phase
Science Advisory Council
Signal to Noise Ratio
Square Root Sum of the Square
Science Working Group
Technical Advisory Council
To Be Determined
Jansky Very Large Array
Water Vapor Radiometer

Page 41 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

12.2 Coordinate System
12.2.1 Antenna Pad Coordinate System
The antenna pad coordinate system (or foundation coordinate system) is indicated by Op, Xp, Yp, Zp. todenote the origin and three Cartesian coordinate vectors, as shown in Figure 2.
The pad coordinate system is based on the right-hand rule, with the Zp corresponding to the local
vertical, positive direction toward zenith, and Xp axis pointing to the geographical north and the YP axis
pointing to geographical west. The system origin is in the plane of the embedded flanges at the antennapad, at the nominal center of the as-built pad, as defined by the antenna’s kinematic mount.

Figure 2 - Diagram of the antenna pad coordinate system and major axes. Separate Cartesian reference frames
define each mirror surface, the focus, and the pad respectively. Antenna design is diagrammatic only.

12.2.2 Main Reflector (MR) Coordinate System
The MR coordinate system is a Cartesian coordinate system based on the right-hand rule, fixed to thereflector focus. This coordinate system is indicated by OMR, XMR, YMR , ZMR as shown in Figure 3.

Page 42 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

The X–Y plane is perpendicular to the antenna beam, with the XMR axis perpendicular to the elevation
axis; the ZMR axis is parallel to the nominal boresight of the antenna, positive toward the source, and the
YMR axis according to the right-hand rule. As such, when the antenna azimuth equals zero, the YMR axis isparallel to the Yp axis.

12.2.3 Secondary Reflector (SR) Coordinate System
The SR coordinate system is a Cartesian coordinate system, based on the right hand rule, fixed to thefocus of the main reflector (OSR = OMR). This system of coordinates is indicated by OSR, XSR, YSR , ZSR as
shown in Figure 3.
The Y-axis is shared with the MR coordinate system. The XSR-axis and ZSR-axis are rotated from the MRaxes by the tilt angle beta (Ⱦ).

Figure 3 - Antenna optical coordinate system. Separate Cartesian reference frames define each reflector
surface and the secondary focus.

Page 43 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

12.2.4 Focal Plane Coordinate system
The focal plane coordinate system is defined in Figure 3. This coordinate system is also a Cartesian
coordinate system, with coordinates indicated by F0, XF, YF, ZF.
The position of the origin, F0, is the nominal secondary focus of the antenna. ZF is towards the projected
midpoint of the secondary mirror as seen from OF. The YF axis is parallel to YMR and YSR, and the XF axis
according to the right hand rule.

12.2.5 Antenna Azimuth
The azimuth angle shall be zero when the antenna is rotated so that YMR is pointing west. The azimuth
angle origin is then counted from the negative XP (south), positive direction when the antenna moves in
the clockwise direction (azimuth angle = 90 when YMR is pointing north).

12.2.6 Antenna Elevation
The elevation shall be set to zero when the ZMR axis is pointing to horizon and to +90 when the ZMR axis
is pointing toward zenith.

Page 44 of 45

Title: Short Baseline Array Antenna:
Owner: Dunbar
Preliminary TechnicalRequirements
NRAO Doc. #: 020.47.05.00.00-0001-REQ-ASBA_ANTENNA_TECH_REQS

Date: 2019-07-23
Version: A

12.3 Maintenance Definitions
12.3.1 Maintenance Approach
Required maintenance tasks shall be minimized. Maintenance shall be mainly performed at assembly andsubassembly level by exchange of Line Replaceable Units (LRUs). LRUs are defined as units that can beeasily exchanged (without extensive calibration, of sufficient low mass and dimension for handling ease,etc.) by technician-level maintenance staff. LRU exchange shall be possible by two trained people withinfour working hours on the installed antenna. It is desirable that LRU replacement be possible without aboom truck, basket, or scissor lift, using only standard tools and special tools identified in the antenna
maintenance manual. A step-by-step procedure for safe exchange of every LRU shall be provided in the
Maintenance Manual. The following equipment shall be considered a LRU as a minimum:x Sub-reflector mechanism (if provided)x Elevation encoder(s)x Azimuth encoder(s)x Drive Motors
x Electronic cards and drivesx Stow pin assemblies (if provided)
x End stops
x Elevation cable wrap parts (excluding cables and cable installation)x Locking pins
x Lightning arrestorsx Temperature sensors
x Anemometersx Additional metrology sensors (if provided)
x Limit switches
Other LRUs shall be defined by the antenna designer, depending on the design. The LRUs will bemaintained by the ngVLA project (with or without industrial support).

12.3.2 Periodic Preventive MaintenancePreventive maintenance is performed at planned intervals to keep the antenna operational and within its
specified performance. This includes checking, greasing, substitution of consumables, visual inspection, etc.
All maintenance operations shall be planned in a Programmed Check and Intervention List (PCIL) of theMaintenance Manual, which shall list the tools, the procedures and the time necessary for their execution
and periodicity. The antenna design shall enable these maintenance activities to be performed with theantenna stowed in the “maintenance stow” position as defined in Section 4.10. The normal preventive
maintenance shall not exceed the requirements established in Section 4.15. Any greasing operation or
lubrication activity that must be performed at intervals shorter than 12 months shall be automatic.

12.3.3 Overhaul
Overhaul is a planned major maintenance operation performed at the antenna site. The following applies:x No overhaul operation shall last longer than three weeks.
x No overhaul operation shall be required at intervals shorter than 20 years.
x Periodic painting and surface protection shall not be necessary more often than every ten years.
x Overhaul activities, including painting and possible exchange of Azimuth and Elevation bearings, shallbe described in the Maintenance Manual.

Page 45 of 45

102-0000-001-CDD-001
Revision: 1

ngVLA 6m Antenna Concept Design Document
Document Number...................................................................................... 102-0000-001-CDD-001
Revision: ......................................................................................................................................... 1
Author ...................................................................................................................... Dean Chalmers
Date ................................................................................................................................ 2019-07-25
Status ................................................................................................................................ Released
Classification..................................................................................................................Unrestricted

Prepared By
Reviewed By

Approved By
Issued By

Name
Organisation
Name
Organisation
Name
Organisation
Name
Organisation
Name
Organisation
Name
Organisation

Dean Chalmers
NRC
Gordon Lacy
NRC

Signature
Signature
Signature
Signature

Scott Roberts
NRC
Donna Morgan
NRC

Signature
Signature[This document describes concept design for the ngVLA 6m Antenna Design project.]2019-07-25

Page 1 of 45

102-0000-001-CDD-001
Revision: 1

DOCUMENT HISTORY
Revision

Date

Change Request

Change Description

A

04July2018

Initial draft for comment

1

25July2019

Approved for release

DOCUMENT SOFTWARE
Application

Wordprocessing

VersionFilename

102-0000-001-CDD001_CoDesignDoc_A_2019-07-25.docx

MSWordORGANISATION DETAILSDesignation

Primary Author and Responsible Organisation
Contributors

2019-07-25

Name

Dean Chalmers
G. Lacy
M. Islam
M. Fleming
M. Wessel
R. Osterried
R. Hellyer

Organisation

NRC
NRC
NRC
Minex
SED Systems
SED Systems
NRC

Page 2 of 45

102-0000-001-CDD-001
Revision: 1

TABLE OF CONTENT
1INTRODUCTION................................................................................................................. 7
1.1
Purpose of Document .............................................................................................. 7
1.2
Scope of Document ................................................................................................. 7
1.3
Intended Audience................................................................................................... 7
1.4
Design Context ........................................................................................................ 7

2

APPLICABLE AND REFERENCE DOCUMENTS .............................................................. 8
2.1
Applicable Documents ............................................................................................. 8
2.2
Reference Documents ............................................................................................. 8

3

OPERATIONAL CONTEXT ................................................................................................ 9
3.1
Operational Environment ......................................................................................... 9

4

RISKS ............................................................................................................................... 12
4.1
Risks...................................................................................................................... 125

DESIGN OVERVIEW ........................................................................................................ 15
5.1
Design Overview.................................................................................................... 16
5.1.1
Elevation Rotating Assembly .................................................................. 16
5.1.2
Mount ..................................................................................................... 24

6

ERROR BUDGETS ........................................................................................................... 25
6.1
Surface Accuracy Error Budget.............................................................................. 25
6.2
Pointing Error Budget............................................................................................. 27

7

PERFORMANCE .............................................................................................................. 29
7.1
System Noise Contribution..................................................................................... 29
7.2
Aperture Efficiency................................................................................................. 30
7.2.1
Gravitational Deformations...................................................................... 31
7.2.2
Results.................................................................................................... 34
7.2.3
Manufacturing Errors .............................................................................. 37
7.2.4
Surface Adjustment................................................................................. 37
7.3
Pointing.................................................................................................................. 37
7.4
Survivability ........................................................................................................... 38
7.5
Drives .................................................................................................................... 38
7.5.1
Elevation Drive........................................................................................ 38
7.5.2
Azimuth Drive ......................................................................................... 41

2019-07-25

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102-0000-001-CDD-001
Revision: 1
8

PRODUCTION LOGISTICS .............................................................................................. 44
8.1
Primary Reflector Transport ................................................................................... 44

9

FUTURE WORK ............................................................................................................... 45
9.1
Design and Analysis .............................................................................................. 45
9.1.1
iBUS Design ........................................................................................... 45
9.1.2
Feed/Secondary Support Structure......................................................... 45
9.1.3
Mount Design.......................................................................................... 45
9.1.4
Integrated FEA Model ............................................................................. 45

LIST OF TABLES
Table 1 Applicable Documents........................................................................................................ 8
Table 2 Reference Documents........................................................................................................ 8
Table 3 Precision Operating Conditions [AD01] .............................................................................. 9
Table 4 Normal Operating Conditions [AD01] ............................................................................... 10
Table 5 Limit to Operating Conditions [AD01] ............................................................................... 10
Table 6 Survival Conditions [AD01]............................................................................................... 11
Table 7 Project Risks .................................................................................................................... 13
Table 8 Product Risks................................................................................................................... 14
Table 9 Antenna Surface Accuracy Error Budget – Precision Operating Conditions .................... 26
Table 10 Antenna Surface Accuracy Error Budget – Normal Operating Conditions...................... 26
Table 11 Example Pointing Error Budget from 18m ..................................................................... 28
Table 12 System Noise Contributions Requirement ...................................................................... 29
Table 13 Aperture Efficiency Related Requirements [AD01] ......................................................... 30
Table 14 Precision Pointing Requirements.................................................................................... 37
Table 15 Normal Pointing Requirements....................................................................................... 38
Table 16 Elevation Drive Loads .................................................................................................... 39
Table 17 Elevation Drive Performance Matrix ............................................................................... 41
Table 18 Azimuth Drive Loads ...................................................................................................... 41

2019-07-25

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102-0000-001-CDD-001
Revision: 1

LIST OF FIGURES
Figure 1 NRC ngVLA 6m Antenna Design Concept ...................................................................... 15
Figure 2 Primary surface edge adjuster tab concept ..................................................................... 17
Figure 3 Primary surface edge adjuster with oBUS ....................................................................... 17
Figure 4 Assembled oBUS structure ............................................................................................. 18
Figure 5 oBUS components in colour............................................................................................ 19
Figure 6 Cross Section of Antenna at Low (12º) Elevation Angle .................................................. 20
Figure 7 6m iBUS structure........................................................................................................... 21
Figure 8 6m Secondary Support Structure. ................................................................................... 22
Figure 9 Stiffening Ribs on Primary Reflector to Support Secondary Support Structure ................ 23
Figure 10 Secondary and Feed Support Structure for 6m dish...................................................... 23
Figure 11 Complete 6m telescope with mount .............................................................................. 24
Figure 12 Reflector Surface Noise Measurement Results ............................................................. 29
Figure 13 6m Reflector Assembly ................................................................................................. 31
Figure 14 6m oBUS ...................................................................................................................... 32
Figure 15 Primary surface Laminate schedule (blue layer: carbon qiso, red layer: triaxial
carbon). ................................................................................................................. 32
Figure 16 oBUS Laminate schedule (blue layer: carbon qiso, pink layer: foam core) .................... 33
Figure 17 oBUS rib Laminate schedule (green layer: carbon qiso, pink layer: foam core) ............. 33
Figure 18 Cone back-primary laminate schedule and foam core (blue layer: carbon QISO,
magenta layer: carbon uni, grey layer: foam core). ................................................ 34
Figure 19 ngVLA 6m FE model constraints ................................................................................... 35
Figure 20 ngVLA 6m surface RMS error under Gravity load cases (a) 15° and (b) 90° elevation
angle...................................................................................................................... 35
Figure 21 Surface RMS error under Gravity load cases for ngVLA 18m (a) 15° and (b) 90°
elevation angles and ngVLA 6m (c) 15° and (d) 90° elevation angles. ................... 36
Figure 22 Elevation Drive Configuration........................................................................................ 40
Figure 23 Azimuth Drive Options .................................................................................................. 42
Figure 24 Example direct drive configuration ................................................................................ 42
Figure 25 Example Direct Pinion Drive.......................................................................................... 43

2019-07-25

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102-0000-001-CDD-001
Revision: 1

LIST OF ACRONYMS AND ABBREVIATIONS
BUS

BackUp Structure

CTE

Coefficient of Thermal Expansion

DVA

Dish Verification Antenna

ERA

Elevation Rotating Assembly

FE

Finite Element

FEA

Finite Element Analysis

iBUS

Inner Backup Structure

ngVLA

next generation Very Large Array

NRAO

National Radio Astronomy Observatory (USA)NRC

National Research Council (Canada)oBUS

Outer Backup Structure

PE

Pointing Error

QISO

Quasi-Isotropic

RMS

Root Mean Square

SPEM

Systematic Pointing Error correction Model

SRC

Single-piece Rim-supported Composite

VLA

Very Large Array

XEL

Cross-elevation

2019-07-25

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102-0000-001-CDD-001
Revision: 1

1

INTRODUCTION

1.1

Purpose of Document

The purpose of this document is to describe the Conceptual Design of the National Research Councilof Canada (NRC) Next Generation Very Large Array (ngVLA) 6m Antenna Design as called out inStatement of Work NRC ngVLA 6m Antenna Study, [AD02].

1.2

Scope of Document

This document describes the operational context of the design and the operating conditions as definedin the ngVLA Antenna: Preliminary Technical Specifications, [AD01].
The project assumptions and risks are presented with their status and mitigation plans.
Methods of accounting for system budgets are described, example budgets and initial analysis
results for key performance requirements are presented.
Production logistics concepts are described for on-site manufacturing and assembly.
Finally a summary of the key future tasks is provided.

1.3

Intended Audience

This document is expected to be used by the NRC ngVLA Antenna Design Team, National Radio
Astronomy Observatory (NRAO) Antenna Integrated Product Team and Management Teams, and thengVLA System Engineering and Management Team.

1.4

Design Context

NRC is conducting two design studies in parallel for the ngVLA; one for the 6m antenna, the focus of
this document, and one for the 18m antenna. Due to the relative cost impacts for the project, 214 18m
antenna could constitute ~50% of the overall project cost vs <5% for the 19 6m antennas, a muchgreater emphasis has been put on the 18m design. The 6m antenna design presented here is basedon the extensive development work that has been performed at NRC for the 18m ngVLA antenna. The
ngVLA 6m and 18m antennas, essentially, must meet the same requirements (other than opticalsurface sizes); however, designing the 18m antenna to meet these requirements is much more difficult
than the 6m. Given limited resources the bulk of design and analysis effort has therefore been put into
the 18m design with the understanding that there will very low risk in meeting the requirements withthe 6m design by the application of the same design concepts. Therefore this document contains aminimal amount of analysis of the performance of the 6m. Its ability to meet the requirements isinferred by analogy to the 18m design.

2019-07-25

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102-0000-001-CDD-001
Revision: 1

2

APPLICABLE AND REFERENCE DOCUMENTS

2.1

Applicable Documents

The following documents at their indicated revision form part of this document to the extent specified
herein.
Table 1 Applicable Documents
Document/Drawing
Number

Ref NoDocument Title

AD01020.47.05.00.00-0001-SPE ngVLA Short Baseline Array SBA Antenna: PreliminaryTechnical Specifications

AD02

020.05.40.05.01-0002SOW

Statement of Work, NRC ngVLA 6m Antenna Study

AD03

101-0000-001-CDD

ngVLA 18m Antenna Concept Design Document

2.2

Revision
2

A

Reference Documents

The following documents provide useful reference information associated with this document. These
documents are to be used for information only. Changes to the date and/or revision number do notmake this document out of date.
Table 2 Reference Documents
Ref NoDocument/Drawing Number

Document Title

RD01“Fabry-Perot Resonator Design for the Measurementof Surface Reflectivity,” D. Henke et al. in 9th Global
Symp. on Millimeter-Waves., Espoo, Finland, Jun. 6–8, 2016.

RD02“Measurements of Composite Reflectors across QBand (33–50 GHz) and W-Band (75–115 GHz),” D.
Henke et al. [accepted] in 18th Int. Symp. Antenna
Technol. Appl. Electromagn. (ANTEM), Aug. 19–22,
2018.

RD03

101-0000-001-REG-001

ngVLA 6m Antenna Risk RegisterRD04

9P033REP01

ngVLA ngVLA Report Main Drive Axes

RD05

101-0000-004-PLN

ngVLA 18m Antenna Preliminary Production Plan

2019-07-25

RevisionA

A

Page 8 of 45

102-0000-001-CDD-001
Revision: 1

3

OPERATIONAL CONTEXT

The ngVLA array will consist of 214 x 18m antennas and 19 x 6m antennas. The 6m antennas will be
deployed on the Plains of San Agustin in New Mexico at the core of the array with baselines from 11
to 60m, [AD01]. All antennas will be fixed position, the array will not be reconfigurable.
The project has defined four functional regimes;
1. Precision Operating: low wind speed, at night, low temperature rate of change and no
precipitation.
2. Normal Operating: moderate wind speed, day/night, moderate temperature rate of change andno precipitation.
3. Limit to Operations: higher wind speed, low and high temperature limits and precipitation
resulting in ice build-up.
4. Survival Conditions: high winds, extreme temperatures, snow and/or ice accumulation and hail.
Additionally, requirements are identified for seismic and lightning strike events.

3.1

Operational Environment

The defined operating conditions for the antennas are shown in Table 3, Table 4, Table 5 and Table 6.
Table 3 Precision Operating Conditions [AD01]
Parameter

Req. #

Solar Thermal Load

SBA1411 Night time only; no solar
thermal load within last 2
hours.

SYS2411Wind Speed

SBA1412 0 W
average over
10 min time. 10 m/s peakgusts.

SYS2412

Temperature

SBA1413 -15 C

SYS2413

Temperature Rate of Change

SBA1414 1.8°C/Hr.

SYS2414

Precipitation

SBA1415 No precipitation.

SYS24152019-07-25

Value

Traceability

T

25 C

Page 9 of 45

102-0000-001-CDD-001
Revision: 1
Table 4 Normal Operating Conditions [AD01]

Parameter

Req. #

Value

Traceability

Solar Thermal Load

SBA1421 Exposed to full sun.

SYS2421Wind Speed

SBA1422

SYS2422

Temperature

SBA1423 -15 C

Temperature Rate of Change

SBA1424 3.6°C/Hr.

SYS2424

Precipitation

SBA1425 No precipitation.

SYS2425m/s average over 10
min time. 15 m/s peak gusts.
T

35 C

SYS2423

Table 5 Limit to Operating Conditions [AD01]

Parameter

Req. #Wind

SBA1431

Temperature

SBA1432-20 C

Precipitation

SBA1433

Any precipitation rate that does not
result in accumulation of ice on theantenna structure.

2019-07-25

Value

Traceability
SYS2432T

45 C

SYS2433
SYS2434

Page 10 of 45

102-0000-001-CDD-001
Revision: 1
Table 6 Survival Conditions [AD01]

Parameter

Req. #

Value

Wind

SBA14410 m/s

W

50 m/s average.

SYS2441

Temperature

SBA1442

-30 C

T

50 C

SYS2442

Radial Ice

SBA1443

2.5 cmSYS2443

Snow Load

SBA1444

25 cm

SYS2444

Hail Stones

SBA1445

2.0 cmSYS2445

Antenna Orientation

SBA1446

Stow-survival, as defined bydesigner

2019-07-25

Traceability

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102-0000-001-CDD-001
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4

RISKS

4.1

Risks

Risks have been categorized into either Project or Product risks. Project risks are those that might
impact the completion of the design work on budget and schedule, product risks are those that might
impact the ability of the design to meet the requirements. Both project and product risks are further
categorized as to the nature of the impact; Budget, Schedule, Logistical or Technical. All identified
risks are tracked in the project risk register, [RD03].

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102-0000-001-CDD-001
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Table 7 Project Risks
Risk#
102-R5

Description
Work delay due to unexpected loss ofresources

StatusOpen

Type
Project

Category
Schedule

102-R6

Procurement delays related to contracts

Open

Project

102-R7

Loss of personnel due to retirement andemployees seeking employment
elsewhere

Open

Project

2019-07-25

Mitigation Plan

Probability
30%

Impact2

Schedule

50%

2

Schedule

10%

2

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Table 8 Product Risks
Risk#
102-R1

Description
Production cost exceeds ngVLA
expectations

StatusOpen

Type
Product

Category
BudgetMitigation Plan
Initiate cost evaluation early in project andupdate often to track cost.

102-R2

Bond between reflective materialand surface structure is not strong
enoughOpen

Product

Technical

102-R3

Repeatability of single piecereflector surface accuracy during
production cannot be proven.

Open

Product

Technical

102-R4

Long term surface accuracy stability
cannot be proven.

Open

Product

Technical

102-R8

Surface accuracy requirement
cannot be met.

Open

Product

Technical

102-R9Tangential surface adjusters cannot
reduce distortions to meet surface
requirement.

Open

Product

Technical

102-R10

Strength, stiffness and long-term
endurance of surface adjusters are
unproven.

Open

Product

102-R11

Durability of surface reflective
material is compromised bymoisture ingress.

Open

Product

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Probability
20%

Impact2

Send material structure samples forlifecycle testing.

30%

2Provide quality assurance protocols for
production. Compliant connection between
primary surface and BUS with adjustment
is being investigated during concept designphase.
Review and re-issue of report done
produced for SKA project.
Investigate
accelerated life testing.

20%

3

75%

2

Minimize deformation due to environmental
effects to allow maximum allocation to asmanufactured errors.
Model and prototype at an early stage.

20%

3

Technical

Model, prototype and test adjusters at an
early stage.

50%

2

Technical

Provide quality control measures for
production and repair procedures for
operations.

20%

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5

DESIGN OVERVIEW

The preliminary design for the ngVLA 6m antennas is a Single-piece Rim-supported Composite (SRC)
Reflector on a steel yoke and pedestal mount, Figure 1.

Figure 1 NRC ngVLA 6m Antenna Design Concept

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5.1

Design Overview

5.1.1

Elevation Rotating Assembly

The Elevation Rotating Assembly (ERA) design features a SRC primary reflector surface supported by
a composite shell outer BackUp Structure (oBUS) which attaches to a fabricated steel inner BUS(iBUS). The 6 metre iBUS differs from the 18 metre design principally in the fact that it will be built
from steel plate rather than from tubes. A composite space frame secondary support structureattaches to the oBUS at the rim of the primary reflector and supports the feed package and secondaryreflector.

5.1.1.1

Primary Reflector Surface

The primary reflector surface manufacturing technique is based on the vacuum infused carbon
fibre/epoxy resin layup process used in the fabrication of the Dish Verification Antenna (DVA)
antennas. The surface is ~4mm thick and consists of 5 layers of quasi-isotropic carbon fibre fabric, acopper reflective layer and protective layers of thin fibreglass veil. This is nearly identical to that usedin the 18m design except it will be slightly thinner. The primary surface infusion is of uniform thickness
and does not include a rim or other features that may result in process induced distortions. The
exception is the surface adjuster tabs which will be infused with the surface. These will be designed toresult in minimal distortions and are located around the perimeter in a small band of the surface
outside of the optical surface. Figure 2 shows a concept sketch for the adjuster tabs (this concept will
be virtually identical to the one proposed on the 18m). The metal spool would be added at the edge ofthe layup, then overwrapped around its perimeter with a pre-cured carbon-fibre ‘fan’ as illustrated in
the figure. The green zone in the figure represents the 100mm wide extension to the primary surface
which is outside of the aperture. The carbon fibre ‘fan’ would be incorporated into the centre of thelayup (through-thickness) during the primary layup and in this way would form an integral part of thestructure.

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Figure 2 Primary surface edge adjuster tab concept
Figure 3 shows the primary surface edge adjuster concept in context with the oBUS edge structure.
The primary surface (left hand panel) is suspended from the oBUS by the primary surface edge
adjuster tabs shown in Figure 2 together with a clevis and stud arrangement. Nuts and washers
located on each side of the oBUS flange on the studs will allow for the adjustment of the perimeter
tension loads on the surface and, in turn, the shape of the surface.

Figure 3 Primary surface edge adjuster with oBUS

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5.1.1.2

Outer Backup Structure

The oBUS is comprised of 7 panels, and 7 ribs, and is really a scaled down version of the 18m
version. The complete oBUS structure is depicted in Figure 4.

Figure 4 Assembled oBUS structure
The component dimensions are designed to enable standard transport to site. Because the 6m is somuch smaller than the 18m design, the oBUS panels can be larger relative to the total size of theoBUS. For this reason the full circumference of the 6m reflector can be completed with 7 panels
instead of the 22 required for the 18m. The panels and ribs are carbon fibre/epoxy composite layup
similar to that used in the surface (without the reflective layer). The ribs provide stiffening at the panel
joints as well as load paths from the feed/secondary support structure connections to the iBUS. The
outer or top edge of the structure is stiffened by the circumferential rim beam. Figure 5 depicts anassembled oBUS with the components that make up the structure shown in different colours. The 7
panels that make up the oBUS are shown with 6 panels in green and one in grey (the grey panel
shows you the extent of one panel). The top edge circumferential beam is shown in red and the radial
beams in blue. The panels and beams would be built off site and trucked in. The green (and grey)
panels would be assembled on a jig very similar to the one shown in the 18m fabrication document,but of course sized for this structure. Once the panels are in place the red rim beam would be bonded
in place (in sections), and finally the blue radial beams would be bonded in place.

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Figure 5 oBUS components in colour
The resulting structure is very stiff in shear between the reflector surface and iBUS. This is ofparticular importance for the feed-down configuration because the reflector will spend most of its timeoriented in a vertical or near vertical orientation where the shear stiffness of the oBUS will provide thelarger portion of necessary support for the primary surface (imagine the reflector surface being
dragged downward by gravity) in Figure 6.
The oBUS is connected to the iBUS through bolted connections between the bonded-in metal
connectors located at the lower end of each radial beam on the oBUS and connection points definedat the same locations on the iBUS. This will be at 7 discrete points directly over the 7 corners definedby the radial (blue) beams shown in Figure 5. When the iBUS and oBUS are combined, they will
provide the stiffness required to achieve the pointing and surface accuracy. Figure 6 shows the centreplane cutaway view of the 6m dish.

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Figure 6 Cross Section of Antenna at Low (12º) Elevation Angle

5.1.1.3

Inner Backup Structure

The iBUS provides the interface and transfers drive loads between the reflector assembly and theyoke. It is an assembly of machined and fabricated steel components. The iBUS for the 6m antenna
will likely be quite different than that suitable for the 18m. Figure 7 illustrates the current working
solution. As can be seen this is not a tubular space frame concept, but rather a plate structure which
is more suitable for the smaller size of the 6m design. The central band represents the drive magnet
arc required for a linear motor. The 6m iBUS is conceptual at this time, development of a steel plate
structure is seen as low risk and so design resources have been concentrated on other higher risk
aspects.

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Figure 7 6m iBUS structure
Once assembled, the iBUS will be lifted into position onto the yoke-tower assembly. The primaryreflector assembly will be lifted by crane and the connection between the oBUS and iBUS made oncein position.

5.1.1.4

Secondary Support

The secondary support structure is a carbon fibre truss to minimize weight and coefficient of thermal
expansion (CTE), and maximize stiffness. Figure 8 shows the general arrangement.

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Figure 8 6m Secondary Support Structure.
The primary truss structures (orange) support the secondary reflector (black) and attach to the rim of
the primary reflector at two points. A carbon tube on each side (blue in Figure 8) connects to the rim of
the primary reflector as far around the rim as practical while still staying out of the optical path andkeeping the tube length down below practical limits. The design is similar to that proposed for the 18m,
although the reduced size of the optics does help reduce the overall complexity. The feed package
and indexer are shown as a series of components (grey and blue in the rendering), and areplaceholders ready for further development.
Stiffening ribs integrated into the oBUS transfer the loads from the secondary legs to the iBUS, Figure9.

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Figure 9 Stiffening Ribs on Primary Reflector to Support Secondary Support Structure
Figure 10 shows a close-up view of the feed and secondary support structure. The different colours
indicate separate shippable parts. On-site assembly would occur, with a combination of glue-bonded
and bolted connections.

Figure 10 Secondary and Feed Support Structure for 6m dish2019-07-25

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5.1.2

Mount

A pedestal mount based on a modified commercial product has been selected for this early design
study. The mount was designed as a 10m symmetric satcom antenna intended to operate at up to 50
GHz and in winds up to 28 m/s. The principle modifications are: reducing the height of the tower tomatch the 6m requirement, modifying the yoke arms, and adapting the turn-head to accommodate thelinear drive. Figure 11 shows the general configuration of the mount.

Figure 11 Complete 6m telescope with mount
Although no detailed analysis has been performed on the mount with the 6m ngVLA reflector, giventhat it was designed for a 10m reflector and to operate in extreme conditions, there is a high level ofconfidence that with minimal further development the design will meet the ngVAL requirements.

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6

ERROR BUDGETS

6.1

Surface Accuracy Error Budget

Surface accuracy is defined as the deviation of the manufactured reflector surface from the designed
surface profile. The accuracy can be stated either in the plane tangent to the reflector surface or in
the main aperture plane normal to the boresight direction (the main reflector optical axis). For thengVLA the surface accuracy specifications are stated in the main aperture plane (see Table 13 below).
The specifications are for different operating conditions (precision or normal).
Surface error can be caused by the manufacturing process (mould accuracy, part separation from themould, tensioning of the reflector) or by dynamic wind, gravity, and thermal effects (differential rates ofthermal expansion/contraction, or thermal gradients set up by solar irradiation). The dynamic effects
will deform the reflectors and the mounting structure, which will cause surface error.
The surface accuracy error budget identifies sources of surface error for both the primary andsecondary reflectors, allocates error amounts to the sources and both reflectors, and defines thecalculation of overall error using the allocated amounts. The budget is used both to determine
compliance with the specifications when the achievable accuracy is known or estimated for each error
source, and to estimate the available error margin in a source using the total allowed error in thespecification. Surface accuracy budgets with the most recent accuracy data and estimates are shownin Table 9 for precision operating conditions and Table 10 for normal operating conditions. The tables
include manufacturing error derived from the mould surface accuracy and the accuracy ratio of themould and the part built from it. Totals for primary and secondary reflector surface accuracy andoverall combined accuracy are shown, as well as antenna efficiency at selected frequencies acrossthe operational band (calculated from the total surface accuracy).

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Table 9 Antenna Surface Accuracy Error Budget – Precision Operating Conditions

Precision
Wind
Requirement
Primary
Mold
Manufacturing
Gravitational
Wind
ThermalAgeingTotal

5 m/s
160 micron RMS

Night

0.080
0.100 mm rms
0.042 mm rms
0.01 mm rms
0.02 mm rms
0.01
0.137 mm rms

Combined Total (RSS)Frequency (GHz)

Surface eff

2
100.0%

Temperature

20 C min

Secondary
Mold
Manufacturing
Gravitational
Wind
ThermalAgeingTotal

0.05
0.030 mm rms
0.02 mm rms
0.01 mm rms
0.01 mm rms
0.01
0.064 mm rms

0.151 mm rms
10
99.6%

30
96.4%

80
77.3%

100
66.9%

116
58.2%

Table 10 Antenna Surface Accuracy Error Budget – Normal Operating Conditions

NormalWind
Requirement
Primary
Mold
Manufacturing
Gravitational
Wind
ThermalAgeingTotal

7 m/s
Day/night Temperatur
300 micron RMS
Secondary
0.100
Mold
0.100 mm rms
Manufactur
0.042 mm rms
Gravitationa
0.02 mm rms
Wind
0.08 mm rms
Thermal
0.02
Ageing0.170 mm rms
Total

Combined Total (RSS)Frequency (GHz)

Surface eff

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2100.0%

30 C min

0.05
0.030 mm rms
0.02 mm rms
0.020 mm rms
0.05 mm rms
0.01
0.082 mm rms

0.189 mm rms
10
99.4%

30
94.5%

80
67.0%

100
53.5%

116
43.1%

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6.2

Pointing Error Budget

Pointing error is defined as the angular difference between the commanded antenna pointing direction
and the resulting main lobe peak gain. Pointing error specifications are for different operating
conditions (precision or normal) and whether the pointing currently falls within an angular offset andtime offset of a calibration source location that is suitable for a pointing error measurement. The
specifications are shown in Table 14 and Table 15.
Pointing error can be repeatable or non-repeatable. Repeatable pointing error can be compensated tosome degree. Residual error or error introduced by compensations are treated as non-repeatable
pointing error in this document. Systematic pointing errors due to mechanical misalignments andgravity are compensated by using a systematic pointing error correction model (SPEM) as the basis of
a compensation. The SPEM model coefficients are determined from a least squares determinationaccording to measurements of pointing error from calibration sources. Other means of correcting
systematic pointing error include atmospheric refraction correction, tiltmeters, temperature
measurements, and antenna modelling for strain induced by gravity, wind, and thermal effects.
The pointing error budget identifies sources of pointing error in the bias (systematic) and random
categories, allocates error amounts to the different sources, and defines the calculation of total
pointing error from the allocated amounts. The budget is used both to determine compliance with thespecifications when the achievable pointing error contribution for each source is known or estimated,
and to determine the available error margin in a source using the allowed total pointing error from thespecification.
An example pointing error budget from ngVLA 18 m antenna is shown in Table 11. Both elevation andcross-elevation (XEL) errors are included. Each error is given for absolute pointing (pointing directly to
a commanded direction) with and without compensation, and for referenced pointing (pointing relative
to a well-known pointing “landmark”) as an applicable fraction of the absolute pointing error
contribution. Contributions are divided into categories as they apply to the major components of theantenna system (elevation assembly, pedestal, servo system, and foundation). Examples of error
sources include errors in alignment and perpendicularity of the antenna components and deformation
by gravity, wind, and thermal expansion/contraction.

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Table 11 Example Pointing Error Budget from 18m

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7

PERFORMANCE

7.1

System Noise Contribution
Table 12 System Noise Contributions Requirement

Parameter

Req. #

Value

Resistive Losses

ANT1101

The primary and secondary reflector shalleach have a surface resistive loss of lessthan 1.0% over the operating frequency
range.

Traceability

NRC has conducted tests of its reflecting material to determine the system noise contributions. The
test method is detailed in RD01 and the latest results are detailed in RD02 and presented in Figure
12Error! Reference source not found.. Samples A1/2 are the materials developed for DVA1, B1/2
material developed for DVA2 and the most recent material developed for the ngVLA project is C1/2.
Gains were made between DVA1 and 2 by switching from aluminium to copper and further gains to
the most recent material were due to material configuration changes.

Figure 12 Reflector Surface Noise Measurement Results
The worst case noise temperature contribution from the surface for the C materials is ~0.75 K @ 115
GHz. The resistive loss is calculated as follows:

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7.2

Aperture Efficiency

The key requirements for aperture efficiency relate to surface accuracy and reflector surface
continuity, Table 13.
Table 13 Aperture Efficiency Related Requirements [AD01]

Parameter

Req. #

Surface Accuracy, Precision

SBA0501 Surface errors shall not
exceed 160 m RMS, forthe primary and secondaryreflector combined when
operating in the Precision
operating environment.

SYS0501

Surface Accuracy, Normal

SBA0502 Surface errors shall not
exceed 300 m RMS, forthe primary and secondaryreflector combined, when
operating in the Normal
operating environment.

SYS0501

Reflector Construction

SBA0503 Each reflector may beconstructed as a single
piece or as multiple panels.
If constructed of multiple
panels, gaps between paneledges shall not exceed 1
mm.

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Traceability

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7.2.1

Gravitational Deformations

Analysis of the gravitational deformations of the 6m reflector assembly, Figure 13, was performed
early in the design cycle after which resources were focused on the greater challenge of the 18m
design. The results presented here are for the earlier design which did not incorporate many of thefeatures developed for the 18m. They are presented here with the intent to show that the required
accuracy will be achievable for the 6m. Design elements from the 18m study will be incorporated in
the future only as required to meet performance targets while keeping costs in mind.

Figure 13 6m Reflector Assembly
The carbon composite cone back structure was reinforced using 6 height optimized ribs withunidirectional fibers to improve the bending stiffness Figure 14.

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Figure 14 6m oBUS

7.2.1.1

Laminate schedule

The primary surface laminate features of 6 layers of carbon Quasi-Isotropic (QISO) carbon fibre,
Figure 15.

Figure 15 Primary surface Laminate schedule (blue layer: carbon qiso, red layer: triaxial
carbon).

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The oBUS laminate features of 8 layers of carbon Quasi-Isotropic (QISO) carbon fibre, Figure 16.

Figure 16 oBUS Laminate schedule (blue layer: carbon qiso, pink layer: foam core)
The oBUS rib laminate features of 4 layers of carbon Quasi-Isotropic (QISO) carbon fibre and twolayers of unidirectional carbon fibre, Figure 17.

Figure 17 oBUS rib Laminate schedule (green layer: carbon qiso, pink layer: foam core)
The rim laminate features of 3 layers of carbon Quasi-Isotropic (QISO) carbon fibre and 2 layers of
unidirectional carbon and one inch thick foam core to improve the rim stiffness, Figure 18.

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Figure 18 Cone back-primary laminate schedule and foam core (blue layer: carbon QISO,
magenta layer: carbon uni, grey layer: foam core).

7.2.2

Results

Under the gravity load case, FE Analysis was performed for 15 degree and 90 degree elevation
angles. The FE model is constrained at the bottom of the oBUS structure at 7 locations shown in
Figure 19. The iBUS structure is notional at this point and further design is required for the 6m.

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Figure 19 ngVLA 6m FE model constraints
The secondary surface is modelled as a lumped mass supported by four points. The feed is alsomodelled as lumped mass in the analysis. The surface RMS errors are presented in Figure 20.

Figure 20 ngVLA 6m surface RMS error under Gravity load cases (a) 15° and (b) 90° elevation
angle.
The 6m gravity load case results are then compared with 18m analysis. It is important to note that for
proper comparison, the 18m design is also constrained at the bottom of the oBUS structure. Also, theoBUS structure in the 6m design uses 1” thick core while in the 18m design the core thickness is 1.5”.

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The secondary tube sizes are similar although the 6m design is lot more compact than the 18m
design. The comparison is presented in Figure 21.

Figure 21 Surface RMS error under Gravity load cases for ngVLA 18m (a) 15° and (b) 90°
elevation angles and ngVLA 6m (c) 15° and (d) 90° elevation angles.
It is important to note that for the 18m dish structure, there are some additional carbon composite
patches attached. This helps to reduce the surface distortion due to the secondary load (at theconnection points) on the primary and visible in the surface RMS error plots (Figure 21 (a) and (b)).
The 6m design is very compact in comparison to the 18m design. Hence, no additional patches are

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not attached in the primary surface. However, further investigation is required to obtain optimal sizeand shape of the secondary support structures.

7.2.3

Manufacturing Errors

The SRC reflectors are manufactured as the name implies in one piece on a mould. The asmanufactured surface accuracy depends on; mould accuracy, process design and process control. As
illustrated in the Surface Error Budget, Table 9, the required as-manufactured accuracy will depend on
the values achieved through design for the deformation due to gravity, wind and thermal loads. The
values shown in Table 9 represent the current status of the surface accuracy and indicate that therequired as-manufactured accuracy will be ~132µm Root Mean Square (RMS) (80 microns RMS
mould error and 105 microns RMS process induced error added in RSS).
As with the 18m the plan is to attempt to “capture” the surface shape by installing the oBUS on thesurface before it is released from the mould. For serial production it is easy to justify a jig to accuratelyalign the oBUS to the moulded part during installation. Small adjustments will then be made to reachthe final accuracy requirement.

7.2.4

Surface Adjustment

The same surface adjustment scheme as proposed for the 18m will be used for the 6m. Details can befound in [AD03].

7.3

Pointing

The pointing requirements for the ngVLA 6m antenna are shown in Table 14 and Table 15.
Table 14 Precision Pointing Requirements

Parameter

Req. #

Value

Traceability

Non-repeatable Pointing Error

SBA0611 54 arc sec RMS.

SYS0801

Referenced Pointing Error

SBA0612 9 arc sec RMS, within 4º of
the target position and 15
minutes of time.

SYS0701,
SYS0801

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Table 15 Normal Pointing Requirements

Parameter

Req. #

Value

Traceability

Non-repeatable Pointing Error

SBA0621105 arc sec RMS.

SYS0801

Referenced Pointing Error

SBA062215 arc sec RMS, within 4°.
Must maintain spec for aminimum of 15 minutes.

SYS0701,
SYS0801

At this time a comprehensive pointing analysis has not been performed, this will be a priority in thenext phase.

7.4

Survivability

Survivability analysis has not been performed at this time, based on the DVA1/2 experience it is notseen to be a risk but will be analysed in the next phase.
The DVA1/2 design did have a failure mode in survival conditions which was buckling of the surface
due to high wind from the back of the reflector. At the end of the reflector opposite the feed andsecondary the surface has less shape and therefore less stiffness. With the open BackUp Structure(BUS) of the DVA1/2 the surface is exposed to wind directly from the rear. Plans to mitigate that risk
with those designs included adding stiffeners to the back of the surface (not desirable as they might
print through under operational loading) or shielding attached to the BUS. With the proposed ngVLA
design the back side of the reflector is well shielded by the oBUS panels and so the back of thesurface will not be exposed to direct wind and the buckling failure should not occur. Analysis toconfirm this will be performed in the next phase.

7.5

Drives7.5.1

Elevation Drive

A preliminary elevation drive design has been performed by Phase USA based on the mechanicalconfiguration and loading scenarios provided by NRC, [RD04]. Loads, based on the NRC wind tunnel
data scaled for the reflector size and wind speeds of the ngVLA, are shown in Table 16.

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Table 16 Elevation Drive Loads

Max Elevation Drive Loads [kNm]
Precision
0.7

Normal
1.3

Limit
10.5

Survival
65.7

The elevation drive design is a three-Phase, sinusoidal, double-airgap axial-field motor with:Distributed drives, embedded in motor sectors
Dual gap section distributed on a 1.83m arc radius with 130mm stack, 2.8mm air gap per side
Natural convection cooling
Rotor consisting of 4 double sided segments
Windings encapsulated under vacuum in thermal conductive epoxy resin
Exposed surface is protected with a carbon fiber sheet applied during encapsulation
The initial drive sizing is performed based on the Limit condition (with a 20% oversizing margin) underwhich the antenna must be driven to the stow position where brakes and/or stow pins are deployed.
The drive configuration is shown in Figure 22.

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Figure 22 Elevation Drive Configuration

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Table 17 Elevation Drive Performance Matrix

The elevation drive performance matrix is shown in Table 17.

7.5.2

Azimuth Drive

A preliminary azimuth drive design has been performed by Phase USA based on the mechanicalconfiguration and loading scenarios provided by NRC, [RD04]. Loads, based on the NRC wind tunnel
data scaled for the reflector size and wind speeds of the ngVLA, are shown in Table 18.
Table 18 Azimuth Drive Loads

Max Azimuth Drive Loads [kNm]
Precision
0.6

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Normal
1.2

Limit
9.9

Survival
61.7

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Two drive concepts are under consideration for the azimuth drive, Figure 23; direct drive (left) anddirect pinion and gear drive (right).

Figure 23 Azimuth Drive Options

7.5.2.1

Azimuth Direct Drive

The proposed Direct Drive Azimuth system is a Three-Phase, sinusoidal, Single Air Gap design,
Figure 24 featuring;
Distributed Drives, embedded in motor sectors or near by
1.34m diameter, 120mm stack, 4mm air gap
Traditional Direct Drive Configuration
Based on TK13440-120-1000

Figure 24 Example direct drive configuration

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7.5.2.2

Azimuth Direct Pinion/Gear Drive

The direct pinion drive is similar to conventional gear and pinion azimuth drives except that the needfor gearboxes is eliminated. Two motors (to remove backlash) mounted inside the yoke centre withpinions directly mounted to their output shafts, Figure 25, drive a ring gear that is integral with theazimuth bearing.

Figure 25 Example Direct Pinion Drive
The direct pinion/gear drive should offer a lower cost solution but may require more maintenance.
There are pros and cons to all configuration, at this time only very preliminary analysis has been
performed. During the next phase a detailed trade study will be performed to determine the bestsolution from an overall cost/performance/operations perspective.

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8

PRODUCTION LOGISTICS

Production of the proposed design would take place both on and off-site similar to that of the 18m, thedetails of which can be found in [RD05].

8.1

Primary Reflector Transport

As the 6m antennas are all located at the centre of the array core and near to the proposed production
facility location, transport of the assembled primary reflector will be straight forward only requiring astandard flatbed trailer and a support fixture.

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9

FUTURE WORK

9.1

Design and Analysis

Moving forward with the 6m design will require considerable effort in all aspects of the design due tothe minimal effort applied thus far. Having said that much of the design will parallel that of the 18m
and so it should be a matter of modelling and analysis with a minimal design iterations. Most of the
future work outlined for the 18m in [AD03] will apply to the 6m. Particular aspects that differ from the
18m and will require more effort are listed here

9.1.1

iBUS Design

The proposed iBUS for the 6m is a plate steel structure as opposed to the structural steel space frameof the 18m. Design, analysis and optimization will be required for this component.

9.1.2

Feed/Secondary Support Structure

Due to the relative sizes of the primary and secondary reflectors the Feed/Secondary Support
Structure will also differ significantly from that of the 18m and will require detailed analysis to ensure
adequate performance and further design detailing for volume manufacture.

9.1.3

Mount Design

The mount used for the design presented here will need to be further optimized for the ngVLA 6m
application.

9.1.4

Integrated FEA Model

An integrated FEA model will be developed to allow analysis of system level performance including;
Pointing Analysis
Aperture Efficiency Analysis
Survivability

2019-07-25

Page 45 of 45

Title: Front End TechnicalRequirements

Owner: Grammer

NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQS

Date: 2019-07-24
Version: A

Front End Technical Requirements
020.30.03.01.00-0001-REQ-A-FRONT_END_TECH_REQS

Status: RELEASEDPREPARED BY
W. Grammer
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-07-23
2019-07-23

APPROVALS
R. Selina,
Project Engineer

ORGANIZATIONElectronics Division,
NRAO

DATE
2019-07-24

2019.07.24
09:34:52 -06'00'

M. McKinnon,
Asst. Director,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.28 15:22:48 -06'00' NM-Operations, NRAO

2019-07-24

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.28 15:23:03 -06'00'

DATE
2019-07-24

Page 1 of 22

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

Title: Front End TechnicalRequirements

Owner: Grammer

NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQS

Date: 2019-07-24
Version: A

Change Record
Date

AuthorAffected
Section(s)01

2018-07-13

W. Grammer

1–4

02

2018-09-24

W. Grammer

All

03

2018-09-27

All

04

2018-10-17

S. Durand
W. Grammer,
R. Selina

Version

4.3, 4.4, 8.1

05

2018-10-24

W. Grammer,
R. Selina,
J. Jackson06

2018-10-25

W. Grammer,
R. Selina

5.4

07

2018-11-02

W. Grammer

4.2, All08

2019-07-23

W. Grammer

AllA

2019-07-24

A. LearAll

5.3, 6.5

Page 2 of 22

ReasonInitial draft version
Incorporate corrections from R. Selina,
add additional content
Small Edits
Added req #s in tables 4.41, 4.42;
other minor edits.
Added gain slope and ripple
requirements to tables, with
explanation in text.
Corrected M&C system module
designations.
Added a new section on dynamic range
requirements.
Deleted section on ngVLA projectbackground, as directed.
General cleanup and reformatting
done.
Incorporated review comments andcorrections.
Added subsections on feed horns.
Prepared document for approvals andrelease.

Title: Front End TechnicalRequirements

Owner: Grammer

NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQS

Date: 2019-07-24
Version: A

Table of Contents
1

Introduction ................................................................................................... 5

1.1
1.2

Purpose ................................................................................................................................... 5
Scope ...................................................................................................................................... 5

2

Related Documents and Drawings ............................................................... 6

2.1
2.2

Applicable Documents ........................................................................................................... 6
Reference Documents ............................................................................................................ 6

3

Overview of the Front End Technical Requirements ................................ 7

3.1
3.2
3.3
3.3.1
3.3.2

Document Outline ................................................................................................................. 7
General Front End Description ............................................................................................. 7
Summary of Front End Requirements ................................................................................... 7
General Functional Specifications .......................................................................................................... 8
Other General Requirements................................................................................................................. 8

4

Front End Functional and Performance Requirements ............................. 9

4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.8.1
4.8.2
4.9
4.10
4.11

RF Frequency Ranges ............................................................................................................. 9
Sensitivity Requirements........................................................................................................ 9
Feed Horn Performance Requirements ................................................................................ 9Gain Requirements .............................................................................................................. 10
Dynamic Range Requirements ............................................................................................ 10
Cryogenic Cooling Requirements ........................................................................................ 10
Spurious Signals/Radio Frequency Interference Generation ............................................. 10
Environmental Conditions ................................................................................................... 11
Normal Operating Conditions ............................................................................................................. 11
Specific Environmental Requirements................................................................................................. 11
Maintenance and Reliability Requirements ....................................................................... 11
Monitor and Control Requirements ................................................................................... 12
Lifecycle Requirements ........................................................................................................ 125Interface Requirements .............................................................................. 13

5.1
5.2
5.3
5.4
5.5

Interface to the Power Supply Subsystem .......................................................................... 13
Interface to the Cryogenic Subsystem ................................................................................ 13
Interface to the Integrated Receivers and Downconverters (IRD) Subsystem ................. 14Interface to the Antenna Subsystem................................................................................... 14Interface to the Monitor and Control Subsystem .............................................................. 15

6
7

Subsystem Requirements ........................................................................... 16
Safety ............................................................................................................ 16

7.1
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5

General ................................................................................................................................. 16
Safety Design Requirements................................................................................................ 16
Fire Safety .................................................................................................................................................. 16
Vacuum Safety .......................................................................................................................................... 16
Mechanical Safety ..................................................................................................................................... 16
Electrical Safety......................................................................................................................................... 16
Handling, Transport, and Storage Safety ............................................................................................ 16

8

Requirements for Design ............................................................................ 17

8.1
8.1.1
8.2

Analyses and Design Requirements..................................................................................... 17
Reliability Availability Maintainability Analysis ................................................................................... 17
Electromagnetic Compatibility Requirements ................................................................... 17

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8.3
8.3.1
8.3.2
8.3.3
8.3.4
8.3.5

Date: 2019-07-24
Version: A

Materials, Parts, and Processes ........................................................................................... 17
Fasteners .................................................................................................................................................... 17
Paints........................................................................................................................................................... 17
Surface Treatment ................................................................................................................................... 17
Name Plates and Product Marking ...................................................................................................... 17
Labels .......................................................................................................................................................... 18

9Documentation Requirements ................................................................... 18

9.1
9.2

Technical Documentation ................................................................................................... 18
Software and Software Documentation ............................................................................. 18

10
11

Verification and Quality Assurance ........................................................... 19
Key Performance Parameters .................................................................... 20

11.1
11.1.111.1.2

Maintenance Definitions ..................................................................................................... 20
Maintenance Approach ........................................................................................................................... 20
Periodic Preventive Maintenance ......................................................................................................... 20

12

Appendix....................................................................................................... 21

12.1
12.2

Abbreviations and Acronyms ............................................................................................... 21
MTBF Estimation for ngVLA Front End .............................................................................. 22

Page 4 of 22

Title: Front End TechnicalRequirements

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NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQS

Date: 2019-07-24
Version: A

1 Introduction
1.1 Purpose
This document aims to present a set of preliminary technical requirements for the initial design of thengVLA Front End subsystem.
Many requirements flow down from the preliminary ngVLA System Requirements [AD02], which in turnare derived from the preliminary ngVLA Science Requirements [AD01].
The Science goals are presently being elaborated by the Science Advisory Council (SAC) and Science
Working Groups (SWGs), and are captured in a series of use cases. A preliminary analysis of these use
cases, and the flow down recursively to the science, system, and subsystem requirements, is reflected inthis draft.

1.2 Scope
The scope of this document is the ngVLA Front End work package. This consists of the cryogenicallycooled receiver assemblies and their associated support electronics, mounted on the ngVLA antenna. It
includes interface requirements that must be defined in detail.
It should be noted that the physical extent of the Front End work package extends into other subsystems
in some cases: one example is that it includes the displacer cylinder from the cryocooler as part of thecryostat assembly, but not the displacer and motor subassemblies. Other examples of this are detailed
later in this document.
This requirements document establishes the performance, functional, design, and test requirements
applicable to the ngVLA Front End work package.

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Title: Front End TechnicalRequirements

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Date: 2019-07-24

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Version: A

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of this Technical Specification shall be considered as a superseding requirement.
Reference
No.
AD01
AD02
AD03
AD04
AD05
AD06
AD07
AD08
AD09
AD10
AD11
AD12
AD13

Document Title

Rev/Doc. No.

Science Requirements
Preliminary System Requirements
Environmental Specifications
Operations Concept
Protection Against Electric Shock – Common Aspects
for Installation and Equipment
Insulation Coordination for Equipment within LowVoltage Systems
Occupational Safety and Health Standards for GeneralIndustry
Military Handbook, Reliability Prediction of Electronic
Equipment
Non-Electronic Parts Reliability Data
Electromagnetic Compatibility
Subsystem Reference Design Description for Monitor &Control Hardware Interface Layer
DC Power Supply Reference Design Description
EMC & RFI Mitigation Requirements

020.10.15.00.00-0001-REQ
020.10.15.10.00-0003-REQ
020.10.15.10.00-0001-SPE
020.10.05.00.00-0002-PLA
IEC 61140:2016
IEC 60664
29 CFR Part 1910
MIL-HDBK-217F
NPRD-95
IEC 61000-3-5
020.30.45.00.00-0004-DSN
020.30.50.00.00-0002-DSN
020.10.15.10.00-0002-REQ

2.2 Reference Documents
The following references provide supporting context:
Reference
No.
RD01
RD02
RD03

RD04

Document Title

Rev/Doc. No.

Front End Reference Design Description

020.30.05.00.00-0003-DSN

D. Gajewski et. al., “Reliability of GaN/AlGaN HEMTMMIC Technology on 100-mm 4H-SiC”, 26th Annual
JEDEC ROCS Workshop, Indian Wells, CA, May 2011“Multiple Uses of Model 22C/350C Cryodyne
Refrigerators: Installation, Operation and Servicing
Instuctions”, Helix Technology Corporation, July 2002,
page G-3
L. Baker, “Analysis of ngVLA Design #6 with Ideal andActual Feed”, 8 January 2018

Page 6 of 22Doc. # 8040272, Rev. 100
Dwg. # 3695576, Rev. C
020.25.01.00.00-0001-REP

Title: Front End TechnicalRequirements

Owner: Grammer

NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQS

Date: 2019-07-24
Version: A

3 Overview of the Front End Technical Requirements
3.1 Document Outline
This document presents the technical requirements of the ngVLA Front End work package. These
parameters determine the overall form and performance of the Front End work package.
The functional and performance specifications, along with detailed explanatory notes, are found in Section
4. The notes contain elaborations regarding the meaning, intent, and scope of the requirements. These
notes form an important part of the definition of the requirements and should guide the verification
procedures. In many cases, the notes contain an explanation or an analysis of how the numeric values ofrequirements were derived.
Where numbers are not well substantiated, this is also documented in the notes. In this way, the required
analysis and trade-space available is apparent to scientists and engineers who will guide the evolution of
the ngVLA Front End concept.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses.
Safety requirements applicable to both the design phase and the functional Front End are described in
Section 7. Additional requirements for the design phase are described in Section 8. Documentation
requirements for both technical design documentation and software are provided in Section 9.
Requirements for the Verification and Test, from the conceptual design through to prototype, aredescribed in Section 10. Section 11 identifies Key Performance Parameters (KPP) that should be estimatedand monitored throughout the design phase. These are metrics to assist in the trade-off analysis of various
concepts, and help identify and resolve tensions between requirements as the design progresses.

3.2 General Front End Description
The ngVLA will provide near-continuous frequency coverage from 1.2–116 GHz in multiple bands, with a
gap at the atmospheric absorption band between ~50–70 GHz. The primary design goals are maximizing
sensitivity for each band while also minimizing the overall operating cost. Therefore, receivers and feeds
will be cryogenically cooled, with multiple bands integrated into a common cryostat to the greatest extent
possible. Using feed designs that yield broad bandwidths and high aperture efficiencies are key to meetingthese goals.
The proposed receiver configuration [RD01] will be implemented as six independent bands, each with its
own feed. The upper five bands will be integrated into a single compact cryostat, while the lowestfrequency band occupies a second cryostat of similar volume and mass. Components within the cryostats
are cryogenically cooled for optimum noise performance.

3.3 Summary of Front End Requirements
The following table provides a summary of the major subsystem requirements, in order to provide thereader with a high-level view of the Front End. Should there be a conflict between the requirements listed
here and the descriptions in Sections 4 through 10, the latter shall take precedence.

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3.3.1

Version: A

General Functional Specifications

Parameter
Frequency Coverage

Req. #
FE0001Frequency Band Overlap
Output Polarization Type
Number of Pixels/Receiver Band
Number of Receiver Bands
Number of Cryostats/Cryocoolers

FE0002FE0003FE0004FE0005FE00063.3.2

Date: 2019-07-24

Summary of Requirement
1.2–116 GHz continuous, with a
gap between 50.5–70 GHz
1% minimum, at band edges
Dual orthogonal
One
Maximum of 6
Maximum of 2

Traceability
SYS0801

Summary of Requirement
74 kg max., including cryocooler
89 kg max., including cryocooler
163 kg, max.

Traceability
(TBD)
(TBD)
(TBD)

SYS0806
SYS0102
(TBD)
(TBD)
(TBD)

Other General Requirements

Parameter
Mass, Cryostat A
Mass, Cryostat B
Total Mass (Service Limit)

FE0007FE0008FE0009Page 8 of 22

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Date: 2019-07-24
Version: A

4 Front End Functional and Performance Requirements
These requirements apply to a properly functioning system under the normal operating environmental
conditions unless otherwise stated.

4.1 RF Frequency Ranges
The specified frequency range is the minimum over which the sensitivity and gain requirements definedfor that band are met. Bandpass shape and precisely defined band edges are not critical for the Front End;bands may overlap.
Parameter
Band 1 Frequency Range
Band 2 Frequency Range
Band 3 Frequency Range
Band 4 Frequency Range
Band 5 Frequency Range
Band 6 Frequency Range

Req. #
FE0101
FE0102
FE0103FE0104FE0105FE0106Value
1.2–3.5 GHz
3.5–12.3 GHz
12.3–20.5 GHz
20.5–34 GHz
30.5–50.5 GHz
70–116 GHz

Traceability
IRD0711
SYS0801–0806
SYS0801–0806
SYS0801–0806
SYS0801–0806
SYS0801–0806

4.2 Sensitivity Requirements
Receiver noise temperatures shall be measured using the Y-factor method, taken at the frequency intervals
specified in the table for each band. The average given is an overall unweighted average of all values, acrossthe full band. Maximum limit is typically at the band edges, over a single interval.
Parameter
Band 1 Noise Temperatures

Req. #
FE0201

Band 2 Noise Temperatures

FE0202

Band 3 Noise Temperatures

FE0203

Band 4 Noise Temperatures

FE0204

Band 5 Noise Temperatures

FE0205

Band 6 Noise Temperatures

FE0206Value
10.9 K average, 13.8 K maximum,
25 MHz meas. interval
14.2 K, average, 15.5 K maximum,
100 MHz meas. interval
15.8 K, average, 18.6 K maximum
100 MHz meas. interval
16.6 K, average, 19.5 K maximum
100 MHz meas. interval
22.4 K, average, 26.5 K maximum
200 MHz meas. interval
52.4 K, average, 72.6 K maximum
500 MHz meas. interval

Traceability
SYS1011
SYS1011–1012
SYS1012
SYS1012
SYS1012
SYS1013

4.3 Feed Horn Performance Requirements
Feed horn specifications are derived from electromagnetic and physical optics simulations. For calculationof overall aperture efficiency, the antenna optics are included in the simulation [RD04]. The Band 1 and 2
feeds are wideband ridged types, while the Band 3–6 feeds are axially corrugated types.
Parameter
Beam Subtended Angle,
Bands 1–6
Band 1–2 Aperture Efficiency
Band 1–2 Side Lobe Levels

Req. #
FE0301
FE0311
FE0312Value
55 degrees, nom., @ –16 dB edge taper,
all planes
0.80 avg. total, excluding Ruze (surface)–20 dB max., all planes

Page 9 of 22

Traceability
ANT0204
(TBD)
(TBD)

Title: Front End TechnicalRequirements

Owner: Grammer

Date: 2019-07-24

NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQSParameter
Band 1–2 Cross Polarization
Band 1–2 Return Loss
Band 3–6 Aperture Efficiency
Band 3–6 Side Lobe Levels
Band 3–6 Cross Polarization
Band 3–6 Return Loss

Req. #
FE0313
FE0314
FE0321
FE0322
FE0323
FE0324

Version: A

Value–20 dB max., all planes–15 dB max.
0.85 avg. total, excluding Ruze (surface)–30 dB max., all planes–30 dB max., all planes–20 dB max.

Traceability
(TBD)
(TBD)
(TBD)
(TBD)
(TBD)
(TBD)

4.4 Gain Requirements
The minimum Front End gain requirement stems from a need to reduce noise contributions from
subsequent signal amplification and down-conversion stages to <1K of total system noise temperature.
Gain is specified as between the input of the feed horn and the output connector on the cryostat bulkhead.
The gain ripple and slope requirements are derived from the system-level requirement of 3 dB for each.
The system requirement includes contributions from both the Front End and IRD subsystems, but nobudget for sharing this allowance across them has been established.
Tentatively, therefore, 20% of the overall budget (0.6 dB) has been allocated to the Front End. The
remaining 80% (2.4 dB) is allocated to the IRD subsystem, given it has twice as much analog gain andseveral added lossy signal-conditioning components in its cascade.
Parameter
Gain, Bands 1–6
Gain Stability, Bands 1–6

Req. #
FE0401
FE0402Gain Ripple, Bands 1–6
Gain Slope, Bands 1–6

FE0403FE0404Value
30 dB, minimum
Maximum change < 0.01 dB,over 1 hour<0.6 dB peak-to-peak (TBC)<0.6 dB, over 80% BW (TBC)

Traceability
SYS1011–1013
SYS1701,
SYS4901–4902
SYS1702
SYS1703

4.5 Dynamic Range Requirements
Parameter
Input Dynamic Range
Gain Calibrator Dynamic Range
Input Power Damage Threshold

Req. #
FE0501
FE0502
FE0503Value
30 dB min., 50 dB goal
30 dB
+10 dBm, avg. (TBC)

Traceability
SYS1201
SYS1202
SYS1204Value
20W max., 80 K stage temp
5W max., 20 K stage temp
20W max., 80 K stage temp
5W max., 20 K stage temp

Traceability

4.6 Cryogenic Cooling Requirements
Parameter
Cryostat A 1st Stage Loading
Cryostat A 2st Stage Loading
Cryostat B 1st Stage Loading
Cryostat B 2nd Stage Loading

Req. #
FE0601
FE0602
FE0611
FE0612

4.7 Spurious Signals/Radio Frequency Interference Generation
The Front End subsystem shall conform to the system EMC and RFI requirements outlined in [AD13].

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Version: A

4.8 Environmental Conditions
4.8.1

Normal Operating Conditions

Parameter
Temperature (outside)
Temperature Rate of Change
Altitude

4.8.2

Req. #
FE0801
FE0802
FE0803Value–15 C  T  +35 C< 3.6 °C per hourMax. 2500 meters

Traceability
ENV0323
ENV0324
ENV0351

Specific Environmental Requirements

Except for the exposed radome/vacuum window on Cryostat A, the Front End subsystem components
will be located entirely within a weather-tight enclosure with temperature regulation. Other than therequirements below, details about this enclosure are beyond the scope of this document.
Parameter
Temperature (inside)
Temperature Rate of Change

Req. #
FE0811
FE0812Value+20 C  T  +30 C< 1 °C per hour

Traceability

4.9 Maintenance and Reliability Requirements
The maintenance and reliability requirements support high-level requirements that limit the array’s total
operating cost. For the antenna electronics system as a whole, approximately half of the MTBF budget for
the antenna itself (~17,500 hrs.) is assumed.
The dominant maintenance driver for the antenna electronics is likely to be the cryocooler, as on the
VLA. It is estimated to have an MTBF of ~six years, assuming a continuous, average running speed of 40
Hz. Given there will be two basically identical cryocoolers per antenna, the net MTBF is therefore three
years, which is actually less than what is currently specified for the entire antenna electronic system.
However, the actual MTBF in practice will depend on how often the cryocoolers are exchanged duringscheduled periodic maintenance. If this is less than three years, the effective MTBF will be longer. This inturn will determine what fraction of the overall antenna electronic system MTBF can be allocated for the
Front End and other antenna electronic subsystems.
The intrinsic reliability of the Front End is difficult to estimate due to a lack of reliability data for the
cryogenic LNAs under controlled conditions. Life tests of comparable MMIC technology [RD02] indicate
the MTBF should be well into the tens of millions of hours. Given the low power and low temperaturesinherent in our receivers, intrinsic device reliability would likely be even higher. However, overall LNA
reliability will be drastically reduced due to the temperature cycling they are subject to, when a cryocooler
needs to be exchanged, or due to a power failure or vacuum loss that causes a warmup. The failure
mechanism here is mechanical, usually a broken or loosened bond wire to the MMIC chip. Reliability isagain hard to predict, but from the observed failure rate of VLA LNAs, and accounting for a ~3.5-fold
reduction in the number of bonds for an equivalent MMIC, the MTBF of the ngVLA Front End with 14
MMIC LNAs works out to roughly 100,000 hours. See the Appendix for details of this analysis.
Monitor points or sensors should be included in the MTBF/MTTR analysis, but sensors and othercomponents that can be reasonably deemed to be ancillary to operation may be removed from thedetermination of compliance with the MTBF requirement.
“Failure” will be defined as a condition that places the system outside of its performance specifications orinto an unsafe state, requiring repair.

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NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQSParameter
Antenna Electronics MTBF
Front End Subsystem MTBF

Req. #(TBD)
FE0901

Version: AValue
35,000 hrs. (4 years)
100,000 hrs. (~12 years)

Traceability
SYS24024.10 Monitor and Control Requirements
The expectation with self-monitoring is that the monitor and control system expose lower-level sensors
to the monitor and control system when queried. The cadence of access is flexible, and is not expected
at high rates (typical access might be on second to minute scales). Any high-cadence monitoring should
generally be internal to the Front End control system with a summary output on the interface.
Other features of the M&C interface are to be specified in the Monitor and Control ICD.
Parameter
Self-Monitoring

Req. #
FE1001Value
The Front End shall measure, report and monitor a setof parameters that allow for determination of its
status and may help predict or respond to failures.

Traceability
SYS2601

4.11 Lifecycle Requirements
Lifecycle costs include
decommissioning.
Parameter
Design Life

Req. #
FE1101

Lifecycle
Optimization

FE1102

manufacturing,transportation,

construction/assembly,

Value
The Front End shall be designed to be operated andsupported for a period of 20 years.
The Front End design shall minimize its lifecycle costfor 20 years of operation.

Page 12 of 22

operationandTraceability
SYS2801
SYS2802

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Date: 2019-07-24
Version: A

5 Interface Requirements
This section describes Front End interfaces. Interface Control Documents (ICDs) are required between
the Front End and all connecting systems. In many cases, specifications for the interfaces are not yet
available, but the broad scope of the ICDs can be defined.
These interfaces shall be developed and documented by the Front End Designer and approved by ngVLA
as part of the Front End reference and conceptual design efforts, and updated throughout the design. Post
CoDR, the ICD shall only be updated through formal project change control processes.

5.1 Interface to the Power Supply Subsystem
The Power Supply Subsystem provides DC voltages required by the Front End electronics, packaged inmodules F512 and F522 [AD05]. Voltages and currents supplied are: +32.5V @0.5A, +17.5V @6A, +7.5V@0.5A, and –7.5V @0.1A, from the P501 power supply module [AD12].
The electromechanical interface details are presently undefined. However, it will likely consist of a single
multi-pin round, twist-lock, or threaded connector interface, like those widely used by the US military(e.g., MIL-DTL-26482, MIL-DTL-38999, MIL-DTL-22992). These are highly rugged, weather-tight, andreliable, with a multitude of pin sizes and counts available at moderate cost. Location is likely to be on therear panel of the F521 and F522 electronics modules.

5.2 Interface to the Cryogenic Subsystem
The cryocooler unit consists of two parts: a drive motor/valve/displacer assembly, and a polished steel
cylinder that slides over the displacers. The cylinder is the mechanical interface for both cold stages, andis an integral part of the cryostat assembly. The displacer assembly is external to the cryostat andremovable, and is considered part of the cryogenic subsystem. The interface between these parts is aninterface plate or flange pattern that allows a gas-tight seal and properly aligns the two parts. Figure 1
presents a mechanical drawing of this interface pattern [RD03].

Figure 1 - Cryocooler displacer mechanical interface.

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Version: A

5.3 Interface to the Integrated Receivers and Downconverters (IRD) Subsystem
The IRD subsystem module will be mounted in close proximity to Cryostat B to keep the RF interconnects
to it as short as possible. It might even be feasible to bolt them directly together, using blind-mateconnectors instead of cables/waveguides, but this will be decided later on. Longer armored cables will be
used to connect the Band 1RF outputs of the Cryostat A to the IRD module.
The table below shows the type and number of RF interconnects with the Front End subsystem. The
physical locations and outlines of the connectors are still TBD.
Signal at Interface
Band 1 RF

Type
OutputBand 2 RF

OutputBand 3 RF

OutputBand 4 RF

OutputBand 5 RF

OutputBand 6 RF

OutputParameter
Connector
Impedance
NumberConnector
Impedance
NumberConnector
Impedance
NumberConnector
Impedance
NumberWaveguide size
NumberWaveguide size
NumberValue
SMA (F)50 ȍ
2 (one per pol.)SMA (F)50 ȍ
2 (one per pol.)2.92 mm (F)50 ȍ
2 (one per pol.)2.92 mm (F)50 ȍ
2 (one per pol.)WR-22 (UG599)
2 (one per pol.)WR-10 (UG387)
2 (one per pol.)5.4 Interface to the Antenna Subsystem
A dual offset-Gregorian optical configuration for the antenna is assumed. The key interface specificationis the subtended angle of the subreflector at the secondary focal point, which drives the design of all feedhorns, and the physical size of the cryostats as well.
The Front End cryostat assemblies will be mounted at the secondary focus of the antenna, on a platform
attached to the feed arm structure. The platform will include an X-Y axis motorized positioner for focusing
and band selection and the temperature-controlled enclosure.
Figure 2 shows a rendering of the mounting concept, which will be the same for both the 18-meter and6-meter antennas. Detailed mechanical interface drawings are pending completion of the antenna design.

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Date: 2019-07-24
Version: A

Figure 2 - Front End subsystem enclosure, opened to show cryostats and IRD assembly.

Parameter
Feed Subtended
Half Angle

Req. #
FE0301Value
55° between the optical axis and edge of thesubreflector, at the secondary focus

Traceability
ANT0204

5.5 Interface to the Monitor and Control Subsystem
The two Front End cryostat assemblies presently contain only RF electronics. All the analog support
electronics for Cryostats A and B are packaged within two external modules, referred to as F521A and
F521B, respectively. These will be located inside the platform enclosure on the antenna feed arm, in close
proximity to the cryostats. The support electronics provide the following functions:x DC bias/driver circuitry for LNAs, noise calibrator sources, and other active components,
x RF output control/leveling for the noise calibrator sources,
x Input signal conditioning from the cryostat vacuum and temperature sensors, andx Driver circuitry and current monitoring for the cryostat vacuum solenoid valve.
Electrical connection to the cryostats is assumed to be via multi-conductor shielded cables, with abulkhead receptacle/cable plug pair at each end. Specific details are undefined at present; however, thesewill likely consist of single, multi-pin round, twist-locking connector interfaces, with a hermetic glass seal
for contacts on the cryostat receptacle side, to maintain vacuum integrity.
It may be feasible, and even desirable, to integrate some or all of the support electronics into theirrespective cryostats, but for now are they are assumed to be separate assemblies.
The Cryo and LNA Monitor and Control (M&C) module (designated F520) contains the MIB, or Monitor
and Control Interface Board, which provides the communications link to the monitor and control
subsystem. The F522 is similar to the F521A/B but also provides control electronics for the vacuum pumpcommon to both cryostats [AD11].

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Date: 2019-07-24
Version: A

6 Subsystem Requirements
Derivation of any subsystem requirements shall be included as part of the Front End reference andconceptual design efforts and updated throughout the design. Post CDR/FDR, the subsystem requirements
shall only be updated through formal project change control processes, which will include the designer,
manufacturer, and NRAO.

7 Safety
7.1 GeneralIn general, the Front End subsystem is fairly benign from a safety standpoint, posing a low risk of injury to
personnel or damage to other equipment.

7.2 Safety Design Requirements
7.2.1

Fire Safety

There are no combustibles, flammable liquids or gases in the Front End subsystem.

7.2.2

Vacuum Safety

Because the cryostats will usually be under vacuum while in storage or transport, there is a potential
implosion hazard if one of the large cryostat windows or radomes is breached. The chance of this is low,
and will be minimized by proper design, and handling protocols during shipment or installation.

7.2.3

Mechanical Safety

There are no external exposed moving parts, or known pinch points that could cause injury.

7.2.4

Electrical Safety

Electrical equipment installed on the antenna shall comply with their relevant international or US productstandard. Electrical installations and equipment shall be specifically built and/or derated in order to safely
perform their intended functions under the applicable environmental conditions. Insulation shall becoordinated in conformity with IEC 60664 [AD06] while taking into account the altitude of up to 2500 m
above sea level.

7.2.5

Handling, Transport, and Storage Safety

The design of the Front End shall incorporate all means necessary to preclude or limit hazards to personnel
and equipment during assembly, disassembly, test, and operation. These cryostat radomes and windows
are fairly robust, but nevertheless must be protected from any impact or abrasion, to minimize the chanceof breakage and possible injury to personnel from flying debris.
Moderate care must be exercised when removing or installing the Front End cryostat assemblies, as they
are heavy, and can be damaged if dropped more than a few centimeters. A lifting device or small hoist isrecommended for installation and removal of the cryostats. As needed, lift points shall be designed into
the equipment, and clearly labeled.

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Date: 2019-07-24
Version: A

8 Requirements for Design
8.1 Analyses and Design Requirements
8.1.1

Reliability Availability Maintainability Analysis

A Reliability Availability Maintainability analysis shall be performed to locate weak design points anddetermine whether the design meets the Maintenance and Reliability requirements. To this end, the Parts
Count Method for predicting reliability of the system can be applied, as described in the MIL-HDBK-217F[AD08], but the designer may propose to use other methods. For non-electronic parts, the values of
NPRD-95 [AD09] or data from manufacturers or other databases may be used.
Another, more time consuming (and considered more accurate) method, the Parts Stress Analysis
Prediction, is also described in [AD08]. This may be used if the result of the Parts Count Method does
not comply with the Maintenance and Reliability requirements.
The ngVLA equipment will typically operate at an elevation of 2200m above sea level, where temperatureand pressure might decrease the MTBF relative to that at low elevations. These conditions shall be taken
into specific account in the reliability prediction by using the environmental factor given in [AD08]. The
analysis shall result in estimates of the Mean Time Between Failures (MTBF), the Mean Time To Repair(MTTR), assuming that any scheduled preventive maintenance is performed.

8.2 Electromagnetic Compatibility Requirements
The ngVLA Front End element shall exhibit complete electromagnetic compatibility (EMC) among
components (intra-system electromagnetic compatibility).

8.3 Materials, Parts, and Processes
8.3.1

Fasteners

All fasteners shall be metric except those that are on off-the-shelf units. The use of standard metric crosssections for construction materials is preferred but not required.

8.3.2

PaintsAny painted coatings shall be chosen to last at least 20 years without repainting.

8.3.3

Surface Treatment

Any unpainted surfaces shall be treated against corrosion.

8.3.4

Name Plates and Product Marking

As a general rule the main parts and all exchangeable units shall be equipped with nameplates which arevisible after installation of the part/unit and which contain the following information:
x
x
x
x
x

Part/unit nameDrawing number including revision
Serial number
Manufacturing month and year
Name of manufacturer

Alternatively, a system of marking based on barcodes or the like may be used upon approval by ngVLA.

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Version: A

For Line Replaceable Units (LRUs), it is highly desirable that the serial number of the unit be ascertainable
over the monitor and control interface.

8.3.5

LabelsAll cables and switches, junction boxes, sensors, and similar equipment shall be labeled.

9 Documentation Requirements
9.1 Technical Documentation
All documentation related to the Front End shall meet the following requirements:
x The language used for written documentation shall be English.
x Drawings shall be generated according to ISO standards and use metric units.
x Layouts of electronic circuits and printed circuit boards shall also be provided in electronicallyreadable form. The ngVLA preferred formats are Altium Designer files for electronic circuit diagrams
and printed circuit board layouts.
x The electronic document formats are Microsoft Word and Adobe PDF.
x The preferred CAD system used is AutoDesk Inventor and/or AutoCAD.
Any deviation from the above shall be agreed to by ngVLA.

9.2 Software and Software Documentation
The Front End software and any other specially developed software (SW) are deliverables. The SW shallbe delivered in source and object form, together with all procedures and tests necessary for compilation,
installation, testing, upgrades and maintenance.
x Software must be tagged with suitable version numbers that allow identification (also on-line,
remotely) of a Release.
x User manuals of software developed under this specification and of any other commercial software
used (controllers embedded software, special tools, etc.) shall be provided.
x Software maintenance and installation upgrade documentation shall be provided.
x Full Test and Acceptance procedures shall be documented.

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Version: A

10 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A) inspection (I), a factory
acceptance test (FAT) or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which may bechecked by the ngVLA project office during the design phase by review of the design documentation.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which will bechecked by the ngVLA project office during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple inspection
or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item, assembly, or unit
with the specified performance shall be demonstrated by tests. A FAT is performed without integration
with interfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item/assembly/unit with thespecified performance shall be demonstrated by tests. SAT is performed on-site with the equipment as
installed.
Multiple verification methods are allowed.
The following table summarizes the expected verification method for each requirement.
Req. #
FE0101-0106
FE0201-0206
FE0311, 0321
FE0312-0313
FE0322-0323
FE0314,0324
FE0401
FE0402
FE0601-0612
FE0901
FE1101

Parameter/Requirement
Frequency Range, Bands 1–6
Noise Temperatures, Bands 1–6
Overall Aperture Efficiency
Feed Horn Radiation Pattern
Feed Horn Return Loss
Gain, Bands 1–6
Gain Stability, Bands 1–6
Cryocooler Thermal Loading
Front End Subsystem MTBF
Design Life

D

A

X
X

X
X

I

FAT
X
X

X
X
X
X
X
X

Page 19 of 22

X
X

SAT

Title: Front End TechnicalRequirements

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NRAO Doc. #: 020.30.03.01.00-0001-REQ-AFRONT_END_TECH_REQS

Date: 2019-07-24
Version: A

11 Key Performance Parameters
This section provides Key Performance Parameters that should be estimated by the designer andmonitored by NRAO throughout the design phase of the project. These are parameters that have a large
influence on the eventual effectiveness of the facility, and are useful high-level metrics for trade-off
decisions.
These parameters are of higher importance to NRAO. Improved performance above the requirement isdesirable on these parameters. The impact on system-level performance is discussed in the narrative in
Section 4.
The technical requirements are generally specified as minimum values. The goal is to give the designer
some latitude in optimization for a balanced design. Understanding the anticipated performance of the
Front End (not just its specified minimum) on these parameters is of value for system-level analysis andperformance estimation.
These parameters may also be useful for determining the relative priority of the requirements documented
in Section 4 and can assist in the required analysis should tensions be identified between requirements, or
reductions in capability be required to fit within cost constraints.
The Key Performance Parameters that have been identified for monitoring are described in the tablebelow. Note that the order in the table reflects the order in the document, and is not indicative of relative
importance or priority.
Key Performance Parameter
Receiver Noise Temperature
Overall Aperture Efficiency
Feed Horn Performance(side lobes, cross polarization, return loss)
Cryostat Masses
Cryocooler Thermal Loading
Mean Time Between Failures

Req.
FE0201-0206
FE0311, 0321
FE0312-0314
FE0322-0324
FE0007-0009
FE0601-0612
FE0901

11.1 Maintenance Definitions
11.1.1 Maintenance Approach
Required maintenance tasks shall be minimized. Maintenance shall be mainly performed at assembly andsubassembly level by exchange of Line Replaceable Units (LRUs). LRUs are defined as units which can beeasily exchanged (without extensive calibration, of sufficient low mass and dimension for easiness ofhandling, etc.) by maintenance staff of technician level.
LRU exchange shall be possible by two trained people within four working hours. It is desirable that LRU
replacement be possible using only standard tools identified in a maintenance manual for the Front End.
A step-by-step procedure for safe exchange of every LRU shall be provided in the Maintenance Manual.
LRUs shall be defined by the Front End designer, depending on the design. The LRUs will be maintainedby the ngVLA project (with or without industrial support).

11.1.2 Periodic Preventive MaintenancePreventive maintenance may be performed at planned intervals to keep the Front End operational andwithin its specified performance. Any required preventive maintenance should be documented in the
Maintenance Manual.

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12 Appendix
12.1 Abbreviations and Acronyms
Acronym
AD
CAD
CDR
CoDR
EMC
FAT
FDR
ICD
IRD
KPP
LNA
LRU
MIB
MMIC
MTBF
MTTR
M&C, M/C
ngVLA
RD
RFI
SAT
TBD
VLA

Description
Applicable Document
Computer Aided Design
Critical Design Review
Conceptual Design Review
Electro-Magnetic Compatibility
Factory Acceptance Test
Final Design Review
Interface Control Document
Integrated Receiver Downconverter/Digitizer
Key Performance Parameters
Low Noise AmplifierLine Replaceable Unit
Monitor/Control Interface Board
Monolithic Microwave Integrated Circuit
Mean Time Between Failure
Mean Time To Repair
Monitor and Control
Next Generation VLA
Reference Document
Radio Frequency Interference
Site Acceptance Test
To Be Determined
Jansky Very Large Array

Page 21 of 22

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Version: A

12.2 MTBF Estimation for ngVLA Front End
1. EVLA LNA Failure Rate, from March 2013 to September 2018 (5.5 years)
Year
2013
2014
2015
2016
2017
2018
TOTAL:# repairs*
10
6
17
6
10
5
54

* Excludes LED failures, upgrades

Active Antennas:
Cryo LNAs per antenna:
Total LNAs:
Duration (yrs):
Duration (hrs):

27
16
432
5.5
48,213

Failure Rate (/hr-LNA): 2.593E-06
MTBF (hrs): 3.857E+05

2. Predicted ngVLA MMIC LNA MTBF (1 antenna):
Failure reduction factor:
MMIC LNAs per antenna:

3.6
14(relative wire bond count)(2 ea, Bands 1–5; 4 on Band 6)

Failure Rate (/hr-Ant): 1.008E-05
MTBF (hr-Ant): 9.918E+04

Page 22 of 22

Date: 2019-07-24

Title: Front End Reference Design
Description

Owner: Grammer

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Date: 2019-07-24
Version: A

Front End Reference Design Description
020.30.03.00.00-0002-DSN-A-FRONT_END_REF_DESIGN

Status: RELEASEDPREPARED BY
W. Grammer
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAO
Antenna Electronics

DATE
2019-05-21
2019-04-01

APPROVALS (Name and Signature)
R. Selina,
2019.07.24
Project Engineer
16:22:59 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-24

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 16:51:42 -06'00'

Asst. Director,
NM-Operations, NRAO

2019-07-24

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 16:51:58 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-24

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Title: Front End Reference Design
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Date: 2019-07-24
Version: A

Change Record
Date

AuthorAffected
Section(s)Reason1

2018-07-13

W. Grammer

All

Initial draft

2

2018-07-13

D. Urbain3

2018-07-20

W. Grammer

6.3
6.1, Appendix
A and B4

2018-08-27

W. GrammerAll5

2018-09-11

W. Grammer

5.1, 6.4, Table
2

Location of IR filter was corrected
Updated TLNA, TRX values for updated
cascade analysis.
Update performance tables and plots,
insert block diagram, add content forinterfaces, and other minor changes.
Updated SEFD numbers and text toreflect increase in array to 263
antennas. Completed the interface
section. Modified document number forconsistency with present product tree.

6

2018-09-28

S. Durand, W.
GrammerAll

Small edits and formatting changes.

7

2018-10-10

W. Grammer

All

Corrected the document number on
title page, headers.

8

2018-10-17

5.2

Minor wording changes.

Version9

2018-10-24

10

2018-10-30

11

2018-11-02

W. Grammer
R. Selina
W. Grammer
R. Selina
J. Jackson
W. Grammer
R. Selina
W. Grammer

12

2019-03-15

W. Grammer

All

13

2019-03-29

W. Grammer

4.2, 6.2

14

2019-05-21

W. GrammerAll

Added 1K contribution from IRD to
Tsys. Corrected M&C module
references.
Added calibrator path components to
Front End subsystem block diagram.
Small edits and formatting changes.
Updated content from ASU, JPL, and
EMSS; many formatting changes.
Remove sentence about funding;removed TBD reference in item #11.
Small corrections, formatting changes.

A

2019-07-24

A. LearAll

Prepare PDF for approvals & release.

Table 2, Figs. 67, 6.4.5
Fig. 9All

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Date: 2019-07-24
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings ............................................................... 4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 43
4

Subsystem Overview ..................................................................................... 6
Background and Concept Evolution ............................................................ 6

4.1
4.2
4.2.1
4.2.2
4.3
4.4

General Design Constraints ................................................................................................... 6
Wideband Receiver/Feed Concepts....................................................................................... 7
Caltech Prototype Receiver .................................................................................................................... 8
JPL Prototype Receiver ............................................................................................................................ 8
The “Baseline” Design Concept ............................................................................................ 8
Toward a Reference Design ................................................................................................ 12

5

Reference Design Description .................................................................... 14

5.1
5.2
5.3
5.4
5.4.1
5.4.2
5.4.3
5.4.4
5.4.5

Configuration Description and Performance ..................................................................... 14
Front End Subsystem Block Diagram .................................................................................. 20
Front End Packaging Concept ............................................................................................. 20
Front End Interfaces to Other Subsystems ......................................................................... 22
Interface to the Cryogenic Subsystem................................................................................................ 22
Interface to the Integrated Receivers and Downconverters (IRD) Subsystem ........................ 22
Interface to the Antenna Subsystem ................................................................................................... 23
Interface to the Monitor and Control Subsystem ........................................................................... 24
Interface to the Power Supply Subsystem ......................................................................................... 24

6

Appendix....................................................................................................... 25

6.1
6.2
6.3
6.4

Abbreviations and Acronyms ............................................................................................... 25
Caltech 4-Band Front End Concept .................................................................................... 26
NASA/JPL Ultra-Wideband Receiver (8-48 GHz) ............................................................... 30
ngVLA Reference Front End Receiver Cascade, LNA Noise Tables .................................. 32

Page 3 of 34

Title: Front End Reference Design
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Version: A

1 Introduction
1.1 Purpose
This document provides a description for the Front End subsystem reference design. It covers the design
approach, functions, key components, interfaces, and risks associated with the reference design. This
document will form part of the submission of the ngVLA Reference Design documentation package.

1.2 ScopeThis document covers the entire design of the Front End subsystem as part of the ngVLA Reference
Design. It includes the subsystem design, how it functions, and its interfaces with the necessary hardware
and software systems. It does not include specific technical requirements or budgetary information.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein, but provide necessary context or
supporting material.
Ref. No.
AD01
AD02
AD03
AD04
AD05
AD06

Document Title
Front End Technical Requirements
System Reference Design
Cryogenic Subsystem Reference Design Description
Integrated Downconverters & Digitizers Design Description
Subsystem Reference Design Description for Monitor andControl Hardware Interface Layer
DC Power Supply Reference Design Description

Rev./Doc. No.
020.30.03.01.00-0001-REQ
020.10.20.00.00-0001-REP
020.30.10.00.00-0002-DSN
020.30.15.00.00-0002-DSN
020.30.45.00.00-0004-DSN
020.30.50.00.00-0002-DSN

2.2 Reference Documents
The following documents are referenced within this text:
Ref. No. Document Title
RD01 C. Langley & K. Baker (NRAO), Private
Communication
RD02 L. D’Addario, “Advanced Cryocoolers For Next
Generation VLA,” ngVLA Memo No. 24,
2017-09-19
RD03 S. Weinreb, “Future of the VLA and Other
Topics,” NRAO Socorro Colloquium,
2014-09-26
RD04 S. Weinreb, “Receiver Overview,” ngVLA
Technical Workshop, Pasadena CA,
2015-04-09
RD05 S. Weinreb, A. Soliman, & H. Mani, “Single
Cryocooler 1.2 to 116 GHz Receiver for ngVLA,”
Kavli II Workshop, Baltimore MD, 2016-08-3–5

Page 4 of 34

Rev/Doc. No.
N/A
http://library.nrao.edu/public/
memos/ngvla/NGVLA_24.pdf
N/A
https://safe.nrao.edu/wiki/pub/NGVLA/TechnicalWorkingGroup/Weinreb
ReceiverOverviewApr9_2015.pdf
N/ATitle: Front End Reference Design
Description

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NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

RD06

RD07
RD08

RD09
RD10
RD11
RD12
RD13
RD14
RD15
RD16
RD17
RD18
RD19
RD20
RD21
RD22
RD23

Date: 2019-07-24
Version: A

S. Weinreb & H. Mani, “Low Cost 1.2 to 116 GHz https://science.nrao.edu/science/
Receiver System: A Benchmark for ngVLA,” ngVLA meetings/2017/ngvla-scienceprogram/presentations/monday/
Science Meeting, Socorro NM, 2017-06-26–29
WeinrebManiJun24Receiver.pdf
H. Mani, “Wideband Receiver Prototype for
N/A
ngVLA: Development Report,” NRAO Socorro
Colloquium, 2019-01-25
J. Velazco et al., “Development of an UltraN/A
Wideband Receiver Package for the Next
Generation Very Large Array,” IEEE Aerosp. Conf.,
Big Sky MT, 2019-03-07
J. Shi et al., “Quadruple-Ridged Flared Hornhttps://ieeexplore.ieee.org/document/
Operating from 8 to 50 GHz,” IEEE Trans. Antennas 8060581
Propag., 2017-10-06
M. Pospieszalski, “Low Noise InP HFET Receivers,” https://safe.nrao.edu/wiki/pub/NGVLA/
ngVLA Technical Workshop, Pasadena CA, 2015- TechnicalWorkingGroup/PospiesLNA
04-08–9
Apr9_2015.pdf
A. Akgiray, PhD Thesis, Caltech, 2013https://thesis.library.caltech.edu/7644/1/Akgiray_PhDThesis_FinalVersion.pdf
C. Granet et al., “A Wide-Band 4–12.25 GHz Feed Private communication; publish date is
System for the Australia Telescope 22m Diameter still TBD
Antenna,” 2016
D. Hoppe & E. Long, “Technology Development
Private communication; internal
for the North America Array: Feed Update,” 2016- NASA/JPL presentation
05-06
L. Baker & B. Veidt, “DVA-1 Performance with an Private communication; unpublished
Octave Horn from CST & GRASP Simulations,”
internal memo
2014
L. Baker, “Analysis of ngVLA Design #6 With Ideal 020.25.01.00.00-0001-REP
and Actual Feed,” 2018-01-08
S. Weinreb et al., “Cryogenic 1.2 to 116 GHz
N/A
Receiver for Large Arrays,” EuCAP, London UK,
2018-04-12.
L. Locke et al., “Q-band single pixel receiver
http://library.nrao.edu/public/memos/ndevelopment for the ngVLA and NRC,” Proc. SPIE, gvla/NGVLA_32.pdf
Vol. 10708, 2018-11-14
L. Locke (NRC), Private Communication
N/A
R. Lehmensiek, “Final Report: ngVLA Project PO EMSS Doc#: EA-NGV-DR-01 Rev. 1
No. 362812,” EMSS Antennas (Pty) Ltd, 2019-0207
D. deVilliers & R. Lehmensiek, “SKA Reflector and N/AFeed Design,” Caltech ngVLA Optics Workshop,
2018-06-19
B. Butler (NRAO), Private Communication
N/A
R. Selina, “System-Level Cost Comparison of
http://library.nrao.edu/public/memos/
Offset and Symmetric Optics,” ngVLA Antenna
ngvla/NGVLA_24.pdf
Memo No. 1, 2019-04-26
L. Locke & S. Srikanth, (title TBD), NRAO, 2019
Internal memo in preparation

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Title: Front End Reference Design
Description

Owner: Grammer

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Date: 2019-07-24
Version: A

3 Subsystem Overview
The basic purpose of the ngVLA Front End subsystem is the reception and amplification of incoming signals
from astronomical sources collected by the antenna optics, over a broad frequency range. Given theextremely low input levels, very high gain is required, with the lowest possible added instrumental noisefor maximum sensitivity. The receivers must also have a good temporal gain and phase stability, and highlinearity. Weight is an important concern given that the antenna optics places the Front End package on a
movable platform within the feed arm, rather than at a fixed location under the main reflector as on the
VLA antennas.
The ngVLA science goals require continuous frequency coverage from 1.2–116 GHz in multiple receiverbands, with a gap at the atmospheric absorption band between ~50–70 GHz. Maximizing overall sensitivity
in each receiver band, while minimizing the total operating cost are the primary design goals. Therefore,
receivers will be cryogenically cooled, with multiple bands integrated into a common cryostat where
feasible. Use of feed horn designs that have broad bandwidth and high aperture efficiency are also key tomeeting these goals. Compact feed designs are also preferred, as they can be integrated into the receivercryostat and cooled, further reducing the system noise.
Section 4 describes evolution of the concept, but it can be skipped without loss of continuity, if desired.

4 Background and Concept Evolution
The ngVLA Front End concept went through a considerable amount of evolution over several years,
including a period where there were three different concepts under development by separateorganizations. However, as the science requirements, technical specifications, and costing for the ngVLA
were all taking shape over the same period, alternative design concepts were a natural and expected partof the process.

4.1 General Design Constraints
One key factor that drove the Front End system design from the start was the need to reduce overall
operating cost, particularly in the cryogenic system. The ngVLA as currently envisioned will have 263
antennas, more than nine times that of the current array, but with an operations budget constrained tojust three times that of the VLA and VLBA. It was immediately apparent that a system with separately
cooled receiver bands and multiple helium compressors on each antenna (as implemented on the VLA
and VLBA) would be inordinately expensive to build, operate and maintain, if directly scaled for the ngVLA.
To attain the desired reduction in overall cost, the following design guidelines or constraints were
gradually recognized:
x Maximize the fractional bandwidth of individual bands to the extent possible to reduce
the total band count. This is critical for bands at the low end of the frequency range: for example,
an octave of bandwidth at the low end is 1.2 GHz, compared to 58 GHz at the high end. Lowfrequency receivers (and feeds) also tend to be large and heavy, so reducing their number is criticalto controlling the total cost and mass of the Front End package. However, the trade-off with wider
bandwidth is degraded performance of the LNA and feed horn; i.e., a higher receiver noise
temperature (TRX) and a lower aperture efficiency (ȘA). Taken too far, the additional antennas needed
to offset this loss in sensitivity would effectively negate any cost savings with fewer bands.
x Minimize the number of cryocoolers and cryostats required per antenna. This isaccomplished by packaging multiple receiver bands into a common cryostat. Benefits are a reduction

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Title: Front End Reference Design
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Date: 2019-07-24
Version: A

in the total cryogenic load, and improvement of overall reliability by having fewer displacers, motors
and seals to wear out or fail. While relatively easy to accomplish for the compact high-frequency
bands, it becomes less practical at lower frequencies, where the size of the feed horn equals or
exceeds the associated receiver package. With large high-gain feeds like those in the VLA antennas,
receiver consolidation is not practical, with the possible exception of the Q- and Ka-bands.
Conversely, low-gain feeds are advantageous in this regard given that they are much smaller than highgain feeds, provided their RF performance is acceptable. This will obviously influence the optical andmechanical design of the antenna as well.
x Use a single helium compressor per antenna. The VLA has three helium compressors perantenna (81 total, running continuously). Together, they consume 57% of the total electrical power
supplied to the VLA antennas, or 46% if the VLA correlator is also included [RD01]. They also require
frequent maintenance. Going to a single, larger compressor designed for longer life and lower
maintenance will result in significant savings, even if the overall helium flow requirement is the same.
One downside is the compressor becomes a single point of failure for the antenna: this risk could be
mitigated with a dual-redundant compressor configuration. However, given the large number ofantennas, loss of a single antenna has less of an impact than in the VLA, so the extra cost may not bejustified.
x Improve the overall efficiency and reliability of the cryogenic system. The VLA cryogenic
system gets the job done, but its design is more than 40 years old. A modern system using variablespeed scroll-type compressors, cryocoolers with variable-speed drives, and intelligent control will
yield much higher overall efficiency than the fixed-speed systems of the VLA. Advanced cryocooler
designs (Stirling, pulse-tube) are also more efficient and reliable than the traditional Gifford-McMahon(G-M) type [RD02], and will be considered for the ngVLA if they are cost effective and can handle thecooling requirements.
The broader objective is to obtain the optimum array sensitivity while remaining within the overall array
construction and operating cost constraints. Low system temperatures are obviously important, driven
largely by the Front End electronics, but the other major factor is the aperture efficiency for theantenna/feed combination. A complex interdependence drives the choice of antenna optics, feed type, andthe number of individual receiver cryostats required.
For example, a symmetric Cassegrain antenna like that of the VLA or VLBA permits using traditional highgain corrugated feed horns with near-optimum beam characteristics, for high illumination efficiency. On
the other hand, blockage and scattering losses can be quite significant, especially for the smaller primary
aperture sizes favored by ngVLA, requiring more antennas to recover the lost collecting area. This has acost penalty [RD22]. An unblocked design like a dual offset Gregorian antenna will have higher efficiency,
though this comes with a higher construction cost and a requirement for compact feeds (possibly withlower illumination efficiency) lightweight enough to be moved onto the focal point.

4.2 Wideband Receiver/Feed Concepts
Discussions on possible receiver/feed configurations for a next-generation VLA began in late 2014, shortly
after an invited talk at NRAO in Socorro given by Dr. Sander (“Sandy”) Weinreb of Caltech [RD03]. His
initial concept used an ultra-wideband (UWB) Quad-Ridge Feed Horn (QRFH) and Low-Noise Amplifier(LNA) to cover a 10–100 GHz frequency range with a single receiver. By the first ngVLA technicalworkshop in April 2015, this initial concept had evolved into a design with two separate 7:1 bandwidth
QRFHs covering 1.2–8.4 GHz and 8–55 GHz, and a conventional corrugated feed with waveguide output
for the 70–116 GHz band [RD04]. Coverage between 55–70 GHz is unnecessary because of the highatmospheric attenuation in this band.

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Title: Front End Reference Design
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NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Date: 2019-07-24
Version: A

By early 2016, funded projects at Caltech and at NASA/JPL were ongoing, with the objective to design
and prototype wideband receivers. Both were largely concluded in 2018, and are described below.

4.2.1

Caltech Prototype Receiver

Sandy Weinreb led a team of graduate students at Caltech to design and build a prototype ngVLA receiverwith their own LNA and QRFH technology. The primary aim was to cover the full 1.2–116 GHz in a single
cryostat that was relatively compact and low in cost.
Initially it was a three-band system (1.2–7.2/8–48/70–116 GHz) using a pair of 6:1 bandwidth QRFHs. In
July 2016, the concept was revised to a four-band configuration with re-optimized 3.5:1 bandwidth QRFHs[RD05]. By mid-2017 the QRFH profile had been re-optimized for better overall illumination efficiency,
but at the expense of higher spillover noise [RD06].
Detailed performance estimates for the Caltech four-band concept and QRFH are given in Section 6.2,
along with renderings and photos of the cryostat concept. Construction of a demonstration cryostat
including a Band 1 receiver was recently completed, and was cooled successfully to below 100K and 20K,
on the QRFH and LNAs respectively [RD07]. Measurement of the receiver noise temperature is pending.

4.2.2

JPL Prototype Receiver

Melissa Soriano and Jose Velazco led a team of engineers at JPL, to design and prototype an 8–48 GHz
UWB receiver under a three-year NASA grant. This ambitious project consisted of three parallel efforts:
x Design, fabrication and testing of an 8–48 GHz cryogenic MMIC LNA. This built on earlier work at
Caltech, using foundries at OMMIC and NGC.
x Design and optimization of a dielectric-loaded QRFH, in collaboration with Caltech. The goal was
improved and flatter efficiency over frequency, with minimal added loss.
x Design, fabrication and testing of a prototype 8–48 GHz receiver cryostat, incorporating the new
LNA and QRFH designs.
Noise and gain measurements of the redesigned LNAs and completed receiver are given in Section 6.3,
along with a rendering and photo of the receiver cryostat [RD08]. The redesigned OMMIC LNA (Figure18) had a TN ~20K from about 4 to 30 GHz, but rose steadily to ~50K by 48 GHz. However the NGC
LNA (Figure 19) achieved a nearly flat 20K to 47 GHz, with gain > 20 dB. Overall, the receiver achieved
an average TRX of ~30K, and less than 40K across the band (Figure 21).
Development of the dielectric-loaded feed was deferred in favor of an all-metal type based on a Caltech
design [RD09], but fabricated at JPL.

4.3 The “Baseline” Design Concept
From almost the beginning, much discussion and debate focused on Caltech’s wideband LNA and feed
performance relative to those used in the VLA and GBT. In these instruments, the “cryo3” InP LNAs
designed and built at the NRAO CDL perform near their theoretical noise limit, over about a waveguide(~1.66:1) fractional bandwidth. Beyond that, the noise performance can be optimized only over a portionof the band (typically the high end) but will suffer at the low end, by a factor of two or more relative tonarrow-band LNAs [RD10].
Similarly, the average illumination efficiency (ɻI) of a low-gain QRFH with 6:1 bandwidth is only around
60% [RD11], quite a bit lower than a conventional waveguide-bandwidth corrugated feed horn (~82%).
Both these factors contribute to a significant loss in antenna sensitivity for spectral line detection. For
continuum detection, the large instantaneous bandwidth of an UWB receiver will yield a ~90% relative

Page 8 of 34

Title: Front End Reference Design
Description

Owner: Grammer

Date: 2019-07-24

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Version: A

gain in sensitivity, somewhat offsetting the performance penalty from the UWB LNA and QRFH.
Nevertheless, it seemed clear the overall negative impact on telescope sensitivity could be substantial.
On the other hand, it was recognized that wideband receivers would likely be required to cover thelowest decade of bandwidth (~1–10 GHz), in order to stay within the operating cost cap for ngVLA. Whilea single QRFH-based design like that proposed in [RD03] is theoretically possible, a pair of receivers with
~3:1 bandwidth would have far better overall performance. By comparison, at least four receivers withoctave and/or waveguide bandwidth are necessary, as implemented in the VLA: this approach was deemed
a non-starter for the ngVLA, due to its cost. Therefore, it was taken that fractional bandwidths > 3:1 would
be required in the receiver bands below ~10 GHz, with a reasonable performance degradation accepted as anecessary compromise. Whether this approach could be extended to higher frequencies was still debated.
To help quantify the performance tradeoffs with the wideband configurations described in the previous
section, a so-called “Baseline” configuration was formulated as a basis for comparison. An initial 4-band
configuration was proposed by Srikanth at NRAO in early 2016, with two low frequency bands added
soon after. The approach was deliberately conservative: only existing LNA, feed horn, and receivertechnologies with known performance would be included.
On the receiver bands above ~10 GHz, fractional bandwidth was limited to 1.67:1 for optimum LNA
performance in low-loss, all-waveguide receivers, and the use of traditional corrugated feed horns. Below
10 GHz, the bandwidth restriction was relaxed to ~3:1 to reduce to two the number of receivers requiredfor coverage down to 1.2 GHz. Broadband, smooth-wall conical feed horns coupled to matching quadridge OMTs were proposed for use on these bands, like those described in [RD12]. A small opening angle(~15°) was prescribed for all the feeds in the Baseline configuration to remain within their design limits.
Table 1 shows a summary of the Baseline configuration definition and estimated performance numbers(aperture efficiency, system temperature, etc.). The assumptions made were:x Unblocked primary aperture (i.e. dual offset Gregorian or Cassegrain optics)
x No antenna shaping; all reflectors are pure conics
x Secondary mirror electrically large at 1.2 GHz, for negligible diffraction losses
x Surface accuracy of 160 ʅm RMS, primary and secondary combined
x Sky temperature (TSKY) based on a PWV of 6 mm, with an elevation angle of 45 degrees
Band Dewar f L
#
#
GHz
1
2
3
4
5
6

A
B
C
C
C
C

1.2
3.6
11
18
30
70

fM
GHz

Spillover, K
Aperture Eff., Ș A
BW Feed Horn Properties
fH
fH:fL
OMT
GHZ Temp L, mm D, mm
GHz@fL @fM @fH @fL @fM @fH

2.1
6.2
14.1
23.2
38.7
90

3.6
10.8
18
30
50
116

3.00
3.00
1.64
1.67
1.67
1.66

2.4
7.2
7
12
20
46

300
300
300
300
20
20

2711
904
410
251
150
64.4

1127
376
241
147
88.4
37.9

QR
QR
WG
WG
WG
WG

0.62
0.62
0.74
0.74
0.72
0.56

0.72
0.72
0.74
0.73
0.70
0.49

0.78
0.78
0.74
0.72
0.67
0.38

3
3
3
3
3
3

3
3
3
3
3
3

3
3
3
3
3
3

T LNA , K
T RX , K
T SKY , K
T SYS , K
(T SYS / Ș A ), K
Band Dewar##@fL @fM @fH @fL @fM @fH @fL @fM @fH @fL @fM @fH @fL @fM @fH
1
2
3
4
5
6

A
B
C
C
C
C

2.5
8
5
7
10
29

2.8
6.5
6
8
12
26

5.2
7.5
7
10
14
40

8
12
10
12
18
39

6
10
11
14
22
41

9
12
12
18
28
60

4.4
4.6
5.1
7.8
11.1
75

4.5
4.7
5.7
20.9
16.3
27

4.6
5.1
7.8
11.1
62.5
123

15
20
18
23
32
117

14
18
20
38
41
71

17
20
23
32
94
186

Table 1 - Parameters and performance estimates for baseline receiver/feed configuration.

Page 9 of 34

25
32
24
31
45
207

19
25
27
52
59
146

21
26
31
45
140
484

Title: Front End Reference Design
Description

Owner: Grammer

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Date: 2019-07-24
Version: A

To allow a fair performance comparison of all three configurations, corresponding estimates werecompiled for the wideband and UWB cases, with the same assumptions for the antenna optics and sky
temperature as above. The different opening angles of the Baseline and wideband/UWB feeds are not a
factor, as they only affect the design of the optics. Given the overall sensitivity of the antenna is
proportional to its aperture efficiency ɻA, and inversely proportional to system temperature TSYS, thequantity (TSYS/ɻA) was defined as the metric for comparison, with lower values implying greater sensitivity
over a fixed (narrow) bandwidth.
Figure 1 shows a comparison plot of (TSYS/ɻA) over frequency between the Baseline configuration (in green)
and two wideband configurations described earlier, for all but the highest band (essentially the same
receiver in all three). The UWB configuration assumes a Caltech-designed QRFH with Teflon dielectric
rod loading; estimated aperture efficiency is taken from [RD13]. Looking at the curves, the following
observations can be drawn:
The Baseline case has significantly better sensitivity at virtually all frequencies, especially against theUWB case. This is primarily due to the much better overall aperture efficiency of its feed horns.
The wideband configuration fares a little better, particularly between 4–10 GHz: the QRFH is cooled
to 20K on this band, giving it a slight advantage.
The 3:1 conical feed suffers from a large drop in aperture efficiency at the lower band edge,
compared to the other feed types. It is also sitting at ambient (~300K), which will contribute an
extra 1–2K over a cooled QRFH.
The step change between band boundaries in the wideband/UWB curves are indicative of their lessthan-optimal LNA noise temperature at the lower band edge, an effect mentioned earlier in thissection. It is particularly noticeable at 15 GHz, the Band 2–3 transition for the wideband
configuration.

Figure 1 - Relative sensitivity of baseline, wideband, and UWB receiver configurations.

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Title: Front End Reference Design
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Version: A

One serious downside of the Baseline configuration are the feed sizes, particularly on Band 1, which isvery large: over 2.7 meters in length and 1.1 meters in diameter at the aperture. This is a directconsequence of the small opening angle required with these types of feeds. The large feeds on Bands 1–4
were impractical to cool and hence are external to the receivers, like those on the VLA. Anotherconsequence of the feed size was the need for three separate cryostats (Band 1, Band 2, and Bands 3–6).
This obviously will have a negative cost impact on both construction and operations compared to thesingle-cryostat wideband configurations.
To visualize all this, Figure 2 shows how the Baseline feeds and cryostats might be arranged for band
selection on a rotating platform, as on a dual-offset antenna. The EVLA L-band and C-band receivers areused to represent the approximate size of the Band 1 and 2 Baseline receivers, and are both roughly ameter in length. Clearly, the size and mass of the Band 1 package likely exceeds all the others combined,
and could make it impractical for anything other than a static location, as on the VLA or VLBA antennas.
In summary, the Baseline configuration offered much better overall sensitivity than either wideband
configuration, achieving the same total effective collecting area with fewer antennas. However, frequency
coverage below 4 GHz in a dual-offset antenna would likely not be feasible, given the size of the feed. The
wide opening angle of the Caltech QRFH offered a distinct advantage in this regard, but had relatively
poor efficiency compared to the corrugated feed.

Figure 2 - Baseline cryostats and feeds, aligned for rotation.

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Title: Front End Reference Design
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Version: A

4.4 Toward a Reference Design
At the start of 2017, there were basically two somewhat viable Front End configurations, neither of which
was entirely satisfactory, and they were unable to coexist on the same antenna because of incompatible
opening angles. However, in the absence of well-defined science cases to drive technical requirements, it
was still unclear whether low frequency coverage was really a priority, or if it was acceptable to give up
some sensitivity in exchange for added frequency coverage or receiver bandwidth.
The situation changed after the ngVLA Science Meeting in June 2017, where concrete science cases wereagreed upon and priorities set. From these, the following became clear:x Maximizing sensitivity was a priority for most of the science cases. This implies receivers with optimum
low noise, feeds with uniformly high aperture efficiency, and shaped antenna optics.
x Frequency coverage down to L-band became a firm requirement, though sensitivity for this band could
be less than optimum, if necessary.
Given the mandate for L-band coverage, the choices seemed to be:
x Revert to a VLA-style symmetric Cassegrain antenna that could accommodate the large low-frequency
feeds of the Baseline configuration, accepting the unavoidable blockage and scattering losses, orx Adopt the wideband configuration, accept the hit to sensitivity at high frequencies as unavoidable, andhope for future performance improvements in the QRFH.
Fortunately, a possible solution to the feed conundrum had been proposed a few months earlier by Lynn
Baker at Cornell University. While under contract by NRC in Canada a few years earlier, he and German
Cortes had designed an octave-band corrugated feed horn with a wide (55°) opening angle for use on the
Canadian SKA prototype antenna, DVA-1. Unlike the traditional type, the corrugations on the DVA-1
feed were radially concentric and oriented along the axial direction. Performance results shown in a report[RD14] indicated it had excellent match, acceptably low cross-polarization, and good aperture efficiency,
relatively flat over frequency. Figure 3 shows a graphic of the feed horn, along with a plot of the DVA-1
aperture efficiency over normalized frequency.

Figure 3 - DVA-1 corrugated feed horn, 3D rendering and aperture efficiency.

Compared to the QRFH, the axially corrugated DVA-1 feed has slightly higher overall aperture efficiency
and a flatter response, but over a narrower (2:1) bandwidth. It is also highly compact compared to the

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Title: Front End Reference Design
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NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Date: 2019-07-24
Version: A

Baseline’s corrugated feeds, though not as small as the QRFH with an equivalent opening angle. While theaperture efficiency is not quite as high as a traditional corrugated horn, it is a viable alternative on Bands
3–6 of the Baseline configuration, and small enough when scaled to be integrated into the cryostat. A
more recent analysis by Baker [RD15] has confirmed the loss in overall efficiency over an ideal Gaussian
feed for an ngVLA antenna at 5 GHz is only about 2%. The backlobe and spillover are also very low,compared to the QRFH.
Best of all, the similar opening angles for the axially corrugated feed horn and QRFH allow them to coexist
on the same antenna or be mixed within a cryostat. The QRFH is well-suited for the bands below about
10 GHz, as it is highly compact, transitions directly to coax (no polarizer needed), and covers the wide
bandwidths needed in this range to reduce cost and weight. The axially corrugated feed is preferred above
10 GHz, with its compact size, uniformly high aperture efficiency, low spillover and waveguide output. It
is also relatively simple to fabricate, making it suitable for mass production.
Selecting these two feeds was a key decision in moving toward the final reference design. Other changes
were made but were relatively minor and are described in the next section.

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Version: A

5 Reference Design Description
The term “reference design” in the context of the ngVLA refers to a technically viable design concept thatcan meet the subsystem requirements with low attendant risks, and is sufficiently detailed and mature topermit accurate costing. While the level of detail is still short of an actual preliminary design, progression
to that stage would be technically straightforward, with minimal development required, and yielding the
expected performance.

5.1 Configuration Description and Performance
The proposed ngVLA reference Front End configuration is implemented as six independent receiver bands,
each with its own feed. The upper five bands will be integrated into a single, moderately sized cryostat(B), while the lowest (Band 1) occupies a second cryostat (A) of comparable volume and mass. All feeds
are sufficiently compact to be cryogenically cooled, reducing losses ahead of the low-noise amplifiers(LNAs). Due to its size, the Band 1 feed will be cooled to 80 K, while all other feeds are cooled to 20 K.
A variable-speed Gifford-McMahon cryocooler with ~5W of cooling capacity on the 20K stage (equivalent
to a CTI Model 350) is used on each cryostat.
Table 2 shows the reference Front End band frequencies, approximate feed dimensions, and estimatedperformance data (aperture efficiency, noise temperatures) at three frequencies: midband, lower, andupper band edge. Frequency coverage is continuous except for the expected break in the atmosphericabsorption band at ~50–70 GHz. The frequency overlap at the boundary between Bands 4 and 5 wasdeliberate: it allows observations at ~30 GHz with higher sensitivity, away from a band boundary. Output
polarization on all receivers is linear, rather than circular as on the VLA: this simplified the receiver design,
reducing receiver noise and allowing greater fractional bandwidth for the all-waveguide receivers on Bands
3–6.
For continuous coverage between 1.2–12.6 GHz, waveguide or even octave-bandwidth receivers are notcost-effective, given the ~10:1 frequency range. On Bands 1 and 2, wideband (up to 3.5:1) receivers matedto a Quad-Ridge Feed Horn (QRFH) are proposed. The QRFH is a very broadband feed, which can be
designed for large opening angles (45–60°), making it highly compact even at low frequencies [RD11]. It
has dual coaxial outputs for both orthogonal linear polarizations, eliminating the need for a separate
polarizer or OMT, with additional savings in space and cost. Aperture efficiency, spillover and loss are lessthan optimum with this feed, and LNA performance will be somewhat compromised over the lower partof the band [RD10]. However, significant cost savings are realized by effectively halving the number ofreceivers and cryostats required per antenna.

Page 14 of 34

Title: Front End Reference Design
Description

Owner: Grammer

Date: 2019-07-24

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGNBand Dewar f L
#
#
GHz
1
2
3
4
5
6

A
B
B
B
B
B

1.2
3.5
12.3
20.5
30.5
70

Version: A

fM
GHzFeed Horn PropertiesfH
BW
f H: f L
OMT
GHZ Temp ɽ͕ĚĞŐ L, mm D, mm
GHz

Pol.
Out

2.0
6.6
15.9
26.4
39.2
90

3.5
12.3
20.5
34
50.5
116

Lin.
Lin.
Lin.
Lin.
Lin.
Lin.

2.92
3.51
1.67
1.66
1.66
1.66

2.3
8.8
8.2
13.5
20
46

80
20
20
20
20
20

58.0
58.0
55.0
55.0
55.0
55.0

330.2
113.2
28.90
17.34
11.65
5.078

360.0
123.4
53.00
31.80
21.37
9.313

QR
QR
WG
WG
WG
WG

Spillover, K
T RX , K
T LNA , KBand Dewar Aperture Eff., Ș A##@fL @fM @fH @fL @fM @fH @fL @fM @fH @fL @fM @fH
1
2
3
4
5
6

A
B
B
B
B
B

0.80
0.80
0.84
0.83
0.81
0.68

0.79
0.78
0.87
0.86
0.82
0.61

0.74
0.76
0.86
0.83
0.78
0.48

12.8
12.8
4.1
4.1
4.1
4.1

10.1
7.0
4.1
4.1
4.1
4.1

4.0
3.9
4.1
4.1
4.1
4.1

2.6
6.7
5
5.7
7.8
25

2.8
7.2
8
6
8.4
26

5
5
8.7
7.8
14.1
42

9.9
13.4
13.9
15.4
19.1
50.6

10.3
15.4
16.9
16.2
20.4
49

13.8
14.4
18.6
19.5
26.5
72.6

Array SEFD, Jy
T SKY , K
T SYS , K
(T SYS / Ș A ), K
Band Dewar##@fL @fM @fH @fL @fM @fH @fL @fM @fH @fL @fM @fH
1
2
3
4
5
6

A
B
B
B
B
B

4.4
4.6
5.3
13.6
11.1
68.3

4.5
4.7
6.3
12.1
16.9
15.4

4.6
5.3
13.6
12.4
70.3
112.3

28.1
31.8
24.3
34.1
35
124

25.9
28.1
28.3
33.4
42
69

23.4
24.6
37.3
37.0
102
190

35
40
29
41
43
182

33
36
32
39
51
113

32
32
43
44
130
396

1.55
1.75
1.27
1.80
1.91
8.02

1.44
1.59
1.43
1.72
2.27
4.99

1.39
1.42
1.91
1.95
5.73
17.45

Table 2 - Performance estimates, 6-band reference design configuration.

Explanatory Notes for Table 2:
1.
Sensitivity (SEFD) calculation is for an array of 244 x 18-meter and 19 x 6-meter diameter
antennas. The optical performance of both antenna types is assumed identical.
1. The aperture efficiency is for the feed with the antenna, and assumes an unblocked primary
aperture, an offset feed (low) Gregorian design, a secondary (subreflector) of 3.5m aperture,shaped optics, and a ground shield for spillover noise reduction.
2. Antenna surface (Ruze) efficiency is included in the aperture efficiencies shown. Surface accuracy
assumed is for precision conditions (160 m RMS, uniformly distributed).
3. Estimates for sky temperature (TSKY) were provided by B. Butler (NRAO), modeling opacity at
VLA site. An elevation angle of 45 degrees was assumed for all bands. The precipitable water
vapor (PWV) was assumed to be 6 mm for Bands 1–5, and 1 mm for Band 6.
4. Outputs on all bands are linearly-polarized.
5. Band 1 feed is cooled to ~80K. Band 2–6 feeds are cooled to ~20K.

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6. Opening angle ( ) is defined here as the angle subtended between the central optical axis and theedge of the subreflector, at the secondary focus of the antenna.
7. Bands 1–2 use a wideband (~3.5:1) QRFH, designed for an opening angle of 58 degrees. The mostrecent version uses a revised spline feed profile on the QRFH to maximize overall aperture
efficiency over the band (H. Mani and W. Zhong, 2017).
8. Bands 3–6 use axially-corrugated feeds, directly scaled from a design by G. Cortes and L. Baker
for the NRC DVA-1 antenna [RD14]. Feed opening angle is 55°.
9. Band 6 LNA and receiver noise temperature estimates shown are courtesy of D. Cuadrado (U.
of Manchester) and S. Weinreb.
10. For Bands 1–2, the illumination efficiency component assumes the mapping (shape) function usedon the SKA antenna; analysis with the ngVLA antenna shaping is TBD.
11. For Bands 3–6, a high-efficiency mapping function for the ngVLA reference optical design was used;
illumination efficiency and spillover noise are taken from [RD15].
12. Bands 1–2 TRX includes contributions from: radome/window, IR filter(s), feed, cal coupler, LNA
and coax cables.
13. Bands 3–6 TRX includes contributions from radome, window, IR filter, feed, OMT, cal coupler,
LNA and waveguides.
14. The TSYS for all bands includes an extra 1 K noise contribution from the IRD subsystem.
15. A detailed breakdown of the cascaded TRX for each band is shown in Section 6.3.
16. LNA noise values are taken from the table at the end of Section 6.3.
Figure 4 shows a photo of a QRFH for Band 1, fabricated by Caltech/ASU in February 2018 for installation
into their test cryostat. The feed was machined from aluminum, then gold plated to lower the infraredemissivity for reduced loading on the cold stage. A ruler next to feed gives an idea of scale, though it isstill remarkably small for an L-band horn. Next to the photo is the measured input return loss on both
ports, which is >10 dB from 1.2 to 5 GHz, and in close agreement with the modeled results [RD16].

Figure 4 - Band 1 quad-ridge feed horn prototype (photos courtesy S. Weinreb).

For optimum performance at the higher frequencies, waveguide-bandwidth (~1.66:1) receivers areproposed to cover 12.3–50.5 GHz and 70–116 GHz, in four separate bands (3–6). Excellent low-noise
amplifier (LNA) performance is readily achievable, and use of waveguide in the signal path up to the LNA

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input minimizes the loss and its associated noise contribution, without adding undue size or weight. An
axially corrugated conical feed horn with a wide opening angle (~55° subtended beam, from center toedge of the subreflector) has been selected as the reference feed design for these receivers. Based directly
on a design by Cortes and Baker [RD14] for the Canadian DVA-1 antenna, it yields aperture efficiency
and cross-polarization performance comparable to a traditional corrugated horn but in a compact size.
Figure 5 shows a photo of this same feed design, scaled to Q-band (35-50 GHz) as a test piece for a future
ngVLA Band 5 receiver [RD17]. Note that the feed is actually smaller than the mating waveguide flange to
the OMT. Despite its size, conventional machining was sufficiently accurate for fabrication. Also included
is a plot of the simulated and measured return loss, which shows excellent input match over the specified
frequency range [RD18].

Figure 5 - Prototype Q-band axially corrugated feed horn.

Scaling this feed a factor of two smaller for W-band (70–116 GHz) seemed a daunting prospect, given thevery small feature sizes and high depth/width (aspect) of the corrugation ring spacings. Therefore, a study
was contracted to a consulting firm, EMSS, who had experience with a similar feed design from the SKA
project. EMSS performed a detailed analysis on sensitivity of electromagnetic performance to dimensionalvariations in the corrugations, and did trial machining and precision metrology of test pieces from various
metals and alloys [RD19]. Their conclusion was that a wide-angle corrugated horn is feasible at W-band,and is manufacturable by conventional subtractive machining. As a further confirmation, the NRAO CDL
successfully machined the Baker corrugated feed design scaled to W-band, for actual RF testing. Both Wband feeds are shown in Figure 6 below. Pattern measurement and RF testing of the feeds were conductedat the Green Bank Observatory, and the results appear to show good agreement with simulations [RD23].

Figure 6 - Prototype W-band axially corrugated feed horns (left - Baker, right - EMSS).

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The relative sensitivity metric (TSYS/ɻA) for ngVLA Reference Bands 1–5 is plotted against the eight VLA
receivers in Figure 7. Data from Caltech’s optimized wideband configuration (WB) in Section 6.2 is also
included in the plot for comparison. Lower numbers indicate greater sensitivity per unit of collecting area.
For the VLA antenna, the high spillover and drop in efficiency are very evident at L-band on the VLA
antenna, due to tradeoffs made in the feed design; above Ku-band, the steady drop in surface (Ruze)
efficiency is evident.
The Reference and WB configurations for Bands 1 and 2 track closely, not surprising as they use the same
feed and antenna optics. Improvement here is possible by using direct noise cal injection into the QRFH
[RD20], and revising the feed illumination efficiency for the ngVLA mapping function. At Ku-band andabove, the Reference configuration outperforms both the VLA and WB configuration by a wide margin.
In the VLA case, the surface is the main reason, while for the WB case it is the combination of high LNA
and spillover noise, and the lower illumination efficiency of the QRFH.

Figure 7 - Relative sensitivity of ngVLA reference Bands 1–5, versus a single VLA antenna.

The estimated relative sensitivity (TSYS/ɻA) for the ngVLA Reference Band 6 is shown in Figure 8. Note that
the PWV assumed for this band is 1mm, not 6mm as with the other bands. The sharp rate of increase
above 113 GHz is primarily due to sky opacity, and to a lesser degree, degradation of the receiver noise
performance.

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Figure 8 - Relative sensitivity of ngVLA reference Band 6.

Finally, for completeness, a plot of sky temperatures at the VLA site is shown in Figure 9. The sky opacity
at the VLA site was modeled for three different values of PWV (13 mm, 6 mm, and 1 mm), representing
various operating conditions [RD21]. A 45 degree antenna elevation angle was assumed.

Figure 9 - Modeled Tsky data, VLA site.

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5.2 Front End Subsystem Block Diagram
Figure 10 below shows the block diagram of the reference Front End subsystem. Each receiver has two
orthogonal linearly polarized outputs, which feed the Integrated Receiver Downconverter/Digitizer (IRD)
modules [AD04]. No frequency conversion is performed on any of the bands in the Front End portion of
the system. There will be at least one multi-stage LNA per channel, though the high frequency bands may
require a cascade of a second amplifier to produce sufficient overall gain to be within the input dynamic
range of the IRDs.
Each receiver contains a calibrated noise injection path for self-calibration during observing. This is shownwith a splitter and pair of directional couplers. The noise source driving this path has an adjustable output
level (~30 dB dynamic range), and will be located outside the cryostat, possibly within the IRD module.
As mentioned before, it may be possible to eliminate the lossy coaxial couplers on Bands 1 and 2 bydirectly injecting the noise into the QRFH itself. But the concept will have to be proven first.

DEWAR ‘B’ SA500B
F506 – Band 6 (70-116 GHz)

F503 – Band 3 (12.3-20.5 GHz)

Trx = 52K

Trx = 15K

20K

20K

Band
3
ACFH
1.67:1

Band
3
OMT

+30

+G

Band 3 OUT, POL-A

F513 – Noise Source
N.D.

20K
SPI

20K

20K

Band
6
ACFH
1.66:1

Band
6
OMT

+20

Band 6 OUT, POL-A

F516 – Noise Source
N.D.

20K
SPI

Trx = 52K

Trx = 15K
+30

+G

+G

Band 3 OUT, POL-B

+20

+G

Band 6 OUT, POL-B

F505 – Band 5 (30.5-50.5 GHz)

20K

Band 2 OUT, POL-A

Trx = 12K

Band
2
QRFH
3.51:1

Trx = 26K

F502 – Band 2 (3.5-12.3 GHz)
+30

20K

Band
5
ACFH
1.66:1

Band
5
OMT

+30

+G

Band 5 OUT, POL-A+G

F512 – Noise Source
N.D.

20K
SPI

Trx = 12K
+30

20K

F515 – Noise Source
N.D.

20K
SPI

+G
Trx = 26K

Band 2 OUT, POL-B

+30

+G

Band 5 OUT, POL-B

F504 – Band 4 (20.5-34 GHz)

80K

Band 1 OUT, POL-A

Trx = 12K

Band
1
QRFH
2.92:1

Trx = 18K

F501 – Band 1 (1.2-3.5 GHz)
+30

F511 – Noise Source
N.D.

20K
SPI

Trx = 12K
+30

20K

20K

Band
4
ACFH
1.67:1

Band
4
OMT

+30

+G

Band 4 OUT, POL-A+G

F514 – Noise Source
N.D.

20K
SPI

+G

Band 1 OUT, POL-B

Trx = 18K
+30

+GBand 4 OUT, POL-B

DEWAR ‘A’ SA500A
Figure 10 - Block diagram of Front End subsystem.

5.3 Front End Packaging Concept
The size and shape of Cryostat A are largely driven by the Band 1 feed, which is by far the largest
component; the LNAs and other RF components are not shown, but take up very little space bycomparison. One challenge with Band I will be reducing the infrared loading through the feed window, toallow cooling all the way to 80K, particularly in the center of feed structure. This will be important in
reducing the contribution to system noise from RF loss in the feed.
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The five receiver bands in Cryostat B are arranged in a line, to allow band selection with linear movement
along a single axis. The relative offsets of the feed apertures from the top plate are adjusted to align thephase centers of all feeds on a same axis. In practice, a fine focal adjustment will likely be necessary whentuning across the bandpass on some of the high-frequency receivers, so the positioner for the Front End
platform will probably have two axes of motion.
Cryostat B is envisioned to be a modular assembly, to allow separate production and testing of individual
receiver bands. Each receiver subassembly is a mechanical integration of the feed horn, IR filter, thermal
gap interface, LNAs and other cooled RF components. The feed windows, output coax and waveguideconnections, bias and sensor wiring harnesses, and vacuum and temperature sensors will be part of thecryostat shell.
Figure 11 and Figure 12 show renderings of packaging concepts for Cryostat A and B, respectively.

Figure 11 - ngVLA reference receiver Band 1 (cryostat A).

Figure 12 - ngVLA reference receiver Bands 2–6 (cryostat B).

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Approximate dimensions and masses for both cryostats are:xx

Cryostat A (Band 1): 458 x 406 mm (Dia. x H); total mass ~ 74 kg
Cryostat B (Bands 2–6): 725 x 260 x 300 mm (L x W x H); total mass ~ 89 kg

5.4 Front End Interfaces to Other Subsystems
This section provides information about the mechanical and electrical interfaces to the Front End cryostat
assemblies. In many cases, detailed specifications for the interfaces are not yet fully defined, but the generalscope of the interfaces are described here. These will eventually be documented in detail with Interface
Control Documents (ICDs), generated jointly by designers from both sides. During the formal design anddevelopment phase of the project, the ICDs will be updated through formal change control processes.
Descriptions given of electrical/RF connectors, waveguide ports and mechanical flanges or attachment
points reference the Front End side of the interface. Cables, waveguide and fiber routing between thecryostats and other electronic subsystems are beyond the scope of this document.

5.4.1

Interface to the Cryogenic Subsystem

The cryocooler unit consists of two separate parts: a drive motor/valve/displacer assembly, and a polishedsteel cylinder that slides over the displacers. The cylinder is the mechanical interface for both cold stages,
and is an integral part of the cryostat assembly. The displacer assembly is external to the cryostat andremovable, and is considered part of the Cryogenic subsystem. The interface between these parts is aninterface plate or flange pattern that allows a gas-tight seal and properly aligns the two parts. A mechanicaldrawing of this interface pattern is shown in Figure 13 [AD03].

Figure 13 - Cryocooler displacer mechanical interface.

5.4.2

Interface to the Integrated Receivers and Downconverters (IRD) Subsystem

The IRD subsystem module will be mounted in close proximity to Cryostat B, to keep the RFinterconnects to it as short as possible. It might even be feasible to bolt them directly together, using
blind-mate connectors instead of cables/waveguides, but this will be decided later on. Longer armoredcables will be used to connect the Band 1 RF outputs of Cryostat A to the IRD module.

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Table 3 shows the type and number of RF interconnects with the Front End subsystem [AD04]. The
physical locations and outlines of the connectors are still TBD.
Signal at Interface
Band 1 RF

Type
OutputBand 2 RF

OutputBand 3 RF

OutputBand 4 RF

OutputBand 5 RF

OutputBand 6 RF

OutputParameter
Connector
Impedance
NumberConnector
Impedance
NumberConnector
Impedance
NumberConnector
Impedance
NumberWaveguide size
NumberWaveguide size
NumberValue
SMA (F)50 ȍ
2 (one per pol.)SMA (F)50 ȍ
2 (one per pol.)2.92 mm (F)50 ȍ
2 (one per pol.)2.92 mm (F)50 ȍ
2 (one per pol.)WR-22 (UG599)
2 (one per pol.)WR-10 (UG387)
2 (one per pol.)Table 3 - Interconnects between the Front End cryostats and IRD module.

5.4.3

Interface to the Antenna Subsystem

The Front End cryostat assemblies will be mounted at the secondary focus of the antenna, on a platform
attached to the feed arm structure. A dual offset Gregorian optical configuration for the antenna isassumed. The platform will include an X-Y axis motorized positioner for focusing and band selection andthe temperature-controlled enclosure. Figure 14 shows a rendering of the mounting concept, which willbe the same for both the 18-meter and 6-meter antennas. Detailed mechanical interface drawings are
pending completion of the antenna design.

Figure 14 - Front End subsystem enclosure, opened to show cryostats and IRD assembly.

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5.4.4

Date: 2019-07-24
Version: A

Interface to the Monitor and Control Subsystem

The two Front End cryostat assemblies presently contain only RF electronics. All the analog support
electronics for Cryostats A and B are packaged within two external modules, referred to as F521A and
F521B, respectively. These will be located inside the platform enclosure on the antenna feed arm, in close
proximity to the cryostats. The support electronics provides the following functions:x DC bias/driver circuitry for LNAs, noise calibrator sources, and other active components
x RF output control/leveling for the noise calibrator sources
x Input signal conditioning from the cryostat vacuum and temperature sensors
x Driver circuitry and current monitoring for the cryostat vacuum solenoid valve
Electrical connection to the cryostats is assumed to be via multi-conductor shielded cables, with abulkhead receptacle/cable plug pair at each end. Specific details are undefined at present; however, thesewill likely consist of single, multi-pin round, twist-locking connector interfaces, with a hermetic glass seal
for contacts on the cryostat receptacle side, to maintain vacuum integrity.
It may be feasible, and even desirable, to integrate some or all of the support electronics into theirrespective cryostats, but for now are they are assumed to be separate assemblies.
The Cryo and LNA M&C module (designated F520) contains the MIB, or Monitor and Control Interface
Board, which provides the communications link to the monitor and control subsystem. The F522 is similar
to the F521A/B but also provides control electronics for the vacuum pump common to both cryostats[AD05].

5.4.5

Interface to the Power Supply Subsystem

The Power Supply Subsystem provides DC voltages required by the Front End electronics, packaged inmodules F521 and F522 [AD05]. Voltages and currents supplied are: +32.5V @ 0.5A, +17.5V @ 6A, +7.5V@ 0.5A and –7.5V @ 0.1A, from the P501 power supply module [AD06].
The electromechanical interface details are presently undefined. However, it will likely consist of a single
multi-pin round, twist-lock, or threaded connector interface, like those widely used by the US military(e.g., MIL-DTL-26482, MIL-DTL-38999, MIL-DTL-22992). These are highly rugged, weather-tight, andreliable, with a multitude of pin sizes and counts available at a moderate cost. Location is likely to be on
the rear panel of the F521 and F522 electronics modules.

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6 Appendix
6.1 Abbreviations and Acronyms
Acronym
AD
CDL
GBT
IF
IRD
LNA
LO
LRU
M&C, M/C
MMIC
NGC
ngVLA
NRC
OMT
QRFH
RD
RF
SEFD
SKA
TBD
UWB
VLA
VLBA

Description
Applicable Document
Central Development Laboratory
Green Bank TelescopeIntermediate Frequency
Integrated Receiver Downconverter/Digitizer (Subsystem)
Low Noise Amplifier
Local Oscillator
Line Replaceable Unit
Monitor and Control
Monolithic Microwave Integrated Circuit
Northrop Grumman Corporation
Next Generation VLA
National Research Council (Canada)
Ortho Mode Transducer
Quad-Ridged Feed Horn
Reference Document
Radio Frequency
System Equivalent Flux Density
Square Kilometer Array (telescope)
To Be Determined
Ultra Wide Band
Jansky Very Large Array
Very Long Baseline Array

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6.2 Caltech 4-Band Front End Concept
Band Dewar f L
#
#
GHz
1
2
3
4

A
A
A
A

1.2
4.2
15
70

f M1
GHz

f M2
GHz

fH
BW Feed Horn Properties
OMT
f H: f L
GHZ
GHz
Temp L, in. ID, in.

2.2
8
23
90

3.4
10
35
105

4.2
15
50
116

3.50
3.57
3.33
1.66

3
10.8
35
46

80
20
20
20

13.0
3.71
1.04
2.54

14.2
4.05
1.13
1.49

none
none
none
WG

Spillover, K
Aperture Eff., Ș A
Band Dewar~T RAD##@ f L @ f M1 @ f M2 @ f H @ f L @ f M1 @ f M2 @ f H (K)
1
2
3
4

A
A
A
A

0.80
0.80
0.79
0.68

0.79
0.79
0.77
0.61

0.72
0.72
0.69
0.54

0.78
0.77
0.70
0.48

12.8
12.8
10.7
4.1

9.4
9.4
4.0
4.1

4.6
4.8
4.8
4.1

3.9
4.0
4.0
4.1

0.0
0.0
3.5
0.0

T LNA , K
T SKY , K
T RX , KBand Dewar##@ f L @ f M1 @ f M2 @ f H @ f L @ f M1 @ f M2 @ f H @ f L @ f M1 @ f M2 @ f H
1
2
3
4

A
A
A
A

3
6
12
25

3
6
12
26

3
7
12
26.5

4
8
20
42

9
14
28
50.6

10
14
28
48.8

10
15
29
51

11
17
38
72.6

4.4
4.6
6
68.3

4.5
4.8
22.1
15.4

4.6
5
13
16.9

4.6
6
62.5
112.3

Array SEFD, Jy(T SYS / Ș A ), K
T SYS , KBand Dewar##@ f L @ f M1 @ f M2 @ f H @ f L @ f M1 @ f M2 @ f H @ f L @ f M1 @ f M2 @ f H
1
2
3
4

A
A
A
A

26
31
48
123

24
28
58
68

19
25
50
72

20
27
108
189

33
39
61
181

30
36
75
111

26
34
73
134

25
35
155
394

1.44
1.73
2.68
7.96

1.33
1.58
3.29
4.91

1.17
1.51
3.23
5.89

1.10
1.54
6.83
17.36

Table 4 - Performance estimates, Caltech 4-band configuration.

Explanatory Notes for Table 4:This band configuration was originally proposed by Dr. Sandy Weinreb, Caltech, August 2016.
Recently, there have been discussions to possibly split Band 3 into two narrower bands for improved
sensitivity, but no formal decision on this has been communicated.
Sensitivity (SEFD) calculation is for an array of 244 x 18-meter and 19 x 6-meter diameter antennas.
The optical performance of both antenna types is assumed identical.
The aperture efficiency is for the feed with the antenna, and assumes an unblocked primary aperture,
an offset feed (low) Gregorian design, a secondary (subreflector) of 3.5m aperture, shaped optics,
and a ground shield for spillover noise reduction.
Antenna surface (Ruze) efficiency is included in the aperture efficiencies shown. Surface accuracy
assumed is for precision conditions (160 m RMS, uniformly distributed).
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Estimates for sky temperature (TSKY) were provided by B. Butler (NRAO), modeling opacity at VLA
site. An elevation angle of 45 degrees was assumed for all bands. The precipitable water vapor(PWV) was assumed to be 6 mm for Bands 1–3, and 1 mm for Band 4.
Outputs on all bands are linearly-polarized.
Band 1 feed is cooled to ~80K. Band 2–4 feeds are cooled to ~20K.
Opening angle (ɽ) is defined here as the angle subtended between the central optical axis and theedge of the subreflector, at the secondary focus of the antenna.
Bands 1–3 use a wideband (~3.5:1) QRFH and Caltech LNAs. The feed is designed for an opening
angle of 58 degrees, and uses a revised spline feed profile to maximize overall aperture efficiency
over the band (H. Mani and W. Zhong, 2017).
Band 4 uses a wide-angle corrugated feed, based on a design by G. Cortes and L. Baker in the NRC
DVA-1 SKA prototype antenna (2014). Band 4 LNA and receiver noise temperature estimates
shown are courtesy of D. Cuadrado (U. of Manchester) and S. Weinreb.
For Bands 1–3, the illumination efficiency component assumes the mapping (shape) function usedon the SKA antenna.
For Band 4, a high-efficiency mapping function for the ngVLA reference optical design was used;
illumination efficiency and spillover noise are taken from [RD15].
Bands 1–3 TRX includes contribution from window+IR filter, feed, coax losses (4-8K) and also thecalibration injection coupler and post-amplifier (1.5+0.5K, 2.5+0.5K and 9+1K, on Bands 1, 2 and 3,
respectively). The cal coupler contributes a significant amount of extra noise, but recent tests by
the SKA project on a probe injection system in the feedhorn [RD20] are promising, and may allow
the coupler to be eliminated entirely.
TRAD is the approximate noise contribution from a weather radome. It is shown in a separate column
for Band 3, but already included in TRX for Bands 1, 2, and 4.

Page 27 of 34

Title: Front End Reference Design
Description

Owner: Grammer

Date: 2019-07-24

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Version: A

Feed cone is external to Dewar. Main effect is on the back lobe

100

90

90

80

80

70

70

60
50

60

Aperture efficiency
Total spillover noise temp

50

40

40

30

30

20

Spillover Noise is with conservative assumptionthat ½ the total spillover is at 250K.

10
0
1.2

20

Spillover Temperature (K)Efficiency (%)

QRFH_60_3p5_1p2_dewar_ext_cone
100

10
1.8

2.4

3.0

3.6

0
4.2

Frequency (GHz)
Figure 15 - QRFH cross section and shield cone, with simulated illumination efficiency andspillover noise.

Page 28 of 34

Title: Front End Reference Design
Description

Owner: Grammer

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Date: 2019-07-24
Version: A

Figure 16 - 3D rendering of Caltech 4-band, single-cryostat Front End concept.

Figure 17 - Caltech/ASU Band 1 cryostat, open and fully assembled (cryocooler is below tabletop).

Page 29 of 34

Title: Front End Reference Design
Description

Owner: Grammer

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

6.3 NASA/JPL Ultra-Wideband Receiver (8-48 GHz)

Figure 18 - OMMIC 70 nm GaAs m-HEMT LNA: gain and noise temperature.

Figure 19 - NGC 35 nm InP HEMT LNA: gain and noise temperature.

Page 30 of 34

Date: 2019-07-24
Version: ATitle: Front End Reference Design
Description

Owner: Grammer

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Date: 2019-07-24
Version: A

Figure 20 - JPL ultra-wideband receiver cryostat, side rendering and inside view.

Figure 21 - JPL UWB receiver noise temperature, measured both with an LN2 load and on cold sky.

Page 31 of 34

Title: Front End Reference Design
Description

Owner: Grammer

Date: 2019-07-24

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN

Version: A

6.4 ngVLA Reference Front End Receiver Cascade, LNA Noise Tables
Band #:
Frequency:

1

Phys. T-Line
Temp. Len.

Component TypeK

Lossless Input
Weather_Radome
Vacuum_Window
IR_Filter
Feed_Horn
OMT
Coax_141Cu
Cal_Coupler
LNA_Band1
Coax_086SS

20
300
300
190
80
50
50
20
20
190

m

0.1

0.4

1.2

Band #:Tcas

G, dB Te, K

Gcas

Tcas G, dB Te, K

Gcas

Tcas

0.00
0.00
-0.02
-0.02
-0.10
0.00
-0.04
-0.45
36.50
-0.62

0.00
0.00
-0.02
-0.04
-0.14
-0.14
-0.18
-0.63
35.87
35.25

0.00
0.00
1.38
2.27
4.15
4.15
4.64
6.91
9.92
9.93

0.00
0.00
-0.02
-0.02
-0.10
0.00
-0.05
-0.45
36.80
-0.81

0.00
0.00
-0.02
-0.04
-0.14
-0.14
-0.19
-0.64
36.16
35.35

0.00
0.00
1.38
2.27
4.15
4.15
4.80
7.08
10.33
10.34

0.00
0.00
-0.02
-0.04
-0.17
-0.17
-0.24
-0.69
36.17
35.11

0.00
0.00
1.38
2.27
4.72
4.72
5.62
7.93
13.77
13.78

35.3

9.9

35.3

10.3

35.1

13.8

0.00
0.00
1.38
0.88
1.86
0.00
0.47
2.18
2.60
29.09

K

Lossless Input
Weather_Radome
Vacuum_Window
IR_Filter
Feed_Horn
OMT
Coax_141Cu
Cal_Coupler
LNA_Band2
Coax_086SS

20
300
300
190
20
20
20
20
20
190

m

0.1

0.4

3.5

Phys.
Temp.

TLine
Len.

Component TypeKm

Lossless Input
Weather_Radome
Vacuum_Window
IR_Filter
Feed_Horn
OMT
Cal_Coupler
WG_WR51
LNA_Band3
WG_WR51

20
300
300
190
20
20
20
20
20
190

Frequency:

Cascaded Values:

0.1
0.3

0.00
0.00
-0.02
-0.02
-0.13
0.00
-0.07
-0.45
36.87
-1.06

0.00
0.00
1.38
0.88
2.43
0.00
0.86
2.18
4.98
52.80

6.6

12.3

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

0.00
0.00
-0.02
-0.02
-0.13
0.00
-0.07
-0.45
35.98
-1.07

0.00
0.00
-0.02
-0.04
-0.17
-0.17
-0.24
-0.69
35.29
34.22

0.00
0.00
1.38
2.27
2.88
2.88
3.24
5.55
13.40
13.41

0.00
0.00
-0.03
-0.03
-0.18
0.00
-0.11
-0.45
34.76
-1.47

0.00
0.00
-0.03
-0.05
-0.24
-0.24
-0.34
-0.79
33.97
32.50

0.00
0.00
1.84
3.01
3.88
3.88
4.40
6.77
15.36
15.39

0.00
0.00
0.00
0.00
-0.03
2.08
-0.03
1.32
-0.30
1.43
0.00
0.00
-0.16
0.73
-0.45
2.18
34.91 5.00
-2.00 111.32

0.00
0.00
-0.03
-0.06
-0.36
-0.36
-0.52
-0.97
33.95
31.94

0.00
0.00
2.08
3.41
4.86
4.86
5.65
8.11
14.35
14.40

34.2

13.4

32.5

15.4

31.9

14.4

0.00
0.00
1.38
0.88
0.61
0.00
0.35
2.18
6.69
52.97

Cascaded Values:

Band #:

0.00
0.00
1.38
0.88
1.86
0.00
0.63
2.18
2.80
38.86

2

Phys. T-Line
Temp. Len.

Component Type

3.5

Gcas

Cascaded Values:

Frequency:

2.0

G, dB Te, K

0.00
0.00
1.84
1.16
0.86
0.00
0.50
2.18
7.16
76.23

3
12.3

15.9

20.5

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

0.00
-0.03
-0.03
-0.03
-0.05
-0.20
-0.20
-0.07
35.08
-0.21

0.00
-0.03
-0.06
-0.09
-0.14
-0.34
-0.54
-0.61
34.46
34.25

0.00
2.08
4.17
5.51
5.75
6.72
7.74
8.11
13.87
13.87

0.00
-0.03
-0.03
-0.03
-0.05
-0.20
-0.20
-0.03
34.64
-0.09

0.00
-0.03
-0.06
-0.09
-0.14
-0.34
-0.54
-0.57
34.07
33.98

0.00
2.08
4.17
5.51
5.75
6.72
7.74
7.90
16.91
16.91

0.00
-0.04
-0.03
-0.03
-0.05
-0.20
-0.20
-0.03
34.30
-0.08

0.00
-0.04
-0.07
-0.10
-0.15
-0.35
-0.55
-0.58
33.72
33.65

0.00
2.82
4.92
6.26
6.49
7.47
8.49
8.62
18.62
18.62

34.3

13.9

34.0

16.9

33.6

18.6

0.00
2.08
2.08
1.32
0.23
0.94
0.94
0.33
5.00
9.57

Table 5 - Cascaded gain and noise, Bands 1–3.

Page 32 of 34

0.00
2.08
2.08
1.32
0.23
0.94
0.94
0.14
7.90
4.13

0.00
2.82
2.08
1.32
0.23
0.94
0.94
0.12
8.75
3.35

Title: Front End Reference Design
Description

Owner: Grammer

Date: 2019-07-24

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGNBand #:
Frequency:

4

Phys. T-Line
Temp. Len.

Component TypeK

Lossless Input
Weather_Radome
Vacuum_Window
IR_Filter
Feed_Horn
OMT
Cal_Coupler
WG_Band4
LNA_Band4
WG_Band4

20
300
300
190
20
20
20
20
20
190

m

0.1
0.3

20.5

Band #:

K

Lossless Input
Weather_Radome
Vacuum_Window
IR_Filter
Feed_Horn
OMT
Cal_Coupler
WG_WR22
LNA_Band5
WG_WR22

20
300
300
190
20
20
20
20
20
190

m

0.05
0.3

Tcas

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

0.00
-0.04
-0.03
-0.03
-0.05
-0.20
-0.20
-0.08
33.65
-0.23

0.00
-0.04
-0.07
-0.10
-0.15
-0.35
-0.55
-0.63
33.02
32.79

0.00
2.82
4.92
6.26
6.49
7.47
8.49
8.90
15.43
15.43

0.00
-0.05
-0.03
-0.03
-0.05
-0.20
-0.20
-0.05
29.16
-0.15

0.00
-0.05
-0.08
-0.11
-0.16
-0.36
-0.56
-0.61
28.55
28.40

0.00
3.33
5.44
6.78
7.02
7.99
9.02
9.29
16.19
16.20

0.00
-0.05
-0.03
-0.03
-0.05
-0.31
-0.24
-0.04
28.00
-0.13

0.00
-0.05
-0.08
-0.11
-0.16
-0.47
-0.71
-0.75
27.25
27.11

0.00
3.47
5.58
6.92
7.16
8.70
9.96
10.20
19.48
19.49

32.8

15.4

28.4

16.2

27.1

19.5

0.00
2.82
2.08
1.32
0.23
0.94
0.94
0.36
5.65
10.42

Frequency:

0.00
3.47
2.08
1.32
0.23
1.49
1.12
0.21
7.80
5.97

39.2

50.5

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

0.00
-0.05
-0.03
-0.03
-0.05
-0.25
-0.22
-0.08
33.25
-0.46

0.00
-0.05
-0.08
-0.11
-0.16
-0.41
-0.62
-0.70
32.55
32.09

0.00
3.47
5.58
6.92
7.16
8.37
9.49
9.90
19.06
19.07

0.00
-0.05
-0.03
-0.03
-0.05
-0.34
-0.23
-0.05
34.12
-0.29

0.00
-0.05
-0.08
-0.11
-0.16
-0.50
-0.73
-0.78
33.34
33.05

0.00
3.47
5.58
6.92
7.16
8.84
10.06
10.32
20.42
20.42

0.00
-0.05
-0.03
-0.03
-0.05
-0.30
-0.20
-0.04
33.13
-0.25

0.00
-0.05
-0.08
-0.11
-0.16
-0.46
-0.66
-0.71
32.42
32.17

0.00
3.47
5.58
6.92
7.16
8.66
9.71
9.94
26.52
26.53

32.1

19.1

33.0

20.4

32.2

26.5

0.00
3.47
2.08
1.32
0.23
1.17
1.02
0.36
7.80
21.18

0.00
3.47
2.08
1.32
0.23
1.62
1.09
0.23
8.44
13.29

0.00
3.47
2.08
1.32
0.23
1.45
0.94
0.20
14.10
11.40

6

Phys. T-Line
Temp. Len.

70.0

Component TypeKm

Lossless Input
Weather_Radome
Vacuum_Window
IR_Filter
Feed_Horn
OMT
Cal_Coupler
WG_WR10
LNA_Band6
WG_WR10

20
300
300
190
20
20
20
20
20
190

0.00
-0.05
-0.03
-0.03
-0.05
-0.49
-0.68
0.025 -0.12
19.00
0.3
-1.42

Cascaded Values:

0.00
3.33
2.08
1.32
0.23
0.94
0.94
0.24
6.00
6.84

5
30.5

Cascaded Values:

Band #:

34.0

Gcas

Phys. T-Line
Temp. Len.

Component Type

26.4

G, dB Te, K

Cascaded Values:

Frequency:

Version: A

G, dB Te, K
0.00
3.56
2.08
1.32
0.24
2.38
3.40
0.55
25.00
73.64

90

116.0

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

G, dB Te, K

Gcas

Tcas

0.00
-0.05
-0.08
-0.11
-0.16
-0.65
-1.33
-1.45
17.55
16.13

0.00
3.56
5.67
7.01
7.25
9.72
13.66
14.41
49.32
50.62

0.00
-0.06
-0.03
-0.03
-0.06
-0.38
-0.53
-0.08
19.00
-0.96

0.00
-0.06
-0.10
-0.13
-0.20
-0.58
-1.11
-1.19
17.81
16.85

0.00
4.44
6.81
8.33
8.63
10.55
13.52
14.00
48.18
48.96

0.00
-0.08
-0.05
-0.05
-0.08
-0.35
-0.50
-0.07
19.00
-0.84

0.00
-0.08
-0.13
-0.18
-0.26
-0.61
-1.11
-1.18
17.82
16.98

0.00
5.58
9.12
11.38
11.77
13.55
16.36
16.78
71.90
72.57

16.1

50.6

16.9

49.0

17.0

72.6

Table 6 - Cascaded gain and noise, Bands 4–6.

Page 33 of 34

0.00
4.44
2.34
1.48
0.30
1.84
2.60
0.37
26.00
47.10

0.00
5.58
3.47
2.20
0.37
1.68
2.44
0.33
42.00
40.64

Title: Front End Reference Design
Description

Owner: Grammer

Date: 2019-07-24

NRAO Doc. #: 020.30.03.00.00-0002-DSN-AFRONT_END_REF_DESIGN
Freq.
GHz
1.2
2.0
3.5
3.5
6.6
12.3
12.3
15.9
20.5
20.5
26.4
34.0
30.5
39.2
50.5
70
90
116

1
2
3
4
5
6

Gain
dB
35.25
35.35
35.11
34.22
32.50
31.94
34.25
33.98
33.65
32.79
28.40
27.11
32.09
33.05
32.17
16.13
16.85
16.98

Trx
K
9.9
10.3
13.8
13.4
15.4
14.4
13.9
16.9
18.6
15.4
16.2
19.5
19.1
20.4
26.5
50.6
49.0
72.6

TRX vs Frequency, ngVLA Bands 1-6
80.0
70.0
60.0

Trx, Kelvin

Band#

Version: A

50.0
40.0
30.0
20.0
10.0
0.0
1

10

100

Frequency, GHz

Figure 22 - Plot of receiver noise vs. frequency, Bands 1–6.

1

2

3

4

6

5

Freq.
(GHz)

Ga [1](dB)

Tn [1]
(K)

Freq.
(GHz)

Ga [2](dB)

Tn [2]
(K)

Freq.
(GHz)

Ga [3](dB)

Tn [3]
(K)

Freq.
(GHz)

Ga [4](dB)

Tn [4]
(K)

Freq.
(GHz)

Ga [5](dB)

Tn [5]
(K)

Freq.
(GHz)

Ga [6](dB)

Tn [6]
(K)

1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0

36.0
36.5
36.5
36.5
36.7
36.8
36.9
37.0
37.0
36.9
36.9
36.9
37.0
36.7
35.0
30.0

2.8
2.6
2.4
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.6
4.0
4.8
5.2
6.0
7.0

3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
9.0
10.0
11.0
12.0
13.0

35.0
36.0
35.0
34.5
34.2
34.0
34.2
34.7
35.0
35.5
36.0
36.5
36.0
35.5
35.0
34.7

7.3
6.7
6.0
6.0
6.7
7.0
7.5
7.2
7.0
6.5
6.0
5.5
5.0
4.7
5.0
5.0

12.0
12.5
13.0
13.5
14.0
14.5
15.0
16.0
17.0
18.0
19.0
20.0
21.0
22.0
23.0
24.0

35.2
35.0
34.6
34.2
34.6
35.0
35.0
34.6
34.0
34.6
35.0
34.6
34.0
33.0
32.5
33.0

5.0
5.0
5.0
5.3
6.0
6.5
7.0
8.0
7.5
6.0
6.0
8.0
9.5
8.5
9.0
10.0

20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35

33.9
33.4
32.8
31.5
31.5
31.0
30.0
27.9
27.5
28.0
28.0
28.0
28.0
28.0
28.0
28.0

6.0
5.3
5.6
6.0
6.0
6.5
6.2
5.7
5.7
6.0
6.3
6.5
6.7
7.3
7.8
8.0

30
31
32
33
34
35
36
37
38
40
42
44
46
48
50
52

33.0
33.5
33.0
32.5
32.5
34.0
33.8
34.0
34.0
34.2
34.5
34.8
35.0
34.8
33.5
32.0

8.0
7.6
7.2
7.0
7.6
7.8
8.0
8.2
8.2
8.6
10.4
11.6
12.4
13.6
14.0
14.4

70
72
74
76
78
80
84
88
92
96
100
104
108
112
114
115
116

19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0
19.0

25.0
23.0
23.5
25.0
26.0
26.5
25.5
26.0
26.0
27.0
27.5
26.5
26.0
25.5
27.0
28.0
42.0

NOTES:[1] - Band 1 LNA data is a CSIRO 1-3 GHz InP LNA, w/100nm NGST devices (2003). CSIRO now has a newer MMIC; details unknown.
[2] - Band 2 LNA data is a Caltech 1-18 GHz GaAs MMIC LNA (p/n CIT-118), based on OMMIC WBA118B device, T=19K (August 2014)[3] - Band 3 LNA data is a Caltech 1-18 GHz GaAs MMIC LNA (p/n CIT-118), based on OMMIC WBA118B device, T=19K (August 2014).
A version with a waveguide input, or an NRAO or Low Noise Factory (LNF) amp would likely perform better, by ~0.5 - 2K.
[4] - Band 4 LNA is a combination of data from Low Noise Factory LNF-LNC16_28WB (20-26 GHz) and LNF-LNC23_42WB (27-35 GHz),
assuming a custom WR-34 housing. A custom MMIC from LNF will be required for Band 4, but N. Wadefalk wrote (8/14/18) that
there would be no added NRE or price change, as it's a simple design change, and the WR-34 launcher exists.
[5] - Band 5 LNA data is a Low Noise Factory LNF-LNC28_52WB, 28-52 GHz, in a WR-22 housing.
[6] - Band 6 LNA data is of a 35nm MMIC LNA based on 35nm NGIC devices, from David Quadrado-Calle, U. of Manchester.
[7] - Numbers highlighted in yellow are either undetermined or rough estimates.

Table 7 - LNA gain and noise temperature vs. Frequency, Bands 1–6.

Page 34 of 34

Title: Cryogenic Subsystem
Requirements

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NRAO Doc. #: 020.30.10.00.00-0001-REQ-ACRYOGENIC_SUBSYSTEM_REQS

Date: 2019-07-24
Version: A

Cryogenic Subsystem Requirements
020.30.10.00.00-0001-REQ-A-CRYOGENIC_SUBSYSTEM_REQS

Status: RELEASEDPREPARED BY
D. Urbain
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-10-24
2019-04-18

APPROVALS (Name and Signature)
R. Selina,
2019.07.24
Project Engineer
10:25:47 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-24

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 12:49:16 -06'00'

Asst. Director for
NM-Operations, NRAO

2019-07-24

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 12:49:35 -06'00'

ORGANIZATION
Asst. Director for
NM-Operations, NRAO

DATE
2019-07-24

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Title: Cryogenic Subsystem
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Change Record
Version1

Date
2018-07-27

AuthorD. Urbain

Affected
Section(s)All2

2018-09-13

D. Urbain

All

Revised draft

3

2018-09-27

S. DurandAll

Small edits42018-10-19

D. UrbainAll

Answered RIDs

A

2019-07-24

A. Lear

All

Incorporated edits by M. McKinnon; prepareddocument for approvals and release

ReasonInitial draft

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Title: Cryogenic Subsystem
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Date: 2019-07-24
Version: A

Table of Contents
1

Introduction ................................................................................................... 5

1.1
1.2
1.3

Purpose ................................................................................................................................... 5
Scope ...................................................................................................................................... 5
Assumptions Made Regarding the ngVLA Cryogenics .......................................................... 5

2

Related Documents and Drawings ............................................................... 6

2.1
2.2

Applicable Documents ........................................................................................................... 6
Reference Documents ............................................................................................................ 63
4
5

Overview of Subsystem Requirements ....................................................... 6
Functional Requirements .............................................................................. 7
Operational Performance Requirements.................................................... 7

5.1
5.2
5.3

Vacuum Pump Requirement .................................................................................................. 7
Cryocooler Requirements ...................................................................................................... 7
Helium Compressor Requirements ....................................................................................... 8

6

Mechanical Interfaces .................................................................................... 9

6.1
6.2
6.2.1
6.2.2
6.3
6.3.1
6.3.2
6.3.3

Receiver/Front End Mechanical Interface ............................................................................ 9
Antenna Mechanical Interface.............................................................................................. 9
Available Space on the Antenna Platform ............................................................................................ 9
Mechanical Interface with the Antenna Platform ............................................................................... 9
Elevation Wrap and Helium Lines ........................................................................................ 9
Flexible Helium Lines ................................................................................................................................ 9
Rigid Helium Lines ................................................................................................................................... 10
Helium Line Fittings................................................................................................................................. 107
8Electrical Interface ...................................................................................... 12
Environmental Conditions and Corresponding Operating Modes ......... 12

8.1
8.2
8.3
8.4
8.5
8.5.1
8.5.2
8.6
8.6.1
8.7
8.7.1
8.7.2
8.8

Site Elevation ....................................................................................................................... 12
Limits of Operating Conditions ........................................................................................... 12
Survival Conditions .............................................................................................................. 12
M&C Interfaces .................................................................................................................... 13
Monitoring Interfaces (Multicast on Ethernet Bus) ........................................................... 13
Interface with Front End M&C ............................................................................................................. 13
Interface with Nearest Weather Station ........................................................................................... 13
Command Interface (Star Configuration Ethernet Bus) ................................................... 13
Interface with Antenna Master M&C Module ................................................................................... 13
Serial RS232/485 Communications ..................................................................................... 13
Interface with the Vacuum Pump Controller ................................................................................... 13
Interface with the Helium Compressor ............................................................................................. 13
SPI Communication with the Power Electronics................................................................ 149

EMC/RFI Requirements .............................................................................. 15

9.1
9.2

Shielding of Compressor Outdoor Unit .............................................................................. 15
Shielding of Cryo M&C Enclosure....................................................................................... 15

10

Maintenance ................................................................................................. 16

10.1
10.2
10.3

Scheduled Maintenance ...................................................................................................... 16
Onsite Maintenance ............................................................................................................ 16
Maintenance at the Service Center(s) ................................................................................ 16

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11

Shipping/Transport and Acceptance Test ................................................. 16

11.1
11.2
11.3

Shipping from Manufacturer to Integration Center .......................................................... 16
Transport between Integration Center and Antenna ........................................................ 16
Acceptance Test ................................................................................................................... 16

12

Appendix....................................................................................................... 17

12.1
12.2

Enclosure .............................................................................................................................. 17
Abbreviations and Acronyms ............................................................................................... 18

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Title: Cryogenic Subsystem
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NRAO Doc. #: 020.30.10.00.00-0001-REQ-ACRYOGENIC_SUBSYSTEM_REQS

Date: 2019-07-24
Version: A

1 Introduction
1.1 Purpose
This document aims to present a set of technical specifications for the ngVLA cryogenic subsystem.
Requirements defined in this document are drawn from the ngVLA preliminary system requirements
document [AD01], the ngVLA environment specification document [AD02] and the ngVLA EMC/RFI
specification document [AD03].

1.2 Scope
The scope of this document includes requirements for the cryogenic subsystem, as delivered for ngVLA
integration. The following requirements will be discussed in this document:
x Operational performance requirementso Vacuum pumpo Refrigerator
o Compressor
x Mechanical interfaceso With receivero With antennax Electrical interfaces
x Environmental conditionso Site elevationo Normal operating conditionso Survival mode conditions
x Operating modes
o Start-up
o Cool downo Regular/observing modeo Warm-up
o Recovery from survival modeo Stand-by modeo By-pass mode
x M&C interfaceso Multicast on Ethernet Buso Command on Ethernet Buso Serial interfaceso SPI communications
x EMC/RFI requirements
x Maintenance requirements
x Transport requirements

1.3 Assumptions Made Regarding the ngVLA Cryogenics
The ngVLA cryogenics subsystem is directly related to the ngVLA Front End. The [AD05] document
decribes the reference design for the ngVLA Front End; based on this document, the cryogenics subsystem
assumes two Dewars, each equipped with a two-stage Gifford McMahon (GM) refrigerator and a single
helium compressor per antenna.

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Version: A

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein, but provide necessary context or
supporting material.
Reference
No.
AD01
AD02
AD03
AD04
AD05
AD06
AD07

Document Title

Rev/Doc. No.

ngVLA Preliminary System Requirements
System Level Environmental Specifications
EMC-RFI Specifications
ngVLA Monitor and Control Interface Layer:
Preliminary Requirements & Design Description
ngVLA Front End Design Description
ngVLA Cryogenic Subsystem Reference Design
Description
Rick Perley, “Notes on RFI Emissions Levels,”
12/21/2006

020.10.15.10.00-0003-REQ
020.10.15.10.00-0001-SPE
020.10.15.10.00-0002-REQ
020.50.25.00.00.0002-DSN
020.30.03.01.00-0003-DSN
020.30.10.00.00-0002-DSN
VLA-VLBA Interference Memo #34

2.2 Reference Documents
The following documents are referenced within this text:
Reference
No.
RD01
RD02

Document Title

Rev/Doc. No.

R. Rayet et. al., “ngVLA Front-End Receivers
Thermal Study Initial Analysis Report,” Callisto
France S.A.S., 7/11/2018
Measured performance data memo, FA-40 helium
compressor with VFD, Sumitomo SHI, July 2018020.30.10.00.00-0004-REP
020.30.10.00.00-0005-REP

3 Overview of Subsystem Requirements
This document presents the ngVLA cryogenic subsystem technical specifications. The cryogenics
performance requirements are driven by the Front End concept described in [AD05] and by maintenanceand power requirements established for the project. It has been emphasized that for the ngVLA project
to be successful, the annual operation cost shall not exceed the current VLA and VLBA budgets by morethan a factor of three. This is quite challenging considering that ngVLA aims for about 10 times the numberof antennas.
To meet the operations budget goal, the number of receivers per antenna has been reduced to two,compared to eight on the VLA, and the cryocoolers and the compressor have been equipped with variablefrequency drives (VFDs) for adjustable cooling capacity. Having the capability to adjust the cooling power
allows the supply of pressurized helium to be matched to the demand, while minimizing power
consumption.

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Version: A

4 Functional Requirements
The purpose of the cryogenic subsystem is to cool the sensitive receiver electronics to reduce intrinsic
thermal noise and maximize sensitivity. The key functions include
x Establish Dewar vacuum.
x Cooling of feeds and receiver gain stages.
x Maintain Dewar vacuum through cryo-pumping.
x Adjust cooling capacity to meet the temperature requirements while minimizing the power
consumption.

5 Operational Performance Requirements
5.1 Vacuum Pump Requirement
The vacuum pump removes air trapped inside the closed volume of the Front End cryostat. When theatmosphere is evacuated, heat transfer by convection between the outside walls and the insidecomponents of the Dewar becomes negligible. In practice, a minimum vacuum is required before starting
the refrigerator. If this threshold is not reached, the thermal loading is high enough to overcome its coolingpower, preventing the electronics from reaching the desired temperature. It has been established that a
Dewar pressure of 10-2 mbar is needed at the start for a successful cool down. Therefore, the vacuum
pump selected must have a base pressure lower than this 10-2 mbar threshold (Table 1).
The ngVLA Front End concept has two cryostats, each with an approximate volume of 60–70 liters. It is
desired to pump down both receivers in less than 15 minutes. The actual pump down time is difficult toestimate because it depends on many factors (pumping orifice size, presence of multi-layer insulation(MLI), cleanliness of the surfaces, etc.). Nevertheless, a quick calculation shows that an empty volume of
130 liters will require a 2 l/s pumping speed to reach 10-2 mbar in approximately 14 minutes. The
minimum pumping speed is therefore specified at 2 l/s, but a larger capacity is recommended.
Vacuum pump minimum base pressure
Minimum pumping speed

10-2 mbar
2 l/s

Table 1 - Minimum requirements for the vacuum pump.

5.2 Cryocooler Requirements
The Front End design description [AD05] presents the ngVLA receiver concept. A new type of feed-horn
selected for Bands 3–6 has allowed all six frequency bands to be fitted in two cryostats. A thermal analysis
done by Callisto [RD01] (Table 2) gives us preliminary numbers for heat loads on both cryostats.
Cold-Head
1st stage
2nd stage

Dewar A (Band 1)
9.88 W at 50 K
3.08 W at 15 K

Dewar B (Bands 2–6)
18.4 W at 50 K
4.3 W at 15 K

Table 2 - Calculated thermal loads for the ngVLA cryostats (ambient temperature 20°C and vacuum pressure
10-6 mbar).

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These calculated values are preliminary and some load reductions are possible by receiver design
optimization. The sensitive electronics need not be cooled down to 15 K to give the desired sensitivity;
20 K is the temperature limit that needs to be achieved by the second stage of the cryocooler.
Based on this information, the following cooling capacities for the refrigerator have been selected (Table3):
x 1st stage: The cold-head shall have enough cooling capacity on the first stage when running at
maximum speed to absorb 20W of heat and maintain the stage temperature at 80 K or below.
x 2nd stage: The cold-head shall have enough capacity on the second stage when running at maximum
speed to absorb 5W of heat and maintain the stage temperature at 20 K or below.
Cold-head
1st stage
2nd stage

Cooling capacity
20 W
5W

Temperature
80 K
20 K

Speed
60 Hz
60 Hz

Table 3 - Cold-head specifications.

5.3 Helium Compressor Requirements
The helium compressor shall have enough flow capacity to run two medium-size refrigerators at nominal
speed, each with a flow requirement that does not exceed 20 scfm for a supply pressure of 300psi. Because
the energy cost is a major concern for ngVLA, the power consumption of the helium compressor shallnot exceed 5 kW when operating at 60 Hz.
Table 4 lists the compressor performance requirements.
Electrical supply
Power consumption
Ambient temperature
Flow at 60 Hz and 300 psi supply pressure
Weight
Maintenance3 phase 200V 60 Hz
Max 5kW at 60 Hz–30°C to 45°C
40 scfm min< 150 kg
30,000 hours

Table 4 - Helium compressor specifications.

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6 Mechanical Interfaces
The various mechanical interfaces described below will be documented in greater detail in future ICDs.

6.1 Receiver/Front End Mechanical Interface
Each Front End assembly is equipped with one cold-head that can be removed for service. However, thecylinder housing the cold-head displacer shall be permanently attached to the cryostat because it has many
hardware connections to the rest of the Dewar assembly.

6.2 Antenna Mechanical Interface
6.2.1

Available Space on the Antenna Platform

The antenna platform shall provide a volume of L(1.8m) x W(1.75m) x H(1.2m) for the compressor.

6.2.2

Mechanical Interface with the Antenna Platform

The helium compressor will be installed on an antenna platform above the azimuth bearing but below theelevation axis. The platform shall support the weight of the compressor and service personnel with therequired safety factor (TBD). The mounting brackets that attach the compressor to the platform shallsupport the mechanical stresses induced by antenna rotation at full speed, followed by maximum
deceleration, and the force applied by high winds on the compressor outdoor unit. Table 5 lists the mostimportant parameters.
Inclination
Slew
Wind
Magnetic field
Weight (compressor plus 2 people)

Within 5 degrees of horizontal
180 deg/min
Max 50 m/s*DXVV
350 kgTable 5 - Mechanical limits for the compressor mount on the antenna platform.

6.3 Elevation Wrap and Helium Lines
The compressor is located on a platform behind the dish and above the azimuth bearing, and the Front
End cryostats are located on a platform supported by the subreflector feedarm. The helium lines (twolines: one supply, one return) are run from the compressor to the receiver platform, through the elevation
axis cable wrap. On the receiver platform, the supply line connects to a two-way manifold that splits theflow between the two refrigerators. A second two-way manifold recombines the refrigerator output flows
into the return line. The helium lines shall be built with a combination of rigid seamless stainless steel
tubing that is securely attached to the antenna structure and some flexible sections; see details below.
The helium lines are part of the cryogenic subsystem, and their exact location and mounting points shallbe described in a future antenna ICD.

6.3.1

Flexible Helium Lines

The various sections of flexible lines are described below:
x Between compressor and antenna platform, the flex-lines will allow easy connection to thecompressor using Aeroquip 5400 series refrigerant couplings.
x Through the elevation wrap, a set of armored flex-lines will join the rigid sections of lines from thecompressor platform and the sub-reflector feed harm. The armored flexible shell (Figure 1) will help
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minimum bend radius is not exceeded. The life expectancy of the flex-lines shall exceed 20 years ofantenna operation (number of flex cycles is TBD).
o Static bending radius 25 cm (10”)
o Dynamic bending radius 70 cm (28”)
x Between the antenna feedarm and receiver platform, the flex-lines will allow free translation of thereceiver platform for band selection, and easy connection to the refrigerators mounted to thecryostats.

Figure 1 - Armored flex-line cross section view.

6.3.2

Rigid Helium Lines

The rigid helium lines are made of seamless stainless steel ½” ID line, thoroughly cleaned inside toremove contaminants (oil and other chemical residues). The specified wall thickness is 0.065”, with aworking pressure of 4500 psig (e.g., Swagelok stainless steel seamless tubing).

6.3.3

Helium Line Fittings

The interconnection between two rigid lines will use Swagelok compression fittings (Figure 2).

Figure 2 - Swagelok fittings for rigid helium line connections.

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The other connections will use Aeroquip 5400 series (or similar) self-sealing gas fittings (Figure 3), which
are standard couplings for cryogenic equipment. The O-ring and gasket material shall be made out of butyl
rubber, to meet the environmental requirement and avoid leaks in extremely cold weather conditions.

Figure 3 - Aeroquip 5400 series couplings.

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Version: A

7 Electrical Interface
Table 6 shows the cryogenics subsystem electrical power requirements from the antenna. These
requirements will be described in more detail in a future antenna ICD.
Description

Voltage

Single phase
3 Phase Delta
configuration, 5 wires
Ph1, Ph2, Ph3 andNeutral plus GND

120 (±5%) VAC
200 (±10%) VAC

Current max
breaker protection
35 A
25 A

Frequency Powerconsumption
60 Hz
1 kW max
60 Hz
5 kW max

Table 6 - Antenna power requirements.

8 Environmental Conditions and Corresponding Operating Modes
8.1 Site Elevation
The ngVLA core array will be located at the Very Large Array site, on the plains of San Agustin (elevation
2100 m). The array will include stations in other locations throughout New Mexico, west Texas, eastern
Arizona, and northern Mexico. The cryogenic subsystem shall be designed to operate at altitudes ranging
from sea level up to 2500 m.

8.2 Limits of Operating Conditions
The cryogenic subsystem shall operate normally within the environmental limits listed in Table 7.
Parameter
Solar Thermal LoadWind
Temperature
Precipitation
Ice

Req. #
ENV0321
ENV0331
ENV0332
ENV0333
ENV0334

Value
Exposed to full Sun:PVaverage over 10 min.; :PVJXVW–20 &7 °C
5 cm/hr over 10 min
No ice accumulation on outdoor compressor unit

Table 7 - Operating conditions.

8.3 Survival Conditions
Outside of the operating condition limits (Table 8) some degradation in performance is acceptable.
Parameter
Wind
Temperature
Radial Ice
Rain Rate
Snow load
Hail stones

Req. #
ENV0341
ENV0342
ENV0343
ENV0344
ENV0346
ENV0347

Value
PV:PVDYHUDJH–&7&2.5 cm
16 cm/hr. over 10 min
100 kg/m2 on horizontal surfaces
2.0 cm diameter

Table 8 - Survival conditions.

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8.4 M&C Interfaces
The compressor M&C Module will be delivered with the Cryo M&C Enclosure. It shall control the helium
compressor and both refrigerators as well as the vacuum pump. It will collect monitoring informationfrom various sub assemblies but will only receive commands from the antenna M&C.

8.5

Monitoring Interfaces (Multicast on Ethernet Bus)

8.5.1

Interface with Front End M&C

The compressor M&C Module will use temperature and pressure information provided by the individual
cryostat M&C Modules to adjust independently the speed of each cold-head. The temperature andpressure data will be multicast by the Cryostat M&C modules on the Ethernet bus.

8.5.2

Interface with Nearest Weather Station

The compressor M&C Module will use monitored information from the nearest ngVLA weather station
to select or modify certain modes of operation. For example, the starting speed during the start-up
procedure will be adjusted based on the ambient temperature. The weather station M&C module will
multicast the data on the Ethernet bus, and the compressor M&C Module will subscribe to the data stream
and collecting the information as needed.

8.6 Command Interface (Star Configuration Ethernet Bus)
8.6.1

Interface with Antenna Master M&C Module

The control messages to the compressor M&C Module will always come from the antenna master M&C
module. Any other module that needs to send a control message to the compressor M&C Module will doso through the antenna master M&C module and reciprocally. The flow of control messages will use the
Ethernet bus in star configuration with the antenna master M&C module as the central hub for the antenna.

8.7 Serial RS232/485 Communications
8.7.1

Interface with the Vacuum Pump Controller

For the reference design, the vacuum pump controller is located inside the cryo M&C enclosure. The
compressor M&C module will communicate with the vacuum pump controller through a serial RS232/485
connection. A hardware interlock will prevent the pump from running if oil temperature is not within the
manufacturer’s recommended range.

8.7.2

Interface with the Helium Compressor

The compressor M&C module is located with the compressor power electronics (VFD) inside a shielded
weather proof enclosure. The temperature and pressure sensors listed in Table 9 are placed in various
locations inside the compressor outdoor unit. The compressor M&C module will communicate with thecompressor outdoor unit and retrieve the information through a serial interface. The compressor
information will be multicast by the compressor M&C module on the Ethernet bus to make it available toother modules.

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Sensor type
Temperature
Ts
Tx
Tr
Tg
Tc
PressurePs
Pr
Frequency/speed
Fc
Current
Is
If

Date: 2019-07-24
Version: A

Location
Scroll capsule
Oil heat exchanger input
Oil return line to Scroll capsule
Heat exchanger output gas
Coalescer input
Supply line
Return line
Cooling fan speed
Scroll capsule current
Fan current

Table 9 - Outdoor compressor monitor points.

8.8 SPI Communication with the Power Electronics
The cryo M&C enclosure will house the compressor M&C module and the power electronics (VFDs) andshelter them from the environment while also providing RFI shielding. The compressor M&C module willcommunicate with the power electronics that drives the compressor capsule and cold-heads via SPI Bus.
Table 10, Table 11, and Table 12 show monitor points for compressor VFD and Dewars A and B.
Sensor type
Frequency/speed
Fcomp
Current
Icomp1
Icomp2
Icomp3
VoltageVcomp1
Vcomp2
Vcomp3

Location
Speed scroll capsuleCompressor Scroll capsule current phase 1
Compressor Scroll capsule current phase 2
Compressor Scroll capsule current phase 3
Compressor Scroll capsule voltage phase 1
Compressor Scroll capsule voltage phase 2
Compressor Scroll capsule voltage phase 3

Table 10 - Compressor VFD monitor points.

Sensor type
Frequency/speed
FDWA
Current
IDWA-1
IDWA-2
Voltage
VDWA-1
VDWA-2

Location
Speed cold-head receiver Dewar A
Dewar A cold-head current phase 1
Dewar A cold-head current phase 2
Dewar A cold-head current voltage phase 1
Dewar A cold-head current voltage phase 2

Table 11 - Dewar A VFD monitor points.

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Sensor type
FDWB
Current
IDWB-1IDWB-2
Voltage
VDWB-1VDWB-2

Date: 2019-07-24
Version: A

Location
Speed cold-head receiver Dewar B
Dewar B cold-head current phase 1
Dewar B cold-head current phase 2
Dewar B cold-head current voltage phase 1
Dewar B cold-head current voltage phase 2

Table 12 - Dewar B VFD monitor points.

9 EMC/RFI Requirements
The digital electronics in the M&C modules and the high power switching electronics in the VFD drives
require shielding from RFI emissions. The following sections describe the measures taken in this regard.

9.1

Shielding of Compressor Outdoor Unit

The compressor outdoor unit has a Scroll capsule that runs at variable speed due to a VFD located in the
Cryo M&C Enclosure. The cable that carries the three-phase power between them will have to be shieldedand have a ground connection at both ends.

9.2

Shielding of Cryo M&C Enclosure

The Cryo M&C Enclosure contains the compressor M&C interface LRU, the VFD LRUSs for the Scroll
capsule, and the two cold-heads, as well as controllers for the cooling fan and vacuum pump. All theelectronics listed above can generate RFI and must be contained within an RFI-tight enclosure(s). The
connections to the M&C enclosure shall be done through special filtered connectors. The whole assemblymust meet the VLA RFI requirements [AD07]. The validation of the shielded enclosure will be done in
the VLA reverberation chamber with a specially designed test set.

Page 15 of 18

Title: Cryogenic Subsystem
Requirements

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0001-REQ-ACRYOGENIC_SUBSYSTEM_REQS

Date: 2019-07-24
Version: A

10 Maintenance10.1 Scheduled Maintenance
Scheduled maintenance will be performed on the cryogenics system when the antenna is being serviced(Table 13). Because of the large number of antennas, it is anticipated that one antenna will have a major
overhaul every 35,000 hours.
Compressor Charcoal trap adsorberCompressor heat exchanger cleaning
Compressor fan motor bearing replacement
Cold-head replacement
System static pressure recharge (He)Compressor oil refill35,000 hrs of operation
35,000 hrs of operation
35,000 hrs of operation
35,000 hrs of operationKUV 7%&KUVRIRSHUDWLRQ

Table 13 - Scheduled maintenance.

10.2 Onsite MaintenanceAll scheduled maintenance (see Table 13) shall be performed at the site when the antenna is being serviced.
Unscheduled repairs shall also be done at the site, unless it is a compressor failure that requires
depressurization of the helium circuit to be fixed.

10.3 Maintenance at the Service Center(s)All compressor repairs that require depressurization of the helium circuit shall be done at the service
center(s). Cold-head overhaul shall also be done at the service center(s).

11 Shipping/Transport and Acceptance Test
11.1 Shipping from Manufacturer to Integration Center
The compressor shall be mounted on a wood pallet with tilt sensors and shock sensors to ensure safedelivery by truck and early detection of possible abuse.

11.2 Transport between Integration Center and Antenna
The compressor shall be transported from the integration center to the antenna in a truck equipped witha crane that will allow the compressor to be lifted up to the antenna platform.

11.3 Acceptance Test
The compressor shall be tested at the factory and delivered with a complete set of test data and acompliance report. The cold-heads shall also be tested at the factory and delivered with the load maps
and the compliance reports.
The M&C enclosure will be tested in the reverberation chamber to ensure compliance with the VLA
requirements. A recently-serviced compressor or cold-head will be tested at the integration center andwill have to pass a series of acceptance tests prior to being released as a spare unit.

Page 16 of 18

Title: Cryogenic Subsystem
Requirements

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0001-REQ-ACRYOGENIC_SUBSYSTEM_REQS

Date: 2019-07-24
Version: A

12 Appendix
12.1 Enclosure
For the reference design we are not considering an outside enclosure for the outdoor compressor unit;
however, the possibility to add such an enclosure to the antenna platform will be evaluated during thedesign phase. Some parameters to consider for the enclosure include:
x Weather protectiono Avoid snow/ice accumulation on compressoro Minimize exposure to rain water (corrosion)o Shield the cooling fan from high winds
o Prevent damage from hailstorms
o Reduce sun damage (UV)x Impact on antenna designo Extra weight on platformo Extra volume on platformo Extra costo Reduced accessibility
o Increased maintenance time (enclosure must be removed to access compressor outdoor unit)

Page 17 of 18

Title: Cryogenic Subsystem
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Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0001-REQ-ACRYOGENIC_SUBSYSTEM_REQS

12.2 Abbreviations and Acronyms
Acronym
AD
ICD
LNA
LRU
M&C
MLI
ngVLA
NRAO
RD
SPI
VFD
VLA

Description
Applicable Document
Interface Control Document
Low Noise Amplifier
Line-Replaceable Unit
Monitor and Control
Multi Layer Insulation
Next Generation VLA
National Radio Astronomy Observatory
Reference Document
Serial Peripheral Interface
Variable Frequency Drive
Jansky Very Large Array

Page 18 of 18

Date: 2019-07-24
Version: ATitle: Cryogenic Subsystem Reference
Design Description

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

Cryogenic Subsystem Reference Design Description
020.30.10.00.00-0002-DSN-A-CRYOGENIC_SUBSYSTEM_REF_DESIGN

Status: RELEASEDPREPARED BY
D. Urbain
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-10-30
2019-04-18

APPROVALS (Name and Signature)
R. Selina,
2019.07.24
Project Engineer
12:12:18 -06'00'
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 12:56:16 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-24

Asst. Director,
NM-Operations, NRAO

2019-07-24

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 12:56:32 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-24

Page 1 of 32

Title: Cryogenic Subsystem Reference
Design Description

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Date: 2019-07-24

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Version: A

Change Record
Version

Date

AuthorAffected
Section(s)0.1

2018-04-17

D. Urbain

All

Initial Draft

0.2

2018-05-15

D. Urbain

All

Revision after Rob Selina review

2.0

2018-06-05

S. Durand

All

3.0

2018-06-07

D. Urbain

7,10,114.0

2018-06-15

D. Urbain

All

5.0

2018-06-22

D. Urbain

10,11,12June Update
Revise mainly section 10 after conversation
with W. Koski
Reorganize document; add vacuum pumprequirements
Revise the communication sections

6.0

2018-07-18

D. Urbain

All

Change vacuum pump description

7.0

2018-07-23

D. UrbainAll

Update document after R. Selina review

8.0

2018-09-13

D. Urbain

All

Revise document

8.1

2018-09-13

S. Durand

All

Revise document

8.2

2018-10-05

D.Urbain

Number8.3

2018-10-23

D. UrbainAll

Answer RIDs

8.4

2018-10-30

D. Urbain

6.2

A

2019-07-24

A. LearAll

Add information on vacuum pump
Incorporate minor edits by M. McKinnon;
prepare document for approvals andreleasePage 2 of 32

ReasonCorrect document number

Title: Cryogenic Subsystem Reference
Design Description

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NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

Table of Contents
1

Introduction ................................................................................................... 5

1.1
1.2
1.3

Purpose ................................................................................................................................... 5
Scope ...................................................................................................................................... 5
Assumptions Made Regarding the ngVLA Cryogenics .......................................................... 5

2

Related Documents and Drawings ............................................................... 6

2.1
2.2
2.3

Applicable Documents ........................................................................................................... 6
Reference Documents ............................................................................................................ 6
Vocabulary .............................................................................................................................. 6

3
4

Overview of Subsystem Requirements ....................................................... 7
Key Experiments that Led to the Reference Design .................................. 7

4.1
4.2
4.3
4.4

The Green Antenna VFD Experiment ................................................................................... 7
The Variable-Speed Compressor Experiment ...................................................................... 7
How Reliability is Linked to Operating Frequency .............................................................. 8
Comparison of VLA and ngVLA Reference Design ............................................................... 85

Monitor and Control Interfaces ................................................................. 10

5.1
5.1.1
5.1.2
5.1.3
5.2
5.2.1
5.3
5.3.1
5.3.2
5.4

Monitoring Interfaces (Multicast on Ethernet bus) ........................................................... 11Interface with Front End M&C ............................................................................................................. 11Interface with the Nearest Weather Station .................................................................................... 11M504 Weather Station Module............................................................................................................ 12
Command Interface (Star Configuration Ethernet Bus) ................................................... 12Interface with Antenna Master M&C Module ................................................................................... 12
Serial RS232/485 Communications ..................................................................................... 12Interface with the Vacuum Pump Controller ................................................................................... 12Interface with the Helium Compressor ............................................................................................. 13
SPI Communication with the Power Electronics................................................................ 13

6

Operational Performance Requirements.................................................. 15

6.1
6.2
6.3
6.4
6.5
6.6
6.7

Vacuum Pump Requirement ................................................................................................ 15
Onboard Vacuum Pump ...................................................................................................... 15
Vacuum Pump Equipment for the Integration Center and Service Vehicle ..................... 16
Cryocooler Requirements .................................................................................................... 16
Cold-Head Selection ............................................................................................................ 17
Helium Compressor Requirements ..................................................................................... 18
Helium Compressor Selection ............................................................................................. 18

7

Mechanical Interfaces .................................................................................. 21

7.1
7.2
7.2.1
7.2.2
7.2.3
7.3
7.3.1
7.3.2
7.3.3

Receiver/Front End Mechanical Interface .......................................................................... 21
Antenna Mechanical Interface............................................................................................ 22
Required Space on the Antenna Platform ......................................................................................... 22
Mechanical Interface with the Antenna Platform ............................................................................. 22
Compressor M&C Enclosure Interface .............................................................................................. 23
Elevation Wrap and Helium Lines ...................................................................................... 23
Flexible Helium Lines .............................................................................................................................. 23
Rigid Helium Lines ................................................................................................................................... 24
Helium Line Fittings................................................................................................................................. 24

8

Electrical Interface ...................................................................................... 25

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Title: Cryogenic Subsystem Reference
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NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

9Environmental Conditions and Corresponding Operating Modes ......... 25

9.1
9.2
9.3
9.3.1
9.3.2
9.3.3

Site Elevation ....................................................................................................................... 25
Limits of Operating Conditions ........................................................................................... 25
Survival Conditions .............................................................................................................. 25
Extreme Heat ........................................................................................................................................... 26
Extreme Cold ........................................................................................................................................... 26
Extreme Wind .......................................................................................................................................... 26

10Modes of Operation ..................................................................................... 27

10.1
10.2
10.3
10.4
10.5
10.6
10.7

Start-Up Mode ..................................................................................................................... 27
Cool-Down Mode................................................................................................................. 27
Observing Mode ................................................................................................................... 27
Warm-Up Mode ................................................................................................................... 27
Recovery Mode .................................................................................................................... 27
Stand-By Mode .................................................................................................................... 27
Bypass Mode ........................................................................................................................ 28

11

EMC/RFI Requirements .............................................................................. 29

11.1
11.2
11.3

Shielding of Compressor Outdoor Unit .............................................................................. 29
Shielding of Cryo M&C Enclosure....................................................................................... 29
Cooling of Cryo M&C Enclosure ......................................................................................... 29

12

Maintenance ................................................................................................. 30

12.1
12.2
12.3

Scheduled Maintenance ...................................................................................................... 30
Onsite Maintenance ............................................................................................................ 30
Maintenance at the Service Center(s) ................................................................................ 30

13

Shipping/Transport and Acceptance Test ................................................. 30

13.1
13.2
13.3

Shipping from Manufacturer to Integration Center .......................................................... 30
Transport between Integration Center and Antenna ........................................................ 30
Acceptance Test ................................................................................................................... 30

14

Appendix....................................................................................................... 31

14.1
14.2

Compressor Enclosure ......................................................................................................... 31
Abbrevations and Acronyms ................................................................................................ 32

Page 4 of 32

Title: Cryogenic Subsystem Reference
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NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

1 Introduction
1.1 Purpose
This document provides a description for the cryogenic subsystem reference design. The purpose of thecryogenic subsystem is to cool the sensitive receiver electronics to reduce intrinsic thermal noise andmaximize sensitivity. During the selection process emphasis was placed on power consumption andreliability as well as maintenance cost in order to meet the operating budget target.

1.2 Scope
The scope of this document is to present the complete cryogenic equipment selected for the ngVLA
Reference Design. It starts with a hardware description of the pump, the refrigerator, and the compressor
and it follows with the antenna interfaces requirements. The environmental conditons and the various
mode of operation are also presented. The M&C interface with the rest of the control electronics is
described in detail, but no budgetary information is listed.

1.3 Assumptions Made Regarding the ngVLA Cryogenics
The ngVLA cryogenics is directly related to the ngVLA Frontends. [AD05] describes the reference designfor the ngVLA Front End. Based on this information, the cryogenics subsystem assumes two Dewars perantenna, each equipped with a two-stage Gifford McMahon (GM) refrigerator, with both connected to asingle Helium compressor.

Page 5 of 32

Title: Cryogenic Subsystem Reference
Design Description

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Date: 2019-07-24

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Version: A

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein, but provide necessary context or
supporting material:
Ref. No.
AD01
AD02
AD03
AD04
AD05
AD06
AD07

Document Title
Preliminary System Requirements
System Level Environmental Specifications
EMC-RFI Specifications
Monitor and Control Interface Layer: Preliminary
Requirements & Design Description
Front End Design Description
Cryogenics Subsystem Requirements
R. Perley, “Notes on RFI Emissions Levels”
12/21/2006

Rev/Doc. No.
020.10.15.10.00-0003-REQ
020.10.15.10.00-0001-SPE
020.10.15.10.00-0002-REQ
020.30.45.00.00.0004-DSN
020.30.03.01.00-0003-DSN
020.30.10.00.00.0001-REQ
VLA-VLBA Interference Memo #34

2.2 Reference Documents
The following documents are referenced within this text:
Ref. No.
RD01
RD02
RD03
RD04
RD05
RD06
RD07
RD08

Document Title
R. Rayet et. al., “ngVLA Front-End Receivers Thermal
Study Initial Analysis Report,” Callisto France S.A.S.,
7/11/2018
Measured performance data memo, FA-40 Helium
compressor with VFD, Sumitomo SHI, July 2018
Wootten, D. Urbain, W. Grammer and S. Durand, “ThengVLA Cryogenics,” 231th AAS meeting, January 8–12
2018 National Harbor, MD
D. Urbain, “ngVLA Cryogenics Subsystem Concept,” URSI
meeting, January 4–7, 2017, Boulder, CO
D. Urbain, W. Grammer, et al.,“Improved Power Efficiency for Cryogenics at the VLA,”
ICC19 June 20–23 2016, San Diego CA
D. Urbain, W. Grammer, S. Sturgis, “ngVLA Cryogenics
Reference Design,” ngVLA Reference Design Workshop,
Socorro NM, July 2018; private communication
James Gregg, “MTBF Report on EVLA Cryogenics,”
NRAO, Socorro NM, 3/29/2016, Private Communication
Adixen_SD Pump Service Manual

Rev / Doc. No.
020.30.10.00.00-0004-REP
020.30.10.00.00-0005-REP
Poster sessionn/aCryocoolers 19, Edited by
S.D. Miller and R.G. Ross Jr,
pp. 505–511
n/an/aAlcatel Vacuum Technology
pp. 54-98, 2011

2.3 Vocabulary
In the following document, refrigerator, cold-head, and cryocooler represent the same piece of equipment.
Dewar and cryostat are also interchangeable.

Page 6 of 32

Title: Cryogenic Subsystem Reference
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NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

3 Overview of Subsystem Requirements
This document presents the design discription of the ngVLA cryogenic subsystem. The performancerequirements for the cryogenics are driven by the Front End concept and by maintenance and power
requirements established for the project. It has been emphasized that for the ngVLA project to be
successful, the annual operation cost shall not exceed the current VLA and VLBA budget by more than afactor of three. This is quite challenging considering that the project is aiming for about ten times thenumber of antennas.
In order to meet the operations budget goal, the number of receivers per antenna has been reduced totwo, compared to eight on the VLA, and the cryocoolers and the compressor have been equipped withvariable frequency drives (VFDs) for adjustable cooling capacity. Having the capability to adjust the coolingpower allows the supply of pressurized Helium to be matched to the demand, while minimizing power
consumption.

4 Key Experiments that Led to the Reference Design
4.1 The Green Antenna VFD Experiment
The Green Antenna initiative was initiated by the NRAO Socorro Electronics Division in 2015, with a goalof finding ways to reduce the power consumption and improve reliability of the VLA. The VFD experimentdescribed in [RD05] demonstrated the speed of the refrigerators used to cool the Front Ends could be
reduced, with limited impact on the temperature of the cooled electronics. Table 1 shows the temperature
variations for six VLA Dewars as the refrigerator speed is reduced to 30 Hz in 5 Hz steps. This experiment
was essential in showing that most of the VLA receivers do not require the full cooling capacity of theirrefrigerator after cooldown. In addition, a variable-speed refrigerator could reduce the total helium flow
required from the associated compressor.
Frequency
50 Hz
45 Hz
40 Hz
35 Hz
30 Hz

C BandD1st D2ndin K in K
0.0
0.1
1.3
0.2
2.6
0.3
5.2
1.2
7.8
1.3

X BandD1st D2ndin K in K
0.0
0.2
1.3
0.6
2.6
0.8
5.1
2.0
9.0
2.5

Ku Band
D1st D2ndin K in K
0.0
0.6
1.3
0.8
1.3
1.2
2.6
3.1
3.9
5.6

K BandKa BandQ BandD1st D2nd D1st D2nd D1st D2ndin K in K in K in K in K in K
1.2
0.1
1.3
0.1
2.6
0.4
2.5
0.2
3.9
0.6
7.7
0.7
3.8
0.4
5.2
1.2 12.8 1.8
5.1
0.6
3.9
4.4
17.9
2.6
9.0
1.1
7.8
6.0
33.0
7.7

Table 1 - Results of the VFD experiment at the VLA.

4.2 The Variable-Speed Compressor ExperimentThis experiment used a Quantum Design HAC4500 helium compressor equipped with a commercial
inverter, to show how the speed of the compressor could be adjusted to meet the flow requirement as
the number of refrigerators connected to it increases. Figure 1 [RD03] shows the results of theexperiment. As the number of refrigerators drops, the demand for pressurized helium from thecompressor is reduced and the speed of the motor can be lowered. When the motor slows down, its
power consumption drops, and the operating cost is reduced proportionally.

Page 7 of 32

Title: Cryogenic Subsystem Reference
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Date: 2019-07-24
Version: A

Figure 1 - Variable-speed compressor: capacity and power consumption vs. speed.

4.3 How Reliability is Linked to Operating Frequency
The two experiments described above were key to development of the ngVLA cryogenic reference design,
and address how operations cost can be reduced by lowering power consumption. However, speed
reduction has the added benefit of reducing mechical wear and improving associated reliability. This wasclearly seen in the VLA maintenance data collected over several years [RD07]. The data did show a direct
correlation between the refrigerator MTBF and their operating speed: a Model 22 refrigerator operates
at 200 rpm, while a Model 350 runs at 72 rpm, and the maintenance interval for the Model 350 is on
average three times longer than the Model 22.

4.4 Comparison of VLA and ngVLA Reference Design
Table 2 shows a direct comparision between the VLA and the ngVLA reference design. The data comefrom a VLA maintenance survey and from power measurements conducted on a prototype compressor
and published in [RD02]. The maintenance index is a normalized reliability measure, based on VLA
maintenance data, and scaling with total number of refrigerators. For instance, a single Model 350
refrigerator in the VLA run at full speed (60 Hz) has an index of 1, while a single Model 22 has an index
of 3. The ngVLA reference design calls for running Model 350 refrigerators at 40 Hz, or 2/3 their nominal
speed, so their associated index is 0.66. These indices are used to then estimate total maintenance effort
based on number of refrigerators and their respective operating speeds, in both the VLA and ngVLA.

Page 8 of 32

Title: Cryogenic Subsystem Reference
Design Description

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: AVLA

ngVLA Reference Design

Ratio (ngVLA
to VLA)
9.74

Number of Antennas

27 x 25m

Helium Compressor

3 x 27 = 81

214 x 18m + 19 x 6m + 30
18m
1 x 263 = 263

AC Power
Consumption
Cryocoolers Per
Antenna
Total Number of
Cryocoolers
Estimated Cryocooler
Maintenance Index

81 x 6 = 486kW

263 x 3.75 = 986kW

2.03

1 x Model 22, 6 x Model
350, 1 x Model 1050
27 x 8 = 216

2 x Model 350

n/a

263 x 2 = 526

2.43

27 x (1 x 3 +6 x 1+1 x 1)
= 270

263 x (2 x 0.66) = 350

1.3

3.25

Table 2 - Comparison of VLA and ngVLA reference design.

The table shows that while the ngVLA has almost 10 times the number of antennas, the estimated energy
cost from the cryogenic equipment should only double, and the maintenance required (and associatedcost) is only 1.3 times that of the VLA. These numbers show that the reference design is well within theoperating cost that was set initially for the ngVLA proposal.

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Title: Cryogenic Subsystem Reference
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Version: A

5 Monitor and Control Interfaces
The cryogenic subsystem (Figure 2) is composed of the cryo M&C enclosure (compressor M&C [F525],
compressor VFD, Dewar A VFD, Dewar B VFD and vacuum pump controller), the vacuum pump, thecompressor outdoor unit, and the Dewar A and B cold-heads. The cryo M&C enclosure shall control thehelium compressor and the vacuum pump, and drive both refrigerators. It will collect monitoring
information from the weather station and the Front End M&C modules (F521 and F522), but will only
accept commands from the antenna M&C module (M500).

MobileFeedharm
Platform

Coldh
dB
head

F522

F521

Weather
StationDewar A

Dewar B

Cold
Coldh
head
A

M504

Data Multicast

Antenna Ethernet Bus

StaticFeedharm
Platform

Vacuumpump

VFD
Cold-headA

Antenna Platform

M500
VacuumPump
Controller

AntennaPedestal

Cryo M&C Shielded Enclosure Located On The Antenna Platform

VFD
Cold-head
B

Command LineSPIPower Connection

VFD

F525

HeliumCompressor

RS232/485

Figure 2 - Cryogenics Monitor and Control subsystem block diagram.

Page 10 of 32

HeliumCompressorTitle: Cryogenic Subsystem Reference
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Date: 2019-07-24
Version: A

5.1 Monitoring Interfaces (Multicast on Ethernet bus)
5.1.1

Interface with Front End M&C

The compressor M&C (module F525) will use temperature and pressure information provided byindividual cryostat M&C modules (F521, F522) to adjust independently the speed of each cold-head.
Temperature and pressure data will be multicast by the F521 and F522 modules on the Ethernet bus andthe F525 will collect the information stream directly.
5.1.1.1

F521 Dewar A Interface Module

The following values shall be monitored by the F521.
Dewar A
Band 1
Tb1-1 Temperature 1st stage
Tb1-2 Temperature 2nd stage
Vd1 Vacuum pressure
Vp1 Vacuum pressure

Location
Feed
LNA
Dewar A base plate
Vaccuum manifold

Table 3 - F521 Dewar A monitor points.

5.1.1.2

F522 Dewar B Interface Module

The following values shall be monitored by the F522.
Dewar B
LocationBand 2
Tb2-1 Temperature 1st stage
Radiation shield
Tb2-2 Temperature 2nd stage
LNA band 2Band 3Tb3-2 Temperature 2nd stage
LNA band 3
Band 4Tb4-2 Temperature 2nd stage
LNA band 4
Band 5
Tb5-2 Temperature 2nd stage
LNA band 5
Band 6Tb6-2 Temperature 2nd stage
LNA band 6
Vd2 Vacuum Pressure
Dewar B base plate
Vp2 Vacuum pressure
Vacuum manifold
Table 4 - F522 Dewar B monitor points.

5.1.2

Interface with the Nearest Weather Station

The compressor M&C will use monitored information from the nearest ngVLA weather station to selector modify certain modes of operation. For example, the starting speed during the start-up procedure will
be adjusted based on the ambient temperature. The selected weather station M&C module (M504-xx,
Table 5) will multicast the data on the Ethernet bus, and the F525 module will subscribe to the data stream
and collect the information as needed.

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5.1.3

Date: 2019-07-24
Version: A

M504 Weather Station Module

Environmental conditions
Tamb Outside temperature
Wspd Wind Speed

Weather station
Weather station

Table 5 - M504 weather station monitor points.

5.2

Command Interface (Star Configuration Ethernet Bus)

5.2.1

Interface with Antenna Master M&C Module

The control messages to the compressor M&C will always come from the antenna master M&C module(M500). Any other module that needs to send a control message to the F525 will have to send it throughthe M500 and reciprocally. The flow of control messages (Table 6) will use the Ethernet bus in a starconfiguration with M500 as the central hub for the antenna.
Heat Dewar A
Heat Dewar B
Start Pump
Pump Dewar A
Pump Dewar B
Start Compressor
Cool Dewar A
Cool Dewar B
Stop Pump
Stop Compressor
Standby Dewar A
Standby Dewar B
Close Solenoid Dewar A
Close Solenoid Dewar B

Turn on the heater inside Dewar A
Turn on the heater inside Dewar B
Start the vacuum pumpOpen Dewar A solenoid vacuum valve
Open Dewar B solenoid vacuum valve
Start Helium compressor
Start cold-head Dewar A
Start cold-head Dewar B
Stop vacuum pump
Stop Helium compressor
Put the Dewar A in stanbby mode
Put the Dewar B in standby mode
Close Dewar A solenoid vacuum valve
Close Dewar B solenoid vacuum valve

Table 6 - List of cryogenic commands from antenna master M&C module.

5.3 Serial RS232/485 Communications
5.3.1

Interface with the Vacuum Pump Controller

For the reference design, the vacuum pump controller (Table 7) is located inside the cryo M&C enclosure.
The compressor M&C module will communicate with the vacuum pump controller through a serial
RS232/485 connection. A hardware interlock will prevent the pump from running if the oil temperature
is not within the manufacturer’s recommended range (Table 8).
Tpump Temperature of vacuum pump
Pvl Pressure vacuum line

Physical temperature of the pump. Must be within range tostart the pump.
Pressure between the pump and the receiver vacuum
manifolds.

Table 7 - Vacuum pump monitor points.

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Start pump
Stop pumpDate: 2019-07-24
Version: A

Turn on heater backing pump to bring its temperature within operating range
Turn on the pumps
Turn off the pumps

Table 8 - Vacuum pump list of commands.

5.3.2

Interface with the Helium Compressor

The compressor M&C module (F525) is located with the compressor power electronics (VFD) inside ashielded weather proof enclosure. The temperature and pressure sensors listed in Table 9 are placed invarious locations inside the compressor outdoor unit. The F525 module will communicate with thecompressor outdoor unit and retrieve the information through a serial interface. The compressor
information will be multicast by the compressor M&C module on the Ethernet bus to make it available toother modules.
Sensor type
Temperature
Ts
Tx
Tr
Tg
Tc
PressurePs
Pr
Frequency/speed
Fc
Current
Is
If

Location
Scroll capsule
Oil heat exchanger input
Oil return line to Scroll capsule
Heat exchanger output gas
Coalescer input
Supply line
Return line
Cooling fan speed
Scroll capsule current
Fan current

Table 9 - F525 compressor M&C module monitor points.

5.4 SPI Communication with the Power Electronics
The cryo M&C enclosure will house the compressor M&C module (Table 10) and power electronics VFDs
(Table 11, Table 12), and will shelter them from the environment while providing RFI shielding. The
compressor M&C module will communicate with the power electronics that drive the compressor capsuleand the two cold-heads via SPI Bus (Table 13, Table 14, Table 15).
Frequency/speed
Fcomp
Current
Icomp1
Icomp2
Icomp3
VoltageVcomp1
Vcomp2
Vcomp3

Speed scroll capsuleCompressor scroll capsule current phase 1
Compressor scroll capsule current phase 2
Compressor scroll capsule current phase 3
Compressor scroll capsule voltage phase 1
Compressor scroll capsule voltage phase 2
Compressor scroll capsule voltage phase 3

Table 10 - Compressor VFD monitor points.

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Frequency/speed
FDWA
Current
IDWA-1
IDWA-2
Voltage
VDWA-1
VDWA-2

Speed cold-head receiver Dewar A
Dewar A cold-head current phase 1
Dewar A cold-head current phase 2
Dewar A cold-head voltage phase 1
Dewar A cold-head voltage phase 2

Table 11 - Dewar A VFD monitor points.

Frequency/speed
FDWB
Current
IDWB-1IDWB-2
Voltage
VDWB-1VDWB-2

Speed cold-head receiver Dewar B
Dewar B cold-head current phase 1
Dewar B cold-head current phase 2
Dewar B cold-head voltage phase 1
Dewar B cold-head voltage phase 2

Table 12 - Dewar B VFD monitor points.

Start Scroll
Scroll Speed
Stop Scroll

Start Scroll capsule
Set speed of the Scroll capsule
Stop Scroll capsule

Table 13 - List of SPI commands with compressor VFD.

Start DWA
DWA speed
Stop DWA

Start Dewar A cold-head
Set speed of Dewar A cold-head
Stop Dewar A cold-head

Table 14 - List of SPI commands with Dewar A VFD.

Start DWB
DWB speed
Stop DWB

Start Dewar B cold-head
Set speed of Dewar B cold-head
Stop Dewar B cold-head

Table 15 - List of SPI commands with Dewar B VFD.

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Date: 2019-07-24
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NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

6 Operational Performance Requirements
6.1 Vacuum Pump Requirement
The purpose of the vacuum pump is to remove the air trapped inside the closed volume of the Front End
cryostat. When the atmosphere is evacuated, heat transfer by convection between the outside walls andthe inside components of the Dewar becomes negligible. In practice, there is a minimum vacuum required
before the refrigerator can be started. If this threshold is not reached, the thermal loading is high enoughto overcome its cooling power, preventing the electronics from reaching the desired temperatures. It has
been established that a dewar pressure of 10-2 mbar is needed at the start for a successful cool down.
Therefore, the vacuum pump selected must have a base pressure lower than this 10-2 mbar threshold.
The Front End concept for ngVLA has two cryostats, each with an approximate volume of 60–70 liters. It
is desired to pump down both receivers in less than 15 minutes. The actual pump down time is difficult
to estimate, because it depends on many factors (pumping orifice size, presence of multi-layer insulation(MLI), cleanliness of the surfaces, etc.). Nevertheless, a quick calculation shows that an empty volume of
130 liters will require a 2 l/s pumping speed to reach 10-2 mbar in approximately 14 minutes (Table 16).
The minimum pumping speed is therefore specified at 2 l/s, but a larger capacity is recommended.
Vacuum pump minimum base pressure
Minimum pumping speed

10-2 mbar
2 l/s

Table 16 - Minimum requirements for the vacuum pump.

6.2 Onboard Vacuum Pump
The antenna will be equipped with a vacuum pump powerful enough to evacuate the Front End cryostats
below the 10-2 mbar pressure limit required to start the cryocoolers. A combination of a roughing pumpand turbo pump was initially considered, but the overall cost was too high and not justified on the antenna.
A simpler dual-stage rotary vane pump will provide the vacuum required to start the refrigerator, and will
cost less than half as much.
It is important to note that an oil pump will introduce some restriction on the antenna movement while
in operation, because oil could spill out of the vent port if tilted to certain orientations. A solenoid valvethat can be remotely operated will provide the vacuum seal between the pump and the cryostat. The valve
will be computer controlled to open during cool down but to close as soon as the Dewar pressure goes
below 2.0 x 10-3 mbar, at which point the cryo pumping by the refrigerator becomes more efficient thana mechanical pump. This is very important to avoid back streaming and contamination of the vacuum spacewith oil. A second solenoid valve is placed at the exhaust port to backfill the pump and vacuum line when
the pump is turned off, to prevent the vacuum from sucking oil through the inlet port and into the line.
The vacuum pumps commercially available are designed to operate in a controlled environment and havea limited temperature range for operation. For example, the viscosity of the oil will change with theambient temperature, affecting the performance of the pump or possibly causing premature failure if thepump is run outside its recommended operating range. The pump and control electronics should also beprotected from rain or any excess moisture, and if the temperature of the enclosure is not controlled, aheating blanket should be used to warm up the oil in the pump before a cold start-up.
For the reference design, the Alcatel rotary vane vacuum pump model Adixen 2015SD was selected. The
basic specifications are listed in the Table 17. The pump will be equipped with the oil level switch (OLS36)
and the oil mist eliminator (OME 25HP) combined with the oil drain kit (ODK 2). The first option will

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Date: 2019-07-24
Version: A

monitor the oil level, while the second kit will help with the recovery of the oil that accumulates in themist eliminator when the pump operates at high pressure [RD08].
VoltageStartup current at 12°C
Current at maximum flow
Power
Rotation speed
Pumping speed
Base pressure closed gas ballast
Environment storage
Operating (mineral oil)
Maximum relative humidity

120 VAC @ 60 Hz
35A (recommended fuse protection 20A)
5.7A
3/4 HP, 0.55 kW
1800 rpm @ 60Hz
10.6 cmf / 5 l/s
2.0 x 10–3 mbar
–5°C to +40°C+12°C to +40°C
80% up to 30°C decrease linearly to 50% at 40°C

Table 17 - Alcatel Adixen 2015SD vacuum pump specifications.

6.3 Vacuum Pump Equipment for the Integration Center and Service Vehicle
When a Front End cryostat is assembled for the first time or after being opened for repair, it isrecommended to run the pump for an extended period to remove as many contaminants as possible andallow some of the internal components to outgas. It is therefore recommended to use a turbo pump witha scroll backing pump at the Front End integration center, to achieve a much lower cryostat pressure
before cool down. In addition to a powerful vacuum pump, a heating blanket might be used to accelerate
the outgassing of the Dewar walls, and obtain a better vacuum in a reduced amount of time.
For the integration center, we have selected the Agilent Varian vacuum system with TwistTorr 304FS
turbo and TS 300 dry scroll pump. Table 18 lists the key specifications.
Voltage
Power
Scroll pumping speed
Scroll TS 300 Base pressure
TwisTorr 304FS max frequency
TwisTorr 304Fs pumping speed
TwisTorr 304FS Base pressure
Environment storage
Operating

120 VAC @ 60Hz
450 VA max
8.8 cfm / 4.15 l/s
1.3 x 10-2 mbar
1350 Hz180 l/s
1.0 x 10–10 mbar
–20°C to +70°C / 0–95% humidity+5°C to +4 °C / 0–90% humidity

Table 18 - Agilent TwisTorr 304FS turbo pump system.

6.4 Cryocooler Requirements
The Front End Design Description [AD05] presents the ngVLA receiver concept. A new type of feedhorn selected for Bands 3–6 allows all six frequency bands to fit in two cryostats. A thermal analysis done
by Callisto [RD01] (Table 19) gives us preliminary numbers for the heat loads on both cryostats.
Cold-head
1st stage
2nd stage

Dewar A (Band 1)
9.88 W at 50 K
3.08 W at 15 K

Dewar B (Bands 2–6)
18.4 W at 50 K
4.3 W at 15 K

Table 19 - Calculated thermal loads for the ngVLA cryostats (ambient temperature 20°C and vacuum pressure
10–6 mbar).

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Title: Cryogenic Subsystem Reference
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These calculated values are only preliminary and some load reductions are possible by optimization of thereceiver design. The sensitive electronics do not need to be cooled down to 15 K to give the desired
sensitivity; 20 K is the temperature limit to be achieved by the second stage of the cryocooler. Based on
this information, the following cooling capacities for the refrigerator have been selected (Table 20).
x 1st stage: The cold-head shall have enough cooling capacity on the first stage when running at
maximum speed to absorb 20W of heat and maintain the stage temperature at 80 K or below.
x 2nd stage: The cold-head shall have enough capacity on the second stage when running at maximum
speed to absorb 5W of heat and maintain the stage temperature at 20 K or below.
Cold-head
1st stage
2nd stage

Cooling capacity
20 W
5W

Temperature Speed
80 K
60 Hz
20 K
60 Hz

Table 20 - Cold-head specifications.

6.5 Cold-Head Selection
Several GM refrigerators on the market have the required cooling capacities, but fewer are designed tooperate at variable speed. For the ngVLA reference design, we selected the Trillium 350CS (Figure 3;
Table 21) because it has the right cooling capacities and can run at variable speed. This model has beenused at the VLA for many years and has demonstrated good reliability. It is easy to maintain and could
be repaired in-house at very reasonable cost in parts and labor: estimated at ~$250 and six hours,
respectively [RD07].

Figure 3 - Trillium 350CS refrigerator.

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NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Cold-head
1st stage cooling capacity
2nd stage cooling capacity
Flow
WeightVersion: A

Trillium 350CS
20 W
5W
12.5 scfm
22lbs

Table 21 - Trillium 350CS specifications at 60 Hz.

6.6 Helium Compressor Requirements
The helium compressor shall have enough flow capacity to run two Trillium 350CS refrigerators at nominal
speed. Because energy cost is a major concern for ngVLA, the power consumption of the helium
compressor shall not exceed 5kW when operating at 60 Hz. The Trillium 350CS has an estimated flow of
12.5 scfm when operating at 60 Hz [RD07]. Table 22 lists the performance requirements.
Compressor Speed
60 Hz

Supply pressure
300 psi

Return pressure<100 psi

Flow>30 scfm

Power
<5kW

Table 22 - Helium compressor specifications at 60Hz.

6.7 Helium Compressor Selection
The Scroll capsules that are used in modern helium compressors are manufactured mostly by twocompanies, Hitachi and Copeland, and are only available in a limited range of sizes. Numerous companies
on the market use their Scroll capsules to build helium compressors for the cryogenic market. However,
only a very limited number of these are designed for outdoor application. Because the radio astronomy
market is small in comparison with the medical field (MRI) and the semiconductor industry (sputter
deposition), the development of a custom model designed from the ground up for outdoor use would becost prohibitive, especially given the limited applications for such an item.
For the reference design, the solution was to enter into a collaborative effort with Sumitomo SHI in
Allentown, PA, to suitably modify one of their existing products. Basically, they took their mid-size
compressor model, the FA-40, and added a commercial VFD for variable-speed operation. The flow andpower measurements done at the factory on this hybrid unit have shown it has the right capacity for ourapplication (Figure 4).

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Title: Cryogenic Subsystem Reference
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Date: 2019-07-24
Version: A

Figure 4 - Sumitomo FA-40 helium compressor flow and power measurement versus VFD operating frequency,
20-70 Hz.

The second phase of the collaboration will integrate the FA-40 compressor capsule within the outdoor
enclosure developed for the FA-70 model (Figure 5), to create the first ngVLA helium compressor
prototype (model “FA-40S”).

Figure 5 - Sumitomo FA-70 outdoor enclosure.

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Title: Cryogenic Subsystem Reference
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Table 23 lists the preliminary specifications for the modified FA-40 compressor.
ModelElectrical supply
Power consumption
Flow capacity
Cooling Air
Maintenance Interval
Ambient temperature

FA-40S3-phase 200V at 60 Hz
4.8 kW at 60 Hz
49.2 scfm at 60 Hz *22 m3/min at 60 Hz **35,000 hours-30°C to 45°C **Table 23 - Sumitomo FA-40S specifications. Notes: * data from Copeland catalog, ** data from Sumitomo FA70 compressor specifications.

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Title: Cryogenic Subsystem Reference
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NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

7 Mechanical Interfaces
The various mechanical interfaces described below will be documented in greater detail in future ICDs.

7.1 Receiver/Front End Mechanical Interface
Each Front End assembly is equipped with one cold-head that can be removed for service. However, thecylinder housing the cold-head displacer shall be permanently attached to the cryostat because it has many
hardware connections to the rest of the Dewar assembly. The mechanical interface for the Trillium 350Cs
is described below and shown in Figure 6.

Figure 6 - Cold-head mechanical interface with cryostat.

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Title: Cryogenic Subsystem Reference
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Date: 2019-07-24
Version: A

7.2 Antenna Mechanical Interface
7.2.1

Required Space on the Antenna Platform

The antenna platform shall allow a 30 cm space behind the compressor outdoor unit for air suction, anda 100 cm space in front of the heat exchange for air discharge. An additional 15 cm space on the left sideand 50 cm space on the right side shall be available; see Figure 7.

Figure 7 - Compressor space requirements on the antenna platform.

7.2.2

Mechanical Interface with the Antenna Platform

The helium compressor will be installed on an antenna platform above the azimuth bearing but below theelevation axis. The platform shall support the weight of the compressor and service personnel with therequired safety factor (TBD). The mounting brackets that attach the compressor to the platform shallsupport the mechanical stresses induced by rotation of the antenna at full speed, followed by maximum
deceleration, and the force applied by high winds on the compressor outdoor unit. Table 24 lists the mostimportant parameters.
Inclination
Slew
Wind
Magnetic field
WeightWithin 5 degrees of horizontal
180 deg/min
Max 50 m/s*DXVV kg

Table 24 - Mechanical limits for the compressor mount on the antenna platform.

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7.2.3

Date: 2019-07-24
Version: A

Compressor M&C Enclosure Interface

The compressor M&C enclosure contains the Control and Power electronics for the cryogenics
subsystem. It will be located on the antenna platform and have a cold plate where glycol is circulating forcooling.

7.3 Elevation Wrap and Helium Lines
The compressor is located on a platform behind the dish and above the azimuth bearing, and the Front
End cryostats are located on a platform supported by the subreflector feedarm. The helium lines (twolines: one supply, one return) are run from the compressor to the receiver platform, through the elevation
axis cable wrap. On the receiver platform, the supply line connects to a two-way manifold that splits theflow between the two refrigerators. A second two-way manifold recombines the refrigerator output flows
into the return line. The helium lines shall be built with a combination of rigid seamless stainless steel
tubing that is securely attached to the antenna structure and some flexible sections; see details below.
The helium lines are part of the cryogenic subsystem, and their exact location and mounting points shallbe described in a future antenna ICD.

7.3.1

Flexible Helium Lines

The various sections of flexible line are specified as follows:
x Between compressor and antenna platform, the flex-lines will allow easy connection to thecompressor using Aeroquip 5400 series refrigerant couplings.
x Through the elevation wrap, a set of armored flex-lines will join the rigid sections of lines from thecompressor platform and the sub-reflector feed harm. The armored flexible shell (Figure 8) will help
maintain a uniform bending radius on the line through the elevation wrap, and will guarantee theminimum bend radius is not exceeded. The life expectancy of the flex-lines shall exceed 20 years ofantenna operation (number of flex cycles is TBD).
o Static bending radius 25 cm (10”)
o Dynamic bending radius 70 cm (28”)
x Between the antenna feedarm and receiver platform, the flex-lines will allow free translation of thereceiver platform for band selection, and easy connection to the refrigerators mounted to thecryostats.

Figure 8 - Armored flex-line cross-section view.

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7.3.2

Date: 2019-07-24
Version: A

Rigid Helium Lines

The rigid helium lines are made of seamless stainless steel 0.5” ID line that have been thoroughly cleaned
inside to remove contaminants (oil and other chemical residues). The specified wall thickness is 0.065”
with a working pressure of 4500 psig (Swagelok stainless steel seamless tubing).

7.3.3

Helium Line Fittings

The interconnection between two rigid lines will use Swagelok type compression gas fittings (Figure 9).

Figure 9 - Swagelok fittings for rigid helium lines.

The other connection will use Aeroquip 5400 series self-sealing gas fittings (Figure 10), standard forcryogenic equipment. The O-ring and gasket material shall be made out of butyl rubber to meetenvironmental requirements and avoid leaks in extremely cold weather conditions.

Figure 10 - Aeroquip 5400 series couplings.

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Version: A

8 Electrical Interface
The cryogenics subsystem electrical power requirements from the antenna are shown in Table 25. The
electrical power requirements will be described in more detail in a future antenna ICD.
Description
Single phase

Voltage
120 VAC ±5%

Current max
breaker protection
35 A

3-phase Delta config., 5
wires (Ph1, Ph2, Ph3,
Neutral, GND)

200 VAC ±10%

25 A

Power
Frequency consumption
60 Hz
1 kW max
60 Hz

5 kW max

Table 25 - Cryogenic subsystem power requirements.

9 Environmental Conditions and Corresponding Operating Modes
9.1 Site Elevation
The ngVLA will have a core array located at the Very Large Array site, on the plains of San Agustin(elevation 2100 m). The array will include stations in other locations throughout New Mexico, west Texas,
eastern Arizona and northern Mexico. The cryogenic subsystem shall be designed to operate at altitudes
ranging from sea level up to 2500 m.

9.2 Limits of Operating Conditions
The cryogenic subsystem shall operate normally within the environmental limits listed in Table 26.
Parameter
Solar Thermal LoadWind
Temperature
Precipitation
Ice

Req. #
ENV0321
ENV0331
ENV0332
ENV0333
ENV0334

Value
Exposed to full Sun:PVDYHUDJHRYHUPLQVPVJXVW–&7&5 cm/hr. over 10 mins
No ice accumulation on outdoor compressor unit

Table 26 - Normal operating conditions.

9.3 Survival Conditions
Subsystem survival conditions are detailed in Table 27. Outside of the limits of the operating conditions,some degradation in performance is acceptable. It is difficult to address every possible weather condition,
but we can review a few scenarios and describe how the cryogenic subsystem is expected to respond.
Parameter
Wind
Temperature
Radial Ice
Rain Rate
Snow load
Hail stones

Req. #
ENV0341
ENV0342
ENV0343
ENV0344
ENV0346
ENV0347

Value
PV:PVDYHUDJH–&7&2.5 cm
16 cm/hr. over 10 min
100 kg/m2 on horizontal surfaces
2.0 cm diameter

Table 27 - Survival conditions.

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9.3.1

Date: 2019-07-24
Version: A

Extreme Heat

When the ambient temperature rises above 45°C the compressor might have difficulties maintaining thetemperature of the Scroll capsule within the operating range. The cooling fan in front of the compressor’s
heat exchanger operates at variable speed: as the oil temperature increases with outside temperature, thecompressor control electronics ramps the fan speed up to maximum. If the cooling fan is not capable ofmaintaining the system temperature below the upper limit, the speed of the Scroll capsule shall bedecreased slowly to reduce the heat dissipation. The compressor M&C module will adjust the speed of
the two cold-heads accordingly to maintain the delta pressure (Supply pressure minus Return pressure)and keep both receivers as cold as possible.
In an extreme case, the internal thermal protection will shut down the compressor to protect the Scroll
capsule from overheating. The compressor will re-start automatically when the temperature drops below
a manufacturer preset value. However, the compressor M&C will disable the compressor auto-restart if
the ambient temperature is too high, in order to avoid repetitive ON/OFF cycles.

9.3.2

Extreme Cold

When the ambient temperature drops below –20°C, keeping the Scroll capsule properly lubricated might
be problematic. The compressor M&C shall use information from internal temperature sensors and thenearest weather station to control the cooling fan. The fan cools the Helium and the oil that runs throughthe heat exchanger: when the fan slows down the cooling efficiency of the system drops and thetemperature of the oil and helium gas should rise.
If stopping the fan is not enough to keep the oil temperature within range, the compressor M&C will needto start reducing the speed of the refrigerators. This is because when the cold-heads run slower, lesshelium gas flows through the lines that are exposed to the cold weather and more gas is recirculated
internally, which should raise the internal system temperature. In very extreme conditions, bothrefrigerators may need to be turned off completely, to allow the compressor to run in bypass mode.
As a last resort, the compressor M&C might have to lower the speed of the Scroll capsule and bypass theheat exchanger to keep the Scroll capsule running. As long as the capsule is running and some oil iscirculating, the time to get the system operational again when the weather improves is minimized.

9.3.3

Extreme Wind

In extreme wind conditions, the antenna will be parked and observing suspended. It is unlikely that highwinds could damage the cooling fan, but the compressor M&C monitors the fan current and will power it
off if needed. If the fan is turned off, the compressor will rely on the wind to cool the heat exchanger. The
compressor M&C will then use the wind speed information provided by the weather station and theinternal monitor points to adjust the speed of the capsule and the cold-heads.
Note: It is recommended an outdoor enclosure be placed over the helium compressor for protection
against heavy rain, hail storms and high winds, and to avoid snow and ice accumulation directly on the
structure.

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10 Modes of Operation
10.1 Start-Up Mode
The start-up procedure will depend on the ambient temperature. The compressor M&C will use
environmental data provided by the nearest weather station and internal monitor points to set the Scroll
capsule start-up speed, and will determine if the heat exchanger should be bypassed or not. As the oiltemperature increases, the scroll capsule speeds up and the oil starts flowing through the heat exchanger.
The compressor M&C starts the cooling fan and adjusts its speed as needed. When the compressor isfully operational and ready, the cold-heads can be started.

10.2 Cool-Down Mode
The cool-down mode is also the high power mode. The Cool command is sent by the antenna M&C andthe compressor M&C to start the cold-heads: they are initially run at maximum speed to minimize thecool down time. The compressor capsule speed and fan speed are adjusted to provide the right amountof flow at the right pressure in order to maintain optimum cooling efficiency. This is the phase when the
power consumption is the highest.

10.3 Observing Mode
Observing mode starts when the cryostats are cold and ready for science. The individual Front End M&C
modules relay temperature information to the compressor M&C that controls the speed of the coldheads and the Scroll capsule. The system will constantly adjust the speed of the compressor and therefrigerators to maintain the sensitive electronics at the required temperature, and at the same timeminimize the power consumption.

10.4 Warm-Up Mode
To warm up a cryostat to service its cold-head, or to replace it with a spare unit, it is sufficient to stop
the cold-head drive. If both systems are turned off simultaneously, the compressor can be switched off. In
cold weather, if the system will be down for a limited time, the compressor could be left running in bypass
mode at low speed to keep the oil warm and minimize start-up time.

10.5 Recovery Mode
We consider recovery mode any start-up procedure after the cryogenics subsystem suffers anunscheduled shutdown. This situation is usually due to loss of power to the compressor. The compressor
M&C will analyze its monitor points and collect information about environmental conditions to determine
if it is safe to proceed with the start-up procedure.

10.6 Stand-By Mode
A cryostat may be placed in stand-by mode when it is not scheduled for observations for a period of time(length TBD). The antenna M&C directs the compressor M&C to run the cryostat warmer by slowing
down the refrigerator(s). The second-stage temperature is nevertheless kept below 30 K to maintainactive cryo pumping and prevent vacuum run-away. Stand-by is the lowest power mode, and is notconsidered an observing mode. The cryogenic subsystem shall be able to transition to observing mode inless than 30 minutes (TBC). The stand-by mode could be total, when both cryostats are not used or
partial if only one of the cryostats is not needed.

Page 27 of 32

Title: Cryogenic Subsystem Reference
Design Description

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

10.7 Bypass Mode
Bypass mode is active in extremely cold weather conditions, when the Front End and other antenna
subsystems are non-operational. In this mode, both cold-heads are turned off to keep the compressor oilwarm and minimize start-up time when weather conditions improve. Bypass mode could also be used fortroubleshooting and monitoring the compressor performance. In this mode, the helium is recirculating
inside the compressor through an internal bypass valve.

Page 28 of 32

Title: Cryogenic Subsystem Reference
Design Description

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

11 EMC/RFI Requirements
The digital electronics in the M&C modules and high-power switching electronics in the VFD drives create
RFI emissions and are a concern and RFI shielding is necessary. The following measures will be taken inthis regard.

11.1 Shielding of Compressor Outdoor Unit
The compressor outdoor unit has a Scroll capsule that runs at variable speed due to a VFD located in the
Cryo M&C Enclosure. The cable that carries the 3-phase power between them will have to be shieldedand have a ground connection at both ends.

11.2 Shielding of Cryo M&C Enclosure
The Cryo M&C Enclosure contains the compressor M&C interface LRU, the VFD LRUSs for the Scroll
capsule and the two cold-heads, as well as controllers for the cooling fan and vacuum pump. All theelectronics listed above can generate RFI and must be contained within an RFI-tight enclosure(s). The
connections to the M&C enclosure shall be done through special filtered connectors. The whole assemblymust meet the VLA RFI requirements [AD07]. The validation of the shielded enclosure will be done in
the VLA reverberation chamber with a specially designed test set.

11.3 Cooling of Cryo M&C Enclosure
The active electronics inside the M&C enclosure will generate heat. Because it is a shielded enclosure, it
is recommended to use a cold plate cooled by Glycol, instead of forced-air cooling. It will be easier tokeep the box RFI tight and weatherproof if air vents are not used.

Page 29 of 32

Title: Cryogenic Subsystem Reference
Design Description

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

12 Maintenance12.1 Scheduled Maintenance
Scheduled cryogenics maintenance (Table 28) will be performed when the antenna is serviced. Because of
the large number of antennas, one antenna will have a major overhaul every 35,000 hrs (four years).
Compressor charcoal trap adsorber replacement
Compressor heat exchanger cleaning
Compressor fan motor bearing replacement
Cold-head replacement
System static pressure recharge (He)Compressor oil refill35,000 hrs of operation
35,000 hrs of operation
35,000 hrs of operation
35,000 hrs of operationKUV 7%&KUVRIRSHUDWLRQ

Table 28 - Scheduled maintenance.

12.2 Onsite MaintenanceAll scheduled maintenance shall be performed at the site when the antenna is serviced. Unscheduled
repairs shall also be done at the site. When a compressor fails the unit will be replaced. This requires
depressurization of the helium circuit.

12.3 Maintenance at the Service Center(s)All compressor repairs that require depressurization of the helium circuit shall be done at the service
center(s). Cold-head overhaul shall also be done at the service center(s).

13 Shipping/Transport and Acceptance Test
13.1 Shipping from Manufacturer to Integration Center
The compressor shall be mounted on a wood pallet with tilt sensors and shock sensors to ensure safedelivery by truck and early detection of possible abuse.

13.2 Transport between Integration Center and Antenna
The compressor will be transported from the integration center to the antenna in a truck equipped witha crane that will allow the compressor to be lifted up to the antenna platform.

13.3 Acceptance Test
The compressor shall be tested at the factory and delivered with a complete set of test data and acompliance report. The cold-heads shall also be tested at the factory and delivered with the load maps
and the compliance reports.
The M&C enclosure will be tested in the reverberation chamber to ensure compliance with the VLA
requirements. A recently-serviced compressor or cold-head will be tested at the integration center andwill have to pass a series of acceptance tests prior to being released as a spare unit.

Page 30 of 32

Title: Cryogenic Subsystem Reference
Design Description

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

Date: 2019-07-24
Version: A

14 Appendix
14.1 Compressor Enclosure
For the reference design we are not considering an outside enclosure for the outdoor compressor unit;
however, the possibility to add such an enclosure to the antenna platform will be evaluated during thedesign phase. Some of the parameters to consider for the enclosure include the following:x Weather protectiono Avoid snow/ice accumulation on compressoro Minimize exposure to rain water (corrosion)o Shield the cooling fan from high winds
o Prevent damage from hailstorms
o Reduce sun damage (UV)x Impact on antenna designo Extra weight on platformo Extra volume on platformo Extra costo Reduced accessibility
o Increased maintenance time (enclosure must be removed to access compressor outdoor unit)

Page 31 of 32

Title: Cryogenic Subsystem Reference
Design Description

Owner: Urbain

NRAO Doc. #: 020.30.10.00.00-0002-DSN-ACRYOGENIC_SUBSYSTEM_REF_DESIGN

14.2 Abbrevations and Acronyms
Acronym
AD
LNA
LRU
M&C
MLI
MRI
MTBF
ngVLA
NRAO
RD
rpm
SPI
UV
VFD
VLA

Description
Applicable Document
Low Noise Amplifier
Line-Replaceable Unit
Monitor and Control
Multi Layer Insulation
Magnetic Resonance Imaging
Mean Time Between Failure
Next Generation VLA
National Radio Astronomy Observatory
Reference Document
Revolution per minute
Serial Peripheral Interface
UltraViolet
Variable Frequency Drive
Jansky Very Large Array

Page 32 of 32

Date: 2019-07-24
Version: ATitle: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

Integrated Receivers and Downconverters:
Preliminary Technical Requirements
020.30.15.00.00-0001-REQ-A-INTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Status: RELEASEDPREPARED BY
M. Morgan
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2019-10-31
2019-04-15

APPROVALS (Name and Signature)
R. Selina,
2019.07.25
Project Engineer
12:36:45 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-25

M. McKinnon,
Asst. Director for
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.25 16:14:36 -06'00' NM-Operations, NRAO

2019-07-25

RELEASED BY (Name and Signature)
ORGANIZATION
M. McKinnon,
Asst.
Director for
Digitally signed by Mark McKinnon
Mark
McKinnonDate:2019.07.25
16:14:56-06'00'
Project Director
NM-Operations, NRAO

DATE
2019-07-25

Page 1 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

Change Record
Version

Date

AuthorAffected
Section(s)ReasonFirst draft. Used ngVLA Antenna Specs as atemplate, and took some data from ngVLA
memo #29, “An Integrated Receiver Concept
for the ngVLA.”
Modified Band 5 LO frequencies.

1

201801-10

M. MorganAll2

2018-03-29

M. Morgan

4.1, 4.2

3

2018-04-16

M. Morgan

5.4

4

2018-04-26

M. Morgan

many5

2018-05-03

M. Morgan

4.6.3

6

2018-05-16

M. Morgan

many7

2018-06-24

M. Morgan

headerRemoved reference to TEC supply.
Increased Bands 4 and 5 to 8 bits, added two
Band 4 modules for WVR, added 3.3 V digital
supply.
Changed spurious spec to –43 dBm/MHz.
Re-harmonized with updated system
requirements.
Corrected file number.

8

2018-07-03

M. Morgan

Fig. 1

Corrected Band 2 edge frequency.

92018-07-31

M. Morgan

4.10, 6

Added mass and physical dimension specs.

9.9

2018-09-06

S. DurandAll

10

2018-10-01

M. MorganAll11

2018-10-19

M. Morgan

5.6, 2.1

12

2018-10-31

M. Morgan

headerA

2019-07-25

A. LearAll

Minor changes, number of antennas.
Updates from Internal Pre-Decadal
Submission Review.
Clarified number of fibers. Removed rev
numbers in AD reference table.
Changed title block to show author/owner.
Also deleted ngVLA project background.
Prepared PDF for approvals and release.

Page 2 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

Table of Contents
1

Introduction ............................................................................................... 4

1.1
1.2

Purpose .............................................................................................................................. 4
Scope ................................................................................................................................. 4

2

Related Documents and Drawings ........................................................... 4

2.1
2.2

Applicable Documents ...................................................................................................... 4
Reference Documents ....................................................................................................... 4

3

Overview of Technical Specifications ...................................................... 5

3.1
3.2
3.3

Document Outline ............................................................................................................ 5
General Description .......................................................................................................... 5
Summary of Integrated Downconverter Requirements .................................................. 6

4

Functional and Performance Requirements ........................................... 7

4.1
4.2
4.3
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.5
4.6
4.6.1
4.6.2
4.6.3
4.7
4.7.1
4.7.2
4.8
4.8.1
4.8.2
4.9
4.10

RF Frequency Ranges ........................................................................................................ 7
LO Frequencies.................................................................................................................. 8
IF Bandwidth ..................................................................................................................... 9
Analog Gain ....................................................................................................................... 9
Nominal Gain .........................................................................................................................................9Gain Flatness ..........................................................................................................................................9Gain Adjustment ................................................................................................................................ 10
Gain Stability ....................................................................................................................................... 10
Sensitivity ......................................................................................................................... 10
Spurious Signals............................................................................................................... 11
Image Rejection .................................................................................................................................. 11
Alias Rejection .................................................................................................................................... 11
Spurious Narrowband Tones ......................................................................................................... 11
Digitization ...................................................................................................................... 12
Sample Rate ......................................................................................................................................... 12
Bit Resolution ..................................................................................................................................... 12
Operating Conditions ..................................................................................................... 12
Nominal Operating Conditions ...................................................................................................... 12
Limiting Operational Conditions.................................................................................................... 12
Monitor & Control Requirements .................................................................................. 13
Mass and Physical Dimensions ....................................................................................... 135Interface Requirements .......................................................................... 14

5.1
5.2
5.3
5.4
5.5
5.6

Interface to the Cryogenic Front End Subsystem.......................................................... 14Interface to Water Vapor Radiometer........................................................................... 14Interface to the Timing Reference/LO Subsystem ........................................................ 15
Interface to the Monitor and Control Subsystem ......................................................... 15
Interface to the Power Supplies ..................................................................................... 16
Interface to the Data Transmission Subsystem............................................................. 16

6
7

Verification and Quality Assurance ....................................................... 17
Appendix................................................................................................... 20

7.1

Abbreviations and Acronyms .......................................................................................... 20

Page 3 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

1 Introduction
1.1 Purpose
This document presents a preliminary set of technical specifications for the ngVLA Integrated Receiverand Downconverter (IRD) modules.
Many requirements flow down from the preliminary ngVLA System Requirements [AD01], which inturn flow down from the preliminary ngVLA Science Requirements.
The integrated receiver packages further amplify the signals provided by the cryogenic stage, down
convert them where necessary, digitize them, and deliver the resultant data streams by optical fiber toa moderately remote collection point from the focal plane (but possibly still inside the antenna base).
From there, they are time-stamped and launched onto a conventional network for transmission backto the array correlator and central processing facility. Hooks are needed to provide for synchronizationof local oscillators (LOs) and sample clocks, power leveling, command and control, health andperformance monitoring, and diagnostics for troubleshooting in the event of component failure.

1.2 Scope
The scope of this document is the set of ngVLA Integrated Receiver and Downconverter modules. Thisconsists of direct-sampled and sideband-separating modules for all telescope bands, which include warm
amplification, filtering, power leveling, analog-to-digital conversion, and fiber-optic transmission. It also
covers external splitters and combiners as needed to feed them from the cryogenic signal paths.
Cryogenic systems and thermal transitions, as well as front-end cabling, waveguide runs, and fiber-optic
signal paths outside the IRD modules themselves are outside the scope of this work package, thoughinterfaces must be considered. This specification establishes the performance, functional, design, andtest requirements applicable to the ngVLA IRD modules.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In theevent of conflict between the documents referenced herein and the content of this Technical
Specification, the latter shall be considered as a superseding requirement.
Reference
No.
AD01
AD02

Document Title

Rev / Doc. No.

ngVLA Preliminary System Requirements
ngVLA System Environmental Specifications

020.10.15.10.00-0003-REQ
020.10.15.10.00-0001-SPE

2.2 Reference Documents
The following references provide supporting context:
Reference
No.
RD01
RD02

Document Title

Rev / Doc. No.

An Integrated Receiver Concept for the ngVLA
Unformatted Digital Fiber-Optic Data
Transmission for Radio Astronomy Front-Ends

ngVLA Memo #29, Nov. 2017
PASP, vol. 125, no. 928, June 2013

Page 4 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

3 Overview of Technical Specifications
3.1 Document Outline
This document presents the technical specifications of the ngVLA Integrated Downconverters. These
parameters determine the overall form and performance of the downconverter modules.
The functional and performance specifications, along with detailed explanatory notes, are found in
Section 4. The notes contain elaborations regarding the meaning, intent, and scope of the requirements.
These notes form an important part of the definition of the requirements and should guide theverification procedures.
In many cases the notes contain an explanation or an analysis of how the numeric values ofrequirements were derived. Where numbers are not well substantiated, this is also documented in thenotes. In this way, the required analysis and trade-space available is apparent to scientists and engineers
who will guide the evolution of the ngVLA Integrated Downconverter concept.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully
define the interfaces as the design progresses.
Requirements for the Verification and Test of the integrated modules, from the conceptual design
through to prototype, are described in Section 6.

3.2 General Description
The integrated downconverters will take cryogenically amplified RF inputs ranging from 1.2 to 116 GHz
in bands and perform all necessary conversions from RF to baseband, from analog to digital, and fromcopper to fiber in compact, integrated, line-replaceable units (LRUs). The lower bands may be digitized
directly (without down conversion) in the first-, second-, and/or third-Nyquist zones, while the higher
bands may be down converted with in-phase and quadrature (I and Q) baseband outputs. Final
sideband-separation will be performed numerically by the backend (outside the scope of this work
package) with calibrated amplitude and phase coefficients. The initial concept and frequency plan forthis subsystem (now somewhat modified, and still evolving) was presented in [RD01].
Due to instantaneous digital bandwidth limitations, more than one downconverter module may berequired to service a single RF feed band. Where needed, passive splitters/combiners will be provided
within this scope to divide the RF band into more manageable chunks for the integrated modules.
The digitized I and Q or direct-sampled data streams will be transmitted by optical fiber as unformatted
serial data. The mathematical basis of operation and methodology for parsing the bit stream at thereceive end is described in detail in [RD02].
Auxiliary inputs to the integrated downconverters will include LOs, sample clocks, power supplies, andthe monitor and control (M&C) serial bus. Sufficient on-board monitoring will be provided to isolate
most failures to a single LRU.

Page 5 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

3.3 Summary of Integrated Downconverter Requirements
The following table provides a summary of the major integrated downconverter requirements in orderto provide the reader with a high-level view of the desired subsystem. Should there be a conflict
between the requirements listed here and the descriptions in Sections 4 through 6, the latter shall takeprecedence.
Parameter

Summary of Requirement

RF Input FrequencyBands

1.2–3.5 GHz
3.5–10.5 GHz
10.5–20.5 GHz
20.5–34 GHz
30.5–50.5 GHz
70–116 GHz
3.5 GHz (RF < 10.5 GHz)
3.5 GHz per sideband, 2SB (10.5 < RF < 50.5 GHz)
7 GHz per sideband, 2SB (70 < RF < 116 GHz)
>30 dB (calibrated)
60 dB (TBC)<2.7 dB slope, plus <2dB peak-to-peak ripple±12 dB min. (from nominal)<1000 K
8 bits (RF < 50.5 GHz)
4 bits (70 < RF < 116 GHz)

IF Bandwidth
Image Rejection
Gain (nominal)
Gain Flatness
Gain Adjust
Noise Temperature
Bit Resolution

Page 6 of 20

Reference
Reqs.
IRD0101
IRD0102
IRD0103
IRD0104
IRD0105
IRD0106
IRD0301–0302
IRD0303–0305
IRD0306
IRD0611–0614
IRD0411–0416
IRD0421–0422
IRD0431
IRD0501–0506
IRD0721–0725
IRD0726

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

4 Functional and Performance Requirements
All function and performance requirements apply to a properly functioning system, with nominal inputs
and control settings (e.g., attenuator states), under normal operating environmental conditions(temperature, power, etc.), and with normal operational calibrations applied, unless otherwise stated.

4.1 RF Frequency Ranges
Parameter
Band 1 RF Frequency
Band 2 RF Frequency
Band 3 RF Frequency
Band 4 RF Frequency
Band 5 RF Frequency
Band 6 RF Frequency

Req. #
IRD0101
IRD0102
IRD0103
IRD0104
IRD0105
IRD0106

Value
1.2–3.5 GHz
3.5–10.5 GHz
10.5–20.5 GHz
20.5–34 GHz
30.5–50.5 GHz
70–116 GHz

Traceability
SYS0801–0806
SYS0801–0806
SYS0801–0806
SYS0801–0806
SYS0801–0806
SYS0801–0806

The total RF frequency range flows down from the system requirements, and the selection of bandedges stem from a combination of engineering feasibility, hardware efficiency, and the system
requirement that the band edges do not coincide with important spectral features.
It should be noted that the Band 2/3 transition at 10.5 GHz for the IRD modules do not coincide withthose of the planned feed and cryogenic amplifier bands. This is because 10.5 GHz marks the transition
from one type of integrated module (direct-sampled) and another (sideband-separating), which in turnis driven by the expected analog bandwidth of the digitizers.
A general frequency plan for the integrated receivers is shown in Figure 1 (next page). Unless otherwise
noted, all references to RF bands within this document shall refer to the integrated module band ranges,
not the cryogenic front-end band ranges.
The RF signal path will include a set of passive splitters and combiners to feed the correct bandwidth
to each module. Note that the wider RF bands will require more than one module for complete
frequency coverage. Although the reference design anticipates that all modules within a given RF band
will be identical, this is not a requirement.
A subset of antennas (their number as yet undetermined) will require additional Band 4 modules toservice the water vapor radiometer (WVR).

Page 7 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

BandFrequency

Receiver Type# bits123

1.2–3.5 GHz
3.5–7.0 GHz
7.0–10.5 GHz
10.5–20.5 GHz

4

20.5–34 GHz

WVR (4)20.5–34 GHz

5

30.5–50.5 GHz

6

70–116 GHz

DS
DS
DS
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB

8
8
8
8
8
8
8
8
8
8
8
8
4
4
4
4

Date: 2019-07-25
Version: A

SampleRate
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s14 GS/s
14 GS/s
14 GS/s
14 GS/s

Figure 1 - Integrated downconverter frequency plan. DS refers to direct-sampled receivers, while 2SB refers
to sideband-separating receivers.

4.2 LO Frequencies
Parameter
Band 3 LO Frequencies
Band 4 LO Frequency
Band 5 LO Frequencies
Band 6 LO Frequencies
LO Frequency Tunability

Req. #
IRD0201
IRD0202
IRD0203
IRD0204
IRD0205Value
14 and 21 GHz
23.6 and 30.6 GHz
33.6, 40.6, and 47.6 GHz
70, 84, 98, and 112 GHz±2 GHzTraceability
SYS0906
SYS0906
SYS0906
SYS0906
SYS0806

The LO frequencies above were selected to allow complete coverage of the RF bands in Section 4.1
with only minimal gaps at near-DC IF frequencies and at the edges between sidebands of adjacentdownconverters. LOs were also selected, where reasonable, to be harmonically related to the sample
clock frequencies to minimize the chance of spurious mixing products between the two. For simplicity,
we do not require the LOs to tune over very wide ranges, but a minimal LO tuning requirement(IRD0205) permits access to these nominal gap frequencies at the discretion of the telescope operator

Page 8 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A(with the exception of the gaps at 3.5 GHz and 7 GHz between Nyquist zones of the direct-sampled
receivers).

4.3 IF BandwidthParameter
Band 1 IF BandwidthBand 2 IF BandwidthBand 3 IF BandwidthBand 4 IF BandwidthBand 5 IF BandwidthBand 6 IF Bandwidth

Req. #
IRD0301
IRD0302
IRD0303
IRD0304
IRD0305
IRD0306

Value
3.5 GHz
3.5 GHz
3.5 GHz
3.5 GHz
3.5 GHz
7 GHz

Traceability

Note that these bandwidths correspond to the maximum theoretical bandwidths sampled by thedigitizers, and do not necessarily represent alias-free bandwidth. Bands 3 and above are sidebandseparating, while the Band 2 module is expected to utilize two Nyquist zones with 3.5 GHz bandwidtheach. Further, all modules are dual polarization. Finally, as noted earlier, some bands will be populatedwith more than one module. Consequently, the numbers above represent the IF bandwidth per sidebandor Nyquist zone, per polarization, and per module, as applicable for each band.

4.4 Analog Gain
The net warm electronic gain is required to amplify the weak output spectra of the cryogenic system
to a level at the digitizers that balances quantization efficiency and dynamic range. It is specified in termsof nominal (average) value, flatness, and adjustment range. The final values of these specs will dependon the gain specification of the cryogenic amplifiers and the full-scale range of the samplers.

4.4.1

Nominal Gain

Parameter
Band 1 Nominal GainBand 2 Nominal GainBand 3 Nominal Conversion GainBand 4 Nominal Conversion GainBand 5 Nominal Conversion GainBand 6 Nominal Conversion Gain

Req. #
IRD0411
IRD0412
IRD0413
IRD0414
IRD0415
IRD0416Value
60 dB (TBC)
60 dB (TBC)
60 dB (TBC)
60 dB (TBC)
60 dB (TBC)
60 dB (TBC)

Traceability

Nominal gain is defined as the average analog signal gain between the RF inputs of the IRD modules
and the inputs to the samplers over the RF operating frequency for each band defined in Section 4.1.
The nominal setting of the internal step attenuators are determined post-fabrication as that setting
which most closely achieves the desired gain. The modules will further be required to have enoughattenuator control range leftover to meet the gain adjustability requirements in Section 4.4.3.

4.4.2

Gain Flatness

Parameter
Gain Slope
Gain Ripple

Req. #
IRD0421
IRD0422Value<2.4 dB (80% BW) TBC<2.4 dB peak-to-peak TBC

Traceability
SYS1703
SYS1702

Gain slope is measured as the best fit line over that 80% of each IF band (defined in Section 4.3) which
minimizes its value. Gain ripple is defined as the residual variation over the same 80% bandwidth after
Page 9 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

the slope is removed from the data. The system requirements for gain slope and ripple are 3 dB each.
No budget for sharing this allowance across subsystems has been completed, but it can be assumed
80% of that can be allocated to the IRD system and 20% to the cryogenic front-ends, for two reasons.
First, IRD comprises roughly two-thirds of the net analog gain (60 dB out of roughly 90 dB). Second,
several lossy signal-conditioning components such as mixers, filters, and variable attenuators, must be
further compensated by gain stages in the IRD.

4.4.3

Gain Adjustment

Parameter
Gain Adjustment Range
Gain Adjustment Step Size
Solar Mode Adjustment

Req. #
IRD0431
IRD0432
IRD0433Value±12 dB
1 dB+30 dB up to 10.5 GHz (TBC)

Traceability
SYS1203

Analog gain shall be adjustable in discrete steps via integrated step attenuators. The nominal setting ofthese attenuators shall be determined on a per module basis to most closely meet the nominal gain
targets, with enough range left over to meet the requirements above. An additional 30 dB attenuatorshall be available in the lower frequency bands to support solar observations. At present, it is assumed
the extra attenuation is not needed for the higher frequency bands.

4.4.4

Gain Stability

Parameter
Gain Amplitude Stability
Gain Phase Stability
Allan VarianceReq. #
IRD0441
IRD0442
IRD0443

Value<0.01 dB per hour
<0.01 degrees over 300 sec
TBD

Traceability
SYS1701
SYS1504

Gain amplitude and phase stability is required to reach the ngVLA’s ultimate sensitivity goals, as well as
to enable a low-overhead calibration policy in which bandpass and gain solutions for each antenna andreceiver are stored for use in subsequent observations. The stability of gain amplitude and phase shallapply at any point in the pass-band, and shall be met under nominal environmental conditions (especiallytemperature gradient) given in Section 4.8.1. Allan variance is measured on amplitude only. As
described in the system-level requirements, the phase drift specification is an rms residual, after
subtraction of any linear trend over the specified time period.

4.5 Sensitivity
Parameter
Band 1 Noise Temperature
Band 2 Noise Temperature
Band 3 Noise Temperature
Band 4 Noise Temperature
Band 5 Noise Temperature
Band 6 Noise Temperature

Req. #
IRD0501
IRD0502
IRD0503
IRD0504
IRD0505
IRD0506

Value<1000 K
<1000 K
<1000 K
<1000 K
<1000 K
<1000 K

Traceability
SYS1011
SYS1011, SYS1012
SYS1012
SYS1012
SYS1012
SYS1013

These noise temperatures ensure that the warm electronics contribute less than 1K to the system
noise temperature, assuming the cryogenic input stage has 30 dB gain. Noise temperature shall bemeasured by Y-factor over the integrated noise of the IF bandwidth with the internal step attenuators
at nominal setting.

Page 10 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

4.6 Spurious Signals
Spurious signals in this document may include any unwanted signal power (aside from in-band noise)that leak into the signal path. These may include image bands, alias bands, and spurious CW or
narrowband tones.

4.6.1

Image Rejection

Parameter
Band 3 Image Rejection
Band 4 Image Rejection
Band 5 Image Rejection
Band 6 Image Rejection

Req. #
IRD0611
IRD0612
IRD0613
IRD0614Value>30 dB>30 dB>30 dB>30 dB

Traceability
SYS1704
SYS1704
SYS1704
SYS1704

Image rejection shall be measured with calibrated corrections applied and all internal attenuators andLOs at nominal settings.

4.6.2

Alias Rejection

Parameter
Band 1 Alias-Free IF FBWBand 2 Alias-Free IF FBWBand 3 Alias-Free IF FBWBands 4–6 Alias-Free IF FBWBand 1 Alias Rejection
Band 2 Alias Rejection
Band 3 Alias Rejection
Bands 4–6 Alias Rejection

Req. #
IRD0621
IRD0622
IRD0623
IRD0624
IRD0625
IRD0626
IRD0627
IRD0628

Value
80%
80%
80%
80%
>55 dB>55 dB>55 dB>55 dB

Traceability
SYS1703
SYS1703
SYS1703
SYS1703“Alias-free” IF fractional bandwidth (FBW) is the percentage of the theoretical IF band defined in
Section 4.3 in which the aliased signals are attenuated by the given alias rejection levels. The rejection,in turn, is measured relative to the corresponding in-band gain. It is inevitable that anti-aliasing filters
will introduce gain slope at the edges of the IF band. The 80% fractional bandwidth specifications above
flow down from the System Requirement SYS1703 that the IF slope shall be restricted over 80% of theband.
Note that at the broadest IF bandwidth (7 GHz), an 80% FBW specification allows for a gap of 0.2 x 7
GHz = 1.4 GHz, which is not “alias-free.” The LO tuning requirement (IRD0205) ensures that all
frequencies within the instrument’s RF range (except for the Nyquist zone boundaries at 3.5 GHz and
7 GHz) are accessible with “alias-free” levels of rejection.

4.6.3

Spurious Narrowband Tones

Parameter
Spurious Tone Power

Req. #
IRD0631

Value<–43 dB/MHz above noise floor

Traceability
SYS2104

Spurious tones in this context refers to any narrowband spurious signal, regardless of its source (e.g.,
mixing products, clock harmonics, switching transients, oscillations). The relative “spurious power” ina given spectral bin will be calculated as (P–N)/N, where P is the total power in the bin and N is theaverage power in the adjacent two bins. The bin size will be chosen as large as possible to include
broad spurs, while narrow enough to exclude microscale baseband ripples to >10 dB below the spec
limit.
Page 11 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

4.7 Digitization
4.7.1

Sample Rate

Parameter
Band 1 Sample Rate
Band 2 Sample Rate
Band 3 Sample Rate
Band 4 Sample Rate
Band 5 Sample Rate
Band 6 Sample Rate

4.7.2

Req. #
IRD0711
IRD0712
IRD0713
IRD0714
IRD0715
IRD0716Value
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s14 GS/s

Traceability

Req. #
IRD0721
IRD0722
IRD0723
IRD0724
IRD0725
IRD0726

Value
8 bits8 bits8 bits8 bits8 bits4 bitsTraceability
SYS1034
SYS1034
SYS1034
SYS1034
SYS1034
SYS1035

Bit Resolution

Parameter
Band 1 Bit Resolution
Band 2 Bit Resolution
Band 3 Bit Resolution
Band 4 Bit Resolution
Band 5 Bit Resolution
Band 6 Bit Resolution

Note that these represent the bit resolutions at the front-end. The correlator may requantize thesedata streams at lower resolution levels (with appropriate care for sensitivity and dynamic range).

4.8 Operating Conditions
All functional and performance specifications given herein are to be met at nominal operating
conditions, while basic functionality is required over the limiting operational conditions.

4.8.1

Nominal Operating Conditions

Parameter
Nominal Temperature
Nominal Temperature GradientReq. #
IRD0811
IRD0812Value–15 C  T  35 C
<3.6°C per hour

Traceability
ENV0323
ENV0324

Verification tests shall be considered successful if the measurement passes while environmental
conditions are within the ranges of the nominal operating conditions, unless otherwise explicitly stated.

4.8.2

Limiting Operational Conditions

Parameter
Limiting Temperature
Limiting Temperature GradientReq. #
IRD0821
IRD0822Value–20 C  T  45 C
<3.6°C/Hr.

Traceability
ENV0332

The limiting operational conditions define the ranges over which basic functionality is assured without
necessarily meeting specifications. They are not intended to define safe storage or working limits
beyond which permanent damage may occur.

Page 12 of 20

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

4.9 Monitor & Control Requirements
Parameter
RF Signal Monitors
IF Signal Monitors
Electronic Serial
NumberStandby Mode

Automatic
Initialization

Req. #Value
IRD0901 The integrated modules shall measure and report
total signal power entering each RF input.
IRD0902 The integrated modules shall measure and report
total IF signal power entering each digitizer
channel.
IRD0903 The integrated modules shall report a uniqueelectronic identification upon request.
IRD0904 The integrated modules shall be capable ofentering a low-power standby mode oncommand. M&C communications shall still befunctional in this mode.
IRD0905 The integrated modules shall automatically bootinto a nominal operational mode on power-up,
absent any command from M&C.

Traceability

The monitor points (IRD0901 and IRD0902) may comprise raw voltages or digital values in arbitrary
units, subject to appropriate scaling and translation to recover meaningful values. No specific precisionor accuracy is implied in these requirements.

4.10 Mass and Physical Dimensions
Parameter
PhysicalDimensions
Mass
Connector
Orientation

Req. #
IRD1001

Mounting
Holes

IRD1004

IRD1002
IRD1003

Value
Each integrated module shall fit within a physicalenvelope measuring 40 x 80 x 160 mm in size.
Each integrated module shall weigh less than 1.5 kg.
RF input connectors/flanges shall be located at one
end of the physical envelope above, while theoutputs and LO, clock, bias, and M&C inputs shall belocated at the opposite end.
Each integrated module shall include at least four
clear holes (sized for #4 screws) oriented to mountagainst a temperature-controlled surface in contact
with the largest face of the above physical envelope.

Page 13 of 20

Traceability

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

5 Interface Requirements
This section provides information about the interfaces of the integrated modules. Interface Control
Documents (ICDs) are required between the integrated modules and all connecting systems. In manycases, specifications for the interfaces are not yet available, but the broad scope of the ICD can be
defined.
These interfaces shall be developed and documented by the Integrated Receivers and Downconverters
designer. Post CoDR, the ICD shall only be updated through formal project change control processes.
Unilateral aspects of the connector interfaces (e.g., M or F) shall refer to the connector on the
integrated modules. Cables, waveguide, and fiber runs between the integrated modules and otherelectronic subsystems are not included in this work package.

5.1 Interface to the Cryogenic Front End Subsystem
Signal at
Interface
Band 1 RF

TypeParameter

Value

Input

Band 2 RF

Input

Band 3 RF

Input

Band 4 RF

Input

Band 5 RF

Input

Band 6 RF

Input

Connector
Impedance
Multiplicity
Connector
Impedance
Multiplicity
Connector
Impedance
Multiplicity
Connector
Impedance
Multiplicity
FlangeMultiplicity
FlangeMultiplicity

2.92 mm (F)50 ȍx2 (one per pol.)2.92 mm (F)50 ȍx2 (one per pol.)2.92 mm (F)50 ȍx2 (one per pol.)2.92 mm (F)50 ȍx2 (one per pol.)WR-22 (UG599)
x2 (one per pol.)WR-10 (UG387)
x2 (one per pol.)Comments

The frequency ranges for these inputs are given in Section 4.1. The RF splitters and combiners areincluded in the Integrated Receivers and Downconverters subsystem.

5.2 Interface to Water Vapor Radiometer
Signal at Interface TypeBand 4 RF
Input

Parameter
Connector
Impedance
Multiplicity

Value
2.92 mm (F)50 ȍx2 (one per pol.)The Water Vapor Radiometer will be present on all antennas.

Page 14 of 20

Comments

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

5.3 Interface to the Timing Reference/LO Subsystem
Signal at Interface
Sample Clock
Reference

Type
Input

Band 3 LO

Input

Band 4 LO

Input

Band 5 LO

Input

Band 6 LO

Input

Parameter
Frequency
Electrical Format
Connector
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity

Value
156.25 MHz
LVDS
TBD
x13 (TBC)>+13 dBm (CW)
TBD
2.92 mm (F)50 ȍx2>+13 dBm (CW)
TBD
2.92 mm (F)50 ȍ
x4>+13 dBm (CW)TBD
WR-22 (UG599)
50 ȍ
x3>+13 dBm (CW)TBD
WR-10 (UG387)
50 ȍ
x4

Comments
Coaxial, shielded

The LO nominal frequencies and tuning ranges are given in Section 4.2.

5.4 Interface to the Monitor and Control Subsystem
Signal at Interface
M&C Serial Bus

Type
Input /
OutputParameterProtocolConnector
Number of Pins
Multiplicity

Page 15 of 20

Value
SPI (mode 0)
Nano-D (F)TBD
x15 (TBC)

Comments
May be combined on thesame cable harness withpower supplies.

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

5.5 Interface to the Power Supplies
Signal at Interface
Analog Positive
SupplyType
Input

Digital Positive
SupplyInput

Main Negative Supply

Input

Parameter
Voltage
Current Draw
Multiplicity
Voltage
Current Draw
Multiplicity
Voltage
Current Draw
Multiplicity

Value
+5 V
<1 A (TBC)
x13+3.3 V<1 A (TBC)
x15–5 V<100 mA (TBC)
x15

Comments
Internally regulated for
multiple voltages.
Internally regulated.
Primarily (exclusively?) for
transistor gates.

5.6 Interface to the Data Transmission Subsystem
Signal at
Interface
Digital IFs

TypeParameter

Value

Comments

OutputData Format
Data Content
Connector
Physical Format
Nominal Wavelength
Colors/Lanes
Baud Rate
Effective Bit Rate
Modulation
Multiplicity

Unformatted
I/Q or Nyquist
QSFPSingle-Mode Fiber
1310 nm
428 Gbaud/lane
56 Gbps per lane
PAM4
x15

PAM4 modulation carries 2
bits per symbol, so“effective” 56 Gbps perlane is achieved bytransmitting 28 billion
symbols per second.

Page 16 of 20

Number of fibers: 13
Nominal, plus 2 for WVR

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

6 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A) inspection (I), a factory
acceptance test (FAT) or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which may bechecked by the ngVLA project office during the design phase by review of the design documentation.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which will bechecked by the ngVLA project office during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple
inspection or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item / assembly / unit
with the specified performance shall be demonstrated by tests. A FAT is performed without integration
with interfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item / assembly / unit
with the specified performance shall be demonstrated by tests. SAT is performed on-site with theequipment as installed.
Multiple verification methods are allowed. The following table summarizes the expected verification
method for each requirement.
Req. #
IRD0101
IRD0102
IRD0103
IRD0104
IRD0105
IRD0106
IRD0201
IRD0202
IRD0203
IRD0204
IRD0205
IRD0301
IRD0302
IRD0303
IRD0304
IRD0305
IRD0306
IRD0411
IRD0412
IRD0413
IRD0414
IRD0415
IRD0416
IRD0421

Parameter / Requirement
Band 1 RF Frequency
Band 2 RF Frequency
Band 3 RF Frequency
Band 4 RF Frequency
Band 5 RF Frequency
Band 6 RF Frequency
Band 3 LO Frequencies
Band 4 LO Frequency
Band 5 LO Frequencies
Band 6 LO Frequencies
LO Frequency Tunability
Band 1 IF BandwidthBand 2 IF BandwidthBand 3 IF BandwidthBand 4 IF BandwidthBand 5 IF BandwidthBand 6 IF BandwidthBand 1 Nominal GainBand 2 Nominal GainBand 3 Nominal Conversion GainBand 4 Nominal Conversion GainBand 5 Nominal Conversion GainBand 6 Nominal Conversion Gain
Gain Slope

Page 17 of 20

D
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*

A

*
*
*
*
*
*

I

FAT

*
*
*
*
*
*
*

SAT

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Req. #
IRD0422
IRD0431
IRD0432
IRD0433
IRD0441
IRD0442
IRD0443
IRD0501
IRD0502
IRD0503
IRD0504
IRD0505
IRD0506
IRD0611
IRD0612
IRD0613
IRD0614
IRD0621
IRD0622
IRD0623
IRD0624
IRD0625
IRD0626
IRD0627
IRD0628
IRD0631
IRD0711
IRD0712
IRD0713
IRD0714
IRD0715
IRD0716
IRD0721
IRD0722
IRD0723
IRD0724
IRD0725
IRD0726
IRD0811
IRD0812
IRD0821
IRD0822
IRD0901
IRD0902
IRD0903
IRD0904

Parameter / Requirement
Gain Ripple
Gain Adjustment Range
Gain Adjustment Step Size
Solar Mode Adjustment
Gain Amplitude Stability
Gain Phase Stability
Allan Variance
Band 1 Noise Temperature
Band 2 Noise Temperature
Band 3 Noise Temperature
Band 4 Noise Temperature
Band 5 Noise Temperature
Band 6 Noise Temperature
Band 3 Image Rejection
Band 4 Image Rejection
Band 5 Image Rejection
Band 6 Image Rejection
Band 1 Alias-Free IF FBWBand 2 Alias-Free IF FBWBand 3 Alias-Free IF FBWBands 4–6 Alias-Free IF FBWBand 1 Alias Rejection
Band 2 Alias Rejection
Band 3 Alias Rejection
Bands 4–6 Alias Rejection
Spurious Tone PowerBand 1 Sample Rate
Band 2 Sample Rate
Band 3 Sample Rate
Band 4 Sample Rate
Band 5 Sample Rate
Band 6 Sample Rate
Band 1 Bit Resolution
Band 2 Bit Resolution
Band 3 Bit Resolution
Band 4 Bit Resolution
Band 5 Bit Resolution
Band 6 Bit Resolution
Nominal Temperature
Nominal Temperature Gradient
Limiting Temperature
Limiting Temperature Gradient
RF Signal Monitors
IF Signal Monitors
Electronic Serial Number
Standby Mode

Page 18 of 20

D

A

*
*
*

*

I

Date: 2019-07-25
Version: A

FAT
*
*

SAT

*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*

*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*

*
*
*
*
*
*

*
*
*
*
*

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Req. #
IRD0905
IRD1001
IRD1002
IRD1003
IRD1004

Parameter / Requirement
Automatic Initialization
Physical Dimensions
Mass
Connector Orientation
Mounting Holes

Page 19 of 20

D
*
*

A

I
*

*
*

Date: 2019-07-25
Version: A

FAT
*

SAT

Title: Integrated Receivers andOwner: Morgan
Downconverters: PreliminaryTechnical Requirements
NRAO Doc. #: 020.30.15.00.00-0001-REQ-AINTEGR_RECVR_DOWNCONVERTER_TECH_REQS

Date: 2019-07-25
Version: A

7 Appendix
7.1 Abbreviations and Acronyms
Acronym
AD
CDR
CoDR
CW
FBW
FDR
HVAC
ICD
IF
IRD
KPP
LO
LRU
M&C
MTBF
MTTF
MTTR
ngVLA
RD
RF
RFI
RMS
RSS
RTP
SNR
TBC
TBD
VLA
WVR

Description
Applicable Document
Critical Design Review
Conceptual Design Review
Continuous Wave (Sine wave of fixed frequency and amplitude)
Fractional Bandwidth
Final Design Review
Heating, Ventilation & Air Conditioning
Interface Control Document
Intermediate Frequency
Integrated Receivers and Downconverters
Key Performance Parameters
Local Oscillator
Line Replaceable Unit
Monitor and Control
Mean Time Between Failure
Mean Time To Failure
Mean Time To Repair
Next Generation VLA
Reference Document
Radio Frequency
Radio Frequency Interference
Root Mean Square
Root of Sum of Squares
Round Trip Phase
Signal to Noise Ratio
To Be Confirmed
To Be Determined
Jansky Very Large Array
Water Vapor Radiometer

Page 20 of 20

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

Integrated Downconverters and Digitizers
Design Description
020.30.15.00.00-0002-DSN-A-INTEGR_RECVR_DOWNCONVERTER_REF_DSN

Status: RELEASEDPREPARED BY
M. Morgan
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-11-01
2019-04-12

APPROVALS (Name and Signature)
R. Selina,
2019.07.25
Project Engineer
12:37:44 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-25

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.25 16:16:30 -06'00'

Asst. Director for NMOperations, NRAO

2019-07-25

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.25 16:16:52 -06'00'

ORGANIZATION
Asst. Director for NMOperations, NRAO

DATE
2019-07-25

Page 1 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

Change Record
Affected
Section(s)ReasonM. Morgan

All

Initial Draft, based on template provided.

2018-03-29

M. Morgan

3

2018-04-16

M. Morgan

5.1–5.3
4, 5.1, 5.2.3,
5.3.4

4

2018-04-26

M. Morgan

Many5

2018-05-24

M. Morgan

HeaderModified LO frequencies for Band 5.
Removed references to thermoelectriccoolers.
Increased to 8 bits in Bands 4 and 5, andadded two Band 4 modules for WVR.
Added 3.3 V digital supply.
Corrected file number.

6

2018-06-26

M. Morgan

HeaderRecorrected file number.

7

2018-07-03

M. Morgan

Fig. 2

Corrected Band 2 edge frequencies.

8

2018-09-06

S. DurandAll

9

2018-09-25

M. Morgan

5.2.1

A

2019-07-25

A. LearAll

Minor changes.
Clarified that cooling fans on the pictured
prototype will not be present in reference
design version.
Prepared PDF for approvals and release.

Version

Date

Author1

2018-03-13

2

Page 2 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings ............................................................... 4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 43
4

Subsystem Overview ..................................................................................... 5
Subsystem Design .......................................................................................... 5

4.1
4.2
4.2.1
4.2.2
4.2.3
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6

Subsystem Block Diagram ..................................................................................................... 7
Subsystem Components ......................................................................................................... 8
Sideband-Separating (2SB) Receiver Modules ..................................................................................... 8
Direct-Sampled (DS) Receiver Modules ............................................................................................ 11
Other Components ................................................................................................................................ 12Interfaces with Other Subsystems ....................................................................................... 12Interface to the Cryogenic Front-End Subsystem............................................................................ 12Interface to the Water Vapor Radiometer ....................................................................................... 13
Interface to the Timing Reference/LO Subsystem ........................................................................... 13
Interface to the Monitor and Control Subsystem ........................................................................... 13
Interface to the Power Supplies ........................................................................................................... 14Interface to the Data Transmission Subsystem ................................................................................ 14

5

Appendix....................................................................................................... 15

5.1
5.2

Abbreviations & Acronyms................................................................................................... 15
Bibliography ......................................................................................................................... 16

Page 3 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

Date: 2019-07-25

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Version: A

1 Introduction
1.1 Purpose
This document provides a description for the Integrated Downconverters and Digitizers subsystemreference design. It covers the design approach, functions, description of key components, interfaces, andrisks associated with the reference design. This document will form part of the submission of the ngVLA
Reference Design documentation package.

1.2 Scope
The scope of this document covers the entire design of the Integrated Downconverters and Digitizers
subsystem, as part of the ngVLA Reference Design. It includes the subsystem’s design, how it functions,and interfaces with the necessary hardware and software systems. It does not include specific technicalrequirements or budgetary information.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein, but provide necessary context or
supporting material.
Ref. No.
AD01

Document Title
Integrated Receivers and Downconverters PreliminaryTechnical Specifications/Requirements

Rev/Doc. No.
020.30.15.00.00-0001-REQ

2.2 Reference Documents
The following documents are referenced within this text:
Ref. No.
RD01

Document Title
Experiments With Digital Sideband-Separating
Downconversion

RD02

Unformatted Digital Fiber-Optic Data
Transmission for Radio Astronomy Front Ends

RD03

A highly-sensitive cryogenic phased array feed
for the Green Bank Telescope

RD04

SO-QSFP28-PAM4-Dxxx datasheet

RD05

Eoptolink 200G-400G solutions

Page 4 of 16

Rev/Doc. No.
M. Morgan and J. Fisher, Publications of the
Astronomical Society of the Pacific, vol. 122,
no. 889, pp. 326–335, March 2010.
M. Morgan, J. Fisher, and J. Castro,
Publications of the Astronomical Society of the
Pacific, vol. 125, no. 928, pp. 695–704, June2013.
D. Roshi, W. Shillue, J. Fisher, M. Morgan,
J. Castro, W. Groves, T. Boyd, B. Simon,
L. Hawkins, V. van Tonder, J. Nelson, J.
Ray, T. Chamberlain, S. White, R. Black, K.
Warnick, B. Jeffs, and R. Prestage, 32nd
URSI General Assembly and ScientificSymposium, Montreal, August 2017.
https://www.smartoptics.com/wpcontent/uploads/2017/10/SO-QSFP28PAM4-DWDM-R4.0.pdf
http://www.eoptolink.com/200g-400g

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

3 Subsystem Overview
The Integrated Receiver and Digitizer (IRD) packages further amplify the signals provided by the cryogenic
stage, downconvert them where necessary, digitize them, and deliver the resultant data streams by opticalfiber to a moderately remote collection point from the focal plane (but possibly still inside the antennabase). From there, they can be time-stamped and launched onto a more conventional network fortransmission back to the array correlator and central processing facility. Hooks are needed to provide forsynchronization of local oscillators (LOs) and sample clocks, power leveling, command and control, healthand performance monitoring, and diagnostics for troubleshooting in the event of component failure.
This subsystem consists of direct-sampled and sideband-separating modules for all telescope bands, which
include warm amplification, filtering, power leveling, analog-to-digital conversion, and fiber-optic
transmission. It also includes external splitters and combiners as needed to feed them from the cryogenic
signal paths. Cryogenic systems and thermal transitions, as well as front-end cabling, waveguide runs, andfiber-optic signal paths outside the IRD modules themselves, are outside the scope of this work package,
though interfaces must be considered.

4 Subsystem Design
The design of the ngVLA IRD modules evolved from an internal research program (the Integrated Receiver
Development program), which has been perfecting the techniques used in their construction for morethan a decade at the time of this writing. The original program aimed to leverage the advantages of modern
electronic integration and digital signal processing, to digitize as closely to the antenna feed-point as
possible without comprising ultimate performance, and to re-optimize legacy receiver architectures inlight of these new techniques and in anticipation of future telescope facilities such as the ngVLA.
Integration and digital signal processing (DSP) are deemed complementary in this program, in that thelatter provides for greater signal fidelity and precision in concert with detailed calibrations than purely
analog techniques, while the former guarantees the long-term stability and uniformity of those calibrations.
This resulted also in compact, low-power, field-replaceable receiver units which were a perfect fit for
ngVLA’s maintenance and operability requirements.
Paramount to the integrated receiver subsystem design is coverage of all operating bands on the telescopewith the minimum number of discrete integrated modules. This minimizes construction, testing, operating,and maintenance costs as well as reducing the complexity of the data transport and timing distribution
subsystems. The limiting factor here is digitizer bandwidth and sample rate. The ngVLA has a requirement
to digitize instantaneously 20 GHz of bandwidth, with a goal of sampling the entire frequency range of any
given RF band simultaneously (Band 6 in particular covering more than 20 GHz of bandwidth). This is
more than can be sampled instantaneously at the bit depth required with a single analog-to-digitalconverter (ADC) having reasonable performance and power dissipation. Thus, the system will consist of
low-loss splitters following the cryogenic front-end feeding a number of integrated receiver modules inparallel.
Due to the compact, integrated construction, it is unwise to perform downconversion in multiple steps.
Integrated modules, though they have many advantages, do not typically have as good of isolation between
inputs as individually connectorized components. Multiple local oscillator tones, then, tend to produce a
copious spread of mixing products that inevitably lead to spurious tones in the output spectrum.
We therefore process the higher frequency bands using a single-stage, direct-to-baseband
downconversion with in-phase and quadrature (I and Q) channels. These channels are then processed
Page 5 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

numerically in the back-end to produce upper and lower sidebands more precisely than an analog hybrid
ever could. The IRD program has a long track record of producing clean output spectra with 50–60 dB
sideband suppression using this technique (e.g. [RD01]).
At the lower frequency bands, downconversion is an unnecessary complexity, usually requiring triplebalanced mixers to achieve the required IF bandwidth while isolating it from the RF and LO inputs which
overlap with it in frequency space. For these bands, instead, we use a direct-digitization approach in thesecond or third Nyquist-zone of the sampler.
To minimize power requirements and the risk of self-interference with integrated digital and high-gain
analog electronics, the IRD program developed a novel approach to digital data transmission. Specifically,
it delivers unformatted digital data streams over optical fiber without any of the usual bit-scrambling,
packetizing, or formatting (e.g. 8b/10b) used in the data-communications industry. This “low-overhead”
digital design [RD02] relies on the statistical characteristics of Gaussian-distributed white noise—which
dominates the signal in any properly designed radio astronomy receiver, even those heavily laced with
man-made interference—to parse the bit stream at the receive-end of the fiber, away from the focal planewhere power and interference are less harmful. Numerous demonstrations of this concept have been
built and proven, and it has now been fielded in a user instrument on the Green Bank Telescope [RD03].
A critical element of the low-overhead serial link described above is the Serial ADC (SADC). Thisessentially marries a conventional ADC and a conventional Serializer (or SerDes) without any of the usual,intervening, complex digital logic. Implemented to date using off-the-shelf parts, fully realizing this idea’s
potential benefits relies on integrating these two components on a single piece of Silicon. This avoids thewasted size, weight, and power (SWaP) associated with chip-to-chip parallel interfaces. The functional
components of this proven technique (the ADC and the Serializer) already exist commercially, making
this a development with very low technical risk, but one that requires a significant investment in producing
the ASIC. Such a development has been initiated with a contract IP vendor. The projected power
dissipation of this chip is 25 times less than that consumed by off-the-shelf solutions.
The unformatted fiber optic links will likely not interface directly with the array correlator/signal
processor. Rather, they will interface with the long-distance data transmission subsystem which will carry
the data the rest of the way on more conventional (possibly commercial) links. The data transmission
subsystem interface could be inside the antenna base or some tens of kilometers away where it will joinwith links from other telescopes in the array. The latter will most likely be the case at least for the antennas
in the array core within reach of the signal processing center.

Page 6 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

4.1 Subsystem Block Diagram
A block diagram of the Integrated Receivers/Downconverters and Digitizers Subsystem is shown in Figure
1, with all electrical interfaces included. The internal block diagrams of the sideband separating (2SB) anddirect-sampled (DS) receiver modules appear in Section 4.2. The gray boxes provide information about
subsystem inputs and outputs.

Figure 1 - Block diagram of Integrated Receivers/Downconverters and Digitizers subsystem.

Page 7 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

4.2 Subsystem Components
By far, the most significant major components of the IRD subsystem are the receiver modules. As
described above, the architecture and frequency distribution of these receiver modules have been
designed to cover the required bandwith with the minimum amount of hardware. Figure 2 summarizes
the resulting frequency. Note that antennas outfitted with a water vapor radiometer will need an additional
two Band 4 modules, included in the table but not shown in the spectrum plot of Figure 2.

Band
1
2
3

Frequency
1.2–3.5 GHz
3.5–7.0 GHz
7.0–10.5 GHz
10.5–20.5 GHz

4

20.5–34 GHz

WVR (4)20.5–34 GHz

5

30.5–50.5 GHz

6

70–116 GHz

Receiver Type
DS
DS
DS
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB
2SB

# bits
8
8
8
8
8
8
8
8
8
8
8
8
4
4
4
4

Sample Rate
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s
7 GS/s14 GS/s
14 GS/s
14 GS/s
14 GS/s

Figure 2 - Integrated Receiver/Downconverters and Digitizers frequency plan.

4.2.1

Sideband-Separating (2SB) Receiver Modules

A block diagram of a typical 2SB receiver module is shown in Figure 3. Each module has two RF inputs,
one for each polarization. These inputs are broadband filtered to limit the power to downstream
components, then amplified.
Preferably following the warm RF amplifier is a step attenuator for level control. This ensures that any
changes here have minimal effect on the calibration coefficients for sideband-separation. At the highest
frequencies, where step-attenuators may not be readily available, this level-control could be moved into
the IF signal path. In that case, the M&C software should be programmed to step the attenuators in the I

Page 8 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

and Q signal paths synchronously after initial balancing in the lab—again, to ensure minimal impact on thecalibration coefficients. Although some uncorrected amplitude imbalance will result from non-uniformityof the step-sizes of the two attenuators, the effect should be sufficiently small that the modules will stilleasily meet the sideband-rejection specification. All 2SB modules will support a power adjustment rangeof ±12 dB from nominal. The lower frequency bands may need an additional 30 dB switchable attenuatorto support solar observing. This 30 dB of extra attenuation will undoubtedly degrade the noise figure, but
this is not a concern for the solar-observing scenario.

Figure 3 - Block diagram of a sideband-separating (2SB) receiver module.

The mixers implement a single-LO, direct-to-baseband I/Q downconversion. Additional warmamplification and anti-alias filtering is present at baseband. This is followed by the Serial-ADC (SADC) chipdescribed earlier, either two dual-channel SADCs or a single quad-channel SADC to capture I and Q fromboth polarizations. The SADC chip is progammable to support multiple bit depths and sample rates. For
the highest bands needing the widest bandwidths, we anticipate 4-bit sampling at 14 GS/s. For lower bands,
where human interference is more likely an issue, we will use 8-bit sampling at 7 GS/s.
Both sample rates are compatibile with the emerging industry standard serial rate of 56 Gbps per lane.
These serial outputs are therefore fed into a quad-channel fiber-optic transceiver capable of transmitting
56 Gbps per lane, where four optical wavelengths are combined onto a single fiber. Although relatively
new, such transceivers conforming to the QSFP28 form-factor (shown in Figure 4) are now becoming
available with reaches of 500m up to 80 km [RD04–05]. These transceivers modulate the optical carrierat 28 giga-symbols per second using four-level pulse-amplitude modulation (PAM4), thus achieveing theserial rate of 56 Gbps.

Figure 4 - Quad Small Form-Factor Pluggable (QSFP28) optical transceiver.

Page 9 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

Date: 2019-07-25

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Version: A

A comparison of the eye-diagrams for the more common binary NRZ modulation and the PAM4
modulation are shown in Figure 5. The implementations of our unformatted serial link in actual telescope
hardware to date have been limited to the NRZ waveform, but calculations show that the PAM4 waveform
would be even more robust in our links due to the higher density of transitions for the clock recovery
loop to lock onto (see Figure 6).

(a)

(b)

Figure 5 - Comparison of (a) binary NRZ and (b) PAM4 optical modulation schemes.

Figure 6 - Transition density for Gaussian-distributed white noise as a function of rms signal amplitude, for both
NRZ and PAM4 encoding.

Although the SADC chip which is critical to realizing the SWaP benefits of the proposed design is not yet
available, prototyping on fully-functional (but not full-spec) receiver modules has already begun. An
example is shown in Figure 7. The internal details of the construction are shown in Figure 7(b).
This dual-polarization module operates in W-band (75–110 GHz) and may be considered an early
prototype for the ngVLA Band 6. It utilizes a Kintex7 FPGA to implement the unformatted serialization of
the ADC outputs at 8 Gbps. When the SADC chip becomes available, the same function as this FPGA
plus the two ADCs will be implemented on a single chip in a 4mm package and consuming 1/25th thePage 10 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

power. This module has two QSFP output connectors (which are really redundant since only one hasenough channels to service the whole module).

(a)

(b)

Figure 7 - Prototype W-band IRD 2SB receiver module. (a) Photo. (b) Exploded view of internal construction.
Note that this is only a prototype. The cooling fans are needed here since the power-saving Serial ADC ASIC
was not yet available. The reference design version will be smaller, consume less power, and be cooled withoutfans by attachment to a temperature-controlled plate.

4.2.2

Direct-Sampled (DS) Receiver Modules

The SADC will have wide analog input bandwidth to support direct-sampling up to the third Nyquist zone
for the lower ngVLA bands. A block diagram for such a receiver module is shown in Figure 8. This module
begins with a filter or diplexer depending on the RF band (the diplexer is shown), which roughly isolates
the individual Nyquist zones for sampling. This is followed by warm amplification, power leveling, additional
amplification, and a final anti-aliasing filter before feeding into the SADC chip and QSFP fiber transceiver.
From the SADC forward, the data path is the same as it was for the 2SB modules.

Figure 8 - Block diagram of a direct-sampled (DS) integrated receiver module.

Page 11 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

Band 1 will only need two channels (corresponding to the first Nyquist zone for two polarizations) insteadof the usual four. Since the commercially available QSFP modules inherently support four duplex, thisleaves two lanes unoccupied. The reference design has no predetermined used for these lanes; however,
one transmit-receive pair could be configured simply to operate in a loopback mode as part of a roundtrip delay measurement in support of the time distribution subsystem, at no extra cost to the IRD modules.
Both the 2SB and DS receiver modules are considered line-replaceable units (LRUs) in this design.

4.2.3

Other Components

Other subsystem components include the splitters/combiners that interface these modules to the frontend cryogenics, and the internal interconnects between them and the 2SB/DS receiver modules.

4.3 Interfaces with Other Subsystems
This section provides information about the interfaces of the integrated modules. Interface Control
Documents (ICDs) are required between the integrated modules and all connecting systems. In manycases, specifications for the interfaces are not yet available, but the broad scope of the ICD can be defined.
These interfaces shall be developed and documented by the Integrated Receivers and Downconverters
designer. Post CoDR, the ICD shall only be updated through formal project change control processes.
Unilateral aspects of the connector interfaces (e.g., M or F) shall refer to the connector on the integrated
modules. Cables, waveguide, and fiber runs between the integrated modules and other electronic
subsystems are not included in this work package.

4.3.1

Interface to the Cryogenic Front End Subsystem

Signal at Interface
Band 1 RF

Type
Input

Band 2 RF

Input

Band 3 RF

Input

Band 4 RF

Input

Band 5 RF

Input

Band 6 RF

InputParameter
Connector
Impedance
Multiplicity
Connector
Impedance
Multiplicity
Connector
Impedance
Multiplicity
Connector
Impedance
Multiplicity
FlangeMultiplicity
FlangeMultiplicity

Value
2.92 mm (F)50 ȍx2 (one per pol.)2.92 mm (F)50 ȍx2 (one per pol.)2.92 mm (F)50 ȍx2 (one per pol.)2.92 mm (F)50 ȍx2 (one per pol.)WR-22 (UG599)
x2 (one per pol.)WR-10 (UG387)
x2 (one per pol.)Comments

The frequency ranges for these inputs are given in Figure 2. The RF splitters and combiners shown in
Figure 1 are included in the IRD subsystem.

Page 12 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

Date: 2019-07-25

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

4.3.2

Interface to the Water Vapor Radiometer

Signal at Interface
WVR RF

4.3.3

Version: A

Type
Input

Parameter
Connector
Impedance
Multiplicity

Value
2.92 mm (F)50 ȍx2 (one per pol.)Comments

Interface to the Timing Reference/LO Subsystem

Signal at Interface
Sample Clock Reference

Type
Input

Band 3 LO

Input

Band 4 LO

Input

Band 5 LO

Input

Band 6 LO

Input

Parameter
Frequency
Electrical Format
Connector
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity
Power Level
Phase Noise
Connector
Impedance
Multiplicity

Value
156.25 MHz
LVDS
TBD
x15 (TBC)>+13 dBm (CW)
TBD
2.92 mm (F)50 ȍx2>+13 dBm (CW)
TBD
2.92 mm (F)50 ȍ
x4>+13 dBm (CW)TBD
WR-22 (UG599)
50 ȍ
x3>+13 dBm (CW)TBD
WR-10 (UG387)
50 ȍ
x4

Comments
Coaxial, shielded

The LO nominal frequencies are given in Figure 1. Each is nominally fixed to simplify calibration andoperations, however a ±2 GHz tuning range is supported in order to provide overlap of the adjacentfrequency bands so that no frequency “blind spots” exist (except for two narrow slivers between the
Nyquist zones of Bands 1 and 2).

4.3.4

Interface to the Monitor and Control Subsystem

Signal at Interface
M&C Serial Bus

Type
Input / Output

ParameterProtocolConnector
Number of Pins
Multiplicity

Page 13 of 16

Value
SPI (mode 0)
Nano-D (F)TBD
x15 (TBC)

Comments
May be combined on thesame cable harness withpower supplies

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

Date: 2019-07-25

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

4.3.5

Interface to the Power Supplies

Signal at Interface
Analog Positive Supply
Digital Positive Supply
Main Negative Supply

4.3.6

Version: A

Type Parameter
Input Voltage
Current Draw
Multiplicity
Input Voltage
Current Draw
Multiplicity
Input Voltage
Current Draw
Multiplicity

Value
+5 V
<1 A (TBC)
x15+3.3 V<1 A (TBC)
x15–5 V<100 mA (TBC)
x15

Comments
Internally regulated for
multiple voltages.
Internally regulated.
Primarily (exclusively?) for
transistor gates.

Interface to the Data Transmission Subsystem

Signal at Interface
Digital IFs

Type
OutputParameter
Data Format
Data Content
Connector
Physical Format
Nominal Wavelength
Colors/Lanes
Baud Rate
Modulation
Multiplicity

Value
Unformatted
I/Q or Nyquist
QSFPSingle-Mode Fiber
1310 nm
4
56 Gbps per lane
PAM4
x15

Page 14 of 16

Comments
PAM4 modulation
carries 2 bits per
symbol, so “effective”
56 Gbps per lane isachieved bytransmitting 28 billion
symbols per second.

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

5 Appendix
5.1 Abbreviations and Acronyms
Acronym
AD
ADC
ASIC
DBE
DSP
DTS
IF
IRD
LO
LRU
M&C, M/C
NES
ngVLA
NRZ
NSF
PAM4
PLL
QSFP28RD
RF
SADC
SerDes
SWaP
TBD
VLA
WVR

Description
Applicable Document
Analog-to-Digital Converter
Application Specific Integrated Circuit
Digital Back End
Digital Signal Processing
Data Transmission System
Intermediate Frequency
Integrated Receiver/Downconverter and Digitizer
Local Oscillator
Line Replaceable Unit
Monitor and Control
Near Earth Sensing
Next Generation VLA
Non-Return to Zero (binary modulation)
National Science Foundation
Four-level Pulse Amplitude Modulation
Phase Locked Loop
Quad Small Form-factor Pluggable 28 (giga-symbols per second)
Reference Document
Radio Frequency
Serial Analog-to-Digital Converter
Serializer/Deserializer
Size, Weight, and PowerTo Be Determined
Jansky Very Large Array
Water Vapor Radiometer

Page 15 of 16

Title: Integrated Downconverters andDigitizers Design Description

Owner: M. Morgan

NRAO Doc. #: 020.30.15.00.00-0002-DSN-AINTEGR_RECVR_DOWNCONVERTER_REF_DSN

Date: 2019-07-25
Version: A

5.2 Bibliography
For more information on the prototypes and techniques employed by the IRD subsystem, the reader isreferred to:
M. Morgan and J. Fisher, "Statistical Word Boundary Detection in Serialized Data Streams," U.S. Patent
No. 8,688,617, April 1, 2014. People's Republic of China Patent No. 201180046318.8, February 5, 2017.
M. Morgan, S. Wunduke, J. Castro, T. Boyd, and W. Groves, "Compact cm-wave and mm-wave integrated
receivers," 32nd URSI General Assembly and Scientific Symposium, Montreal, August 2017.
J. Castro, M. Morgan, J. Ford, and V. van Tonder, "Digital sideband separating downconversion for theGreen Bank Telescope phased array feed," URSI National Radio Science Mtg., Boulder, CO, January 2016.
M. Morgan, J. Fisher, and J. Castro, "Unformatted Digital Fiber-Optic Data Transmission for Radio
Astronomy Front Ends," Publications of the Astronomical Society of the Pacific, vol. 125, no. 928, pp. 695-704,
June 2013.
M. Morgan and J. Fisher, "Experiments With Digital Sideband-Separating Downconversion," Publications of
the Astronomical Society of the Pacific, vol. 122, no. 889, pp. 326-335, March 2010.
M. Morgan and S. Wunduke, "An integrated receiver concept for the ngVLA," ngVLA Memo #29, November
2017.
M. Morgan and J. Fisher, "Word-Boundary Detection in a Serialized, Gaussian-Distributed, White-Noise
Data Stream," Electronics Division Technical Note #213, October 2009.
M. Morgan and J. Fisher, "Simplifying Radio Astronomy Receivers," NRAO eNews, vol. 2, no. 3, March 2009
J. Fisher and M. Morgan, "Analysis of a Single-Conversion, Analog/Digital Sideband Separating Mixer
Prototype," Electronics Division Internal Report #320, June 2008.

Page 16 of 16

Title: Digital Backend/Data Transmission System:

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

Digital Backend/Data Transmission System:
Technical Requirements
020.30.25.00.00-0001-REQ-A-DBE_DTS_TECHNICAL_REQS

Status: RELEASEDPREPARED BY

ORGANIZATIONDATE

J. Jackson
S. Durand, Antenna Electronics IPT Lead

Electronics Div., NRAOElectronics Div., NRAO

2019-04-24
2019-04-25

APPROVALS
R. Selina,
Project Engineer

ORGANIZATIONElectronics Division,
NRAO

DATE
2019-07-24

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 12:40:44 -06'00'

Asst. Director for
NM-Operations, NRAO

2019-07-24

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.24 12:41:10 -06'00'

ORGANIZATION
Asst. Director for
NM-Operations, NRAO

DATE
2019-07-24

2019.07.24
12:11:14 -06'00'

Page 1 of 20

Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

Change Record

J. Jackson

Affected
Section(s)All

Initial draft

2018-06-04

J. Jackson

All

Continued work, many changes

3

2018-07-09

J. Jackson

All

Cleanup4

2018-09-24

J. Jackson

All

Continued editing, new requirements5

2018-09-24

All

Small edits62018-09-24

S. Durand,
J.Jackson
J. JacksonAll

Reorganized Requirements tables

7

2018-11-21

J. Jackson

3.4.1/4.3
5.1
3.2
Multiple
4.1
4.1
4.1
3.4.2
4.3

8

2018-11-27

J. Jackson

Numerous
Various

Fixed typo per RID IPDSR-21
Clarified baud rate per RID IPDSR-22
Added LBA stations per RID IPDSR-66
Typos fixed per RID IPDSR-71
Reworded DEB009 per RID IPDSR-74
DBE005/6 edited per RID IPDSR-72
DBE001/2 edited per RID IPDSR-69
Removed 3.4.2 (empty)
Removed untraceable requirements & specs
per RID IPDSR-78
Added refs and updated tables per IPDSR-79
A few cleanup edits for release9

2019-04-24

S. DurandAll

Small edits102019-04-24

J. Jackson11

2019-05-30

R. Selina

4.2
4.4
4.6
5.2
3.1, 6, 9

Timestamp Jitter Specification
RFI/EMC Specifications
MTBF Specification
Clock & Timecode specs
Minor edits for releaseA

2019-07-24

A. Lear

All

Incorporate minor edits by M. McKinnon;
prepare document for approvals & release

Version

Date

Author1

2018-05-11

2

ReasonPage 2 of 20

Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

Table of Contents
1

Introduction ................................................................................................... 5

1.1
1.2

Purpose ................................................................................................................................... 5
Scope ...................................................................................................................................... 5

2

Related Documents and Drawings ............................................................... 6

2.1
2.2

Applicable Documents ........................................................................................................... 6
Reference Documents ............................................................................................................ 6

3

Overview of DBE/DTS Technical Requirements ........................................ 7

3.1
3.2
3.3
3.4
3.4.1

Document Outline ................................................................................................................. 7
Project Background................................................................................................................ 7
General DBE/DTS Work Package Description ..................................................................... 7
Summary of DBE/DTS Work Package Requirements .......................................................... 8
General Functional Specifications .......................................................................................................... 84

DBE/DTS Functional and Performance Requirements ............................. 9

4.1
4.2
4.3
4.4
4.5
4.5.1
4.5.2
4.6
4.7
4.8

Functional Requirements ....................................................................................................... 9
Performance Requirements ................................................................................................... 9
I/O Requirements ................................................................................................................. 10
Spurious Signals/Radio Frequency Interference Generation ............................................. 10
Environmental Conditions ................................................................................................... 10
Normal Operating Conditions ............................................................................................................. 10
Specific Environmental Requirements................................................................................................. 10
Maintenance and Reliability Requirements ....................................................................... 10
Monitor and Control Requirements ................................................................................... 10
Lifecycle Requirements ........................................................................................................ 115Interface Requirements .............................................................................. 12

5.1
5.2
5.3
5.3.1
5.3.2
5.3.3
5.4

Interface to the Integrated Downconverter/Digitizer Subsystem ..................................... 12Interface to the Reference Signal Subsystem ..................................................................... 12Interface to the Antenna Structure .................................................................................... 13
Electrical Infrastructure .......................................................................................................................... 13
HVAC ......................................................................................................................................................... 13
RFI Mitigation ............................................................................................................................................ 13
Interface to the Monitor and Control System ................................................................... 13

6

Safety ............................................................................................................ 14

6.1
6.2
6.2.1
6.2.2
6.2.3
6.2.4

General ................................................................................................................................. 14
Safety Design Requirements................................................................................................ 14
Fire Safety .................................................................................................................................................. 14
Mechanical Safety ..................................................................................................................................... 14
Electrical Safety......................................................................................................................................... 14
Handling, Transport, and Storage Safety ............................................................................................ 14

7

Design Requirements .................................................................................. 15

7.1
7.1.1
7.2
7.3
7.3.1
7.3.2

Analyses and Design Requirements..................................................................................... 15
Reliability Availability Maintainability Analysis ................................................................................... 15
Electromagnetic Compatibility Requirements ................................................................... 15
Materials, Parts, and Processes ........................................................................................... 15
Fasteners .................................................................................................................................................... 15
Paints........................................................................................................................................................... 15

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Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

7.3.3
7.3.4
7.3.5

Date: 2019-07-24
Version: A

Surface Treatment ................................................................................................................................... 15
Name Plates and Product Marking ...................................................................................................... 15
Labels .......................................................................................................................................................... 16

8

Documentation Requirements ................................................................... 16

8.1
8.2

Technical Documentation ................................................................................................... 16
Software and Software Documentation ............................................................................. 16

9
10

Verification and Quality Assurance ........................................................... 17
Appendix....................................................................................................... 19

10.1
10.2

Maintenance Definitions ..................................................................................................... 19
Abbreviations and Acronyms ............................................................................................... 20

Page 4 of 20

Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

1 Introduction
1.1 Purpose
This document presents a set of technical requirements for the design of the ngVLA Digital Backend/Data
Transmission System (DBE/DTS) work package. Many requirements flow down from the preliminary
ngVLA System Requirements [AD02], which in turn flow down from the preliminary ngVLA Science
Requirements [AD01].
The science goals are presently being elaborated by the Science Advisory Council (SAC) and Science
Working Groups (SWGs), and are captured in a series of draft use cases. This document reflects
preliminary analysis of these use cases and the flow down recursively to the science, system and subsystem
requirements.

1.2 Scope
The scope of this document is the ngVLA DBE/DTS work package. This describes an opto-electronics
system that receives unformatted data streams from the Integrated Downconverter/Digitizer Subsystem,
performs substantial processing and data reduction on them, then formats and modulates them onto
optical carriers for transmission to the Array Center via private and/or commercial fiber optic
infrastructure.
This requirements document establishes the performance, functional, design, and test requirements
applicable to the ngVLA DBE/DTS work package. It also includes interface requirements that must be
defined.

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Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of this Technical Specification shall be considered as a superseding requirement.
Reference
No.
AD01
AD02
AD03
AD04
AD07
AD08
AD10
AD11
AD12
AD13
AD14
AD15
AD16
AD17
AD18
AD19

Document Title

Rev/Doc. No.

Science Requirements
Preliminary System Requirements
Operations Concept
Protection Against Electric Shock – Common Aspects
for Installation and Equipment
Insulation Coordination for Equipment within LowVoltage Systems
Occupational Safety and Health Standards for GeneralIndustry
Military Handbook, Reliability Prediction of Electronic
Equipment
Non-Electronic Parts Reliability Data
Electromagnetic Compatibility
Integrated Downconverters and Digitizers Design
ngVLA Memo 29: An Integrated Receiver Concept for
the ngVLA
System Requirements
System Environmental Specifications
System EMC and RFI Mitigation Requirements
System-Level Electrical Requirements
System-Level Mechanical Requirements

020.10.15.00.00-0001-REQ
020.10.15.10.00-0003-REQ
020.10.05.00.00-0002-PLA
IEC 61140:2016
IEC 60664
29 CFR Part 1910
MIL-HDBK-217F
NPRD-95
IEC 61000-3-5
020.30.15.00.00-0002-DSN
ngVLA Memo 29
020.10.15.10.00-0003-REQ
020.10.15.10.00-0001-SPE
020.10.15.10.00-0002-REQ
020.10.15.10.00-0005-REQ
020.10.15.10.00-0006-REQ

2.2 Reference Documents
The following references provide supporting context:
ReferenceNo.
RD01

Document Title

Rev/Doc. No.

Subsystem Reference Design Description: Digital Back
End/Data Transmission System

020.30.25.00-0002-DSN

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Title: Technical Requirements

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NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

3 Overview of DBE/DTS Technical Requirements
3.1 Document Outline
This document presents the technical requirements of the ngVLA DBE/DTS work package. These
parameters determine the overall form and performance of the DBE/DTS work package.
The functional and performance requirements, along with detailed explanatory notes, are found in Section
4. The notes elaborate on the meaning, intent, and scope of the requirements. These notes form an
important part of the definition of the requirements and should guide the verification procedures. In manycases the notes contain an explanation or an analysis of how the numeric values of requirements were
derived. Where numbers are not well substantiated, this is also documented in the notes. In this way, therequired analysis and trade-space available is apparent to scientists and engineers who will guide theevolution of the ngVLA DBE/DTS work package concept.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses. Safety requirements applicable to both the design phase and thefunctional DBE/DTS work package are described in Section 7. Additional requirements for the designphase are described in Section 8. Documentation requirements for both technical design documentationand software are provided in Section 9. Requirements for the Verification and Test, from the conceptual
design through to prototype, are described in Section 10.

3.2 Project Background
The Next Generation Very Large Array (ngVLA) is a project of the National Radio Astronomy
Observatory (NRAO) to design and build an astronomical observatory that will operate at centimeter
wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116
GHz). The ngVLA will be a synthesis radio telescope composed of approximately 244 reflector antennas
each of 18 meters diameter, and 19 reflector antennas each of 6 meters diameter, operating in a phased
or interferometric mode.
The array’s signal processing center will be located at the Very Large Array site on the Plains of San
Agustin, New Mexico. The array will include stations in other locations throughout New Mexico, west
Texas, eastern Arizona, and northern Mexico. Long baseline stations are located in Hawaii, Washington,
California, Iowa, Massachusetts, New Hampshire, Puerto Rico, the US Virgin Islands, and Canada.
Operations will be conducted from both the VLA Control Building and the Array Operations Center inSocorro, NM.

3.3 General DBE/DTS Work Package Description
This work package leads to the design of a Digital Back End/Data Transmission System Subsystem thatreceives data from the Integrated Downconverter/Digitizer subsystem, performs the primary digitalprocessing required at the antenna, and prepares data for transmission across private and public
telecommunications infrastructure. This subsystem is concentrated in a single, highly integrated RFI
shielded module located in the pedestal area of each ngVLA antenna.
Digital data streams produced in the Integrated Downconverter/Digitizer (IRD) Modules located in the
Front End (FE) are received in the DBE/DTS module via 13 single-mode fibers. Clock recovery and deserialization is performed on the data which is then fed to digital processing blocks where functions suchas channelization, digital downconversion, re-quantization, RFI tagging or excision, etc. can be performed.

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Date: 2019-07-24
Version: A

Processed data is then formatted into standard telecommunication formats (i.e. Ethernet, SONET) andplaced back into the optical domain for transmission over private or commercial fiber-optic networks.

3.4 Summary of DBE/DTS Work Package Requirements
The following table provides a summary of the major requirements in order to provide the reader witha high-level view of the desired system. Should there be a conflict between the requirements listed here
and the descriptions in Sections 4 through 10, the latter shall take precedence.

3.4.1

General Functional Specifications

Parameter

Summary of Requirement

Single Channel Input Data Rate

56,000 Mbps
(on each optical carrier from IRD)
46 (4 each from Bands 2–6 IRD modules,
2 from Band 1 IRD module)
7x109 8-bit samples/sec or
14x109 4-bit samples/sec
Unformatted raw data

Number of Input Channels
Input Data Sample Rate/Bit Depth
Input Data Format

Page 8 of 20

Reference
Reqs.
IRD0711-716
IRD0721-726
IRD0711-716
IRD0721-726
IRD0711-716
IRD0721-726
IRD0711-716
IRD0721-726

Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

4 DBE/DTS Functional and Performance Requirements
These requirements apply to a properly functioning system under normal operating environmental
conditions unless otherwise stated.

4.1 Functional Requirements
Parameter
Clock Recovery

Req. #
DBE001

Coarse Sideband
Separation

DBE002

Digital LO for Mixer

DBE003

Sub-Band Selection

DBE004

RFI Flagging

DBE005RFI Excision

DBE006

Oversampling
Polyphaser Filter

DBE007

Apply Timestamp

DBE008

Data Encoding

DBE009

Data Transmission

DBE010Value
The DBE shall perform clock recovery on theunformatted data streams received from the IRD
modules as described in [AD13] and [AD14].
The DBE must perform coarse sideband separation
into upper and lower sidebands using the IQ pairs
received from the IRD modules as described in[AD13] and [AD14].
The DBE must generate a LO for the sub-band
selection digital mixer and track and control its
phase.
Using a digital mixer and digitally generated LO, theDBE must be able to tune and select multiple subbands.
The DBE must be capable of identifying and flagging
data in the presence of known or suspected radio
frequency interference; details TBD.
The DBE should be capable of performing digital
signal processing to excise certain destructive radio
frequency interference from the data stream using
specially designed excision algorithms; details TBD.
The DBE polyphaser filters must have an
oversampling capability to eliminate concerns withdead zones between sub-bands.
The DBE must apply a timestamp based on thereference clock and timing inputs to data before
transmission to the central signal processor.
The DBE must encode data into format(s)compatible with the data transmission medium
being used. This mainly refers to antennas
connected to commercial networks.
The DBE must output optical data streams that canbe placed directly on fiber to the array center or iscompatible with COTS data transmission
equipment at the site.

Traceability

4.2 Performance Requirements
Parameter
Upper/Lower Sideband Isolation
Timestamp Jitter

Req. #
DBE200
DBE201Value>43 dB
6.4 nsPage 9 of 20

Traceability

Title: Technical Requirements

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NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

4.3 I/O Requirements
Parameter
Input Data Sample Rate/Bit
Depth

Req. #
DBE103Value
7x109 8-bit samples/sec or
14x109 4-bit samples/sec

Traceability
IRD0711-716
IRD0721-726

4.4 Spurious Signals/Radio Frequency Interference Generation
Parameter
Enclosure RFI Shielding @100 MHz
Enclosure RFI Shielding @1 GHz
Enclosure RFI Shielding @10 GHz

Req. #
DBE114
DBE115
DBE116Value
Max EIRP Emission –126 dBm
Max EIRP Emission –126 dBm
Max EIRP Emission –102 dBm

Traceability
EMC3010, SYS2104
EMC3010, SYS2104
EMC3010, SYS2104

4.5 Environmental Conditions
4.5.1

Normal Operating Conditions

Parameter
Operating Temperature Range
Altitude, etc.

4.5.2

Req. #
DBE112
DBE119Value–15 to +35°C
2500 meters

Traceability
ENV0323
ENV0351

Specific Environmental Requirements

Parameter
Storage Temperature Range

Req. #
DBE113Value–20 to +70°C

Traceability
020.10.15.10.00-0001-SPE System-Level
Environmental Specifications

4.6 Maintenance and Reliability Requirements
Parameter
Mean Time Between Failures

Req. #
DBE120Value
MTBF  35,040 hrs.

Traceability
SYS2402

The maintenance and reliability requirements support high-level requirements that limit the total array
operating cost. Monitor points/sensors should be included in the MTBF/MTTR analysis, but sensors andother components that can be reasonably deemed ancillary to operation may be removed from thedetermination of compliance with the MTBF requirement. “Failure” will be defined as a condition thatplaces the system outside of its performance specifications or into an unsafe state, requiring repair.

4.7 Monitor and Control Requirements
The DBE/DTS work package shall measure, report, and monitor parameters that allow for determinationof its status and may help predict or respond to failures.
Parameter
Input Power
Supply Voltage
Input Optical
Power Monitor

Req. #
DBE900
DBE901

Value
Traceability
The DBE/DTS module shall measure, report, andSYS2701
monitor the input DC supply voltage to the module.
The DBE shall report actual optical power or digital
status indicating optical power on all inputs is within an
acceptable limit. Subject to power monitoring capabilityof the optical receiver.

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NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQSParameter
Input Clock
Power

Req. #
DBE902

Input Timing
Signal

DBE903ModuleDBE904Temperature(s)Electronic
Serial Number
Standby Mode

DBE905

Automatic
Initialization

DBE907

Data
Transmission
Link Status
Clocking
System Status

DBE908

Data Quality
Sampling

DBE910

DBE906

DBE909Date: 2019-07-24
Version: A

Value
Traceability
The DBE shall report actual power or digital statusindicating power on the clock input is within an
acceptable limit.
The DBE shall report that a valid timing signal isreceived at an appropriate level and passes all built-in
error checking.
The DBE shall report actual temperatures of heatsinks,
power supply, internal ambient temperatures and thestatus of any internal over temperature protection
circuits.
The integrated modules shall report a uniqueelectronic identification upon request.
The DBE shall be capable of entering a low-power
standby mode on command. M&C communications
shall still be functional in this mode.
The DBE Module shall automatically boot into anominal operational mode on power-up, absent any
command from M&C.
The DBE module shall report the connection status of
the 100 Gbps Ethernet links used for data transmission.
The DBE module shall report the lock/tuning status ofany clock generation circuitry in the module. This
includes FPGA clocking resources and any external PLL
oscillators used in the module.
The DBE module shall be capable of grabbing a chunkof sampled data from multiple points in the system andof sufficient size to be processed into useful diagnostic
data. This could either be passed as raw data orprocessed locally into formats useful for diagnostics.
Results are transmitted via the M&C network.

The expectation with self-monitoring is that the M&C system will expose lower-level sensors to the M&C
system when queried. The cadence of access is flexible, and is not expected at high rates (typical accessmight be on second to minute scales). Any high-cadence monitoring should generally be internal to the
DBE/DTS work package control system with a summary output on the interface.
Other features of the M&C interface are specified in the Monitor and Control ICD. Lifecycle costs include
manufacturing, transportation, construction/assembly, operation, and decommissioning.

4.8 Lifecycle Requirements
Parameter
Design Life
Life Cycle
Optimization

Req. #Value
DBE1801 The DBE/DTS work package shall be designed to be
operated and supported for a period of 20 years.
DBE1802 The DBE/DTS work package design shall minimize its
lifecycle cost for 20 years of operation.

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Traceability
SYS2801
SYS2802

Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

5 Interface Requirements
This section provides information about the interfaces of the DBE/DTS work package. Interface Control
Documents (ICDs) are required between the DBE/DTS work package and all connecting systems. In manycases, specifications for the interfaces are not yet available, but the broad scope of the ICD can be defined.
These interfaces shall be developed and documented by the DBE/DTS work package designer, andapproved by ngVLA, as part of the DBE/DTS work package reference and conceptual design efforts, andupdated throughout the design. Post CoDR, the ICD shall only be updated through formal project change
control processes.

5.1 Interface to the Integrated Downconverter/Digitizer Subsystem
Data processed by the DBE/DTS subsystem is produced in the 13 integrated downconverter/digitizer(IRD) modules located near the receivers in the antenna. These produce data in one of two formats:x 8-bit samples at 7 Giga samples per second, or
x 4-bit samples at 14 Giga samples per second.
The data streams are modulated onto optical carriers at 1310 nm. The outputs of these IRD modules are
optically combined onto 16 single mode fibers. These fibers enter through 16 terminals of a 36-fiber APC
type ruggedized circular connector. Each of these data streams arrives at the DBE/DTS PCBs on a single
mode fiber containing an LC type connector that connects to one of the QSFP28 form factor opticaltransceivers. The optical transceivers achieve 56 Gbps transfer rates using four-level PAM4 modulation.
Signal at
Interface
Digital IFs

TypeParameter

Value

Comments

Input

Data Format
Data Content
Connector
Physical Format
Nominal Wavelength
Colors/Lanes
Baud Rate
Effective Bit Rate
Modulation# of fibers

Unformatted
I/Q or Nyquist
QSFPSingle-Mode Fiber
1310 nm
4 (2 from Band 1)
28 Gbaud/Lane
56 Gbps/Lane
PAM4
13

PAM4 modulation carries 2 bits
per symbol, so “effective” 56
Gbps per lane is achieved bytransmitting 28 billion symbols
per second.
Number of fibers: 13 nominal

5.2 Interface to the Reference Signal Subsystem
The DBE/DTS module receives a 156.25 MHz CW clock from the antenna reference subsystem. Thissignal arrives as a 156.25 MHz CW signal modulated onto a 1310 nm optical carrier. It enters the module
on one terminal of a 36-fiber APC type ruggedized circular connector on the front face of the module.
The reference fiber is connected to an optical receiver to be converted to an electrical 156.25 MHz clockthat feeds all of the FPGAs.
The DBE/DTS module also receives a timecode signal from the antenna reference subsystem. This is adigital timing signal modulated onto a 1310 nm optical carrier. It enters the module on one terminal of a
36-fiber APC type ruggedized circular connector on the front face of the module. The timecode fiber isconnected to an optical receiver to be converted to an electrical timecode signal that feeds the FPGAs.

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Title: Technical Requirements

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NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

Signal at
Interface
Master Clock

Type

Parameter

Value

Comments

Input

Input

156.25 MHz
Sine Wave (CW)
0 dBm
SMA
2.5 ps
Optical/Digital
IRIG-APart of fiber circular connector
1ms

SYS5001

Time CodeFrequency
Signal Type
Level
Connector
Phase Noise/Jitter
Signal Type
FormatConnector
Resolution(or similar)

5.3 Interface to the Antenna Structure
5.3.1

Electrical Infrastructure

Electrical power to the DBE/DTS module(s) is a single –48 VDC connection from the –48 VDC powersubsystem in the antenna pedestal room. This enters the module through a two-terminal filtered, locking
type power connector on the front face of the module. Battery backup is provided through the –48 VDC
power subsystem. No addition batteries are used for the DBE/DTS subsystem. The –48 VDC input to themodule is over-current protected by a single-use fuse internal to the module. The input connector will be
keyed to assure correct polarity, so no reverse polarity protection is required.
Signal at
Interface
Main Power

5.3.2

Type Parameter

Value

Comments

Input

DC Voltage–48 Volts DC
10 Amps Max
Filtered locking circular connector

020.10.15.10.00-0005REQ System-Level
Electrical Requirements

Signal Type
Nominal Level
Current
Connector

HVAC

The DBE/DTS module has external heatsink fins on both sides of the enclosure. Forced-air cooling in therack will move air across these fins. The module is sealed so no air penetrations or air filtering is required.
The module is designed with internal thermal protection to shut down or reduce power dissipation in theevent of HVAC failure.

5.3.3

RFI Mitigation

The module is RFI shielded to prevent interference with the astronomical signals received by the antenna.
Shielding effectiveness is outlined in Section 4.1.

5.4 Interface to the Monitor and Control System
The M&C connection uses Gigabit Ethernet connection to the antenna M&C Ethernet switch. Two fibers(transmit and receive) connect to the module via two terminals of the 36-fiber APC type ruggedized
circular connector on the module face. Internally the fibers connect to an SFP+ type transceiver connectedto the internal M&C processor.

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Title: Technical Requirements

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Date: 2019-07-24
Version: A

6 Safety
6.1 General
Parameter Req. # Value
Weight
DBE121 50 lbs

Traceability
020.10.15.10.00-0006-REQ System-Level Mechanical Requirements

6.2 Safety Design Requirements
6.2.1

Fire Safety

The module will have a sealed metal enclosure with fusing to minimize fire risk in internal electronics orexternal wiring. Thermal protection will minimize power dissipation in the event of HVAC or internal
component failure.

6.2.2

Mechanical Safety

The module weight will be kept below 50 lbs. to minimize the requirement for two-person lift. Secure
handles will be provided to enable easy transportation of the module. The enclosure will be designed tominimize sharp edges.

6.2.3

Electrical Safety

Electrical equipment installed on the antenna shall comply with their relevant international or US productstandard. Electrical installations and equipment shall be specifically built and/or derated to safely performtheir intended functions under the applicable environmental conditions. Insulation shall be coordinated inconformity with IEC 60664 [AD07] while taking into account the altitude of up to 2500 m above sea level.
The –48 VDC will be protected with fuses to protect both internal electronics and external power supply
infrastructure from damage in the event of a failure in the module. Reverse polarity protection on the
power input is provided by a keyed connector. Switching regulator modules will be implemented with all
fuses and noise suppression or safety (X and Y type) film capacitors as recommended by the manufacturer.

6.2.4

Handling, Transport, and Storage Safety

The design of the DBE/DTS work package shall incorporate all means necessary to preclude or limit
hazards to personnel and equipment during assembly, disassembly, test, and operation.

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Title: Technical Requirements

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Date: 2019-07-24
Version: A

7 Design Requirements
7.1 Analyses and Design Requirements
7.1.1

Reliability Availability Maintainability Analysis

A Reliability Availability Maintainability analysis shall be performed to locate weak design points anddetermine whether the design meets the Maintenance and Reliability requirements. The ngVLA projectwill apply the Parts Count Method for predicting system reliability as described in MIL-HDBK-217F, but
the designer may propose to use other methods. For non-electronic parts, the values of NPRD-95 [AD11]
or data from manufacturers or other databases may be used.
Another, but more time-consuming (and considered more accurate) method, the Parts Stress Analysis
Prediction, is also described in MIL-HDBK-217F. This may be used if the result of the Parts Count Method
does not comply with the Maintenance and Reliability requirements.
The ngVLA equipment will typically operate at 2200 m above sea level, where temperature and pressure
might decrease the MTBF relative to that at low elevations. These conditions shall be taken into specificaccount in the reliability prediction by using the environmental factor given in MIL-HDBK-217F. The
analysis shall result in estimates of the mean time between failures (MTBF) and mean time to repair(MTTR), assuming that any scheduled preventive maintenance is performed.

7.2 Electromagnetic Compatibility Requirements
The ngVLA DBE/DTS work package element shall exhibit complete electromagnetic compatibility (EMC)
among components (intra-system electromagnetic compatibility).

7.3 Materials, Parts, and Processes
7.3.1

Fasteners

All fasteners shall be metric except those on off-the-shelf units. The use of standard metric cross-sections
for construction materials is preferred but not required.

7.3.2

PaintsAny painted coatings shall be chosen to last at least 20 years without repainting.

7.3.3

Surface Treatment

Any unpainted surfaces shall be treated against corrosion.

7.3.4

Name Plates and Product Marking

As a general rule, the main parts and all exchangeable units shall be equipped with nameplates which arevisible after installation of the part/unit and which contain the following information:x Part/unit namex Drawing number including revision
x Serial number
x Manufacturing month and year
x Name of manufacturer
Alternatively, a system of marking based on barcodes or similar system may be used upon ngVLA approval.

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Version: A

For Line Replaceable Units (LRUs; see Section 11.1), it is highly desirable that the serial number of the
LRU be ascertainable over the monitor and control interface (See Section 5.4)

7.3.5

LabelsAll cables and switches, junction boxes, sensors, and similar equipment shall be labeled.

8 Documentation Requirements
8.1 Technical Documentation
All documentation related to the DBE/DTS work package shall meet the following requirements:
x The language used for written documentation shall be English.
x Drawings shall be generated according to ISO standards and use metric units.
x Layouts of electronic circuits and printed circuit boards shall also be provided in electronicallyreadable form. The ngVLA preferred formats are Altium Designer files for electronic circuit diagrams
and printed circuit board layouts.
x The electronic document formats are Microsoft Word and Adobe PDF.
x The preferred CAD system used is AutoDesk Inventor and/or AutoCAD.
Any deviation from the above shall be agreed to by ngVLA.

8.2 Software and Software Documentation
The DBE/DTS work package software and any other specially developed software are deliverables. The
software shall be delivered in source and object form, together with all procedures and tests necessary
for compilation, installation, testing, upgrades, and maintenance.
x Software must be tagged with suitable version numbers that allow identification (also on-line remotely)of a release.
x User manuals of software developed under this specification and of any other commercial software
used (controllers embedded software, special tools, etc.) shall be provided.
x Software maintenance and installation upgrade documentation shall be provided.
x Full Test and Acceptance procedures shall be documented.

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Title: Technical Requirements

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Version: A

9 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A) inspection (I), a factory
acceptance test (FAT) or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which may bechecked by the ngVLA project office during the design phase by review of the design documentation.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which will bechecked by the ngVLA project office during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple inspection
or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item/assembly/unit withthe specified performance shall be demonstrated by tests. A FAT is performed w/o integration withinterfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item/assembly/unit with thespecified performance shall be demonstrated by tests. SAT is performed on-site with the equipment as
installed.
Multiple verification methods are allowed.
The following table summarizes the expected verification method for each requirement.
Req. #

Parameter/Requirement

D

DBE001
DBE002
DBE003
DBE004
DBE005
DBE006
DBE007DBE008DBE009DBE010
DBE101
DBE102
DBE103
DBE104
DBE105
DBE106
DBE107
DBE108
DBE109
DBE110
DBE111
DBE112
DBE113Clock Recovery
Coarse Sideband Separation
Digital LO for Mixer
Sub Band Selection
RFI Flagging
RFI Excision
Oversampling Polyphase Filter
Apply Timestamp
Data Encoding
Data Transmission
Single Channel Input Data Rate
Number of Input Channels
Input Data Sample Rate/Bit Depth
Input Data Format
Output Data Format
Number of Output Channels
Output Channel Data Rate
Maximum Total Data RateMin DC Power Supply Voltage
Max DC Power Supply Voltage
Max Supply Current (@ –48VDC)
Operating Temperature Range
Storage Temperature Range

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A

I

FAT

SAT

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

Title: Technical Requirements

Owner: Jackson

Date: 2019-07-24

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Req. #
DBE114
DBE115
DBE116
DBE117
DBE118
DBE119
DBE120
DBE121
DBE200
DBE201
DBE900
DBE901
DBE902
DBE903
DBE904
DBE905
DBE906
DBE907
DBE908
DBE909DBE910Parameter/Requirement
Enclosure RFI Shielding @ 100 MHz
Enclosure RFI Shielding @ 1 GHz
Enclosure RFI Shielding @ 10 GHz
Physical Dimensions
Humidity
Altitude, etc.
Mean Time Between Failures
WeightUpper/Lower Sideband Isolation
Timestamp Jitter
Input Power Supply voltage
Input Optical Power Monitor
Input Clock Power
Input Timing Signal
Module Temperature(s)Electronic Serial Number
Standby Mode
Automatic Initialization
Data Transmission Link Status
Clocking System Status
Data Quality Sampling

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Version: A

D

A

I

FAT
X
X
X

SAT

X
X
X
X
X
X
X

X
X
X
X
X
X
X
X
X
X
X
X
X

Title: Technical Requirements

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0001-REQ-ADBE_DTS_TECHNICAL_REQS

Date: 2019-07-24
Version: A

10 Appendix
10.1 Maintenance Definitions
10.1.1 Maintenance Approach
Required maintenance tasks shall be minimized. Maintenance shall be mainly performed at assembly andsubassembly level by exchange of Line Replaceable Units (LRUs). LRUs are defined as units that can beeasily exchanged (without extensive calibration, of sufficient low mass and dimension for ease of handling,etc.) by technician-level maintenance staff.
A step-by-step procedure for safe exchange of every LRU shall be provided in the Maintenance Manual.
LRU exchange shall be possible by two trained people within four working hours. LRU replacement should
be possible using standard tools identified in a maintenance manual for the Digital Backend work package.
LRUs shall be defined by the Digital Backend work package designer, depending on the design. The LRUs
will be maintained by the ngVLA project (with or without industrial support).
10.1.2 Periodic Preventive MaintenancePreventive maintenance may be performed at planned intervals in order to keep the digital backend work
package operational and within its specified performance. Any required preventive maintenance should be
documented in the Maintenance Manual.

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Date: 2019-07-24
Version: A

10.2 Abbreviations and Acronyms
Acronym
APC
CDR
CoDR
CW
DBE
DTS
EIRP
EM
EMC
EMP
FDR
FEA
FOV
FPGA
FWHM
HVAC
ICD
IF
KPP
LCD
LED
LO
LRU
M&C, M/C
MTBF
MTTF
MTTR
ngVLA
PCB
RFI
RMS
RSS
RTP
SAC
SFP, SFP+, QSFP, etc.
SNR
SRSS
SWG
TAC
TBD
UPS
VLA
WVR

Description
Angle Polished Cut Fiber Connector
Critical Design Review
Conceptual Design Review
Continuous Wave (Sine wave of fixed frequency and amplitude)
Digital Back End
Data Transmission System
Equivalent Isotropic Radiated PowerElectromagnetic
Electromagnetic Compatibility
Electromagnetic Pulse
Final Design Review
Finite Element Analysis
Field of View
Field Programmable Gate Array
Full Width Half Max (of Primary Beam Power)
Heating, Ventilation, & Air Conditioning
Interface Control Document
Intermediate Frequency
Key Performance Parameters
Liquid Crystal Display
Light Emitting Diode
Local Oscillator
Line Replaceable Unit
Monitor and Control
Mean Time Between Failure
Mean Time to Failure
Mean Time to Repair
Next Generation VLA
Printed Circuit Board
Radio Frequency Interference
Root Mean Square
Root of Sum of Squares
Round Trip Phase
Science Advisory Council
Small Form-Factor Pluggable Optical Transceiver & Connector Standard
Signal to Noise Ratio
Square Root Sum of the Square
Science Working Group
Technical Advisory Council
To Be Determined
Uninterruptible Power Supply
Jansky Very Large Array
Water Vapor Radiometer

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Title: Digital Back End/Data Transmission
System Reference Design Description

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0002-DSN-ADBE_DTS_REF_DESIGN

Date: 2019-07-24
Version: A

Digital Back End/Data Transmission System Reference
Design Description
020.30.25.00.00-0002-DSN-A-DBE_DTS_REF_DESIGN

Status: RELEASEDPREPARED BY
J. Jackson, M. Luce, A. Erickson, E. Ford, R. Selina
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-12-04
2019-04-25

APPROVALS
R. Selina,
Project Engineer

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-24

M. McKinnon,
Project Director

Asst. Director for
NM-Operations, NRAO

2019-07-24

RELEASED BY (Name and Signature)
M. McKinnon,
Project Director

ORGANIZATION
Asst. Director for
NM-Operations, NRAO

DATE
2019-07-24

Page 1 of 15

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Date: 2019-07-24
Version: A

Change Record
Date

Author0.1

2018-02-12

E. FordAffected
Section(s)All1

2018-05-08

J. Jackson

All

First main draft

2

2018-06-04

J. Jackson

All

Many changes

3

2018-07-01

J. Jackson

All

Many changes

4

2018-07-09

J. Jackson

All

Editing, interfaces, fixed change record table5

2018-08-17

J. JacksonAll

62018-09-11

J. JacksonAll

7

2018-09-24

S. Durand

All

Added text on Sideband Separating Mixer andsome general editing
Added SysML diagrams and performed significant
final editing
Small edits8

2018-09-27

J. JacksonAll

92018-11-06

J. Jackson102018-11-15

J. Jackson

5.4
6Multiple
5.7.2
5.6
3
2.1
5.3
2.2 & 55
5
4 & 2.2
Many

Reformatting, added SysML structural drawing &text
Fixed Ethernet specs per RID IPDSR-253
Removed empty section 6 per RID IPDSR-283
Typos fixed per RID IPDSR-156
Text updated per RID IPDSR-282
Text updated per RID IPDSR-280
Added SMF per RIDs IPDSR-272 and 227
RD03 Doc # added per RID IPDSR-139
Updated text per RID IPDSR-275
Updated per RID IPDSR-070
Text updated per RID IPDSR-142
Deleted original Fig 5 per RID IPDSR-155
Defined D501 module per RID IPDSR-276
General edits11

2018-11-28

4&5

Major edits122018-12-04

M. Luce
A. Erickson
J. Jackson

All

13

2019-05-30

R. Selina

All

A

2019-07-24

A. Lear

All

General cleanup, added to abbreviations table
Rearranged references
Minor edits for release; replaced a few figures
for readability
Incorporated minor edits by M. McKinnon;
prepared PDF for signatures and release

VersionReasonInitial draft, feedback on Sections 3 & 4

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Title: Digital Back End/Data Transmission
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Owner: Jackson

Date: 2019-07-24
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings...............................................................4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 43
4

Subsystem Overview ..................................................................................... 5
Subsystem Design..........................................................................................6

4.1
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.3
4.4
4.5
4.6
4.7
4.7.1
4.8
4.8.1
4.8.2
4.8.3
4.8.4

IRD Data Stream ................................................................................................................... 8
Digital Processing ................................................................................................................... 9
SERDES......................................................................................................................................................... 9
Unformatted Link Interface ..................................................................................................................... 9Side-Band Separation ................................................................................................................................ 9
Down-Conversion ................................................................................................................................... 10
RFI Excision/Flagging ............................................................................................................................... 11
Data Encoding and Retransmission ..................................................................................................... 11
RFI Tagging and Excision ..................................................................................................... 11
Data Transmission System .................................................................................................. 11
Subsystem Block Diagram ................................................................................................... 12
Mechanical Packaging ......................................................................................................... 13
Subsystem Components ....................................................................................................... 14
High-Level Bill of Materials .................................................................................................................... 14Interfaces with other Subsystems ........................................................................................ 14Power Supply ............................................................................................................................................ 14
LO/Reference ........................................................................................................................................... 14
Integrated Downconverter/Digitizer .................................................................................................. 14
Data Output .............................................................................................................................................. 14

5

Appendix....................................................................................................... 15

5.1

Abbreviations and Acronyms ............................................................................................... 15

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Title: Digital Back End/Data Transmission
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Owner: Jackson

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Date: 2019-07-24
Version: A

1 Introduction
1.1 Purpose
This document provides a description for the Digital Back End/Data Transmission System (DBE/DTS)
subsystem reference design. It covers the design approach, functions, description of key components,
interfaces, and risks associated with the reference design. This document will form part of the submissionof the ngVLA Reference Design documentation package.

1.2 Scope
The scope of this document covers the entire design of the Digital Back End/Data Transmission System
Subsystem, as part of the ngVLA Reference Design. It includes the subsystem’s design, how it functions,and its interfaces with the necessary hardware and software systems. It does not include specific technicalrequirements or budgetary information.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein, but provide necessary context or
supporting material.
Reference
No.
AD01
AD02
AD04

Document Title

Rev/Doc. No.

Digital Back End and Data Transmission System:
Preliminary Requirements
ngVLA Memo 29: An Integrated Receiver Concept for
the ngVLA
Antenna Electronics Front End Enclosure Block Diagram

020.30.25.00.00-0001-REQ
ngVLA Memo 29
020.30.00.00.00-0002-BLK

2.2 Reference Documents
The following documents are referenced within this text:
Reference
No.
RD01
RD02
RD03
RD04

Document Title

Rev/Doc. No.

M. Morgan and J. Fisher, “Statistical Word
Boundary Detection in Serialized Data
Streams”
M. Morgan, J. Fisher, and J. Castro,“Unformatted Digital Fiber-Optic Data
Transmission for Radio Astronomy Front Ends”
Integrated Downconverters and Digitizers
Design Description
Antenna Electronics Pedestal Enclosure Block
Diagram

U.S. Patent No. 8,688,617, 4/1/2014.
People’s Republic of China Patent
No. 201180046318.8, 2/5/2017.
Publications of the Astronomical Societyof the Pacific, vol. 125, no. 928, pp.
695–704, June 2013.
020.30.15.00.00-0002-DSN

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020.30.00.00.00-0003-BLK

Title: Digital Back End/Data Transmission
System Reference Design Description
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Owner: Jackson

Date: 2019-07-24
Version: A

3 Subsystem Overview
The Digital Back End/Data Transmission System receives data from the Integrated Downconverter/
Digitizer subsystem, performs primary digital processing required at the antenna, and prepares data fortransmission across private and public telecommunications infrastructure. This subsystem is concentrated
in a single, highly integrated RFI shielded module located in the pedestal of each ngVLA antenna.
The module is designated as D501 on the Antenna Electronics Pedestal Enclosure Block Diagram [RD04].
Digital data streams produced in the Integrated Downconverter/Digitizer (IRD) modules located in the
Front End (FE) enclosure are received in the D501 DBE/DTS module via 16 single-mode fibers.
Clock recovery and de-serialization is performed on the data, which is then fed to digital processing blocks
for functions such as channelization, digital downconversion, re-quantization, and RFI tagging or excision.
Finally, processed data is formatted into standard telecommunication formats (e.g., Ethernet, SONET) andreturned to the optical domain for transmission over private or commercial fiber optic networks.
Figure 1 and Figure 2 show a SysML block diagram of the Antenna Electronics, highlighting the logical,
behavioral, and structural beginnings of the detailed structural design. The network switch block shown islocated at the array center ahead of the Central Signal Processing subsystem; the remainder is located ateach antenna. The behavioral blocks represent the types of signal processing expected to be performedin the Digital Backend Module FPGA(s).

Figure 1 - SysML representation of signal path ahead of the Central Signal Processing subsystem. Behavioral,
logical, and structural aspects are shown. Components of the Digital Back End work package are shown in thehighlighted block.

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Figure 2 - Close up of SysML representation of DBE subsystem.

4 Subsystem Design
Figure 3 (next page) shows the SysML structural diagram of the Digital Back End (DBE) Module signal path.
The optical input modules receive the unformatted optical streams from the IRD modules. All of the digitalprocessing is performed locally in the antenna. Then the data are transmitted to the optical transceivers
that interface with the fiber optic cables or to the commercial networking infrastructure that leaves theantenna.

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Version: A

Figure 3 - SysML structural diagram of the Digital Back End module.

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Date: 2019-07-24
Version: A

The DBE module, itself heavily shielded against RFI, will be further enclosed in a shielded rack in theantenna pedestal. Inside, the optical streams from all IRD modules feed into quad-channel fiber-optic
transceivers hosted on printed circuit boards (PCB). The transceivers utilize four wavelengths on a single
fiber, one color per lane. They modulate the optical carrier at 28 gigasymbols per second using four-level
pulse-amplitude modulation (PAM4), achieving a serial rate of 56 Gbps per lane. These are described indetail in the Integrated Downconverters and Digitizers Reference Design Description (RD03). Physically,
the transceivers conform to the QSFP28 form-factor, as shown in Figure 4, and are becoming available
with maximum transmission distances between 500 m and 80 km [RD04–05].

Figure 4 - Quad Small Form-Factor Pluggable (QSFP28) optical transceiver.

After conversion to copper (remaining 56 Gbps PAM4) in the fiber transceivers, the IRD data streams willenter one or more large field programmable gate arrays (FPGA) on the PCB via high-speed
serializer/deserializer (SERDES) inputs. Once inside the FPGA, the data stream will be processed in
multiple ways.
The central digital processing pipeline consists of:
1.
2.
3.
4.

SERDES and IRD unformatted link interface,side-band separation,
down-conversion, anddata encoding and retransmission (SERDES)

A separate processing stream will tap the central data stream for the purposes of RFI excision and flagging.
A monitor and control (M&C) processor will also be hosted on a PCB inside the DBE. It will provide allnecessary connectivity to the ngVLA monitor/control system. Lastly, the module will include power
supplies as necessary for all included hardware.

4.1 IRD Data Stream
The fibers coming from the IRD modules will contain optical carriers of different colors, each carrying 56
Gbps of data. Each pair of those carriers represents raw samples (time-series) from the I and Q outputsof a mixer. At Band 6, these will be 4-bit samples (14 GS/s, or 7 GHz of bandwidth in each I and Q). For
simplicity, only one I/Q pair from Band 6 will be transmitted. The data path for each I/Q pair is identical.

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Date: 2019-07-24
Version: A

4.2 Digital Processing
4.2.1

SERDES

Data from the 44 QSFP28 modules are fed into the high-speed SERDES inputs of FPGAs. These blocks
convert the streaming serial data into parallel samples for processing within the FPGA, as Figure 5 shows.

Figure 5 - SERDES functionality.

The current state of the art for production hardware is 58 Gbps/block; technology has been demonstrated
for blocks up to 112 Gbps.

4.2.2

Unformatted Link Interface

The IRD subsystem group will deliver a portable FPGA firmware block that acts as a wrapper around the
FPGA’s built-in Clock and Data Recovery circuitry. This firmware block ensures that the channels arealigned with MSB and LSB in a known, correct state. A monitor/control interface is available to this blockfor reporting status and receiving commands.
The output from this firmware block will be I and Q time-series samples on parallel pins. To realize apractical design, these streams will be demultiplexed into many more parallel streams at a much slower
rate (sequential samples will be clocked out in parallel).

4.2.3

Side-Band Separation

Although sideband separation can be done on time-series data, it is conceptually simpler to do it in thefrequency domain. Therefore, the next functional block will be a poly-phase filter bank (PFB) or FFT
function. The complex spectra generated in the Fourier transform block accumulate prior to sideband
separation. After accumulation, the next functional block separates upper (USB) and lower (LSB) sidebands
with a complex mixer (a weighted cross-sum of I and Q spectra), as Figure 6 shows. The weights, orcalibration coefficients, are receiver- and frequency-dependent but fairly smooth and can be interpolated.

Figure 6 - Side-band separation processor.

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4.2.4

Owner: Jackson

Date: 2019-07-24
Version: A

Down-Conversion

After side-band select, the data-streams will be down-converted into 50 sub-bands to CSP input
specifications (020.40.00.00.00-0001-SPE). Each sub-band will be 200MHz wide and include full bit
resolution. This down-conversion will be performed in an over-sampled poly-phase filter bank. This typeof PFB provides the desired channelization with a flat pass-band response, and minimizes the spectral
image components that are typically found in critically sampled poly-phase filter banks. As Figure 7 shows,the oversampled PFB separates the filter edges in frequency space, reducing the filter overlap which
introduces spurious images.

Figure 7 - Critically sampled (M=D) vs. oversampled (M=D×I) PFB.

The most common design approach to these filters simply adds an interpolator ( ) after the poly-phasecommutator, as shown in Figure 8.

Figure 8 - Oversampled PFB block diagram.

The added interpolator inserts zero padding (1 zeros per sample) to the input stream. Otherwise, thepoly-phase structure is very similar to the critically sampled case implemented elsewhere in NRAO
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Version: A

systems. This can be implemented in an FPGA using multiple copies of a critically sampled poly-phase filterbank, with some complexity in prototype filter generation.

4.2.5

RFI Excision/Flagging

Digital circuitry inside the FPGA will be reserved for RFI processing. This block will be inserted into the
DSP processing pipeline at the appropriate stage. Possible algorithms will be discussed in Section 4.3.

4.2.6

Data Encoding and Retransmission

The last functional block of digital processing will receive data from the down-conversion block andpackage it for further transmission. This will involve re-quantization, possibly of selectable bit-depth, andpacket payload generation. The packets will then flow through an Ethernet IP block and out of the FPGA
through another SERDES block (in serializer mode) in standard 802.3 Ethernet format.

4.3 RFI Tagging and Excision
Radio-frequency interference (RFI) will be present in many and changing forms during the lifetime of
ngVLA. Cellular networks and satellite downlinks will be the sources of the most prominent signals incorrelated data because the same signals will be visible to many antennas, and the signals will be present
over an entire integration period. Generally, automatic flagging algorithms can identify these signals in thedata at data processing time.
There are also many signals that are expected to affect science data that have high energy but low time
occupancy, such as vehicular radar and aviation transponders. These signals are not easily flagged incorrelated data, but can negatively affect the science data. Detecting the signals in a high-time-resolution
and antenna-specific domain can allow data processing to more intelligently process data to improvescience data quality. Firmware in the DBE’s signal processing FPGAs will detect these signals using wellknown algorithms including spectral kurtosis and spectral peak detection. Flags indicating RFI presence
and properties will be transmitted on the Monitor and Control data stream for inclusion into theobservation metadata.

4.4 Data Transmission System
Once all local processing and reduction of data is complete, the data streams are fed into the Data
Transmission System (DTS) for routing back to the Correlator and Signal Processing system located at
the array center. Two configurations shall considered:
The antenna is connected directly to the correlator via NRAO or commercially owned dark fiber.
The data from the antenna is required to be transported through public communications infrastructure.
For antennas in the array core connected directly with dedicated fiber, the data will arrive in sequential
order through a single deterministic path. The data will be transmitted using four 100 Gb/s fiber optic
Ethernet links using the UDP transport layer protocol. All data will be placed on a single SMF fiber using
100 Gb/s wavelength controlled Ethernet Transceivers on 100 GHz spacing Dense Wavelength Division
Multiplexed (DWDM) carriers. Transmission capacity required from each antenna is 400 Gb/s total.
For antennas that cannot be directly connected, the DTS becomes dependent on the telecommunications
carrier chosen to service that infrastructure. The network link will be affected by the carrier’s local andlong haul configuration between the antenna and the array center. NRAO does not have control of the
network configuration or the routing of data on the third party carrier’s infrastructure. The vendor could
either provide dedicated wavelengths on their fibers or require that data be passed through their
networks. Data may arrive out of sequence, with unknown transmission delays, error rates and missing

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Version: A

packets. The present design can accommodate a 250 ms delay and tolerates dropped packets.
Transmission capacity from the antenna is ideally 400 Gb/s but could be restricted depending on cost andcapacity of the commercial carrier and infrastructure local to the antenna.

4.5 Subsystem Block Diagram
Figure 9 shows a block diagram of the hardware structure inside a D501 module. Data stream processing
will reside on a high performance PCB. This PCB will contain all of the optical receivers necessary forreceiving data from the IRD modules, optical transceivers for the Ethernet links leaving the antenna, anda large FPGA. The FPGA will perform clock recovery, data stream alignment, digital signal processing, andEthernet framing.
The module will contain a separate PCB to provide all necessary monitor and control. The M&C board
will interface to the antenna M&C Ethernet switch via standard SFP modules. It will contain a highperformance microprocessor as defined in the M&C subsystem documentation (020.30.45.00.00-0004DSN). A high-performance microprocessor is necessary in this application because this board will betasked with acquiring and analyzing multiple data samples for diagnostic and system setup purposes. It will
run an embedded variant of the LINUX operating system.
The last PCB in the module will be a high efficiency power supply that converts the antenna’s –48 VDC
to the voltages for hardware in this module. It will be consistent with the power supply designs describedin the DC Power Supply subsystem documentation (020.30.50.00.00-0002-DSN). The power supply PCB
will be tailored to provide the unique low-voltage, high-current supply voltages needed by the components
in this module.
D501 - DBE/DTS Module
Processing PCB

BAND6-4
IRD
BAND6-3
IRD
BAND6-2IRD

QSFP56Gx4

QSFP56Gx4

QSFP56Gx4

1:4
Demux
1:4
Demux

QSFP56Gx4

1:4
Demux

QSFP56Gx4

1:4
Demux

QSFP56Gx4

1:4
Demux

BAND5-1
IRD

QSFP56Gx4

1:4
Demux

BAND4-2IRD

QSFP56Gx4

BAND4-1
IRD

QSFP56Gx4

BAND6-1
IRD
BAND5-3
IRD
BAND5-2
IRD

BAND3HIRD
BAND2H/3L
IRD
BAND2L
IRD
BAND1
IRD
SPARE
IRD

156.25 MHz
from L501

QSFP56Gx4

QSFP56Gx4

QSFP56Gx4

QSFP56Gx4

QSFP56Gx4

400 Gbps(4 x 100 Gbps Links)

1:4
Demux

1:4
Mux

QSFP-100G
100 GigE
Carrier 1

1:4
Demux
1:4
Mux

QSFP-100G
100 GigE
Carrier 2

1:4
Demux

Internal Routing Fabric

1:4
Mux

QSFP-100G
100 GigE
Carrier 3

1:4
Demux

1:4
Demux

1:4
Mux

1:4
Demux

QSFP-100G
100 GigE
Carrier 4

1:4
Demux

1:4
Demux

1:4
Mux

1:4
Demux

QSFP-100G
100 GigE
Spare

1:4
Demux

1:4
Demux
1:4
Demux
1:4
Demux

156.25 MHz
CW Clock

FPGA(s)Timecode

SPI
Power Supply+7.5 VDC+17.5 VDC

-17.5 VDC

JTAG

Timecode- 7.5 VDC

FPGA

M&C
Processor(ARM or similar)-48 VDC

Figure 9 - Block diagram of antenna DBE/DTS subsystem.

Page 12 of 15

SFP 1Gb

D501 M&C
Ethernet

Title: Digital Back End/Data Transmission
System Reference Design Description
NRAO Doc. #: 020.30.25.00.00-0002-DSN-ADBE_DTS_REF_DESIGN

Owner: Jackson

Date: 2019-07-24
Version: A

4.6 Mechanical Packaging
The D501 DBE Module consists of high-speed digital components, a high-performance microprocessor,
and switching power supplies. All of these will contribute to high levels of radio frequency interference
that are in-band to the ngVLA, and must be attenuated.
Figure 10 shows a prototype module design based on the Advanced RFI Containment System (ARCS)
module system designed for the ngVLA project. This enclosure is heavily shielded to prevent interferencewith the telescope from the electronics inside. The DBE PCBs will attach to heatsinks inside this module.
Two multi-fiber connectors and a filtered Cannon power connector allow signaling and power across themodule’s RFI shielding.
Module dimensions and aspect ratio are for demonstration purposes and will depend on the space available
in the pedestal area enclosure available in the selected antenna design.

Figure 10 - 3D rendering of D501 module.

Page 13 of 15

Title: Digital Back End/Data Transmission
System Reference Design Description

Owner: Jackson

NRAO Doc. #: 020.30.25.00.00-0002-DSN-ADBE_DTS_REF_DESIGN

Date: 2019-07-24
Version: A

4.7 Subsystem Components
4.7.1

High-Level Bill of Materials

RFI-shielded module metalwork
Polarization processing PCB (2x), with 2 FPGAs
Power supply PCB
Monitor and control PCB
16 x 56 Gb/s QSFP modules
8 x 40 Gb/s extended range SFP modules
Power and RF interconnect cable and connectors
Multi-fiber cables and connectors

4.8 Interfaces with other Subsystems
4.8.1

Power Supply

The D501 will receive –48VDC @10 amps from the power supply subsystem.

4.8.2

LO/Reference

The D501 will require a 156.25 MHz CW tone @0dBm from the LO/Reference subsystem for thegeneration of internal clocks. The module will also require an optical timecode reference from the
LO/Reference subsystem. Specifics of this time code are TBD.

4.8.3

Integrated Downconverter/Digitizer

The D501 will receive data from the Integrated Downconverter/Digitizer modules optically at 56 Gb/s.
Power and wavelengths will be determined from specifications of the QSFP fiber transceiver modules
chosen for the design.

4.8.4

Data Output

Output data from the D501 will be via standard 100 Gb/s Fiber Optic Ethernet links for antennas
connected to NRAO-owned fiber (or located in the central building with the correlator as may be thecase for antennas located near the array center). Outlying antennas could be changed to other formats
depending on the requirements of commercial fiber infrastructure at each site.

Page 14 of 15

Title: Digital Back End/Data Transmission
System Reference Design Description
NRAO Doc. #: 020.30.25.00.00-0002-DSN-ADBE_DTS_REF_DESIGN

Owner: Jackson

Date: 2019-07-24
Version: A

5 Appendix
5.1 Abbreviations and Acronyms
Acronym
AD
ARCS
CSP
DBE
DSP
DTS
ER-QSFP
FE
FFT
FPGA
IF
IRD
LO
LRU
LSB
M&C, M/C
NES
LSB
ngVLA
NSF
PFB
PLL
QSFP
RD
RF
RFI
SERDESSMF
SR-QSFP
TBD
VLA
WVR

Description
Applicable Document
Advanced RFI Containment System
Central Signal Processor Subsystem
Digital Back End
Digital Signal Processing
Data Transmission System
Extended Range Quad Small Form-Factor Pluggable Fiber Optic Transceiver
Front End System
Fast Fourier Transform
Field Programmable Gate Array
Intermediate Frequency
Integrated Downconverter/Digitizer Module
Local Oscillator
Line Replaceable Unit
Lower Sideband
Monitor and Control
Near Earth Sensing
Lower Sideband
Next Generation VLA
National Science Foundation
Poly Phase Filter Bank
Phase Locked Loop
Quad Small Form-Factor Pluggable Fiber-Optic Transceiver
Reference Document
Radio Frequency
Radio Frequency InterferenceHigh Speed Serial/De-Serializer Input of an FPGA
Single Mode Fiber
Short Range Quad Small Form-Factor Pluggable Fiber-Optic Transceiver
To Be Determined
Jansky Very Large Array
Water Vapor Radiometer

Page 15 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

DC Power Supply Preliminary Technical Requirements
020.30.50.00.00-0001-REQ-A-DC_POWER_SUPPLY_PRELIM_REQS

Status: RELEASEDPREPARED BY
P. Lopez
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-11-16
2019-04-23

APPROVALS (Name and Signature)

ORGANIZATION

DATE

R. Selina,
2019.07.17
Project Engineer
16:26:28 -06'00'
M. McKinnon,
signed by Mark McKinnon
Mark McKinnon Digitally
Date: 2019.07.17 16:40:25 -06'00'
Project Director

Electronics Division,
NRAO
Asst. Director for
NM-Operations, NRAO

2019-07-17

RELEASED BY (Name and Signature)
ORGANIZATION
M. McKinnon,
Asst. Director for
Digitally signed by Mark McKinnon
Mark
McKinnonDate: 2019.07.17 16:40:42 -06'00'
Project Director
NM-Operations, NRAO

DATE
2019-07-17

Page 1 of 15

2019-07-17

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

Change Record
Date

AuthorAffected
Section(s)Reason01

2018-05-15

P. Lopez

All

Initial draft

02

2018-06-07

S. DurandAll03

2018-07-01

P. Lopez

2.2

04

2018-09-01

S. Durand

All

Basic edits
Updated reference document titles anddocument numbers
Basic edits05

2018-09-25

P. Lopez06

2018-11-16

P. Lopez07

2019-04-23

S. DurandAllAll
3.3 5.3 5.4
5.1
2.1 & 2.2
All08

2019-05-30

R. Selina

4, 5A

2019-07-17

A. LearAll

VersionBasic edits
Document number update; removed “Not allantennas will have WVR”; corrected typos;
updated document names and numbers
Basic edits
Updated requirement numbering; otherminor edits throughout
Prepared document for approvals & release

Page 2 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings ............................................................... 4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 5

3

Overview of the DC Power Supply Technical Requirements ................... 6

3.1
3.2
3.3
3.4
3.5
3.5.1
3.5.2
3.5.3
3.6
3.6.1

Document Outline ................................................................................................................. 6
Project Background................................................................................................................ 6
General DC Power Supply System Description ................................................................... 6
Summary of DC Power Supply System Requirements ......................................................... 7
Definitions of External Environmental Conditions .............................................................. 7
Precision Operating Conditions ............................................................................................................. 7
Normal Operating Conditions ............................................................................................................... 7
Limits to Operating Conditions ............................................................................................................. 7
General Technical Requirements .......................................................................................... 8
General Requirements.............................................................................................................................. 84

DC Power Supply Functional and Performance Requirements................ 9

4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.2
4.3
4.4
4.5

Functional Requirements ....................................................................................................... 9P500 Functional Specifications ................................................................................................................ 9P501 Functional Specifications .............................................................................................................. 10P502 Functional Specifications .............................................................................................................. 10P503 Functional Specifications .............................................................................................................. 11
Additional Requirements ..................................................................................................... 11
Maintenance and Reliability Requirements ....................................................................... 12
Monitor and Control Requirements ................................................................................... 12
Lifecycle Requirements ........................................................................................................ 125Interface Requirements .............................................................................. 13

5.1
5.2
5.3
5.4
5.5
5.6
5.6.1
5.6.2
5.6.3
5.7

Interface to Digital Back End and Data Transmission System Subsystems ..................... 13
Interface to Front End Subsystem ....................................................................................... 13
Interface to Integrated Downconverter/Digitizers Subsystem .......................................... 13
Interface to the Local Oscillator subsystems ..................................................................... 13
Interface to the WVR subsystem ......................................................................................... 14Interface to the Antenna ..................................................................................................... 14
Electrical Infrastructure .......................................................................................................................... 14
RFI Mitigation ............................................................................................................................................ 14
HVAC and Cooling System ................................................................................................................... 14Interface to the M&C System ............................................................................................. 14

6

Appendix....................................................................................................... 15

6.1
6.2
6.2.1
6.2.2

Abbreviations and Acronyms ............................................................................................... 15
Maintenance Definitions ..................................................................................................... 15
Maintenance Approach ........................................................................................................................... 15
Periodic Preventive Maintenance ......................................................................................................... 15

Page 3 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

1 Introduction
1.1 Purpose
This document presents a set of preliminary technical requirements for the ngVLA DC Power Supply
system reference design. Many requirements flow down from the preliminary System Requirements[AD02], which in turn flow down from the preliminary Science Requirements [AD01].
The science goals are presently being elaborated by the Science Advisory Council (SAC) and Science
Working Groups (SWGs), and are captured in a series of draft use cases. This draft reflects a preliminary
analysis of these use cases, and the flow down recursively to the science, system, and subsystem
requirements.

1.2 Scope
The ngVLA DC Power Supply system consists of the equipment that creates and provides the power toall Antenna Electronics deliverables on the ngVLA antennas. This requirements document establishes theperformance, functional, design, and test requirements applicable to the DC Power Supply system. It also
includes preliminary interface requirements that must be defined.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of this Technical Specification shall be considered as a superseding requirement.
Reference
No.
AD01
AD02
AD03
AD04
AD05
AD07
AD08
AD10
AD11
AD12
AD13
AD14

Document Title

Rev/Doc. No.

Science Requirements
System Requirements
Operations Concept
Protection Against Electric Shock: Common Aspects for
Installation and Equipment
System-Level Electrical Requirements
Insulation Coordination for Equipment within LowVoltage Systems
Occupational Safety and Health Standards for GeneralIndustry
Military Handbook: Reliability Prediction of Electronic
Equipment
Non-Electronic Parts Reliability Data
Electromagnetic Compatibility
System Electromagnetic Compatibility and RF
Interference Mitigation Requirements
Environmental Specifications

020.10.15.05.00-0001-REQ
020.10.15.10.00-0003-REQ
020.10.05.00.00-0002-PLA
IEC 61140:2016

Page 4 of 15

020.10.15.10.00-0005-REQ
IEC 60664
29 CFR Part 1910
MIL-HDBK-217F
NPRD-95
IEC 61000-3-5020.10.15.10.00-0002-REQ
020.10.15.10.00-0001-SPE

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

2.2 Reference Documents
The following references provide supporting context:
Reference
No.
RD01
RD02
RD03
RD04
RD05
RD06
RD07
RD08

Document Title

Rev/Doc. No.

Antenna Electronics Front End Enclosure Block Diagram
Antenna Electronics Pedestal Enclosure Block Diagram
Antenna time & Frequency Reference Requirements
Digital Back End Requirements
Front End Requirements
Independent Phase Cal System Requirements
Integrated Down Converter Requirements
Monitor and Control Requirements

020.30.00.00.00-0002-BLK
020.30.00.00.00-0003-BLK
020.35.20.00.00-0001-REQ
020.30.25.00.00-0001-REQ
020.30.03.01.00-0001-REQ
020.45.00.00.00-0001-SPE
020.30.15.00.00-0001-REQ
020.30.45.00.00-0002-REQ

Page 5 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

3 Overview of the DC Power Supply Technical Requirements
3.1 Document Outline
This document presents the DC Power Supply system technical requirements, which determine overall
form and performance.
Section 4 details the functional and performance specifications, along with explanatory notes. The notes
elaborate on the requirements’ meaning, intent, and scope. The notes form an important part of therequirements definition and should guide the verification procedures. In many cases, the notes containexplanation or analysis of how the numeric values of requirements were derived. Where numbers are notwell substantiated, this is also documented in the notes. This makes the required analysis and trade-space
available apparent to scientists and engineers guiding evolution of the DC Power Supply system concept.
Section 5 describes requirements pertinent to interfacing systems. Initial requirements are noted byinterface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses.

3.2 Project Background
The Next Generation Very Large Array is a project of the National Radio Astronomy Observatory todesign and build an astronomical observatory that will operate at centimeter wavelengths (25 to 0.26
centimeters, corresponding to a frequency range extending from 1.2 GHz to 116 GHz). The observatory
will be a synthesis radio telescope constituted of approximately 263 reflector antennas of 18 meters and6 meters diameter, operating in a phased or interferometric mode.
The array signal-processing center will be located at the Very Large Array site on the Plains of San Agustin,
New Mexico. The array will include stations in other locations throughout New Mexico, west Texas,
eastern Arizona, northern Mexico, and across the US. Operations will be conducted from both the VLA
Control Building and the Array Operations Center in Socorro, NM.

3.3 General DC Power Supply System Description
The DC Power Supply System (specifically, P500) receives 208V 3-phase AC @17A and converts it to–48V DC. Lithium batteries will be used as a backup source for the 48V if the AC is lost. A battery charger
will be used to charge the batteries when AC is available. The batteries and battery charger will be locatedin the pedestal area of each antenna. The 48V is then fed into three power supply modules (P501, P502,
and P503) that convert the 48V to +32.5V, ±17.5V, +15.5V, ±7.5V, ±5.5V, and +3.8V depending on themodule. Each power supply module has monitor and control (M&C) and temperature sensors for
shutdown in case of over current or over temperature. The P500 also powers the fire alarm, Ethernet
switch, Digital Back End (DBE), and Data Transmission System (DTS).
The P501 module powers the Front End (FE) Low Noise Amplifier (LNA) noise diodes, and bias voltages
for Bands 1–6. The P501 also powers the Local Oscillator (LO) Reference Sample Clock Generator and
LO A–K Generator modules as well as the Integrated Downconverter/Digitizers (IRD) for Bands 1–6.
The P501 will be located next to the IRDs in the Front End Enclosure.
The P502 module powers the LO Clock Receiver module, two Band 4 IRDs, the Water Vapor Radiometer(WVR) antenna amplifier, and cooling system. The P502 will be located in the WVR Enclosure.
The P503 module powers the LO Reference Receiver Generator and Distribution module and the four
Monitor & Control modules located in the pedestal area of each ngVLA antenna.

Page 6 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

3.4 Summary of DC Power Supply System Requirements
The following sections summarize the major requirements to provide a high-level view of the desired
system. Should a conflict exist between the requirements listed here and the descriptions in Sections 4
and 5, the latter shall take precedence.

3.5 Definitions of External Environmental Conditions
Based on historical VLA site weather data and other public weather databases, the following definitions ofenvironmental conditions are adopted. The power supplies shall conform to these requirements.

3.5.1

Precision Operating Conditions

The precision operating environment defines the conditions under which the system is expected to meetthe most stringent requirements and provide optimal system performance.
Parameter
Solar Thermal Load

Req. #
ENV0311Wind Speed

ENV0312

Temperature
Temperature Rate of Change
Precipitation

ENV0313
ENV0314
ENV0315

Value
Nighttime only; no solar thermal load within last
2 hours0  W  m/s average over 10 min; 7 m/s peakgusts
–15 C  T  25 C
1.8°C/Hr.
No precipitation.

The solar thermal load requirement limits this environment to two hours after sunset through sunrise, solong as other requirements of this section are met. The two-hour restriction is intended to allow sufficient
time for the system to equilibrate.

3.5.2

Normal Operating Conditions

When the environment meets normal operating constraints, system performance requirements arerelaxed but are still expected to provide adequate performance for operation below 50 GHz.
Parameter
Solar Thermal LoadWind Speed
Ambient Temperature
Ambient Temperature Rate of Change
Precipitation

3.5.3

Req. #
Value
ENV0321 Exposed to full sun, 1200 W/m2
ENV0322 :7 m/s average over 10 mins; 10 m/s peakgusts
ENV0323 –15 C  T 45 C
ENV0324 3.6°C/Hr
ENV0325 No precipitation

Limits to Operating Conditions

A third category establishes hard limits to the operating conditions. While outside the bounds of thenormal operating environment but within this regime, no performance guarantees are expected, but thesystem shall still be capable of safe operation. Once these limits are exceeded, the antenna will be moved
to its stow-survival orientation to prevent damage. The relevant performance specifications are discussed
in the ngVLA Environmental Specifications document [AD14].

Page 7 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

3.6 General Technical Requirements
The DC Power Supply system receives 208V 3-phase AC @17A and converts it to –48VDC. Lithium ion
batteries will be used as a backup source for the 48V if AC is lost. A battery charger will be used to charge
the batteries when AC is available. The batteries and battery charger will be located in the pedestal areaof each antenna. The 48V is then regulated and power is delivered to all antenna electronics equipment.
Each power supply module has M&C, power control relays, and temperature sensors so it can be shut
down for over-current or over-temperature.

3.6.1

General Requirements

Parameter

Req. #

Summary of Requirement

AC Input
AC to DC Conversion
DC Regulation

PSU0001
PSU0002
PSU0003

M&C for Battery System
M&C for Power Supply
Modules
Design Life

PSU0004
PSU0005
PSU0006

Maintenance Interval

PSU0007

Mean Time Between
Failure (MTBF)
Modularization

PSU0008

208V 3 Phase AC @17A
208V 3 Phase AC to –48VDC–48V DC will be regulated down to voltages
that each module as required.
Required to monitor battery system healthRequired to monitor power supply module
healthDesign for an expected operational life no lessthan 20 years, excluding batteries
Preventive maintenance interval of no shorter
than 2 years, with a goal of 4 years
Antenna electronics: MTBF of 35,040 hrs each

Altitude Range
Lightning Protection
Equipment Protection
Against Dust
Rodent Protection

PSU0010
PSU0011
PSU0012

Transportation
Environment

PSU0014

Mechanical ShockEquipment Shielding

PSU0015
PSU0016

EMC Test Frequencies

PSU0017

Hazard Analysis

PSU0018

Storage Requirements

PSU0019

PSU0009

PSU0013

Line Replaceable Units (LRUs) to facilitate site
maintenanceSea level to 2500 meters
Protect against lightning electromagnetic impulse
Exposed equipment shall be protected against
windblown dust, ashes, and grit
Exposed equipment shall be designed to prevent
rodent damage
Designed to withstand typical loads andenvironments encountered duringtransportation
Designed to survive mechanical shock levels
All equipment shall be shielded and have AC
power line and communication lines filtered at
the chassis
RFI suppression shall extend from 50 MHz up to
12 GHzHazard analysis shall be performed for all highpower systems; include lock-outs for service bytechnicians
10 ๦C to 25 ๦C for batteries–5 ๦C to 45 ๦C for power supply modules

Page 8 of 15

Reference
Reqs.

SYS2701
SYS2701
SYS2701
SYS2401
SYS2402
SYS2403
ENV0351
ENV0512
ENV0541
ENV0551
ENV0581
ENV0582
ENC0327
NRAO IPG
Memo 34,
EMC0328
SYS2703

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

4 DC Power Supply Functional and Performance Requirements
These requirements apply to a properly functioning system under normal operating environmental
conditions unless otherwise stated.

4.1 Functional Requirements
4.1.1

P500 Functional Specifications

Parameter
AC Input Requirements
AC to DC Conversion
DBE Load Power Requirements
Fire Alarm Load Power
Requirements
Ethernet Switch Load Power
Requirements
P501 Load Power Requirements
P502 Load Power Requirements
P503 Load Power Requirements
Battery System Capacity (Li-ion
batteries)
Battery Lifetime
Backup Power Available
Battery-Only Load Support
Low Voltage Disconnect Voltage
Pedestal Environmental Temp
Forced Air Inlet Temp
Forced Air Outlet Temp
P500 Dissipation Including Battery
Fire Alarm Shunt Trip
Emergency Communication Time
Battery Backup

Req. #Value
PSU0101 208V 3 Phase @17Amps AC
PSU0102 208V 3 Phase AC to –48 VDC(–46.0 to –54.2 VDC)
Maximum –60 ADC
PSU0103 –46 to –54.2 VDC, 5 ADC
PSU0104 –46 to –54.2 VDC, 2 ADC
PSU0105 –46 to –54.2 VDC, 2 ADC
PSU0106
PSU0107
PSU0108
PSU0109–46 to –54.2 VDC, 18 ADC–46 to –54.2 VDC, 14 ADC–46 to –54.2 VDC, 14 ADC
40 Ah @20-hour rate

PSU0110
PSU0111
PSU0112
PSU0113
PSU0114
PSU0115
PSU0116
PSU0117
PSU0118
PSU0119

3–6 Years
40 Ah assuming fully charged
10 minutes
40.5 VDC
15๦&7๦C
4๦&7๦C
7๦
165 Watts
Disconnects AC & DC loads
Min I Minutes
Max 2 Minutes

Page 9 of 15

Traceability[AD05]

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

4.1.2

Version: A

P501 Functional Specifications

Parameter
Input Power Requirement
FE (Band 1–6) Load Power
Requirements

IRD (x13) Load Power
Requirements
LO Modules Load Power
Requirements
SA501 Environmental Temperature
Cooling Technique
P501 Dissipation
M&C for Power Supply Modules

4.1.3

Date: 2019-07-17

Req. #
Value
Traceability
PSU0201 –46 to –54.2 VDC, 18 ADC[AD05]
PSU0202 +32V (28V) @ 0.5 A,+17.5V (+15V, +12V) @ 6 A (2.5A,
3.5A)+5.5V (3.3V) @ 0.5 A–5.5V (–3.3V) @ 0.5 A
PSU0203 +5.5V (+5V) @ 1 A+3.8 (+3.5V) @ 1 A–5.5V (–5V) @ 0.1 A
PSU0204 +17.5V (+15V) @ 2.5 A+5.5V (+5V) @ 1.5 A–5.5V (–5V) @ 0.25 A–17.5V (–15V) @ 0.25 A
PSU0205 14϶&7϶C
PSU0206 Single cold plate; temp 4–14 ๦C
PSU0207 ~195 Watts
PSU0208 Required to monitor power supply
module healthP502 Functional Specifications

Parameter
Input Power Requirement
Load Power Requirements for
FE (Band 4)

Req. #
PSU0301
PSU0302

Load Power Requirements for
IRD (x2)

PSU0303

Load Power Requirements for LO
ModulePSU0304

WVR Cooling System
SA502 Environmental Temperature
Cooling technique

PSU0305
PSU0306
PSU0307

P502 Dissipation
M&C for Power Supply Modules

PSU0308
PSU0309Value–46 to –54.2 VDC, 14 ADC+32 (28V) @ 0.3 A+17V (+12V) @ 0.3 A+5.5V (3.3V) @ 0.01 A–5.5V (–3.3V) @ 0.5 A+5.5V (+5V) @ 1 A+3.8 (+3.5V) @ 1 A–5.5V (–5V) @ 0.1 A+17.5V (+15V) @ 2.5 A+5.5V (+5V) @ 1.5 A–5.5V (–5V) @ 0.25 A–17.5V (–15V) @ 0.25 A+15.5V (+12V) @11.4 A
14 ϶&7϶C
Single cold plate
Temp 4–14 ϶C~145 Watts
Required to monitor power
supply module healthPage 10 of 15

Traceability[AD05]

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

4.1.4

Date: 2019-07-17
Version: A

P503 Functional Specifications

Parameter
Input Power Requirement
Load Power Requirements for LO
SystemReq. #
PSU0401
PSU0402

Load Power Requirements for M&C
SystemPSU0403

SA503 Environmental Temperature
Cooling Technique

PSU0404
PSU0405

P503 Dissipation
M&C for Power Supply Modules

PSU0406
PSU0407Value–46 to –54.2 VDC, 14 ADC+17.5V (+15V) @ 2.5 A+7.5V (5V) @ 1.5 A–7.5V (–5V) @ 0.25 A–17.5V (–15V) @ 0.25 A+17.5V (+15V) @ 1 A+7.5V (5V) @ 2 A–17.5V (–15V) @ 1 A
14϶&7϶C
Forced air in pedestal rack; Temp
4–14 ϶C~145 Watts
Required to monitor power
supply module healthTraceability[AD05]

4.2 Additional Requirements
Parameter
Battery System Location
Battery Operating Temperature
Requirements

Req. #
PSU0501
PSU0502

DC Filtering on Outputs

PSU0503

Value
Antenna Pedestal
10϶C to 25϶C for batteries(15϶C  T  20϶C is specified forthe pedestal environment)
Hermetically glass sealed
High EMI feedthrough data line
filters
Max operating range: 100 VDC @20 A Capacitance of 2.6 μF

Traceability[AD05]

The weight of the batteries and battery charging system require that the battery system be located in theequivalent of the antenna pedestal room. The lithium batteries require that the operating temperature be
10϶C to 25϶C to maintain battery lifecycle.

Page 11 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

Owner: Lopez

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Date: 2019-07-17
Version: A

4.3 Maintenance and Reliability Requirements
Parameter
MTBF
Modularization

Req. #
PSU0601
PSU0602

Value
Antenna electronics: 35,040 hours each
Replaceable by 2 qualified technicians with minimal
tools

Traceability
SYS2402
Ops ConThe maintenance and reliability requirements support high-level requirements that limit total array
operating cost.

4.4 Monitor and Control Requirements
Parameter
Self-Monitoring

Req. #Value
PSU0701 The DC Power Supply system shall measure, report,
and monitor a set of parameters that allow for
determination of its status and may help predict or
respond to failures

Traceability
SYS2601

The self-monitoring expectation is that the M&C system expose lower-level sensors to the M&C system
when queried. The access cadence is flexible and is not expected at high rates (typical access might be on
second to minute scales). Any high-cadence monitoring should generally be internal to the DC Power
Supply System control system with a summary output on the interface.
Other M&C interface features will be specified in the Monitor and Control ICD.

4.5 Lifecycle Requirements
Parameter
Design Life

Req. #
PSU0801

Lifecycle
Optimization

PSU0802Value
The DC Power Supply system shall be designed to be
operated and supported for 20 years, excluding
batteries
The DC Power Supply design shall minimize its lifecycle
cost for 20 years of operation, including batteries

Traceability
SYS2701
SYS2701

Lifecycle costs include manufacturing, transportation, construction/assembly, operation, maintenance, anddecommissioning.

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Title: DC Power Supply PreliminaryTechnical Requirements

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NRAO Doc. #: 020.30.50.00.00-0001-REQ-ADC_POWER_SUPPLY_PRELIM_REQS

Date: 2019-07-17
Version: A

5 Interface Requirements
This section describes the DC Power Supply system interfaces. ICDs are required between the DC Power
Supply and all connecting systems. In many cases, interface specifications are not yet available, but thebroad scope of the ICD can be defined. These interfaces shall be developed and documented by the DC
Power Supply system designer and approved by ngVLA as part of the DC Power Supply system reference
and conceptual design efforts, and updated throughout the design. Post CoDR, the ICD shall only be
updated through formal project change control processes.

5.1 Interface to Digital Back End and Data Transmission System Subsystems
The Digital Back End (DBE) and Data Transmission System (DTS) request –48V from the DC Power
Supply. The total current requested is 5 amps. The DBE/DTS system is located in the pedestal room andwill receive power from the P500.

5.2 Interface to Front End Subsystem
The Front End (FE) system requests +32V, +17V, +5V, and –5V from the DC Power Supply for Bands
1–6. The FE system will receive power from the P501, located in the FE Enclosure.
x The +32V will be regulated down to +28V with a current draw around 0.5A for the noise diodes.
x The +17V will be regulated down to +15V and +12V. The +15V current draw will be about 2.5A. The+12V current draw will be about 3.5A. The total current draw from the +17V will be about 6A.
x The +5V will be regulated down to +3.3V. The +3.3V current draw will be around 0.5A. The total
current draw for the +5V will be 0.5A.
x The –5V will be regulated to –3.3V. The –3.3V current draw will be about 0.5A. The total current
draw for the –5V will be 0.5A.

5.3 Interface to Integrated Downconverter/Digitizers Subsystem
The Integrated Downconverter/Digitizers (IRD) system request +5V, +3.3V, and –5V from the DC Power
Supply. Thirteen of the IRDs will receive power from the P501 in the FE Enclosure and the two WVRIRDs will receive power from the P502 in the WVR Enclosure.
x The +5V will be regulated down to multiple internal voltages. The IRD will draw 1A from the +5V.
x The +3.3V will be regulated down to an internal voltage that it can use. The +3.3V will draw 1A.
x The –5V will also be regulated down to an internal voltage it can use. The –5V current draw will be
about 100 mA.

5.4 Interface to the Local Oscillator subsystems
The Local Oscillator (LO) system Reference Sample Clock Generator, A-K LO Generator, and LO Clock
Receiver modules request +17V, +5V, –5V, and –17V from the DC Power Supply. The Reference Sample
Clock Generator module and A-K LO Generator module are located in the FE enclosure and will be
powered by the P501. The other LO Clock Receiver module is located in the WVR enclosure and will be
powered by the P502.
x The +17V will be regulated down to +15V and will draw about 2.5A.
x The +5V will be regulated down to multiple internal voltages and will draw about 1.5A.
x The –5V will be regulated down to an internal voltage that it can use, and will draw about 0.25A.
x The –17V will be regulated down to –15V and will draw about 0.25A.

Page 13 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

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Date: 2019-07-17
Version: A

The LO system Reference Receiver, Generator, and Distributor module requests +17V, +7V, –7V, and–17V from the DC Power Supply System. This module is located in the pedestal room and will be poweredby the P503.
x The +17V will be regulated down to +15V and will draw about 2.5A.
x The +7V will be regulated down to multiple internal voltages and will draw about 1.5A.
x The –7V will be regulated down to an internal voltage that it can use and will draw about 0.25A.
x The –17V will be regulated down to –15V and will draw about 0.25A.

5.5 Interface to the WVR subsystem
The Water Vapor Radiometer (WVR) system uses an LO Sample Clock Generator and Distributor (seeSection 5.4), two Band 4 IRDs (see Section 5.3), the Band 4 receiver, and a cooling system.
The Band 4 receiver is powered by the P502 located in the WVR Enclosure and requests +32V, +17V,+5.5V, and –5.5V from the DC Power Supply.
x The +32V will be regulated down to +28V and will draw about 0.03A.
x The +17V will be regulated down to +12V and will draw about 0.3A.
x The +5V will be regulated down to +3.3V. The +3.3V current draw will be about 0.01A.
x The –5V will be regulated to –3.3V. The –3.3V current draw will be about 0.5A.
The WVR cooling system requests +15V from the DC Power Supply. The +15V will be regulated down
to +12V @ around 12A. The WVR cooling system will receive power from the P502 that is located in the
WVR Enclosure.

5.6 Interface to the Antenna
5.6.1

Electrical Infrastructure

208V 3-Phase AC @17A is required for the AC to DC battery charging system. The ICD shall describe
both the mechanical and electrical specifications of the electrical interfaces.

5.6.2

RFI Mitigation

RFI suppression shall extend from 50 MHz up to 12 GHz (NRAO IPG Memo 34).

5.6.3

HVAC and Cooling System

The P500 located in the antenna pedestal room rack requires 165 Watts of cooling and will be cooled via
forced air.
The P501 in the antenna FE Enclosure requires 195 Watts of cooling and will be cooled via cold plate.
The P502 in the antenna WVR Enclosure requires 145 Watts of cooling and will be cooled via cold plate.
The P503 in the antenna pedestal room rack requires 145 Watts of cooling and will be cooled via forced
air.

5.7 Interface to the M&C System
The DC Power Supply will use a Module Interface Board (MIB) to interface with the M&C system. Eachpower supply module will be capable of remote power on/off and powering down due to over-current orover-temperature conditions. Each module will have a different set of over-current specifications
depending on the electronics connected to it. Other conditions that power the module on/off will belisted in the ICD.
Page 14 of 15

Title: DC Power Supply PreliminaryTechnical Requirements

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6

Date: 2019-07-17
Version: A

Appendix

6.1 Abbreviations and Acronyms
Acronym
AD
CDR
CoDR
DBE
DTS
FE
HVAC
ICD
IRD
LO
LNA
LRU
M&C
MIB
MTBF
ngVLA
NRAO
PPE
RD
RFI
SAC
SWG
VLA
WVR

Description
Applicable Document
Critical Design Review
Conceptual Design Review
Digital Back End
Data Transmission System
Front End
Heating, Ventilation & Air Conditioning
Interface Control Document
Integrated Downconverter/Digitizers
Local Oscillator
Low Noise AmplifierLine Replaceable Unit
Monitor and Control
Module Interface Board
Mean Time Between Failure
Next Generation VLA
National Radio Astronomy Observatory
Personal Protective Equipment
Reference Document
Radio Frequency Interference
Science Advisory Council
Science Working GroupJansky Very Large Array
Water Vapor Radiometer

6.2 Maintenance Definitions
6.2.1

Maintenance Approach

Maintenance shall be mainly performed at assembly and subassembly level by exchange of Line Replaceable
Units (LRUs). LRUs are defined as units that can be easily exchanged by technician-level maintenance staff.
LRU exchange shall be possible by two trained/qualified people within four working hours. It is desirable
that LRU replacement be possible using only standard tools identified in a maintenance manual for the DC
Power Supply. A step-by-step procedure for safe exchange of every LRU shall also be provided in themaintenance manual and will list Personal Protective Equipment (PPE). The LRUs will be maintained by
the ngVLA project (without industrial support).

6.2.2

Periodic Preventive Maintenance

The Power Supply system will use monitor points to check on the health of the batteries and Power
Supply. These monitor points will help determine when maintenance is required for each antenna’s Power
Supply system. Monitor point thresholds will be listed in the Power Supply Manual.

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Title: DC Power Supply Reference
Design Description

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0002-DSN-ADC_POWER_SUPPLY_REF_DESIGN

Date: 2019-07-18
Version: A

DC Power Supply Reference Design Description
020.30.50.00.00-0002-DSN-A-DC_POWER_SUPPLY_REF_DESIGN

Status: RELEASEDPREPARED BY
P. Lopez
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-11-16
2019-04-23

APPROVALS (Name and Signature)
R. Selina,
2019.07.18
Project Engineer
08:46:55 -06'00'
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.18 11:50:22 -06'00'

ORGANIZATIONElectronics Division,
NRAO

DATE
2019-07-18

Asst. Director for
NM-Operations, NRAO

2019-07-18

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.18 11:50:39 -06'00'

ORGANIZATION
Asst. Director for
NM-Operations, NRAO

DATE
2019-07-18

Page 1 of 11

Title: DC Power Supply Reference
Design Description

Owner: Lopez

Date: 2019-07-18

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Version: A

Change Record
VersionDate

01

2018-05-15

P. Lopez

Affected
Section(s)All02

2018-06-13

S. DurandAll03

2018-07-01

P. Lopez

2.2

04

2018-09-21

05

2018-09-24

S. Durand
P. Lopez
S. Durand06

2018-10-24

P. Lopez07

2018-11-13

08
A

AuthorReasonInitial draft
Small edits
Updated reference document titles anddocument numbers

All

More small edits

S. DurandAllAll4, 5.2.3
4
2.1 & 2.2
All

More small edits
Document number update
Removed “Not all antennas will have WVR”
Updated P500 – P503 descriptions
Updated document names and numbers
Small edits

2019-05-30

R. Selina

All

Minor edits throughout for release2019-07-17

A. LearAll

Prepared document for approvals & release

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Title: DC Power Supply Reference
Design Description

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0002-DSN-ADC_POWER_SUPPLY_REF_DESIGN

Date: 2019-07-18
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings ............................................................... 4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 53
4

DC Power Supply System Overview ........................................................... 6
DC Power Supply System Design ................................................................ 6

4.1
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.3
4.3.1
4.3.2
4.3.3
4.3.4
4.3.5
4.3.6
4.3.7

DC Power Supply System Block Diagram ............................................................................ 7
DC Power Supply System Components ................................................................................ 7P500 Power Supply.................................................................................................................................... 7P501 Power Supply.................................................................................................................................... 8P502 Power Supply.................................................................................................................................... 8P503 Power Supply.................................................................................................................................... 9
DC Power Supply System Interfaces with Other Subsystems ............................................. 9
Antenna Non-Electronics ........................................................................................................................ 9
Digital Back End (DBE)/Data Transmission Systems (DTS) .......................................................... 10
Front End (FE) .......................................................................................................................................... 10
Integrated Downconverter/Digitizers (IRD) ..................................................................................... 10
LO Reference Receiver, Generator, and Distributor ..................................................................... 10
Monitor and Control (M&C) ................................................................................................................ 10
Water Vapor Radiometer (WVR) ....................................................................................................... 10

5

Abbreviations and Acronyms ..................................................................... 11

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Title: DC Power Supply Reference
Design Description

Owner: Lopez

Date: 2019-07-18

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Version: A

1 Introduction
1.1 Purpose
This document describes the DC Power Supply subsystem reference design and covers the design
approach, functions, key components, interfaces, and associated risks. This document forms part of thengVLA design documentation package submission.

1.2 Scope
The scope of this document is the entire design of the DC Power Supply system as part of the ngVLA
design. It details the subsystem design, how it functions, and interfaces with the necessary hardware andsoftware systems. This document does not include specific technical requirements, which are documented
in [AD14].

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein but provide necessary context or
supporting material.
Reference Document Title
No.
AD01
Science Requirements

Rev/Doc. No.

AD02

System Requirements

020.10.15.10.00-0003-REQ

AD03

Operations Concept

020.10.05.00.00-0002-PLA

AD04

Protection Against Electric Shock: Common Aspects
for Installation and Equipment

IEC 61140:2016

AD07

Insulation Coordination for Equipment within LowVoltage Systems

IEC 60664

AD08

Occupational Safety and Health Standards for GeneralIndustry

29 CFR Part 1910

AD10

Military Handbook: Reliability Prediction of Electronic
Equipment

MIL-HDBK-217F

AD11

Non-Electronic Parts Reliability Data

NPRD-95

AD12

Electromagnetic Compatibility

IEC 61000-3-5

AD13

System Electromagnetic Compatibility and RF
Interference Mitigation Requirements

020.10.15.10.00-0002-REQ

AD14

DC Power Supply Preliminary Technical Requirements

020.30.50.00.00-0001-REQ

020.10.15.05.00-0001-REQ

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Title: DC Power Supply Reference
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Date: 2019-07-18
Version: A

2.2 Reference Documents
The following documents are referenced within this text:
ReferenceNo.
RD01

Document Title

Rev/Doc. No.

Antenna Electronic Front End Enclosure Block Diagram

020.30.00.00.00-0002-BLK

RD02

Antenna Electronics Pedestal Enclosure Block Diagram

020.30.00.00.00-0003-BLK

RD03

Antenna Time & Frequency Reference Requirements

020.35.20.00.00-0001-REQ

RD04

Digital Back End Requirements

020.30.25.00.00-0001-REQ

RD05

Front End Requirements

020.30.03.01.00-0001-REQ

RD06

Independent Phase Cal System Requirements

020.45.00.00.00-0001-SPE

RD07

Integrated Down Converter Requirements

020.30.15.00.00-0001-REQ

RD08Monitor and Control Requirements

020.30.45.00.00-0002-REQ

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Title: DC Power Supply Reference
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Date: 2019-07-18
Version: A

3 DC Power Supply System Overview
A block diagram of the DC Power Supply system is shown in Figure 1. The system (specifically, P500)
receives 208V 3-phase AC @17A and converts it to –48V DC. Lithium batteries will be used as a backup
source for the 48V if the AC is lost. A battery charger will charge the batteries when AC is available. The
batteries and battery charger will be located in the pedestal area of each antenna.
The 48V is then fed into three power supply modules (P501, P502, and P503) that convert the 48V to+32.5V, ±17.5V, +15.5V, ±7.5V, ±5.5V, and +3.8V depending on the module. Each power supply module
has Monitor and Control (M&C) and temperature sensors so they can be shut down for over-current orover-temperature conditions. The P500 is also used to power the fire alarm, Ethernet switch, Digital Back
End (DBE), and Data Transmission System (DTS).
The P501 power supply module powers the Front End (FE) Low Noise Amplifier (LNA) noise diode, andbias voltages for Bands 1–6. The P501 also powers the Local Oscillator (LO) Reference Sample Clock
Generator and LO A–K Generator modules and the Integrated Downconverter/Digitizers (IRD) for Bands
1–6. The P501 will be located next to the IRDs in the FE Enclosure.
The P502 power supply module powers the LO Clock Receiver module, two Band 4 IRDs, the Water
Vapor Radiometer (WVR) antenna amplifier, and cooling system. The P502 will be located in the WVR
Enclosure.
The P503 powers the LO Reference Receiver Generator and Distribution module and the four M&C
Modules located in the pedestal area of each ngVLA antenna.

4 DC Power Supply System Design
The ngVLA DC Power Supply System design considered two existing designs: those at the Atacama Large
Millimeter Array (ALMA) and the Jansky Very Large Array (VLA). Both observatories bring in AC and use
commercial off-the-shelf (COTS) parts to convert the AC power to DC power. Both supply DC power
to the antenna electronics where each module regulates the DC power to voltages that they can use
inside the module.
The two observatories differ when it comes to backup power and the input to the module power supplies.
ALMA uses Uninterruptible Power Source (UPS) and feeds the modular power supplies AC power. The
VLA uses four 12V lead-acid in series to make up the 48V, which is then fed into the modular power
supplies.
Because the ngVLA antenna electronics, environment, and specifications more closely resemble that of
the VLA, the ngVLA DC Power Supply system logically follows the VLA design. The ALMA design has had
several issues, including operation site altitude and the reliability of the COTS AC-to-DC power supplies.
The manufacturer was not helpful pinpointing causes or sources of failures with the module power
supplies. The VLA DC Power Supply modules, by contrast, have been highly reliable and experience few
failures.
The VLA design was also chosen because it provides multiple stages of regulation. This allows the power
going into the antenna electronics to be clean. The ALMA design only has two stages of regulation, one
at the power supply module and another inside the antenna electronics. The VLA design has an extra
stage of regulation at the AC to 48VDC sub-assembly. Finally, the DC distribution system is more
conducive to supporting the system-level RFI emission requirements [AD13].

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Title: DC Power Supply Reference
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Date: 2019-07-18
Version: A

4.1 DC Power Supply System Block Diagram

Figure 1 - Block diagram of DC Power Supply system.

4.2 DC Power Supply System Components
4.2.1

P500 Power Supply

The P500 receives 208V 3-phase AC and converts it to –48V DC. The P500 requires 3.2 kW of input
power. Lithium batteries will be used as a backup source for the 48V in the event the AC is lost. A battery
charger will be used to charge the batteries when AC is available. The batteries and battery charge will belocated in the pedestal area of each antenna.
As Figure 1 shows, the P500 feeds 48V into three power supply modules (P501, P502, and P503) thatconvert the 48V to +32.5V, ±17.5V, +15.5V, ±7.5V, ±5.5V, and +3.8V, depending on the module. The
P500 has M&C so it can be shut down for over-current or over-temperature conditions. P500 also powers
the fire alarm, Ethernet switch, Digital Back End (DBE), and Data Transmission system (DTS). Figure 2(next page) shows the P500 block diagram.

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Date: 2019-07-18
Version: A

Figure 2 - P500 block diagram.

4.2.2

P501 Power Supply

The P501 power supply module receives –48V @18A from the P500. The P501 uses Vicor DC-DC
converter modules to convert the 48V into +3.8V, ±5.5V, ±17.5V, and +32.5V. The P501is used to power
the Front End (FE) Low Noise Amplifier (LNA) noise diodes, and bias voltages for Bands 1–6.
The P501 also powers the LO Clock Receiver module and the Integrated Downconverter/Digitizers (IRD)
for Bands 1–6. The P501 will be located next to the IRDs in the Front End Enclosure. Figure 3 shows theP501 block diagram.

Figure 3 - P501 block diagram.

4.2.3

P502 Power Supply

The P502 power supply module receives –48V @14A from the P500. The P502 uses Vicor DC-DC
converter modules to convert the 48V into 3.8V, ±5.5V, +15.5V, ±17.5V, and +32.5V. The P502 power
supply module is used to power the LO Clock Receiver, two Band 4 IRDs, the Water Vapor Radiometer(WVR) antenna amplifier, and cooling system. It will be located in the WVR Enclosure. Figure 4 (nextpage) shows the P502 block diagram.

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Title: DC Power Supply Reference
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Date: 2019-07-18
Version: A

Figure 4 - P502 block diagram.

4.2.4

P503 Power Supply

The P503 power supply module receives –48V @14A from the P500. The P503 uses Vicor DC–DC
converter modules to convert the 48V into ±7.5V and ±17.5V. The P503 is used to power the LO
Reference Receiver Generator and Distribution module and four Monitor Control modules. The P503
module will be located in the pedestal area of each ngVLA antenna. Figure 5 shows the P503 block diagram.

Figure 5 - P503 block diagram.

4.3 DC Power Supply System Interfaces with Other Subsystems
Below are other subsystem requirements from the DC Power Supply system.

4.3.1
4.3.1.1

Antenna Non-Electronics
Antenna AC

The P500 requires 208V 3-phase AC @3.2 kW. The P500 will supply the fire alarm system –48V @2A.
4.3.1.2

Antenna HVAC

The P500 requires cooling for 165W of heat dissipation. The P501 requires cooling for 195W of heatdissipation. The P502 requires cooling for 145W of heat dissipation. The P503 requires cooling for 145W
of heat dissipation.

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Design Description

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0002-DSN-ADC_POWER_SUPPLY_REF_DESIGN

4.3.1.3

Date: 2019-07-18
Version: A

WVR Cooling System

The P502 will supply +15.5 V @11.4A to the WVR cooling system, which will then regulate that voltage
down to the voltage that it requires.

4.3.2

Digital Back End (DBE)/Data Transmission Systems (DTS)

The whole DBE/DTS requires –48V @10A from the P500. The DBE/DTS system will have its own powersystem inside that regulates the –48V down to voltages it requires.

4.3.3

Front End (FE)The Front End consists of six bands. The P501 will supply the FE with +32.5V @0.5A, +17.5V @6A, +7.5V@0.5A, and –7.5V @0.5A for all six bands.

4.3.4

Integrated Downconverter/Digitizers (IRD)

The IRDs consist of 13 modules. Each requires +5.5V @1A, +3.8V @1A and –5.5V @0.1A from P501.

4.3.5
4.3.5.1

LO Reference Receiver, Generator, and Distributor
LO Clock Module

The LO Clock Module is located in the FE Enclosure and in the WVR Enclosure. These modules require+17.5V @2.5A, +5.5V @1.5A, –5.5V @0.25A, and –17.5V @–0.25A from the P501 and P502.
4.3.5.2

LO Reference Receiver, Generator, and Distributor Module

The Reference Receiver, Generator, and Distributor module in the pedestal room requires +17.5V@2.5A, +7.5V @1.5A, –7.5V @0.25A, and –17.5V @0.25A from the P503.

4.3.6

Monitor and Control (M&C)

The monitor and control system requires that a Module Interface Board (MIB) be used inside the P500,
P501, P502, and P503 modules.
The P500 will power the Ethernet switch located in the pedestal room with –48V @2A.
The P503 will also power the four M&C modules located in the pedestal room of the antennas. The P503
will supply each M&C module with +17.5V @1 A, +7.5V @2A, and –17.5V @1A.

4.3.7

Water Vapor Radiometer (WVR)

The WVR will use two Band 4 IRDs. The IRDs will only require +5.5V @2A, +3.8V @2A and –5V @0.2A
from the P502.
The P502 will also be used to power the amplifiers and other electronics in the WVR antenna. The P502
will supply the antenna with +32.5V @30 mA, +17.5V @30 mA, +5.5V @10 mA, and –5.5 @0.5A.

Page 10 of 11

Title: DC Power Supply Reference
Design Description

Owner: Lopez

NRAO Doc. #: 020.30.50.00.00-0002-DSN-ADC_POWER_SUPPLY_REF_DESIGN

5 Abbreviations and Acronyms
Acronym
AD
ALMA
DBE
DTS
FE
HVAC
IRD
LNA
LO
M&C
ngVLA
RD
UPS
VLA
WVR

Description
Applicable Document
Atacama Large Millimeter Array
Digital Back End
Data Transmission System
Front End
Heating, Ventilation, and Air Conditioning
Integrated Downconverter/Digitizers
Low Noise Amplifier
Local Oscillator
Monitor and Control
Next Generation VLA
Reference Document
Uninterruptible Power Source
Jansky Very Large Array
Water Vapor Radiometer

Page 11 of 11

Date: 2019-07-18
Version: ATitle: Bins, Modules, and Racks Work
Owner: Sturgis
Package: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

Bins, Modules, and Racks Work Package:
Preliminary Technical Requirements
020.30.55.00.00-0001-REQ-A-BINS_MODULES_RACKS_PRELIM_REQS

Status: RELEASEDPREPARED BY
D. Gerrard, S. Sturgis, J. Allison
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-10-26
2019-05-03

APPROVALS
R. Selina,
Project Engineer

ORGANIZATIONElectronics Division,
NRAO

DATE
2019-07-17

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.17 16:34:10 -06'00'

Asst. Director,
NM-Operations, NRAO

2019-07-17

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.17 16:34:26 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-17

2019.07.17
16:13:09 -06'00'

Page 1 of 15

Title: Bins, Modules, and Racks Work
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NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

Change Record
AuthorAffected
Section(s)VersionDate

Reason01

2018-05-24

J. Allison

1, 3, 4.1

Initial Draft Version

02

2018-07-09

S. Sturgis

All

Revised and updated

03

2018-09-24

S. Durand

All

Basic edits04

2018-10-19

J. Allison

All

05

2018-10-23

J. Allison

All

06

2018-10-26

J. Allison

1007

2019-05-30

R. Selina

2.1, 3.2, 4

Misc. edits and corrections
Misc. edits and corrections. Addressed RID
numbers: IPDSR-594, 592, 531, 530
Addressed RID number IPDSR-593
Edits throughout for release. Updated
requirements numbering scheme, refinedsome requirements, etc.

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Title: Bins, Modules, and Racks Work
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NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

Table of Contents
1

Introduction ................................................................................................... 5

1.1
1.2

Purpose ................................................................................................................................... 5
Scope ...................................................................................................................................... 5

2

Related Documents and Drawings ............................................................... 6

2.1
2.2

Applicable Documents ........................................................................................................... 6
Reference Documents ............................................................................................................ 6

3

Overview of the Bins, Modules, and Racks Technical Requirements ....... 7

3.1
3.2
3.3
3.4
3.4.1
3.4.2

Document Outline ................................................................................................................. 7
Project Background................................................................................................................ 7
General Bins, Modules, and Racks Description ................................................................... 7
Summary of Bins, Modules, and Racks Requirements ......................................................... 8
General Functional Specifications .......................................................................................................... 8
Other General Requirements................................................................................................................. 8

4

Functional and Performance Requirements ............................................... 9

4.1
4.2
4.2.1
4.2.2
4.3

RF Shielding ............................................................................................................................ 9
Environmental Conditions ..................................................................................................... 9
Normal Operating Conditions ............................................................................................................... 9Specific Environmental Requirements................................................................................................... 9Life Cycle Requirements ........................................................................................................ 95Interface Requirements .............................................................................. 10

5.1
5.2
5.3
5.3.1
5.3.2
5.3.3
5.4

Interface between Modules and Bins ................................................................................. 10Interface between Bins and Rack ....................................................................................... 10Interface between Racks and Antenna ............................................................................... 10
Electrical Interface ................................................................................................................................... 10
Mechanical Interface ................................................................................................................................ 10
HVAC ......................................................................................................................................................... 10Interface to the Monitor & Control System ....................................................................... 10

6

Safety ............................................................................................................ 11

6.1
6.2

Electrical Safety ................................................................................................................... 11
Handling, Transport, and Storage Safety ........................................................................... 11

7

Requirements for Design ............................................................................ 11

7.1
7.1.1
7.1.2
7.1.3
7.1.4
7.1.5

Materials, Parts and Processes ............................................................................................ 11
Fasteners .................................................................................................................................................... 11
Paints........................................................................................................................................................... 11
Surface Treatment ................................................................................................................................... 11
Name Plates and Product Marking ...................................................................................................... 11
Labels .......................................................................................................................................................... 11

8

Documentation Requirements ................................................................... 12

8.1

Technical Documentation ................................................................................................... 12

9
10
11

Verification and Quality Assurance ........................................................... 12
Key Performance Parameters .................................................................... 13
Appendix....................................................................................................... 14

11.1
11.2

Abbreviations & Acronyms................................................................................................... 14
Maintenance Definitions ..................................................................................................... 15

Page 3 of 15

Title: Bins, Modules, and Racks Work
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NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

11.2.111.2.2

Date: 2019-07-17
Version: A

Maintenance Approach ........................................................................................................................... 15
Periodic Preventive Maintenance ......................................................................................................... 15

Page 4 of 15

Title: Bins, Modules, and Racks Work
Owner: Sturgis
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NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

1 Introduction
1.1 Purpose
This document aims to present a set of technical requirements for the reference design of the ngVLA Bins,
Modules, and Racks work package. Many requirements flow down from the preliminary ngVLA System
Requirements [AD02], which in turn flow-down from the preliminary ngVLA Science Requirements[AD01].
The Science goals are presently being elaborated by the Science Advisory Council (SAC) and Science
Working Groups (SWGs), and are captured in a series of draft use cases. A preliminary analysis of theseuse cases, and the flow down recursively to the science, system and subsystem requirements, are reflectedin this draft.

1.2 Scope
The scope of this document is the ngVLA Bins, Modules, and Racks work package. This consists of any
modular unit housing electronic components within the Antenna and the bins in which they are mounted.
This requirements document establishes the performance, functional, design, and test requirements
applicable to the ngVLA Bins, Modules, and Racks. It also includes interface requirements that must be
defined.

Page 5 of 15

Title: Bins, Modules, and Racks Work
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NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of this Technical Specification shall be considered as a superseding requirement.
Reference
No.
AD01
AD02
AD03
AD04
AD07
AD08
AD10
AD11
AD12

Document Title

Rev/Doc. No.

ngVLA Science Requirements
ngVLA Preliminary System Requirements
ngVLA Operations Concept
ngVLA System Electromagnetic Compatibility
and Radio Frequency Interference Mitigation
Requirements
Insulation Coordination for Equipment within LowVoltage Systems
Occupational Safety and Health Standards for
General Industry
Military Handbook, Reliability Prediction ofElectronic Equipment
Non-electronic Parts Reliability Data
Electromagnetic Compatibility

020.10.15.00.00-0001-REQ
020.10.15.10.00-0003-REQ
020.10.05.00.00-0002-PLA
020.10.15.10.00-0002-REQ
IEC 60664
29 CFR Part 1910
MIL-HDBK-217F
NPRD-95
IEC 61000-3-5

2.2 Reference Documents
The following references provide supporting context:
ReferenceNo.
RD01

Document Title

Rev / Doc. No.

Cabinets, Racks, Panels, and Associated Equipment

EIA/ECA-310 Rev. E

Page 6 of 15

Title: Bins, Modules, and Racks Work
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NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

3 Overview of the Bins, Modules, and Racks Technical Requirements
3.1 Document Outline
This document presents the technical requirements of the ngVLA Bins, Modules, and Racks work package.
These parameters determine the overall form and performance of the Bins, Modules, and Racks work
package.
The functional and performance specifications, along with detailed explanatory notes, are found in Section
4. The notes contain elaborations regarding the meaning, intent, and scope of the requirements. These
notes form an important part of the definition of the requirements and should guide the verification
procedures.
In many cases the notes contain an explanation or an analysis of how the numeric values of requirements
were derived. Where numbers are not well substantiated, this is also documented in the notes. In thisway, the required analysis and trade-space available is apparent to scientists and engineers who will guidethe evolution of the ngVLA Bins, Modules, and Racks Work Package concept.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses.
Safety requirements applicable to both the design phase and the functional Bins, Modules, and Racks aredescribed in Section 7. Additional requirements for the design phase are described in Section 8.
Documentation requirements for both technical design documentation and software are provided in
Section 9.
Requirements for the Verification and Test, from the conceptual design through to prototype, aredescribed in Section 10.
Section 11 identifies Key Performance Parameters (KPP) that should be estimated and monitored
throughout the design phase. These are metrics to assist in the trade-off analysis of various concepts, andhelp identify and resolve tensions between requirements as the design progresses.

3.2 Project Background
The Next Generation Very Large Array (ngVLA) is a project of the National Radio Astronomy
Observatory (NRAO) to design and build an astronomical observatory that will operate at centimeter
wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116
GHz). The observatory will be a synthesis radio telescope constituted of reflector antennas of 18 meters
diameter and 6 meters diameter, operating in a phased or interferometric mode.
The array’s signal processing center will be located at the Very Large Array site on the Plains of San
Agustin, New Mexico. The array will include stations in other locations throughout New Mexico, west
Texas, eastern Arizona, and northern Mexico. Long baseline stations are located in Hawaii, Washington,
California, Iowa, Massachusetts, New Hampshire, Puerto Rico, the US Virgin Islands, and Canada.

3.3 General Bins, Modules, and Racks Description
The Bins, Modules, and Racks work package consists of individual modules (LRUs) housed in a number ofbins all inside of an EIA standard electronics rack located in the pedestal room of the antenna. The work
package may also include a number of modules and bins in other locations as well. Its key function is toPage 7 of 15

Title: Bins, Modules, and Racks Work
Owner: Sturgis
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Date: 2019-07-17
Version: A

modularize the electronics, and make assembly and maintenance of the antenna electronics as simple aspossible, while providing adequate RFI shielding for the antenna and any other sensitive equipment.

3.4 Summary of Bins, Modules, and Racks Requirements
The following table summarizes major requirements to give the reader a high-level view of the subsystem.
Should a conflict arise between requirements listed here and descriptions in Sections 4–10, the latter shalltake precedence.

3.4.1

General Functional Specifications

Parameter
Ease of Access

Req. #
BMR0001

Ease of Installation

BMR0002

RFI Shielding
Heat Dissipation

BMR0003
BMR0004

VolumeBMR0005

Mass

BMR0006

3.4.2

Summary of Requirement
Must be simple and quick to access contained
components.
Must be simple and quick to install anduninstall.
Must provide RFI shielding where needed.
Must provide a means of expelling heat
where needed.
Must be configurable to different volumes ofelectronic components.
Must be low enough for a single person to lift
and manipulate.

Traceability
SYS2403

Summary of Requirement
Must have adequate corrosion prevention.
Metric hardware, whenever possible.
Modules must be made up of standardized
components requiring little alteration toaccommodate different systems’ needs.
The use of as few external connectors as
possible is encouraged.
Any connectors entering/exiting any modules
or racks must maintain RFI shielding levels.
General dimensions of machined parts must
fit the tolerances outlined in manufacturing
drawing of the parts to ensure everything fits
together correctly and mounting properly.
Surface flatness and finish of machined parts
must fit those outlined in manufacturing
drawing to ensure surface contact for heattransfer spec. RFI is mitigated properly, andparts are kept safe from corrosion.

Traceability
SYS2801

SYS2403
SYS2106
SYS2403
SYS2403

Other General Requirements

Parameter
Corrosion resistance
HardwareStandardized
Components

Req. #
BMR0101
BMR0102
BMR0103

Minimize External
Connectors
Shielded Connectors

BMR0104

Meet Specified
General Dimensions

BMR0106

Meet Specified Surface
Flatness and Finish

BMR0107

BMR0105

Page 8 of 15

SYS2106
SYS2106

Title: Bins, Modules, and Racks Work
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NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

4 Functional and Performance Requirements
These requirements apply to a properly functioning system, under the normal operating environmental
conditions unless otherwise stated.

4.1 RF Shielding
Parameter
Module RF Shielding
Rack RF Shielding

Req. #
BMR0401
BMR0402

Value>50 dB from 1–30 GHz>80 dB from 1–30 GHz

Traceability
SYS2106
SYS2106

Module and rack required RF shielding levels are not presently defined, and dependent on emission levels
within the enclosures, so starting at a conservative level is prudent.

4.2 Environmental Conditions
4.2.1

Normal Operating Conditions

The modules, bins, and racks are not designed to withstand outside environmental conditions. The costof an outdoor RFI-shielded rack is expected to be significantly higher compared to an indoor shielded
rack. Each module, bin, or rack located outside of the pedestal room will reside inside of a separate,environmentally-sealed enclosure.

4.2.2

Specific Environmental Requirements

Parameter
Rack Cooling
Bins and Module Cooling

Req. #
BMR0501
BMR0502

Rack air inlet
temperature
Maximum airtemperature difference
from inlet to exit

BMR0503

Value
Must be forced-air cooled
Forced air must be directed to only flow
through the bins and past the modules andnot in the space between the doors or wallsof the rack and the modules/bins.
4 ± 2°C

BMR0504

10°C

Traceability

Any rack with heat generating modules contained within it must be able to be cooled with forced air.
Typically this means honeycomb filters top and bottom and forced air flows from bottom to top. The
forced air system may be an open or closed system.

4.3 Lifecycle Requirements
Parameter
Design Life
Lifecycle
Optimization

Req. #
Value
BMR0601 The Bins, Modules, and Racks shall be designed to be
operated and supported for a period of 20 years.
BMR0602 The Bins, Modules, and Racks design shall minimize its
lifecycle cost for 20 years of operation.

Traceability
SYS2701
SYS2702

Lifecycle costs include manufacture, transport, construction/assembly, operation, and decommissioning.

Page 9 of 15

Title: Bins, Modules, and Racks Work
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Date: 2019-07-17
Version: A

5 Interface Requirements
This section provides information about the interfaces of the Bins, Modules, and Racks. Interface Control
Documents (ICDs) are required between the Bins, Modules, and Racks and all connecting systems. In
many cases, specifications for the interfaces are not yet available, but the broad scope of the ICD can be
defined.
These interfaces shall be developed and documented by the Bins, Modules, and Racks Designer, andapproved by ngVLA, as part of the Bins, Modules, and Racks reference and conceptual design efforts, andupdated throughout the design. Post CoDR, the ICD shall only be updated through formal project change
control processes.

5.1 Interface between Modules and Bins
The module shall slide into the bin and be secured in such a manner that it is easy and quick to install or
remove with minimal hand tools.

5.2 Interface between Bins and Rack
The bins will mount to the standard EIA rack mounting rails and will conform to EIA rack mount standards[RD01].

5.3 Interface between Racks and Antenna
5.3.1

Electrical Interface

The ICD should describe both the mechanical and electrical specifications of the electrical interfaces.

5.3.2

Mechanical Interface

The rack base will be bolted to the floor, and at least one point at the top of the rack will be anchored toa point on a wall or other secure mounting point.

5.3.3

HVAC

The rack will have an HVAC interface at both the top and bottom, for a closed system. This will effectively
prevent the ingress of dust and other contaminants, and allow a much longer service interval.

5.4 Interface to the Monitor and Control System
The rack air inlet and exit temperature should be monitored.

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Date: 2019-07-17
Version: A

6 Safety
6.1 Electrical Safety
Electrical equipment installed on the antenna shall comply with their relevant international or US productstandard. Electrical installations and equipment shall be specifically built and/or derated in order to safely
perform their intended functions under the applicable environmental conditions. Insulation shall becoordinated in conformity with IEC 60664 [AD07] while taking into account the altitude of up to 2500 m
above sea level.

6.2 Handling, Transport, and Storage Safety
The design of the Bins, Modules, and Racks shall incorporate all means necessary to preclude or limit
hazards to personnel and equipment during assembly, disassembly, test, and operation.

7 Requirements for Design
7.1 Materials, Parts and Processes
7.1.1

Fasteners

Where reasonably possible, all fasteners shall be metric.

7.1.2

PaintsAny painted coatings shall be chosen to last at least 20 years without repainting.

7.1.3

Surface Treatment

Any unpainted surfaces shall be treated against corrosion.

7.1.4

Name Plates and Product Marking

As a general rule the main parts and all exchangeable units shall be equipped with nameplates which arevisible after installation of the part/unit and which contain the following information:x Part/unit namexxxx

Drawing number including revision
Serial number
Manufacturing month and year
Name of manufacturer

Alternatively, a system of marking based on barcodes or similar system may be used upon approval by
ngVLA.

7.1.5

LabelsRacks, bins and modules, and all associated electrical interconnects shall be labeled.

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Date: 2019-07-17
Version: A

8 Documentation Requirements
8.1 Technical Documentation
All documentation related to the Bins, Modules, and Racks shall meet the following requirements:
x The language used for written documentation shall be English.
x Drawings shall be generated according to ISO standards and use both metric and imperial units.
x Drawings will be archived in Adobe PDF format.
x All CAD source files will be provided.
x The CAD system used is AutoDesk Inventor and/or AutoCAD (not preferred).
x The electronic document formats are Microsoft Word and Adobe PDF.
Any deviation from the above shall be agreed to by ngVLA.

9 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A) inspection (I), a factory
acceptance test (FAT) or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which may bechecked by the ngVLA project office during the design phase by review of the design documentation.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which will bechecked by the ngVLA project office during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple inspection
or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item / assembly / unit
with the specified performance shall be demonstrated by tests. A FAT is performed w/o integration withinterfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item / assembly / unit withthe specified performance shall be demonstrated by tests. SAT is performed on-site with the equipment
as installed.
Multiple verification methods are allowed.
The following table summarizes the expected verification method for each requirement.
Req. #
BMR0313
BMR0314
BMR0401
BMR0402

Parameter / Requirement
Machined Part Dimensions
Machined Part Surface Flatness/Finish
Module RF Shielding
Rack RF Shielding

Table 1 - Expected requirements verification method.

Page 12 of 15

D
X
X

A

I
X
X

FAT
X
X

SAT

Title: Bins, Modules, and Racks Work
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Date: 2019-07-17
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10 Key Performance Parameters
This section provides Key Performance Parameters that should be estimated by the designer andmonitored by NRAO throughout the design phase of the project. These are parameters that have a large
influence on the eventual effectiveness of the facility, and are useful high-level metrics for trade-off
decisions.
These parameters are of higher importance to NRAO. Improved performance above the requirement isdesirable on these parameters. The impact on system-level performance is often discussed in the narrativein Section 4.
The technical requirements are generally specified as minimum values. The goal is to give the designer
some latitude in optimization for a balanced design. Understanding the anticipated performance of theBins, Modules, and Racks (not just its specified minimum) on these parameters is of value for system-level
analysis and performance estimation.
These parameters may also be useful for determining the relative priority of the requirements documented
in Section 4 and can assist in the required analysis should tensions be identified between requirements, or
reductions in capability be required to fit within cost constraints.
The Key Performance Parameters that have been identified for monitoring are described in Table 2. Notethat the order in the table reflects the order in the document, and is not indicative of relative importanceor priority.
Key Performance Parameter
Module RF Shielding
Rack RF Shielding
Table 2 - Key performance parameters for monitoring during design.

Page 13 of 15

Req. #
BMR0401
BMR0402

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11 Appendix
11.1 Abbreviations and Acronyms
Acronym
AD
CDR
CoDR
FDR
HVAC
ICD
IF
KPP
LRU
MTBF
MTTF
MTTR
ngVLA
RD
RFI
TAC
TBD
VLA

Description
Applicable Document
Critical Design Review
Conceptual Design Review
Final Design Review
Heating, Ventilation & Air Conditioning
Interface Control Document
Intermediate Frequency
Key Performance ParametersLine Replaceable Unit
Mean Time Between Failure
Mean Time To Failure
Mean Time To Repair
Next Generation VLA
Reference Document
Radio Frequency Interference
Technical Advisory Council
To Be Determined
Jansky Very Large Array

Page 14 of 15

Date: 2019-07-17
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Owner: Sturgis
Package: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.55.00.00-0001-REQ-ABINS_MODULES_RACKS_PRELIM_REQS

Date: 2019-07-17
Version: A

11.2 Maintenance Definitions
11.2.1 Maintenance Approach
Required maintenance tasks shall be minimized.
Maintenance shall be mainly performed at assembly and subassembly level by exchange of Line Replaceable
Units (LRUs). LRUs are defined as units which can be easily exchanged (without extensive calibration, of
sufficient low mass and dimension for easiness of handling, etc.) by maintenance staff of technician level.
In the context of this subsystem, an LRU is defined as any ARCS module.
LRU exchange shall be possible by 2 trained people within 4 working hours. It is desirable that LRU
replacement be possible using only standard tools identified in a maintenance manual for the Bins, Modules,
and Racks.
A step-by-step procedure for safe exchange of every LRU shall be provided in the Maintenance Manual.

11.2.2 Periodic Preventive Maintenance
The ARCS modules require no preventive maintenance. The shielded racks will periodically require
replacement of air filters at the HVAC inlet or outlet, where used.

Page 15 of 15

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Date: 2019-07-17
Version: A

Bins, Modules, and Racks Reference Design Description
020.30.55.00.00-0002-DSN-A-BINS_MODULES_RACKS_REF_DSN

Status: RELEASEDPREPARED BY
D. Gerrard, S. Sturgis, J. Allison
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-10-23
2019-05-04

APPROVALS (Name and Signature)
R. Selina,
2019.07.17
Project Engineer
16:50:09 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-17

M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.17 16:58:15 -06'00'

Asst. Director,
NM-Operations, NRAO

2019-07-17

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.17 16:58:39 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-17

Page 1 of 11

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

Date: 2019-07-17

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Version: A

Change Record
Version

Date

AuthorAffected
Section(s)01

2018-05-24

J. Allison

1-5Initial draft

02

2018-06-25

S. DurandAll

Small edits

03

2018-07-10

S. Sturgis

All

Revised and updated04

2018-09-24

S. DurandAll

More small edits05

2018-10-19

J. Allison

All

06

2018-10-23

J. Allison

All

07

2019-05-30

R. Selina

2, 3, 4A

2019-07-17

A. Lear

All

Small edits and corrections
Small edits and corrections, addressed RID
numbers: IPDSR-532 & 591
Minor edits for release throughout; struckinterface section (duplicate to requirements
doc)
Prepared document for approvals & release

ReasonPage 2 of 11

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Date: 2019-07-17
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings ............................................................... 4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 43
4

Subsystem Overview ..................................................................................... 5
Subsystem Design .......................................................................................... 5

4.1
4.2
4.3
4.4

Modules .................................................................................................................................. 5
Bins.......................................................................................................................................... 6
Racks ....................................................................................................................................... 6
Subsystem Components ......................................................................................................... 6

5

Appendix....................................................................................................... 10

5.1
5.2

Abbreviations and Acronyms ............................................................................................... 10
ARCS Module Testing Results ............................................................................................. 11

Page 3 of 11

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Date: 2019-07-17
Version: A

1 Introduction
1.1 Purpose
This document provides a description for the Bins, Modules, and Racks subsystem reference design. It
covers the design approach, functions, description of key components, interfaces, and risks associatedwith the reference design. This document will form part of the submission of the ngVLA Reference Design
documentation package.

1.2 Scope
The scope of this document covers the entire design of the Bins, Modules, and Racks subsystem at the
Antenna, as part of the ngVLA Reference Design. It includes the subsystem’s design, how it functions, andinterfaces with the necessary hardware and software systems.
It does not include specific technical requirements [see AD01] or budgetary information.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein, but provide necessary context or
supporting material.
Reference
No.
AD01
AD02
AD03
AD04
AD05

Document Title

Rev/Doc. No.

ngVLA Bins, Modules, and Racks Subsystem
Preliminary Requirements
ngVLA Preliminary System Requirements
ngVLA EMC & RFI Mitigation Requirements
Antenna Electronics Front End Enclosure
Block Diagram
Antenna Electronics Pedestal Enclosure
Block Diagram

020.30.55.00.00-0001-REQ
020.10.15.10.00-0003-REQ
020.10.15.10.00-0002-REQ
020.30.00.00.00-0002-BLK
020.30.00.00.00-0003-BLK

2.2 Reference Documents
The following documents are referenced within this text:
Reference
No.
RD01
RD02

Document Title

Rev/Doc. No.

ALMA Back End IPT Shielded Rack
Specification
ARCS Module RFI Test Report

BEND-57.02.00.00-004-A-SPE

Page 4 of 11

D. Mertely, 2018.

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Date: 2019-07-17
Version: A

3 Subsystem Overview
The Bins, Modules, and Racks subsystem consists of individual modules (LRUs) housed in a number of bins
all inside of an EIA standard electronics rack located in the antenna’s pedestal room. The work package
may also include a number of modules and bins in locations other than the electronics rack and other thanthe pedestal room. Its key function is to house the LRUs that make up the antenna electronics, and makeassembly and maintenance of the antenna electronics as simple as possible while providing adequate RFI
shielding for the antenna and any other sensitive equipment.

4 Subsystem Design
4.1 Modules
The proposed modules for this subsystem are the Advanced RFI Containment System (ARCS) modules
that were recently developed by NRAO. There are three primary types of ARCS modules, designated asseries 100, 200, and 300. The 100 series modules consist of two high-tolerance machined pieces ofaluminum that fit together like a clamshell, leaving a cavity in the middle for mounting electronics. The 200
series modules consist of three pieces, and allow for dual internal cavities that are independently RFI
shielded. The 300 series modules are also three-piece modules, but with individually removable side panels
that allow access to the internal electronics from either side of the module. The module style to be
selected is dependent on the degree of access required for the components within, and the desired
mounting layout of said components.
All module types have double-gasket seams around the edge, utilizing specialized RFI gaskets. A series ofcompression latches compress the gasket, and ensure a high level of RFI shielding is achieved. All modules
will have guide blocks that help guide the module into the bin, as well as a front panel that is used tosecure the module into the bin via four captive thumbscrews.
The modules are made out of ATP5 aluminum tool plate to prevent warping during machining. This helps
ensure that the modules will meet their dimensional specifications so that they may mitigate RFI effectively
and fit into their bins with ease. All module pieces will be chromated per MIL-C-5541-CL.III after machining
in order to maintain a conductive surface. Each piece of every module also has its own RFI gasket which
is attached using electrically conductive adhesive.
All of the individual module pieces can vary in width by half-inch increments, so a large variety of sizes andstyles can be achieved in order to optimize space for electrical components. Furthermore, the outer
covers may be produced with heatsink fins for heat-generating components, and the interiors can becustomized with pockets or ridges to better accommodate mounting of electrical components.
Input/output connections can be made on either the front or rear of the module. Blind mate connections
are also possible with the addition of a panel on the rear of the bin, to hold one side of the blind mateconnector.
Another benefit of these modules is that there is no designated front, rear, top or bottom of the module.
Modules may be inserted into the bin from either the front or the rear, and either right side up or upsidedown.
The ARCS module concept can be readily adapted for applications where rack or bin mounting is not arequirement or desired. For example, the IRD enclosure is expected to be variant of a 100 series module,
but with a form factor of 24” x 20” instead of the standard 8” x 20”.

Page 5 of 11

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Date: 2019-07-17
Version: A

4.2 Bins
Bins provide a convenient and reliable method of organizing groups of modules near one another. The
standard ARCS bin is six rack units (6 RU) tall by 20 inches deep, and is designed to fit into a standard EIA
19 inch wide rack. However, bins can be configured for any rack height, width or depth.
There is not a fixed number of modules per bin, because of the varying module widths. To accommodate
a mix of module widths, bins are designed for module widths in increments of ½”. The bins simply mountto the vertical rails of the rack using #10 machine screws.

4.3 Racks
The racks will be a variant of the ALMA Back End racks [RD01], as they are a proven solution. These
racks provide a high level of RFI shielding, using a combination of a welded steel external shell, RFI gaskets,and an RFI-absorbing foam. The rack typically has multiple I/O panel location options for running powerand signals in or out of the rack, and honeycomb filters on the top and bottom to allow airflow throughthe rack for cooling without compromising the RFI shielding. The dimensions and I/O panel locations of
the racks will be dependent on the design and available space of the pedestal room in the selected antenna.

4.4 Subsystem Components
Figures 1–4 show examples of different ARCS module configurations.

Figure 1 - Series 100 ARCS module.

Page 6 of 11

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Figure 2 -100 Series ARCS module with integrated heatsink.

Figure 3 - 200 Series ARCS module (two cavity) with one integrated heatsink.

Page 7 of 11

Date: 2019-07-17
Version: ATitle: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Figure 4 - 300 Series ARCS module (components accessible from either side).

Figure 5 shows an example of modules installed in a bin.

Figure 5 - ARCS modules installed in a bin.

Page 8 of 11

Date: 2019-07-17
Version: ATitle: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Date: 2019-07-17
Version: A

Figure 6 shows an example of the rack used to house the ARCS bin. Note the different possible locationsof the I/O panel, on top (and bottom) or the side.

Figure 6 - Shielded rack.

Page 9 of 11

Title: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

5 Appendix
5.1 Abbreviations and Acronyms
Acronym
ARCS
BE
EIA
FE
HVAC
ICD
IRD
LRU
ngVLA
RFI
RU
UPS
VLA
WVR

Description
Advanced RFI Containment System
Back EndElectronics Industries Alliance
Front End
Heating, Ventilation and Air Conditioning
Interface Control Document
Integrated Receiver Downconverter/Digitizer
Line Replaceable Unit
Next Generation VLARadio Frequency Interference
Rack Units
Uninterruptible Power Supply
Jansky Very Large Array
Water Vapor Radiometer

Page 10 of 11

Date: 2019-07-17
Version: ATitle: Bins, Modules, and Racks
Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.55.00.00-0002-DSN-ABINS_MODULES_RACKS_REF_DSN

Date: 2019-07-17
Version: A

5.2 ARCS Module Testing Results

Figure 7 - Preliminary shielding effectiveness of 100 series ARCS module [RD02]. Note: tests were performedin reverb chamber, not anechoic chamber.

Page 11 of 11

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

Antenna Electronics Environmental Control System:
Preliminary Technical Requirements
020.30.60.00.00-0001-REQ-A-ANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Status: RELEASEDPREPARED BY
S. Sturgis, J. Allison
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2019-07-19
2019-07-19

APPROVALS (Name and Signature)
R. Selina,
2019.07.25
Project Engineer
10:54:39 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-25

M. McKinnon,
Asst. Director,
Digitally signed by Mark McKinnon
Mark
McKinnonDate:2019.07.25
16:20:21-06'00'
Project Director
NM-Operations, NRAO

2019-07-25

RELEASED BY (Name and Signature)
ORGANIZATION
M. McKinnon,
Asst.
Director,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.25 16:20:37 -06'00' NM-Operations, NRAO

DATE
2019-07-25

Page 1 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

Change Record
Date

AuthorAffected
Section(s)01

2018-05-22

J. Allison

1-4

02

2018-07-12

S. Sturgis

All

03

2018-09-02

S. DurandAll05

2018-09-19

S. DurandAll

06

2018-11-09

J. Allison

All

07

2018-11-12

All

08

2019-07-19

S. Sturgis
L. LeybaNewton

09

2019-07-22

R. Selina

1.1, 2.2, 3.4

A

2019-07-25

A. LearAll

Version2, 4, 7, 11

ReasonInitial Draft
Updated and revised doc number, title, allsections.
Small edits
More Small edits
Addressed RID numbers 630 & 631. Added
references to Cryogenics, IRD, and WVR
specifications documents. Added information
about verification & QA
Minor edits
Restructured, added clarity, completed
sections.
Updated functional requirements. Other edits
for release.
Prepared PDF for approvals & release

Page 2 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

Table of Contents
1

Introduction ................................................................................................... 5

1.1
1.2

Purpose ................................................................................................................................... 5
Scope ...................................................................................................................................... 5

2

Related Documents & Drawings .................................................................. 5

2.1
2.2

Applicable Documents ........................................................................................................... 5
Reference Documents ............................................................................................................ 5

3

Overview of Antenna Electronics Environmental Control System
Technical Requirements ............................................................................... 6

3.1
3.2
3.3
3.4
3.4.1

Document Outline ................................................................................................................. 6
Project Background................................................................................................................ 6
General Antenna Electronics Environmental Control System Description ........................ 6
Summary: Antenna Electronics Environmental Control System Requirements ................. 7
General Functional Specifications .......................................................................................................... 7

4

Environmental Control System Functional and Performance
Requirements ................................................................................................. 8

4.1
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.3
4.4
4.5

Functional Requirements ....................................................................................................... 8
Additional Requirements ....................................................................................................... 9Operating Conditions ............................................................................................................................... 9
Survival Conditions.................................................................................................................................. 11
Solar Radiation ......................................................................................................................................... 11
Rain/Water Infiltration ........................................................................................................................... 12
Mechanical Shock ..................................................................................................................................... 12
Maintenance and Reliability Requirements ....................................................................... 12
Monitor and Control Requirements ................................................................................... 12
Lifecycle Requirements ........................................................................................................ 135
67Interface Requirements .............................................................................. 13
Subsystem Requirements ........................................................................... 13
Safety ............................................................................................................ 14

7.1
7.2
7.2.1
7.2.2

General ................................................................................................................................. 14
Safety Design Requirements................................................................................................ 14
Electrical Safety......................................................................................................................................... 14
Handling, Transport, and Storage Safety ............................................................................................ 14

8

Requirements for Design ............................................................................ 15

8.1
8.1.1
8.2
8.3
8.3.1
8.3.2
8.3.3
8.3.4
8.3.5

Analyses and Design Requirements..................................................................................... 15
Reliability, Availability, Maintainability Analysis ................................................................................. 15
Electromagnetic Compatibility Requirements ................................................................... 15
Materials, Parts and Processes ............................................................................................ 15
Fasteners .................................................................................................................................................... 15
Paints........................................................................................................................................................... 15
Surface Treatment ................................................................................................................................... 15
Name Plates and Product Marking ...................................................................................................... 15
Labels .......................................................................................................................................................... 16

9

Documentation Requirements ................................................................... 17

9.1

Technical Documentation ................................................................................................... 17

Page 3 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

9.2

Date: 2019-07-25
Version: A

Software and Software Documentation ............................................................................. 17

10
11
12

Verification and Quality Assurance ........................................................... 18
Key Performance Parameters .................................................................... 20
Appendix....................................................................................................... 21

12.1
12.2
12.2.112.2.2Abbreviations and Acronyms ............................................................................................... 21
Maintenance Definitions ..................................................................................................... 22
Maintenance Approach ........................................................................................................................... 22
Periodic Preventive Maintenance ......................................................................................................... 22

Page 4 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

1 Introduction
1.1 Purpose
This document aims to present a set of technical requirements for the reference design of the ngVLA
Antenna Electronics Environmental Control System. These parameters determine the overall form andperformance of the environmental control of the antenna electronics. Many requirements flow down fromthe preliminary ngVLA System Requirements [AD02], which in turn flow down from the preliminary
ngVLA Science Requirements [AD01].

1.2 Scope
The scope of this document is the environmental control for the ngVLA antenna electronics. This consistsof temperature control of all electronics enclosures as well as protecting electrical components at theantenna from the environment. It includes interface requirements that must be defined. This requirements
document establishes the performance, functional, design, and test requirements applicable to theenvironmental control for the ngVLA antenna electronics.

2 Related Documents & Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of this Technical Specification shall be considered as a superseding requirement.
Ref. No.
AD01
AD02
AD03
AD04
AD05
AD06

Document Title
ngVLA Science Requirements
ngVLA Preliminary System Requirements
ngVLA Electronics Environmental Control System:
Reference Design Description
Insulation Coordination for Equipment within Low-Voltage
Systems

Rev/Doc. No.
020.10.15.00.00-0001-REQ
020.10.15.10.00-0003-REQ
020.30.60.00.00-0002-DSN

Enclosures for Electrical Equipment (1000 Volts Maximum)
System Environmental Specifications

NEMA 250
020.10.15.10.00-0001-SPE

IEC-60664

2.2 Reference Documents
The following references provide supporting context:
Reference
No.
RD01
RD02
RD03
RD04
RD05

Document Title

Rev/Doc. No.

System EMC Compatibility and RFI Mitigation
Requirements
ngVLA Cryogenic Subsystem Requirements
ngVLA Integrated Receivers and Downconverters:
Preliminary Technical Requirements
ngVLA Water Vapor Radiometer Preliminary TechnicalRequirements
ngVLA Front End Technical Requirements

020.10.15.10.00-0002-REQ

Page 5 of 22020.30.10.00.00.0001-REQ
020.30.15.00.00-0001-REQ
020.45.00.00.00-0001-REQ
020.30.03.01.00-0001-REQ

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

3 Overview of Antenna Electronics Environmental Control System
Technical Requirements
3.1 Document Outline
The functional and performance specifications, along with detailed explanatory notes, are found in Section
4. The notes contain elaborations regarding the meaning, intent, and scope of the requirements. These
notes form an important part of the definition of the requirements and should guide the verification
procedures.
In many cases, the notes contain an explanation or an analysis of how the numeric values of requirements
were derived. Where numbers are not well substantiated, this is also documented in the notes. In thisway, the required analysis and trade-space available is apparent to scientists and engineers who will guidethe evolution of the ngVLA Antenna Electronics Environmental Control System.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses. Subsystem requirements appear in Section 6.
Safety requirements applicable to both the design phase and the functional environmental control of theantenna electronics are described in Section 7. Additional requirements for the design phase are describedin Section 8. Documentation requirements for both technical design documentation and software areprovided in Section 9.
Requirements for Verification and Test, from the conceptual design through to prototype, are describedin Section 10.
Section 11 identifies Key Performance Parameters (KPP) that should be estimated and monitored
throughout the design phase. These are metrics to assist in the trade-off analysis of various concepts, andhelp identify and resolve tensions between requirements as the design progresses.

3.2 Project Background
The Next Generation Very Large Array (ngVLA) is a project of the National Radio Astronomy
Observatory (NRAO) to design and build an astronomical observatory that will operate at centimeter
wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116
GHz). The observatory will be a synthesis radio telescope constituted of reflector antennas of 18 meters
diameter and 6 meters diameter, operating in a phased or interferometric mode.
The signal-processing center of the array will be located at the Very Large Array site, on the plains of San
Agustin, New Mexico. The array will include stations in other locations throughout the state of New
Mexico, west Texas, eastern Arizona, and northern Mexico.
Operations will be conducted from both the VLA Control Building and the Domenici Science Operations
Center in Socorro, NM.

3.3 General Antenna Electronics Environmental Control System Description
Antenna electronics are located in various places around the antenna. Primary locations include, but are
not limited to, the electronics rack in the pedestal room, front end enclosures on the feed arm, the WVR
enclosure along the edge of the primary reflector, and the compressor platform at the top-rear of thepedestal. Environmental control of the antenna electronics involves temperature control of all electronics
in these locations as well as protection from water, dust, animals, or other environmental hazards.

Page 6 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

The primary temperature control system consists of a heated and cooled liquid loop, most likely glycol,
which runs from the compressor at the top-rear of the pedestal to the WVR module and the front end
enclosures. Liquid cold plates, made of copper tubing running through an aluminum block which
components may be directly mounted to, will cool electronics in both the front end enclosures and the
WVR, as well as heat or cool components on the compressor platform. The pedestal room electronics
rack will be forced-air-cooled via a commercial air conditioning unit which will likely mount to the side of
the rack and be purchased from the rack manufacturer.
Protection from water, dust, animals, or other environmental hazards will be accomplished with custom
sealed enclosures for the front end, WVR, and Cryo M&C enclosure. The electronics rack in the pedestal
room will be protected from such hazards by the antenna structure.

3.4 Summary: Antenna Electronics Environmental Control System Requirements
The following table provides a summary of the major requirements in order to provide the reader with ahigh-level view of the desired system. Should there be a conflict between the requirements listed here
and the descriptions in Sections 4 through 10, the latter shall take precedence.

3.4.1

General Functional Specifications

Parameter
Front End Receiver
Enclosure
Front End Auxiliary
Enclosure
WVR Receiver
EnclosureCompressor
Platform
Pedestal Room
Rack

Summary of Requirement
NEMA 4X [AD05], Cooled per [RD05]
NEMA 4X [AD05], Cooled per [RD02]
NEMA 4X [AD05], Cooled per [RD04]
Cooled/heated per [RD02]
Cooled as required

Page 7 of 22

Reference Reqs.
020.30.03.01.00-0001-REQ ngVLA
Front End Technical Requirements
020.30.10.00.00-0001-REQ ngVLA
Cryogenic Subsystem Requirements
020.10.15.10.00-0001-SPE SystemLevel Environmental Specifications
020.30.10.00.00-0001-REQ ngVLA
Cryogenic Subsystem Requirements
020.10.15.10.00-0001-SPE SystemLevel Environmental Specifications

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

4 Environmental Control System Functional and Performance
Requirements
These requirements apply to a properly functioning system, under normal operating environmental
conditions, unless otherwise stated.

4.1 Functional Requirements
Parameter
Front End
Enclosure

Req. #
EEC0100

Front End Auxiliary
Enclosure

EEC0101WVR Enclosure

EEC0102

Front End
Enclosure Thermal
Regulation

EEC0103

Front End Auxiliary
Enclosure Thermal
Regulation

EEC0104

WVR Enclosure
Thermal Regulation

EEC0105

Compressor
Enclosure Thermal
Regulation

EEC0106

Value
The environmental control systemshall provide a protective enclosure
meeting NEMA 4X standards for thefront end receivers and ancillaryequipment mounted on the feedindexing mechanism.
The environmental control systemshall provide a protective enclosure
meeting NEMA 4X standards for thevacuum pump and ancillaryequipment mounted adjacent to thefeed indexing mechanism.
The environmental control systemshall provide a protective enclosure
meeting NEMA 4X standards for the
WVR front-end electronics mounted
to the feed arm adjacent to the mainreflector.
The front end enclosure shall provide
an active heat exchanger service forheat-generating electronics within theenclosure.
The front end auxiliary enclosure
shall provide an active heat exchanger
service for heat-generating
electronics within the enclosure.
The WVR enclosure shall provide anactive heat exchanger service forheat-generating electronics within theenclosure.
The environmental control systemshall provide an active heat exchanger
service for heat-generating
electronics within the compressor
enclosure.

Page 8 of 22

Traceability
020.30.03.01.00-0001-REQ
Front End TechnicalRequirements

020.30.10.00.00-0001-REQ
Cryogenic Subsystem
Requirements

020.10.15.10.00-0001-SPE
System-Level
Environmental
Specifications
020.30.03.01.00-0001-REQ
ngVLA Front End TechnicalRequirements
020.30.10.00.00-0001-REQ
ngVLA Cryogenic
Subsystem Requirements
020.10.15.10.00-0001-SPE
System-Level
Environmental
Specifications
020.30.10.00.00-0001-REQ
ngVLA Cryogenic
Subsystem Requirements

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQSParameter
Pedestal Room
Rack Thermal
Regulation

Req. #
EEC0107

Value
The environmental control systemshall provide an active forced-air heatexchanger service for heat-generating
electronics in the pedestal roomrack.

Date: 2019-07-25
Version: A

Traceability
020.10.15.10.00-0001-SPE
System-Level
Environmental
Specifications

4.2 Additional Requirements
Parameter
Vibration

Req. #
EEC0152

Dust

EEC0153

Rodents

EEC0154

4.2.1

Value
All Antenna Electronics Environmental
Control exposed equipment, including all
equipment within the antenna, shall be
designed to withstand persistent windinduced vibration.
All Antenna Electronics Environmental
Control exposed equipment shall beprotected against windblown dust, ashes,and grit.
All Antenna Electronics Environmental
Control exposed equipment shall be
designed to prevent rodent damage. At aminimum, this may involve protecting all
cables with flexible or rigid conduit orequivalent. Any penetrations within
enclosures and raceways shall mitigate
the risk of rodent damage.

Traceability
020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0531020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0541020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0551

Operating Conditions

Parameter
Solar Thermal
Load

Req.#
EEC0250

Wind Speed

EEC0251

Outdoor
Temperature

EEC0252

Value
Antenna Electronics Environmental
Control equipment shall provide needed
environmental conditioning to theantenna electronics while meeting thecondition: Exposed to full Sun.
Antenna Electronics Environmental
Control equipment shall provide needed
environmental conditioning to theantenna electronics while meeting thecondition: :PVDYHUDJHRYHUmin. :PVJXVWAntenna Electronics Environmental
Control equipment shall provide needed
environmental conditioning to theantenna electronics while meeting thecondition: –20 C  T 45 C

Page 9 of 22

Traceability
020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0321020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0322020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0323

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQSParameter
Outdoor
Temperature
Rate of
ChangeReq.#
EEC0253

Precipitation

EEC0254

Cooling Temp
Front End
Enclosure

EEC0255

Cooling Temp
Front End
Auxiliary
Enclosure

EEC0256

Cooling
TempCompressor
Platform

EEC0257

Heat
Exchanger
ServiceTemperature

EEC0258

Value
Antenna Electronics Environmental
Control equipment shall provide needed
environmental conditioning to theantenna electronics while meeting thecondition: ¨T = 3.6°C/hr.
Antenna Electronics Environmental
Control equipment shall provide needed
environmental conditioning to theantenna electronics while meeting thecondition: 5 cm/hr. precipitation. (TBC)
The Front End enclosure shall provide
needed environmental conditioning toprovide an internal operationaltemperature range of –15 to 35°C; witha temp gradient of less than 3.6°C/hr.
The Front End Auxiliary enclosure shallprovide needed environmental
conditioning to provide an internal
operational temperature range of 12 to
45°C
Antenna Electronics Environmental
Control components shall provide
needed environmental conditioning toprovide an internal operationaltemperature range, within thecompressor enclosure, of –30 to 45°C
The Heat Exchanger Service provided tovarious locations around the antenna
shall maintain an operationaltemperature >28 C; with a temp grad.
Of less than 0.1°C/hr.

Date: 2019-07-25
Version: A

Traceability
020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0324020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
020.30.15.00.00-0001-REQ

020.30.10.00.00.0001-REQ

020.30.10.00.00.0001-REQ

020.45.00.00.00-0001-REQ

This section describes the operating conditions under which the environmental control system is
expected to meet its full specification. This environmental definition is consistent with the limit to theoperating conditions in [AD06].

Page 10 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

4.2.2

Date: 2019-07-25
Version: A

Survival Conditions

Parameter
Wind

Constraints
EEC0350

Temperature

EEC0351

Radial Ice

EEC0352

Snow Load –Equipment

EEC0354

Hail Stones

EEC0355

Value
Antenna Electronics Environmental
Control equipment shall survive windspeeds of 0 m/s  W 50 m/s average020.10.15.10.00-0001-SPE
System-Level Environmental
Specifications
ENV0341
Antenna Electronics Environmental
020.10.15.10.00-0001-SPE
Control equipment and the
System-Level Environmental
electronics they house shall survive
Specifications
outdoor temperatures of –30 C  T  ENV0342
50 C
020.10.15.10.00-0001-SPE
Antenna Electronics Environmental
System-Level Environmental
Control equipment and theSpecifications
electronics they house shall survive
radial ice of 2.5 cm
ENV0343
Antenna Electronics Environmental
020.10.15.10.00-0001-SPE
Control equipment and the
System-Level Environmental
electronics they house shall survive
Specifications
snow loads of 100 kg/m2 on horizontal ENV0345
surfaces.
020.10.15.10.00-0001-SPE
Antenna Electronics Environmental
System-Level Environmental
Control equipment and theSpecifications
electronics they house shall survive
hail stones of 2.0 cm diameter
ENV0346

The survival conditions describe the environment that the antenna and all outside structures should be
able to withstand without damage when placed in its least-vulnerable state. For the antenna, the designer
will specify the orientation that will result in minimum stress to the structure at the maximum wind speed
and maximum snow and ice loading. Systems housed within or on the antenna (including the environmental
control system) shall assume this orientation.
The temperature limits, radial ice, snow load and hail stone requirements are based on experience at the
VLA site and a survey of conditions throughout the extent of the array.

4.2.3

Solar Radiation

Parameter Req. #Solar Flux
EEC0360

UV
Radiation

EEC0361Value
All environmental control equipment
exposed to outside environment shall be
designed to allow normal operations given
the condition: a maximum diurnal solar fluxof 1200 W/m2 from 0.3–60 m.
All environmental control equipment
exposed to outside environment shall be
designed to allow normal operations, overthe full operating life of the array, given thecondition: a maximum diurnal UV radiatedflux of 100W/m2 from 280–400 nm.

Page 11 of 22

Traceability
020.10.15.10.00-0001-SPE
ENV0561020.10.15.10.00-0001-SPE
ENV0562

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

4.2.4

Version: A

Rain/Water Infiltration

Parameter
Rain/Water
Infiltration

4.2.5

Date: 2019-07-25

Req. #Value
EEC0450 All environmental control exposed equipment
shall be designed to withstand rainfall intensity
up to 10 cm/hr., with droplets sized 0.5 to
4.5mm, at wind velocity of 18 m/s from thevertical to horizontal direction, while
protecting any housed equipment.

Traceability
020.10.15.10.00-0001-SPE
ENV0571

Mechanical ShockParameter
Req. #
Value
Transportation EEC0500 All environmental control equipment shall
Environment
be designed to withstand typical loads andenvironments encountered duringtransportation as part of assembly or
maintenance.
Mechanical
EEC0501 All environmental control equipment shall
Shocksbe designed to survive mechanical shocklevels from handling as defined in Table 1 of
AD06.

Traceability
020.10.15.10.00-0001-SPE
ENV0581020.10.15.10.00-0001-SPE
ENV0582

4.3 Maintenance and Reliability Requirements
Parameter
Mean Time
Between Failures

Req. #
EEC0550Value
The Electronics Environmental
Enclosures shall be designed tohave a MTBF TBD hrs.

Traceability
020.10.15.10.00-0003-REQ
SYS2302

The maintenance and reliability requirements are in support of high-level requirements that limit the total
operating cost of the array.
Monitor points/sensors should be included in the MTBF/MTTR analysis, but sensors and othercomponents that can be reasonably deemed to be ancillary to operation may be removed from thedetermination of compliance with the MTBF requirement. “Failure” will be defined as a condition whichplaces the system outside of its performance specifications or into an unsafe state, requiring repair.

4.4 Monitor and Control Requirements
Parameter

Req. #

Value

Traceability

Self-Monitoring

EEC0600

The Electronics Environmental
Enclosures shall measure, report, andmonitor a set of parameters that allow
for determination of its status and may
help predict or respond to failures.

020.10.15.10.00-0003-REQ
SYS2701

The expectation with self-monitoring is that the monitor and control system expose lower-level sensors
to the monitor and control system when queried. The cadence of access is flexible, and is not expected
at high rates (typical access might be on second to minute scales). Any high-cadence monitoring should

Page 12 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

generally be internal to the Antenna Electronics Environmental Control System with a summary output
on the interface.
Other features of the M&C interface are to be specified in the Monitor and Control ICD.

4.5 Lifecycle Requirements
Parameter
Design Life

Req. #
EEC0650

Lifecycle
EEC0651
Optimization
Lifecycle costs include
decommissioning.

Value
The Electronics Environmental Enclosures
shall be designed to be operated andsupported for a period of 20 years.
The Electronics Environmental Enclosuresdesign shall minimize its lifecycle cost for 20
years of operation.
manufacturing,transportation,

Traceability
020.10.15.10.00-0003-REQ
SYS2801020.10.15.10.00-0003-REQ
SYS2802

construction/assembly,

operation,

and5 Interface Requirements
This section provides information about the interfaces of the Antenna Electronics Environmental Control
System. Interface Control Documents (ICDs) are required between the Antenna Electronics
Environmental Control system and all connecting systems. In many cases, specifications for the interfaces
are not yet available, but the broad scope of the ICD can be defined.
These interfaces shall be developed and documented by the Antenna Electronics Environmental Control
system designer, and approved by ngVLA, as part of the Antenna Electronics Environmental Control
system reference and conceptual design efforts, and updated throughout the design. Post CoDR, the ICD
shall only be updated through formal project change control processes.

6 Subsystem Requirements
Derivation of any subsystem requirements will be included as part of the Antenna Electronics
Environmental Control system conceptual design efforts, and updated throughout the design. Post CoDR,
the subsystem requirements will only be updated through formal project change control processes.

Page 13 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

7 Safety
7.1 General
7.2 Safety Design Requirements
7.2.1

Electrical Safety

Electrical equipment installed on the antenna shall comply with their relevant international or US productstandard.
Electrical installations and equipment shall be specifically built and/or derated in order to safely performtheir intended functions under the applicable environmental conditions. Insulation shall be coordinated inconformity with IEC 60664 while taking into account the altitude of up to 2500 m above sea level.

7.2.2

Handling, Transport, and Storage Safety

The design of the Antenna Electronics Environmental Control system shall incorporate all means
necessary to preclude or limit hazards to personnel and equipment during assembly, disassembly, test, andoperation. A safety hazard analysis shall be completed prior to the system CoDR.

Page 14 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

8 Requirements for Design
8.1 Analyses and Design Requirements
8.1.1

Reliability, Availability, Maintainability Analysis

A Reliability, Availability, Maintainability analysis shall be performed in order to locate weak design points
and to determine whether the design meets the Maintenance and Reliability requirements. ngVLA suggests
to apply the Parts Count Method for predicting the reliability of the system as described in the MIL-HDBK217F, but the designer may propose to use other methods. For non-electronic parts, the values of NPRD95 may be used, or data from manufacturers or other databases may be used.
Another, but more time consuming (and considered more accurate) method, the Parts Stress Analysis
Prediction, is also described in MIL-HDBK-217F. This may be used if the result of the Parts Count Method
does not comply with the Maintenance and Reliability requirements.
The ngVLA equipment will typically operate at an elevation of 2200m above sea level, where temperatureand pressure might decrease the MTBF relative to that at low elevations. These conditions shall be taken
into specific account in the reliability prediction by using the environmental factor given in MIL-HDBK217F.
The analysis shall result in estimates of the Mean Time Between Failures (MTBF), the Mean Time To Repair(MTTR), assuming that any scheduled preventive maintenance is performed.

8.2 Electromagnetic Compatibility Requirements
The ngVLA Antenna Electronics Environmental Control System elements shall exhibit complete
electromagnetic compatibility (EMC) among components (intra-system electromagnetic compatibility).

8.3 Materials, Parts and Processes
8.3.1

Fasteners

All fasteners shall be metric where reasonably possible.

8.3.2

PaintsAny painted coatings shall be chosen to last at least 20 years without repainting.

8.3.3

Surface Treatment

Any unpainted surfaces shall be treated against corrosion.

8.3.4

Name Plates and Product Marking

As a general rule the main parts and all exchangeable units shall be equipped with nameplates which arevisible after installation of the part/unit and which contain the following information:x Part/unit namex Drawing number including revision
x Serial number
x Manufacturing month and year
x Name of manufacturer

Page 15 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

Alternatively, a system of marking based on barcodes or similar system may be used upon approval by
ngVLA. For any Line Replaceable Units (LRUs; see Section 12.2), it is highly desirable that the serial numberof the LRU be ascertainable over the monitor and control interface (see Section 4.4).

8.3.5

LabelsAll cables and switches, junction boxes, sensors, and similar equipment shall be labeled using a marking
based on barcodes.

Page 16 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

9 Documentation Requirements
9.1 Technical Documentation
All documentation related to the antenna electronics environmental control system shall meet thefollowing requirements:
x The language used for written documentation shall be English.
x Drawings shall be generated according to ISO standards and use dual metric and imperial units.
x Layouts of electronic circuits and printed circuit boards shall also be provided in electronicallyreadable form. The ngVLA preferred formats are Altium Designer files for electronic circuit diagrams
and printed circuit board layouts.
x The electronic document formats are Microsoft Word and Adobe PDF.
x The preferred CAD system used is AutoDesk Inventor and/or AutoCAD (discouraged).
Any deviation from the above shall be agreed to by the ngVLA project office.

9.2 Software and Software Documentation
The Antenna Electronics Environmental Control System software and any other specially developed
software (SW), are deliverables. The SW shall be delivered in source and object form, together with allprocedures and tests necessary for compilation, installation, testing, upgrades, and maintenance.
x Software must be tagged with suitable version numbers that allow identification (also on-line remotely)of a release.
x User manuals of software developed under this specification and of any other commercial software
used (controllers embedded software, special tools, etc.) shall be provided.
x Software maintenance and installation upgrade documentation shall be provided.
x Full Test and Acceptance procedures shall be documented.

Page 17 of 22

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

10 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A) inspection (I), a factory
acceptance test (FAT) or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which may bechecked by the ngVLA project office during the design phase by review of the design documentation.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which will bechecked by the ngVLA project office during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple inspection
or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item/assembly/unit withthe specified performance shall be demonstrated by tests. A FAT is performed w/o integration withinterfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item/assembly/unit with thespecified performance shall be demonstrated by tests. SAT is performed on-site with the equipment as
installed.
Multiple verification methods are allowed. The following table summarizes the expected verification
method for each requirement.
Req. #
EEC0100
EEC0101
EEC0102
EEC0103
EEC0104
EEC0105
EEC0106
EEC0107
EEC0152
EEC0153
EEC0154
EEC0250
EEC0251
EEC0252
EEC0253
EEC0254
EEC0255
EEC0256
EEC0257
EEC0258

Parameter/Requirement
Front End Enclosure
Front End Auxiliary Enclosure
WVR Enclosure
Front End Enclosure Thermal Regulation
Front End Auxiliary Enclosure Thermal
Regulation
WVR Enclosure Thermal Regulation
Compressor Enclosure Thermal Regulation
Pedestal Room Rack Thermal Regulation
Vibration
Dust
Rodents
Solar Thermal LoadWind Speed
Outdoor Temperature
Outdoor Temperature Rate of Change
Precipitation
Cooling Temp Front End Enclosure
Cooling Temp Front End Auxiliary Enclosure
Cooling Temp-Compressor Platform
Heat Exchanger Service Temperature

Page 18 of 22

D
X
X
X
X
X

A

I

FAT

SAT

X

X

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Req. #
EEC0350
EEC0351
EEC0352
EEC0354
EEC0355
EEC0360
EEC0361
EEC0450
EEC0500
EEC0501
EEC0550
EEC0600
EEC0650
EEC0651

Parameter/Requirement
Wind
Temperature
Radial Ice
Snow Load – Equipment
Hail Stones
Solar FluxUV Radiation
Rain Infiltration
Transportation Environment
Mechanical Shocks
Mean Time Between Failures
Self-Monitoring
Design Life
Life Cycle Optimization

D
X
X
X

A

Date: 2019-07-25
Version: A

I

FAT

X
X
X
X
X
X
X
X
X
X

X
X

Table 1 - Expected requirements verification method.

Page 19 of 22

SAT

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

11 Key Performance Parameters
This section provides Key Performance Parameters that should be estimated by the designer andmonitored by NRAO throughout the design phase of the project. These are parameters that have a large
influence on the eventual effectiveness of the facility, and are useful high-level metrics for trade-off
decisions.
The technical requirements are generally specified as minimum values. The goal is to give the designer
some latitude in optimization for a balanced design. Understanding the anticipated performance of the
Antenna Electronics Environmental Control System (not just its specified minimum) on these parameters
is of value for system-level analysis and performance estimation.
These parameters may also be useful for determining the relative priority of the requirements documented
in Section 4 and can assist in the required analysis should tensions be identified between requirements, or
reductions in capability be required to fit within cost constraints.
The Key Performance Parameters that have been identified for monitoring are described in Table 9. Notethat the order in the table reflects the order in the document, and is not indicative of relative importanceor priority.
Key Performance Parameter
Front End Receiver Enclosure Temp. Reg.
Heat Exchanger Service Temperature Reg.
Mean Time Between Failures
Table 2 - Key Performance Parameters for monitoring during design.

Page 20 of 22

Req. #
EEC0255
EEC0258
EEC0550

Title: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

12 Appendix
12.1 Abbreviations and Acronyms
Acronym
AD
CoDR
CFD
EM
EMC
EMP
HVAC
ICD
IF
KPP
LRU
MTBF
MTTF
MTTR
ngVLA
RD
RFI
SAC
SWG
TAC
TBD
VLA

Description
Applicable Document
Conceptual Design Review
Computational Fluid Dynamics
Electro-Magnetic
Electro-Magnetic Compatibility
Electro-Magnetic Pulse
Heating, Ventilation & Air Conditioning
Interface Control Document
Intermediate Frequency
Key Performance ParametersLine Replaceable Unit
Mean Time Between Failure
Mean Time To Failure
Mean Time To Repair
Next Generation VLA
Reference Document
Radio Frequency Interference
Science Advisory Council
Science Working Group
Technical Advisory Council
To Be Determined
Jansky Very Large Array

Page 21 of 22

Date: 2019-07-25
Version: ATitle: Antenna Electronics Environmental
Owner: Sturgis
Control System: Preliminary TechnicalRequirements
NRAO Doc. #: 020.30.60.00.00-0001-REQ-AANTENNA_ELECTRONICS_ENVIR_CONTROL_REQS

Date: 2019-07-25
Version: A

12.2 Maintenance Definitions
12.2.1 Maintenance Approach
Required maintenance tasks shall be minimized.
Maintenance shall be mainly performed at assembly and subassembly level by exchange of Line Replaceable
Units (LRUs). LRUs are defined as units that can be easily exchanged (without extensive calibration, of
sufficient low mass and dimension for easiness of handling, etc.) by maintenance staff of technician level.
LRU exchange shall be possible by two trained people within four working hours. It is desirable that LRU
replacement be possible using only standard tools identified in a maintenance manual for the Electronics
Environmental Enclosures.
A step-by-step procedure for safe exchange of every LRU shall be provided in the Maintenance Manual.
LRUs shall be defined by the Antenna Electronics Environmental Control System designer, depending on
the design. The LRUs will be maintained by the ngVLA project (with or without industrial support).

12.2.2 Periodic Preventive MaintenancePreventive maintenance may be performed at planned intervals in order to keep the Antenna Electronics
Environmental Control System operational and within its specified performance. Any required preventive
maintenance should be documented in the Maintenance Manual.

Page 22 of 22

Title: Antenna Electronics
Environmental Control System

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Date: 2019-07-23
Version: A

Antenna Electronics Environmental Control System
Reference Design Description
020.30.60.00.00-0002-DSN-A-ENVIR_CONTROL_REF_DESIGN

Status: RELEASEDPREPARED BY
D. Gerrard, S. Sturgis, and J. Allison
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
2018-11-12
2019-05-04

APPROVALS (Name and Signature)
R. Selina,
2019.07.23
Project Engineer
12:40:36 -06'00'
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.23 14:02:11 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-23

Asst. Director,
NM-Operations, NRAO

2019-07-23

RELEASED BY (Name and Signature)
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.23 14:02:27 -06'00'

ORGANIZATION
Asst. Director,
NM-Operations, NRAO

DATE
2019-07-23

Page 1 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Date: 2019-07-23
Version: A

Change Record
Date

AuthorAffected
Section(s)Reason01

2018-05-22

J. Allison

1-4

Initial Draft

02

2018-07-10

J. Allison

5

Added design descriptions03

2018-07-12

S. Sturgis

All

04

2018-09-21

S. Sturgis

All

05

2018-09-21

S. DurandAll

06

2018-10-09

J. Allison

4, 5

07

2018-10-10

J. Allison

4, 5

08

2018-10-23

J. Allison

4

Updated and revised all sections
Updates throughout to better reflect thecurrent design
Small Edits
Addressed RID numbers: IPDSR-10, IPDSR11, IPDSR-12, IPDSR-15, IPDSR-16
Addressed RID numbers: IPDSR-14, IPDSR17
Addressed RID number IPDSR-13

09

2018-10-26

J. Allison

5102018-11-07

J. Allison

511

2018-11-09

J. Allison

5122018-11-12

S. Sturgis

All

Addressed RID number IPDSR-1
Updated information pertaining to Cryogenics
M&C module
Replaced text explaining temperature control
requirements with a table, added reference
documents
Small edits and clarifications13

2019-05-30

R. Selina

2, 4.2

Minor edits for release.

A

2019-07-23

A. LearAll

Prepared PDF for approvals and release

Version

Page 2 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Date: 2019-07-23
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings ............................................................... 4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 43
4

Antenna Electronics Environmental Control System Overview .............. 5
Antenna Electronics Environmental Control System Design ................... 6

4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.3

Temperature Control Components ...................................................................................... 7
Liquid Loop Chiller.................................................................................................................................... 7
Liquid Loop Heater ................................................................................................................................... 7
Liquid Hot/Cold Plate ............................................................................................................................... 8
Air Handler ................................................................................................................................................. 8
Receiver Enclosure Heater...................................................................................................................... 8
Hazard Control Components ................................................................................................ 8
Front End Receiver Enclosure ................................................................................................................ 8
Front End Auxiliary Enclosure ................................................................................................................ 9
WVR Enclosure ........................................................................................................................................ 10
Compressor Platform/Enclosure ......................................................................................................... 10
Pedestal Room Rack ............................................................................................................................... 10Interfaces with Other Subsystems ....................................................................................... 11

5

Appendix....................................................................................................... 12

5.1

Acronyms and Abbreviations ............................................................................................... 12Page 3 of 12

Title: Reference Design Description

Owner: Sturgis

Date: 2019-07-23

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Version: A

1 Introduction
1.1 Purpose
This document provides a description for the Antenna Electronics Environmental Control systemreference design. It covers the design approach, functions, description of key components, interfaces, andrisks associated with the reference design. This document will form part of the submission of the ngVLA
Reference Design documentation package.

1.2 Scope
The scope of this document covers the entire design of the Antenna Electronics Environmental Control
system, as part of the ngVLA Reference Design. It includes the system’s design, how it functions, andinterfaces with the necessary hardware and software systems.
It does not include specific technical requirements or budgetary information.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein, but provide necessary context or
supporting material.
Reference
No.
AD01
AD02
AD03

Document Title

Rev/Doc. No.

ngVLA Preliminary System Requirements
ngVLA Environmental Specifications
ngVLA Antenna Electronics Environmental
Control System: Preliminary TechnicalRequirements

V1.0, 3/30/2017
020.10.15.10.00-0001-SPE
020.30.60.00.00-0001-REQ

2.2 Reference Documents
The following documents are referenced within this text:
Reference
No.
RD01
RD02
RD03

Document Title

Rev/Doc. No.

ngVLA Cryogenic Subsystem Requirements
ngVLA Integrated Receivers and Downconverters:
Preliminary Technical Specifications/Requirements
ngVLA Water Vapor Radiometer PreliminaryTechnical Requirements

020.30.10.00.00.0001-REQ
020.30.15.00.00-0001-REQ

Page 4 of 12020.45.00.00.00-0001-REQ

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Date: 2019-07-23
Version: A

3 Antenna Electronics Environmental Control System Overview
The antenna electronics are located in various places around the antenna. Primary locations include but
are not limited to the electronics rack in the pedestal room, the Receiver and Auxiliary Enclosures on thefeed arm, the WVR enclosure near the base of the feed arm, and the compressor platform/enclosure at
the top rear of the pedestal. Environmental control of the antenna electronics consists of temperature
control of all the electronics in these locations as well as protection from water, dust, animals, or otherenvironmental hazards.
There are two temperature control systems for the antenna electronics: a hot/cold liquid loop above theazimuth axis and a traditional air-cooling unit in the pedestal room. The first consists of a hot/cold liquidloop, most likely glycol, which runs from a chiller unit at the top-rear of the pedestal to the WVR
Enclosure, and the front end Receiver and Auxiliary Enclosures. At each location a local liquid hot/coldplate that consists of copper tubing running through an aluminum block, which components may be directly
mounted to, will cool components in both the front end enclosures and the WVR enclosure, as well ason the compressor platform/enclosure.
The pedestal room electronics rack will be forced-air-cooled via a local air handler unit to force cold air
through the rack from bottom to top. This system will likely be closed loop so that it does not have tocool the entire pedestal room.
Protection from water, dust, animals, or other environmental hazards will be provided by custom
designed Front End Receiver, Auxiliary, WVR, and compressor platform enclosures as necessary, and anelectronics rack in the pedestal room.

Page 5 of 12

Title: Reference Design Description

Owner: Sturgis

Date: 2019-07-23

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Version: A

4 Antenna Electronics Environmental Control System Design
There are three main parts to the Antenna Electronics Environmental Control system: the hot/cold liquidloop, the cold air blower, and the environmental enclosures. The hot/cold liquid loop was chosen because
it is much easier to move heat around the antenna via a dense liquid than it is via air.
The cold air blower was chosen because the modules in the electronics rack require air-cooling, and it
was undesirable to run a cold liquid line through the azimuth wrap/axis.
The temperature regulation requirements are tabulated by component and location below:

P501 Module

Operational
Temp Range[C]–15 to 35[RD02]
N/A

Vacuum Pump

12 to 45 [RD01]

Location

Component

FE Receiver
Enclosure

IRD Module

FE Auxiliary
Enclosure

Helium Compressor
Compressor
Platform
WVR
Receiver
Enclosure

Back End Rack

Cryo M&C Cold Plate
Glycol Chiller
Cryo M&C Module
Component Cold
Plate
P502 Module
D501 Module
F518 Module
M500 Module
M501 Module
P500 ModuleP503 Module

Temp
Grad
[C/hr]Heat
Dissipation[W]

3.6 [RD02]

115

N/A

195

N/A

TBD

–30 to 45[RD01]
TBD
TBD
TBD

N/A

TBD

N/A
N/A
N/A

200
TBD
TBD

>28

0.02

20 [RD03]

N/A
N/A
N/A
N/A
N/A
N/A
N/A

N/A
N/A
N/A
N/A
N/A
N/A
N/A

145
TBD
100
75
75
165
145

*These are preliminary numbers which will likely change during the development of the conceptual design*Page 6 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Date: 2019-07-23
Version: A

4.1 Temperature Control Components

Figure 1 - Locations of antenna electronics environmental control system components.

4.1.1

Liquid Loop Chiller

There will be an air-cooled chiller unit to cool the liquid (glycol) located on the compressor
platform/enclosure. The chiller shall be capable of delivering +/-1 degree C glycol to all requiredcomponents.

4.1.2

Liquid Loop Heater

The glycol chiller shall be capable of both cooling and heating of the glycol.

Page 7 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

4.1.3

Date: 2019-07-23
Version: A

Liquid Hot/Cold Plate

There will be multiple liquid hot/cold plates located in the front end receiver enclosure to cool the IRD
enclosure, the P501 Module, and the general environment of the enclosure as well as any othercomponents that may require cooling. The IRD module in the receiver enclosure will require a high levelof precise temperature control (0.1°C/20min), which is more precise than the chiller can provide. The
higher precision will be achieved with locally located thermoelectric modules.
There will be a liquid hot/cold plate in the WVR receiver enclosure. The temperature control in the WVR
enclosure will require a high level of precise temperature control (0.05°C/hour), which is more precise
than the chiller can provide. The higher precision will be achieved with locally located thermoelectricmodules.
There will be multiple liquid hot/cold plates located in the auxiliary front end enclosure for coolingcomponents, the full list of which is TBD. The temperature control in the auxiliary enclosure will only
require an average level of temperature control (+/-1°C/hour) and will be achieved with the chilled glycol.
There will be a liquid hot/cold plate on the compressor platform for heating or cooling the M&C module.
The temperature control for the Cryo M&C module will only require an average level of temperature
control (+/-1°C/hour) and will be achieved with the chilled glycol.

4.1.4

Air Handler

There will be an air handler unit located in the pedestal room to force air through the electronics rack.
This is anticipated to be a closed loop system so that the air handler does not cool the entire pedestal
room but only the electronics rack and any associated equipment. Furthermore, the air handler’s heatexchanger may require venting to outside of the pedestal room, depending on how well the room issealed/insulated. The pedestal room electronics rack will only require an average level of temperature
control (+/-1°C/hour).

4.1.5

Receiver Enclosure Heater

To combat condensation on the front of the receiver windows, there will be heaters located on the frontof the environmental receiver enclosure in such a way as to not interfere with the receivers operation.

4.2 Hazard Control Components
4.2.1

Front End Receiver Enclosure

The front end electronics located on the feed arm of the antenna will be housed in environmentally sealed
enclosures to protect them from water and debris. The Receiver Enclosure will house Dewars A & B, theIRD Enclosure, the P501 Module, and the M&C for both Dewars and will be made up of a welded aluminum
frame with removable panels on all sides so that the housed components may be easily accessed formaintenance.
The removable panels will have lockable push-to-close latches and will be located on all sides of theenclosure except for the bottom and the side facing the secondary reflector. The enclosure will have one
fixed plate on the rear side where permanent connections to other systems will be located. This will help
minimize external connectors and simplify the installation and removal of housed +. The removable panels
will be made of an aluminum composite panel, with thin sheets of aluminum on either side of corrugatedplastic. Their edges will be lined with aluminum U-channels which will stiffen the entire panel. Each panel
will also have a layer of insulation on the inside to maintain temperature inside of the enclosure. The
frames will have environmental seals where all removable panels are installed to protect the components

Page 8 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Date: 2019-07-23
Version: Afrom water, dust, and debris. This enclosure is designed to only protect from environmental hazards. All
housed components requiring RFI shielding will have their own RFI tight packaging inside of this enclosure.

Figure 2 - Front End receiver enclosure.

4.2.2

Front End Auxiliary Enclosure

The Auxiliary Enclosure will be located on the feed arm near to the Receiver Enclosure and will be basedon the same design as the Receiver enclosure.
The Auxiliary Enclosure will house any equipment the receivers need to function that doesn’t need to be
co-located with the receivers. Having this enclosure allows us to minimize the amount of mass being
shifted around at the end of the antenna arm.

Figure 3 - Front End auxiliary enclosure.

Page 9 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

4.2.3

Date: 2019-07-23
Version: A

WVR Enclosure

The WVR Enclosure will likely be a welded box located somewhere along the edge of the antenna’s mainreflector, possibly near to the base of the feed arm. The exact location is still to be determined, based on
physical interference between surrounding antennas and signal interference from the structure of the hostantenna.

4.2.4

Compressor Platform/Enclosure

The Compressor Platform/Enclosure is located near the top rear of the pedestal and holds the cryogenic
helium compressor, the liquid glycol chiller and heater, and an RFI-tight cryogenics M&C module.
Depending on the helium compressor’s environmental requirements, this may be more of a vented
enclosure than an open platform. If built as an enclosure it will be similar in design to the Front End
Auxiliary Enclosure.

4.2.5

Pedestal Room Rack

The Pedestal room rack (provide by the Bins, Modules & Racks work package) will be located in thepedestal room and will house all of the modules for the Antenna Electronics that are not housed in thefront end, WVR, or compressor enclosure. The current plan is to use a single 19inch rack, but dependingon the size of the pedestal room and the number of modules housed this may be expanded to two smaller
racks. Smaller racks may be shorter, shallower or both. The standard sized rack is the preferred option.
The modules inside of the rack will be cooled using a closed loop forced air system (provided as part ofthis Antenna Electronics Environmental Control work package) with the air entering the bottom of therack, being directed past the heatsinks on the modules, and then being recirculated out of the top of therack and back to the air handler unit.

Figure 3 - Pedestal room rack.

Page 10 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

Date: 2019-07-23
Version: A

4.3 Interfaces with Other Subsystems
The Environmental Control system will have interfaces as follows:x Pedestal roomo ICD between air handler and electronics racko ICD between air handler and antenna
x Compressor platform/enclosure
o ICD between enclosure and antennao ICD between enclosure and cryogenic compressoro ICD between enclosure and glycol chiller
x WVR
o ICD between environmental enclosure and antennao ICD between environmental control system and WVR subsystem
x Auxiliary front end enclosure
o ICD between auxiliary front end enclosure and antennao ICD between auxiliary front end enclosure and TBD equipment housed within it
x Receiver Front end enclosure
o ICD between receiver front end enclosure and antennao ICD between receiver front end enclosure and Dewar A LRU
o ICD between receiver front end enclosure and Dewar B LRUo ICD between receiver front end enclosure and P501 Module
o ICD between receiver front end enclosure and TBD equipment housed within it

Page 11 of 12

Title: Reference Design Description

Owner: Sturgis

NRAO Doc. #: 020.30.60.00.00-0002-DSN-AENVIR_CONTROL_REF_DESIGN

5 Appendix
5.1 Acronyms and Abbreviations
Acronym
AD
DBE
DTS
IF
LO
LRU
M&C, M/C
NES
ngVLA
NSF
PLL
RD
RF
TBD
VLA
WVR

Description
Applicable Document
Digital Back End
Data Transmission System
Intermediate Frequency
Local Oscillator
Line Replaceable Unit
Monitor and Control
Near Earth Sensing
Next Generation VLA
National Science Foundation
Phase Locked Loop
Reference Document
Radio Frequency
To Be Determined
Jansky Very Large Array
Water Vapor Radiometer

Page 12 of 12

Date: 2019-07-23
Version: ATitle: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

Independent Phase Calibration System:
Preliminary Requirements
020.45.00.00.00-0001-REQ-A-INDEP_PHASE_CALIBRATION_PRELIM_REQS

Status: RELEASEDPREPARED BY
A. Erickson
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
04-30-2019
05-04-2019

APPROVALS (Name and Signature)
R. Selina,
2019.07.26
Project Engineer
13:26:22 -06'00'
M. McKinnon,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.26 19:12:26 -06'00'

ORGANIZATIONElectronics Div., NRAO

DATE
2019-07-26

Asst. Director,
NM-Operations, NRAO

2019-07-26

RELEASED BY (Name and Signature)
ORGANIZATION
M. McKinnon,
Asst. Director,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.26 19:12:43 -06'00' NM-Operations, NRAO

DATE
2019-07-26

Page 1 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

Date: 2019-07-26

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Version: A

Change Record
Version

Date

AuthorAffected
Section(s)01

2018-09-27

EricksonAll

Final 01

02

2018-12-20

EricksonAll

Address RIDs

03

2019-04-30

EricksonAll

Final review

04

2019-05-30

Selina2.1, 4, 11

Minor edits for release. Updated traceability.

A

2019-07-26

Lear

All

Prepared PDF for signatures and release

ReasonPage 2 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

Table of Contents
1

Introduction ................................................................................................... 5

1.1
1.2

Purpose ................................................................................................................................... 5
Scope ...................................................................................................................................... 5

2

Related Documents and Drawings ............................................................... 5

2.1
2.2

Applicable Documents ........................................................................................................... 5
Reference Documents ............................................................................................................ 6

3

Overview of the Independent Phase Calibration System
Technical Requirements ............................................................................... 7

3.1
3.2
3.3
3.4
3.4.1
3.4.2

Document Outline ................................................................................................................. 7
Project Background................................................................................................................ 7
General Description ............................................................................................................... 8
Summary of WVR System Requirements .............................................................................. 8
General Technical Requirements ........................................................................................................... 8
Other General Requirements................................................................................................................. 9

4

Functional and Performance Requirements ............................................. 11

4.1
4.2
4.3
4.4
4.5
4.6

Performance Requirements ................................................................................................. 11
Spurious Signals/Radio Frequency Interference Generation ............................................. 11
Environmental Conditions ................................................................................................... 11
Maintenance and Reliability Requirements ....................................................................... 11
Monitor and Control Requirements ................................................................................... 12
Lifecycle Requirements ........................................................................................................ 125Interface Requirements .............................................................................. 13

5.1
5.2
5.3
5.4
5.5

Interface to the Antenna Liquid Cooling System ............................................................... 13
Interface to the Monitor and Control Network................................................................. 13
Interface to the Antenna Mechanical Structure ................................................................ 13
Interface to the Pedestal Room Rack Cooling System ...................................................... 13
Interface to the Pedestal Room Rack Power System ........................................................ 13

6
7

Subsystem Requirements ........................................................................... 14
Safety ............................................................................................................ 14

7.1
7.2
7.3

Mechanical Safety ............................................................................................................... 14
Electrical Safety ................................................................................................................... 14
Handling, Transport, and Storage Safety ........................................................................... 14

8

Requirements for Design ............................................................................ 15

8.1
8.1.1
8.2
8.3
8.3.1
8.3.2
8.3.3
8.3.4
8.3.5

Analyses and Design Requirements..................................................................................... 15
Reliability Availability Maintainability Analysis ................................................................................... 15
Electromagnetic Compatibility Requirements ................................................................... 15
Materials, Parts, and Processes ........................................................................................... 15
Fasteners .................................................................................................................................................... 15
Paints........................................................................................................................................................... 15
Surface Treatment ................................................................................................................................... 15
Name Plates and Product Marking ...................................................................................................... 15
Labels .......................................................................................................................................................... 16

9

Documentation Requirements ................................................................... 16

9.1
9.2

Technical Documentation ................................................................................................... 16
Software and Software Documentation ............................................................................. 16

Page 3 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

10
11
12

Verification and Quality Assurance ........................................................... 17
Key Performance Parameters .................................................................... 18
Appendix....................................................................................................... 19

12.1
12.2
12.2.112.2.2Abbreviations and Acronyms ............................................................................................... 19
Maintenance Definitions ..................................................................................................... 20
Maintenance Approach ........................................................................................................................... 20
Periodic Preventive Maintenance ......................................................................................................... 20

Page 4 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

1 Introduction
1.1 Purpose
This document aims to present a set of technical requirements for the reference design of the ngVLA
Independent Phase Calibration system.
Many requirements flow down from the preliminary ngVLA System Requirements [AD02], which in turnflow-down from the preliminary ngVLA Science Requirements [AD01].
The Science goals are presently being elaborated by the Science Advisory Council (SAC) and Science
Working Groups (SWGs), and are captured in a series of draft use cases. This document represents apreliminary analysis of these use cases, and the flow down recursively to the science, system and subsystem
requirements.

1.2 Scope
The scope of this document is the ngVLA Independent Phase Calibration system. It includes interface
requirements that must be defined.
This requirements document establishes the performance, functional, design, and test requirements
applicable to the ngVLA Independent Phase Calibration system.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents are applicable to this Technical Specification to the extent specified. In the eventof conflict between the documents referenced herein and the content of this Technical Specification, thecontent of this Technical Specification shall be considered as a superseding requirement.
Ref. No.
AD01
AD02
AD03
AD04
AD07
AD08
AD10
AD11
AD12
AD13

Document Title
ngVLA Science Requirements
Preliminary System Requirements
Operations Concept
Protection Against Electric Shock—Common
Aspects for Installation and Equipment
Insulation Coordination for Equipment within
Low-Voltage Systems
Occupational Safety and Health Standards for
General Industry
Military Handbook, Reliability Prediction ofElectronic Equipment
Non-Electronic Parts Reliability Data
Electromagnetic Compatibility
Monitor & Control Hardware Interface Layer:
Preliminary Requirements

Page 5 of 20

Rev/Doc. No.
020.10.15.00.00-0001-REQ
020.10.15.10.00-0003-REQ
020.10.05.00.00-0002-PLA
IEC 61140:2016
IEC 60664
29 CFR Part 1910
MIL-HDBK-217F
NPRD-95
IEC 61000-3-5
020.30.45.00.00-0002-REQ

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

2.2 Reference Documents
The following references provide supporting context:
Ref. No.
RD01
RD02
RD03
RD04
RD05
RD06

Document Title
Fast Switching Calibration at the ngVLA Site
Calibration Strategies for the ngVLAThe Concept of a Reference Array for the ngVLA
Considerations for a Water Vapor Radiometer System
Results of Water Vapor Radiometry Tests at the VLA
A Study of the Compact Water Vapor Radiometer for
Phase Calibration of the Karl G. Jansky Very Large Array

Page 6 of 20

Rev/Doc. No.
ngVLA Memo No. 1
ngVLA Memo No. 2
ngVLA Memo No. 4
ngVLA Memo No. 10
EVLA Memo No. 73
EVLA Memo No. 203

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

3 Overview of the Independent Phase Calibration System TechnicalRequirements
3.1 Document Outline
This document presents the technical requirements of the ngVLA Independent Phase Calibration system.
These parameters determine this system’s overall form and performance.
The functional and performance specifications, along with detailed explanatory notes, are found in Section
4. The notes contain elaborations regarding the meaning, intent, and scope of the requirements. These
notes form an important part of the definition of the requirements and should guide the verification
procedures. In many cases the notes contain an explanation or an analysis of how the numeric values ofrequirements were derived. Where numbers are not well substantiated, this is also documented in thenotes. In this way, the required analysis and trade-space available is apparent to scientists and engineers
who will guide the evolution of the ngVLA Independent Phase Calibration system concept.
Requirements pertinent to interfacing systems are described in Section 5. Initial requirements are notedby interface, along with identified parameters for Interface Control Documents (ICDs) that will fully define
the interfaces as the design progresses.
Safety requirements applicable to both the design phase and the functional Independent Phase Calibration
system are described in Section 7. Additional requirements for the design phase are described in Section
8. Documentation requirements for both technical design documentation and software are provided in
Section 9.
Requirements for the Verification and Test, from the conceptual design through to prototype, aredescribed in Section 10.
Section 11 identifies Key Performance Parameters (KPP) that should be estimated and monitored
throughout the design phase. These are metrics to assist in the trade-off analysis of various concepts, andhelp identify and resolve tensions between requirements as the design progresses.

3.2 Project Background
The Next Generation Very Large Array (ngVLA) is a project of the National Radio Astronomy
Observatory (NRAO) to design and build an astronomical observatory that will operate at centimeter
wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116
GHz). The ngVLA will be a synthesis radio telescope composed of approximately 244 reflector antennas
each of 18 meters diameter, and 19 reflector antennas each of 6 meters diameter, operating in a phased
or interferometric mode.
The facility will operate as a proposal-driven instrument with Principal Investigator (PI)-led proposals
determining the science program. Data will generally be delivered to PIs and the broader scientificcommunity as Science Ready Data Products; automated pipelines will calibrate raw data and create higherlevel data products (typically image cubes). Data and quality assured data products will be available throughan Observatory science archive. Data exploration tools will allow users to analyze the data directly fromthe archive, reducing the need for data transmission and reprocessing at the user’s institution.
The array’s signal processing center will be located at the Very Large Array site on the Plains of San
Agustin, New Mexico. The array will include stations in other locations throughout New Mexico, west
Texas, eastern Arizona, and northern Mexico. Long baseline stations are located in Hawaii, Washington,
California, Iowa, Massachusetts, New Hampshire, Puerto Rico, the US Virgin Islands, and Canada.

Page 7 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

Array operations will be conducted from both the VLA site and the Array Operations and Repair Centersin Socorro, NM. A Science Operations Center and Data Center will likely be located in a metropolitan
area and will serve as the base for science operations and support staff, software operations, and related
administration. Research and development activities will be split among these centers as appropriate.

3.3 General Description
The independent phase calibration system consists of a water vapor radiometer (WVR) that measuresatmospheric water vapor concentration in the antenna main beam. This data can be used to provide
continuous phase calibration between calibrator source measurements.
The WVR has its own antenna: a fixed dish one meter in diameter mounted below the main dish. A WVR
receiver module sits at the offset Gregorian focus of this antenna, and receives, amplifies, downconverts,
and digitizes a band from 18–30 GHz. The receiver is temperature stabilized by a thermally regulated plateon which the electronics are mounted. The whole unit is thermally stabilized by the antenna liquid coolingsystem with a Peltier thermoelectric device for fine temperature regulation. Power is delivered to thereceiver module and to a feed heater located in front of the module from the –48V antenna power supply
via a junction box near the receiver module.
Digitized data is sent over dedicated fiber to a high-speed FPGA-based processing module in the pedestal
room electronics rack. The low-speed processed data is injected onto the antenna monitor and control
data stream for inclusion in the science data package. The processing module is powered and cooled bystandard rack power and cooling air.

3.4 Summary of WVR System Requirements
The following table provides a summary of the major requirements in order to provide the reader with ahigh-level view of the desired system. Should there be a conflict between the requirements listed here
and the descriptions in Sections 4 through 10, the latter shall take precedence.

3.4.1

General Technical Requirements

Parameter
Precipitable water vapor relative
measurement
Measurement interval
Beam diameter
Pointing offset from main beam
Digitized bandwidth
Receiver temperature stability
Receiver components temperature
Channel count (minimum)

Summary of Requirement
35μm

Reference Reqs.
WVR0001

V18m at 2km
0.7deg
18–26GHz2.5mK over 20 minutes
30C +/– 2C
32

WVR0002
WVR0003
WVR0004
WVR0005
WVR0006
WVR0007
WVR0008x Precipitable water vapor relative measurement: See VLA Memo 203 [RD06] for derivation.
x Measurement interval: Expected wind speeds at the altitude at which most precipitable water
vapor (PWV) is expected from the relationship between WVR spacing and frequency of measurement.
For 100m WVR antenna spacing, 10m/s wind speeds imply a 10s integration time. A factor of ten isincorporated to allow averaging and to give buffer room for faster wind speeds.
x Beam diameter: The WVR beam should sample the main beam at all altitudes where PWVR ispresent, but must sample the main beam accurately where the primary region of turbulent PWVR isknown to exist at 2km above ground level (AGL).

Page 8 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: Ax Pointing offset from main beam: As above, the WVR beam must sample the main beam. The
pointing offset limits the beam offset to a reasonable amount at 2km AGL.
x Digitized bandwidth: The broad water vapor spectral line centered near 22GHz must be sampled
entirely. Additionally, one must separate it from the superimposed liquid water emission and the O2
line emission.
x Receiver temperature stability: The PWVR measurement forces a very tight gain stability
specification, which in turn requires that the components be held to a very tight temperature range.
x Receiver components temperature: The absolute temperature of the components—more
specifically, the connecting wires—is chosen to minimize the effects on the RF signal from thermallyinduced changes in the properties of Teflon and related insulation materials.
x Channel count: High channel count allows excision of expected RFI to be performed without
significantly impacting measurement accuracy.

3.4.2

Other General Requirements

Parameter

Req. #

Summary of Requirement

Design LifeWVR1001

Maintenance Interval

WVR1002

Mean Time Between
Failures (MTBF)
Modularization

WVR1003

Altitude Range
Lightning Protection

WVR1005
WVR1006

Equipment Protection
Against Dust
Rodent Protection

WVR1007

Transportation
Environment

WVR1009

Mechanical ShockWVR1010Equipment Shielding

WVR1011

EMC Test Frequencies

WVR1012Hazzard Analysis

WVR1013

Design for an expected operational life
no less than 20 years, excluding thebatteries
Preventive maintenance interval of no
shorter than 2 years, with a goal of 4
years.
Antenna electronics has MTBF of 35,040
hours each.
Line Replaceable Units (LRU) to
facilitate site maintenanceSea level to 2500 meters
Protect against Lightning
Electromagnetic Impulse
Exposed equipment shall be protectedagainst windblown dust, ashes, and grit
Exposed equipment shall be designed toprevent rodent damage
Designed to withstand typical loads andenvironments encountered duringtransportation
Designed to survive mechanical shocklevelsAll equipment shall be shielded and haveit AC power line and communicationlines filtered at the chassis
RFI suppression shall extend from 50
MHz to 12 GHz
Hazard analysis shall be performed for
all high-power systems. Include lockouts for service by technicians

WVR1004

WVR1008

Page 9 of 20

Reference
Reqs.
SYS2701
SYS2401
SYS2402
SYS2403
ENV0351
ENV0512
ENV0541
ENV0551
ENV0581
ENV0582
ENC0327
EMC0328
SYS2703

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

Parameter

Req. #

Summary of Requirement

Precision Operation
Temperature
Conditions
Precision Operation
Temperature Rate of
Change Conditions
Limits to Operating
Conditions
Survival Temperature
Conditions
Storage Requirements

WVR1014–15°&7° C

Reference
Reqs.
ENV0313

WVR1015

1.8°C/Hour

ENV0314

WVR1016–&7&ENV0332

WVR1017–&750°C

ENV0342

WVR1018–65°C 7125°C

Page 10 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

4 Functional and Performance Requirements
These requirements apply to a properly functioning system, under the normal operating environmental
conditions unless otherwise stated.

4.1 Performance Requirements
Parameter
System temperature (Tsys)
Tsys measurement accuracy
Tsys drift over 1 minuteTcal/Tsys
Gain drift with temperature

Req. #
WVR0009
WVR0010
WVR0011
WVR0012WVR0013

Summary of Requirement
300 K
20 mK
5K
10 %
0.66 %/C

Traceability
SYS1504
SYS1504
SYS1504
SYS1504
SYS1504x Tsys: The WVR is non-cryogenic; ambient Tsys allows WVR data recovery.
x Tsys measurement accuracy: Calibration requires accurate measurement of Tsys.
x Tsys 1-minute drift: Between calibrator fixes, Tsys must be held to close tolerance to allow accurate
measurement of changes in PWVR signal.
x Tcal/Tsys: Lab calibration must be maintained at or below a fixed fraction of Tsys.
x Gain drift with temperature: Highly accurate temperature control of amplifiers reduces variationsin amplitude with temperature. As temperature variation can never be reduced to zero, amplifiersmust meet a requirement for gain drift with temperature to maintain adequate SNR.

4.2 Spurious Signals/Radio Frequency Interference Generation
Processor, receiver, and other WVR-specific modules shall be verified to comply with ngVLA RFI
emissions standards as specified in 020.10.15.10.00-0002-REQ.

4.3 Environmental Conditions
The WVR receiver component must meet both Normal and Precision Environmental conditions as definedin 020.10.15.10.00-0001-SPE.

4.4 Maintenance and Reliability Requirements
Parameter
Mean Time Between Failures

Req. #
WVR0101

Value
MTBF 2000 hrs.

Traceability
SYS2302

The maintenance and reliability requirements are in support of high-level requirements that limit the total
operating cost of the array.
Monitor points/sensors should be included in the MTBF/MTTR analysis, but sensors and othercomponents that can be reasonably deemed to be ancillary to operation may be removed from thedetermination of compliance with the MTBF requirement. “Failure” will be defined as a condition whichplaces the system outside of its performance specifications or into an unsafe state, requiring repair.

Page 11 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

4.5 Monitor and Control Requirements
Parameter
Self-Monitoring

Req. #
WVR0201Value
The Independent Phase Calibration system shallmeasure, report, and monitor a set of parametersthat allow for determination of its status and may
help predict or respond to failures.

Traceability
SYS2601

All WVR modules will provide monitor points per the ngVLA Monitor and Control protocol [AD13] atthe necessary intervals. Control points will be documented and tested to comply with the ngVLA Monitor
and Control protocol.

4.6 Lifecycle Requirements
Parameter
Design Life

Req. #Value
WVR0301 The Independent Phase Calibration system shall be
designed to be operated and supported for a period of
20 years.
Lifecycle
WVR0302 The Independent Phase Calibration system design shall
Optimization
minimize its lifecycle cost for 20 years of operation.

Traceability
SYS2801

Lifecycle costs include
decommissioning.

operation,

manufacturing,transportation,

Page 12 of 20

construction/assembly,

SYS2802andTitle: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

5 Interface Requirements
This section provides information about the interfaces of the Independent Phase Calibration system.
Interface Control Documents (ICDs) are required between the Independent Phase Calibration system
and all connecting systems. In many cases, specifications for the interfaces are not yet available, but thebroad scope of the ICD can be defined.
These interfaces shall be developed and documented by the Independent Phase Calibration system
Designer, and approved by ngVLA, as part of the Independent Phase Calibration system reference andconceptual design efforts, and updated throughout the design. Post CoDR, the ICD shall only be updated
through formal project change control processes.

5.1 Interface to the Antenna Liquid Cooling System
The Receiver Cooling Plate shall interface with the antenna liquid cooling system via standard fittings as
specified by the ALC specification. Protection to the liquid cooling lines shall be applied per the same
specification.

5.2 Interface to the Monitor and Control Network
Interface to the Monitor and Control system shall be per the ngVLA M&C specification for each WVR
component. It should be noted that WVR output data will also be transmitted on the M&C network as astandard monitor point.

5.3 Interface to the Antenna Mechanical Structure
Mechanical connection of the WVR components to the antenna structure shall be evaluated under the
auspices of antenna designers and engineers to ensure that safety and performance specifications are met
for both the mounted module and the structure to which it is attached. Preventive maintenance andinspection items shall be specified for each mounting structure.

5.4 Interface to the Pedestal Room Rack Cooling System
WVR processor module cooling requirements shall be compatible with pedestal room rack coolingsystems.

5.5 Interface to the Pedestal Room Rack Power System
WVR processor module power requirements shall be compatible with pedestal rack power systems.

Page 13 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

6 Subsystem Requirements
Derivation of any subsystem requirements shall be included as part of the Independent Phase Calibration
system reference and conceptual design efforts, and updated throughout the design. Post CDR/FDR, theSubsystem requirements shall only be updated through formal project change control processes, which
will include the designer, manufacturer, and NRAO.

7 Safety
7.1 Mechanical Safety
Mechanical safety assessment will be based on a Safety Hazard Analysis.

7.2 Electrical Safety
Electrical equipment installed on the antenna shall comply with their relevant international or US productstandard.
Electrical installations and equipment shall be specifically built and/or derated in order to safely performtheir intended functions under the applicable environmental conditions. Insulation shall be coordinated inconformity with IEC 60664 [AD07] while taking into account the altitude of up to 2500 m above sea level.

7.3 Handling, Transport, and Storage Safety
The design of the Independent Phase Calibration system shall incorporate all means necessary to preclude
or limit hazards to personnel and equipment during assembly, disassembly, test, and operation.

Page 14 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

8 Requirements for Design
8.1 Analyses and Design Requirements
8.1.1

Reliability Availability Maintainability Analysis

A Reliability, Availability Maintainability analysis shall be performed in order to locate weak design points
and to determine whether the design meets the Maintenance and Reliability requirements. ngVLA suggests
to apply the Parts Count Method for predicting the reliability of the system as described in the MIL-HDBK217F, but the designer may propose to use other methods. For non-electronic parts the values of NPRD95 [AD22] may be used, or data from manufacturers or other databases may be used.
Another, but more time consuming (and considered more accurate) method, the Parts Stress Analysis
Prediction, is also described in MIL-HDBK-217F. This may be used if the result of the Parts Count Method
does not comply with the Maintenance and Reliability requirements.
The ngVLA equipment will typically operate at an elevation of 2200m above sea level, where temperatureand pressure might decrease the MTBF relative to that at low elevations. These conditions shall be taken
into specific account in the reliability prediction by using the environmental factor given in MIL-HDBK217F.
The analysis shall result in estimates of the Mean Time Between Failures (MTBF), the Mean Time To Repair(MTTR), assuming that any scheduled preventive maintenance is performed.

8.2 Electromagnetic Compatibility Requirements
The ngVLA Independent Phase Calibration system element shall exhibit complete electromagnetic
compatibility (EMC) among components (intra-system electromagnetic compatibility). See EMC
specification EMC0328.

8.3 Materials, Parts, and Processes
8.3.1

Fasteners

All fasteners shall be metric except those that are on off-the-shelf units. The use of standard metric crosssections for construction materials is preferred but not required.

8.3.2

PaintsAny painted coatings shall be chosen to last at least 20 years without repainting.

8.3.3

Surface Treatment

Any unpainted surfaces shall be treated against corrosion.

8.3.4

Name Plates and Product Marking

As a general rule the main parts and all exchangeable units shall be equipped with nameplates which arevisible after installation of the part/unit and which contain the following information:x Part/unit namex Drawing number including revision
x Serial number
x Manufacturing month and year
x Name of manufacturer

Page 15 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

Alternatively, a system of marking based on barcodes or similar system may be used upon approval by
ngVLA.
For Line Replaceable Units (LRU, see Section 12.2), it is highly desirable that the serial number of the LRU
be ascertainable over the Monitor and Control interface (see Section 5.2).

8.3.5

LabelsAll cables and switches, junction boxes, sensors, and similar equipment shall be labeled using a system ofmarking based on barcodes.

9 Documentation Requirements
9.1 Technical Documentation
All documentation related to the Independent Phase Calibration system shall meet the following
requirements:
x The language used for written documentation shall be English.
x Drawings shall be generated according to ISO standards and use metric units.
x Layouts of electronic circuits and printed circuit boards shall also be provided in electronicallyreadable form. The ngVLA preferred formats are Altium Designer files for electronic circuit diagrams
and printed circuit board layouts.
x The electronic document formats are Microsoft Word and Adobe PDF.
x The preferred CAD system used is AutoDesk Inventor and/or AutoCAD.
Any deviation from the above shall be agreed to by ngVLA.

9.2 Software and Software Documentation
The Independent Phase Calibration system software and any other specially developed software (SW) aredeliverables. The SW shall be delivered in source and object form, together with all procedures and tests
necessary for compilation, installation, testing, upgrades and maintenance.
x Software must be tagged with suitable version numbers that allow identification (also on-line remotely)of a Release.
x User manuals of software developed under this specification and of any other commercial software
used (controllers embedded software, special tools, etc.) shall be provided.
x Software maintenance and installation upgrade documentation shall be provided.
x Full Test and Acceptance procedures shall be documented.

Page 16 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

Date: 2019-07-26

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Version: A

10 Verification and Quality Assurance
The design may be verified to meet the requirements by design (D), analysis (A), inspection (I), a factory
acceptance test (FAT), or a site acceptance test (SAT). The definitions of each are given below.
Verification by Design: The performance shall be demonstrated by a proper design, which may bechecked by the ngVLA project office during the design phase by review of the design documentation.
Verification by Analysis: The fulfillment of the specified performance shall be demonstrated byappropriate analysis (hand calculations, finite element analysis, thermal modeling, etc.), which will bechecked by the ngVLA project office during the design phase.
Verification by Inspection: The compliance of the developed item is determined by a simple inspection
or measurement.
Verification by Factory Acceptance Test: The compliance of the developed item/assembly/unit withthe specified performance shall be demonstrated by tests. A FAT is performed w/o integration withinterfacing systems.
Verification by Site Acceptance Test: The compliance of the developed item/assembly/unit with thespecified performance shall be demonstrated by tests. SAT is performed on-site with the equipment as
installed.
Multiple verification methods are allowed.
The following table summarizes the expected verification method for each requirement.
Req. #
WVR001
WVR002
WVR003
WVR004
WVR005
WVR006
WVR007
WVR008WVR009WVR010
WVR011
WVR012
WVR013

Parameter/Requirement
Precipitable water vapor relative
measurement
Measurement interval
Beam diameter
Pointing offset from main beam
Digitized bandwidth
Receiver temperature stability
Receiver components temperature
Channel count
System temperature (Tsys)
Tsys measurement accuracy
Tsys drift over 1 minuteTcal/Tsys
Gain drift with temperature

Table 1 - Expected requirements verification method.

Page 17 of 20

D

A
X

I

FAT

X

X

X
X
X
X
X

SAT
X
X
X

X

X
X
X

X
X

X
X
X
X
X
X

X
X
X
X
X

X
X
X

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

11 Key Performance Parameters
This section provides Key Performance Parameters that should be estimated by the designer andmonitored by NRAO throughout the design phase of the project. These are parameters that have a large
influence on the eventual effectiveness of the facility, and are useful high-level metrics for trade-off
decisions.
These parameters are of higher importance to NRAO. Improved performance above the requirement isdesirable on these parameters. The impact on system-level performance is often discussed in the narrativein Section 4.
The technical requirements are generally specified as minimum values. The goal is to give the designer
some latitude in optimization for a balanced design. Understanding the anticipated performance of the
Independent Phase Calibration system (not just its specified minimum) on these parameters is of value forsystem-level analysis and performance estimation.
These parameters may also be useful for determining the relative priority of the requirements documented
in Section 4 and can assist in the required analysis should tensions be identified between requirements, or
reductions in capability be required to fit within cost constraints.
The Key Performance Parameters that have been identified for monitoring are described in Table 9. Notethat the order in the table reflects the order in the document, and is not indicative of relative importanceor priority.
Key Performance Parameter
Precipitable water vapor relative measurement
Pointing offset from main beam
Receiver temperature stability
Table 2 - Key Performance Parameters for monitoring during design.

Page 18 of 20

Req. #
WVR001
WVR004
WVR006

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

12 Appendix
12.1 Abbreviations and Acronyms
Acronym
AD
CDR
CoDR
CW
EIRP
EM
EMC
EMP
FDR
FEA
FOV
FWHM
HVAC
ICD
IF
KPP
LCD
LED
LO
LRU
MTBF
MTTF
MTTR
ngVLA
RD
RFI
RMS
RSS
RTP
SAC
SNR
SRSS
SWG
TAC
TBD
VLA

Description
Applicable Document
Critical Design Review
Conceptual Design Review
Continuous Wave (Sine wave of fixed frequency and amplitude)
Equivalent Isotropic Radiated PowerElectro-Magnetic
Electro-Magnetic Compatibility
Electro-Magnetic Pulse
Final Design Review
Finite Element Analysis
Field of View
Full Width Half Max (of Primary Beam Power)
Heating, Ventilation & Air Conditioning
Interface Control Document
Intermediate Frequency
Key Performance Parameters
Liquid Crystal Display
Light Emitting Diode
Local Oscillator
Line Replaceable Unit
Mean Time Between Failure
Mean Time To Failure
Mean Time To Repair
Next Generation VLA
Reference Document
Radio Frequency Interference
Root Mean Square
Root of Sum of Squares
Round Trip Phase
Science Advisory Council
Signal to Noise Ratio
Square Root Sum of the Square
Science Working Group
Technical Advisory Council
To Be Determined
Jansky Very Large Array

Page 19 of 20

Title: Independent Phase Calibration
System: Preliminary Requirements

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0001-REQ-AINDEP_PHASE_CALIBRATION_PRELIM_REQS

Date: 2019-07-26
Version: A

12.2 Maintenance Definitions
12.2.1 Maintenance Approach
Required maintenance tasks shall be minimized.
Maintenance shall be mainly performed at assembly and subassembly level by exchange of Line Replaceable
Units (LRUs). LRUs are defined as units which can be easily exchanged (without extensive calibration, of
sufficient low mass and dimension for easiness of handling, etc.) by maintenance staff of technician level.
LRU exchange shall be possible by two trained people within four working hours. It is desirable that LRU
replacement be possible using only standard tools identified in a maintenance manual for the Independent
Phase Calibration system.
A step-by-step procedure for safe exchange of every LRU shall be provided in the Maintenance Manual.
LRUs shall be defined by the Independent Phase Calibration system designer, depending on the design.
The LRUs will be maintained by the ngVLA project (with or without industrial support).

12.2.2 Periodic Preventive MaintenancePreventive maintenance may be performed at planned intervals in order to keep the Independent Phase
Calibration system operational and within its specified performance. Any required preventive maintenanceshould be documented in the Maintenance Manual.

Page 20 of 20

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

Water Vapor Radiometer Design Description
020.45.00.00.00-0002-DSN-A-WATER_VAPOR_RADIOMETER_DSN_DESCR

Status: RELEASEDPREPARED BY
A. Erickson
S. Durand, Antenna Electronics IPT Lead

ORGANIZATIONElectronics Div., NRAOElectronics Div., NRAO

DATE
04-30-2019
05-02-2019

APPROVALS
R. Selina,
Project Engineer

ORGANIZATIONElectronics Division,
NRAO

DATE
2019-07-26

Asst. Director, NM-Ops,

2019-07-26

RELEASED BY (Name and Signature)
ORGANIZATION
M. McKinnon,
Asst. Director, NM-Ops,
Digitally signed by Mark McKinnon
Project Director Mark McKinnon Date: 2019.07.26 19:15:14 -06'00' NRAO

DATE
2019-07-26

M. McKinnon,
Project Director

2019.07.26
13:25:49 -06'00'

signed by Mark McKinnon
Mark McKinnon Digitally
Date: 2019.07.26 19:14:56 -06'00'
NRAO

Page 1 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

Date: 2019-07-26

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Version: A

Change Record
AuthorAffected
Section(s)VersionDate

0.1

2018-02-12

Ford

All

Initial draft, feedback on Section 3 & 4

0.2

2018-05-01

EricksonAll

Content

1.0

2018-09-26

EricksonAll

2.0

2019-04-30

EricksonAll

3.0

2019-05-31

Selina3.1, 3.3

Final
Minor revisions to prepare for IPT Leadreview
Minor edits for release.

A

2019-07-26

Lear

All

Prepared PDF for signatures and release

Page 2 of 13

ReasonTitle: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

Table of Contents
1

Introduction ................................................................................................... 4

1.1
1.2

Purpose ................................................................................................................................... 4
Scope ...................................................................................................................................... 4

2

Related Documents and Drawings ............................................................... 4

2.1
2.2

Applicable Documents ........................................................................................................... 4
Reference Documents ............................................................................................................ 4

3

Subsystem Overview ..................................................................................... 5

3.1
3.2
3.3

Motivation .............................................................................................................................. 5
Operation ............................................................................................................................... 5
Construction ........................................................................................................................... 5

4

4.1
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.2.7
4.2.8
4.2.9
4.2.104.2.114.2.124.2.13
4.3
4.4
4.4.1
4.4.2
4.4.3
4.4.4
4.4.5
4.4.6
4.4.7

Subsystem Design .......................................................................................... 7

Subsystem Block Diagram ..................................................................................................... 7
Subsystem Components ......................................................................................................... 7
Antenna ........................................................................................................................................................ 7
Receiver Module ........................................................................................................................................ 8WVR Junction Box .................................................................................................................................... 9
Alignment Wedge ...................................................................................................................................... 9
Cooling Plate ............................................................................................................................................... 9
Feed............................................................................................................................................................. 10
Feed Heater .............................................................................................................................................. 10
Front End ................................................................................................................................................... 10
Integrated Receiver/Digitizer ................................................................................................................ 10
Monitor and Control .............................................................................................................................. 10
Thermal Stabilizer .................................................................................................................................... 10
Processing Module................................................................................................................................... 11
Firmware .................................................................................................................................................... 11
WVR Locations ..................................................................................................................... 11Interfaces with other Subsystems ........................................................................................ 11
Antenna Feed Arm Truss ...................................................................................................................... 11
Antenna Liquid Cooling.......................................................................................................................... 11
Antenna Air Cooling ............................................................................................................................... 11
Local Oscillator ........................................................................................................................................ 11Time ............................................................................................................................................................ 11
Monitor and Control .............................................................................................................................. 12Power ......................................................................................................................................................... 12

5

Appendix....................................................................................................... 13

5.1

Abbreviations and Acronyms ............................................................................................... 13

Page 3 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

Date: 2019-07-26

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Version: A

1 Introduction
1.1 Purpose
This document provides a description for the Water Vapor Radiometer (WVR) subsystem reference
design. It covers the design approach, functions, description of key components, interfaces, and risks
associated with the reference design. This document will form part of the submission of the ngVLA
Reference Design documentation package.

1.2 Scope
The scope of this document covers the entire design of the WVR Subsystem, as part of the ngVLA
Reference Design. It includes the subsystem’s design, how it functions, and interfaces with the necessary
hardware and software systems. It does not include specific technical requirements or budgetary
information.

2 Related Documents and Drawings
2.1 Applicable Documents
The following documents may not be directly referenced herein but provide necessary context or
supporting material.
Ref. No.
AD00
AD01
AD02
AD03
AD04
AD05
AD06

Document Title
ngVLA WVR Subsystem Preliminary Requirements
Fast Switching Calibration at the ngVLA Site
Calibration Strategies for the ngVLAThe Concept of A Reference Array for the ngVLA
Considerations for a Water Vapor Radiometer System
Results of Water Vapor Radiometry Tests at the VLA
A Study of the Compact Water Vapor Radiometer for
Phase Calibration of the Karl G. Jansky Very Large Array

Rev / Doc. No.
020.45.00.00.00-0001-REQ
ngVLA Memo No. 1
ngVLA Memo No. 2
ngVLA Memo No. 4
ngVLA Memo No. 10
EVLA Memo No. 73
EVLA Memo No. 203

2.2 Reference Documents
The following documents are referenced within this text:
Ref. No.
RD01

Document Title
Fast Switching Calibration at the ngVLA Site

Page 4 of 13

Rev / Doc. No.
ngVLA Memo No. 1

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

3 Subsystem Overview
3.1 Motivation
Relative phase across a pair of antennas (a baseline) is a key measurable of synthesis arrays. Noise in thissignal is contributed by the electronics and by the atmosphere. Water vapor is the largest contributor toatmospheric phase noise. One way to reduce the influence of atmospheric phase noise is to slew allantennas to a calibrator source periodically throughout a science observation in order to calculate theatmospheric phase noise contribution so that it may be subtracted from the science data. This is called
fast switching, as the switching interval is much smaller than the science observation.
For a given period in which science may be performed, fast switching reduces the available time-on-sky
for the science data by the time necessary to slew to calibrator, observe the calibrator, and slew back toscience. Worse, the switching interval decreases as observation frequency increases and also as
atmospheric stability decreases. At the highest ngVLA observation frequencies and under normal
atmospheric conditions, switching would occur at 30-second intervals [RD01].
It is the goal of the WVR to allow a dramatic increase in this switching interval, as well as reduce any
residual atmospheric phase perturbations that corrupt the astronomical data between calibrator
observations.

3.2 Operation
The WVR constantly observes an atmospheric water vapor emission line centered at 22 GHz in order totrack changes in the column density of water vapor in the WVR beam. Before the observation, a calibrator
is observed (as in switching) to establish an absolute phase offset between antennas and WVR-estimatedcolumn density is noted. By monitoring changes in the water vapor column density throughout anobservation, estimates of change in phase can be applied to the science data. Periodically—but with amuch larger interval than that of fast switching—the calibrator can be re-observed to re-establish absolutephase offset.

3.3 Construction
The WVR consists of a 1.2-meter antenna mounted to the main feed arm as shown in Figure 1 and Figure
2, in which the WVR dish is colored red.

Page 5 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

Figure 1 - Main and WVR dishes, side view. Antenna design shown is diagrammatic only.

Figure 2 - Main and WVR dishes, front view. Antenna design shown is diagrammatic only.

The fixed WVR beam is aligned parallel to the main antenna beam. The WVR antenna architecture is
Offset Prime Focus. The feed, receivers, digitizers, and support electronics are located in a module
mounted to the main feed arm at the offset focal point. A mounting plate connected to the antenna’s liquid
cooling system provides a heat reservoir. Front End and receiver and digitizer electronics are thermallystabilized using Peltier heat pumps. A band from 18–32 GHz is digitized in the receiver module and digital
data is streamed via fiber to the WVR processor in the pedestal room. Low-data-rate output is emitted
into the Monitor and Control data stream.

Page 6 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

4 Subsystem Design
4.1 Subsystem Block Diagram
Figure 3 shows the basic layout for the WVR subsystem.

Figure 3 - WVR subsystem overview and interfaces.

4.2 Subsystem Components
4.2.1

Antenna

The antenna is a 1.2 by 1.4 m parabolic dish designed for offset prime focus use, built by General Dynamics
and targeted at the Very Small Aperture Terminal (VSAT) customer base. It is constructed of glass fiber
reinforced polyester and is rated for a working wind load of 50 mph and survival to 125 mph. Note that
the WVR antenna is not acting as a power collector, but rather as a view-limiting device to ensure that
atmospheric conditions in the main antenna beam are accurately sampled. The minimum size of theantenna was calculated to achieve a WVR beam diameter at 22 GHz that is close to the beam diameterof the main antenna beam at 2 km altitude, under which most water vapor turbulence has been observed.
The antenna is mounted via truss to the starboard side of the main antenna truss. The WVR side of thetruss supports a connection plate, to which an antenna mounting plate is attached via three adjustment
bolts. The antenna mounts directly to the antenna mounting plate. Fine adjustment of antenna pointing isprovided by the three adjustment bolts. Adjustment is expected to be performed only during installationand major maintenance. Pointing adjustment will be performed by using a software pointing calibration
routine to center the main beam on a geostationary satellite with a K-band downlink, then manually
adjusting the adjustment bolts on the antenna mounting plate to maximize WVR receiver output.
Adjustment bolts are locked with locking nuts and safety wire to prevent motion.

Page 7 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

4.2.2

Date: 2019-07-26
Version: A

Receiver Module

Figure 4 shows the basic WVR receiver module design.

Figure 4 - WVR receiver module layout.

The module contains the feed, receiver, and all digitizing and processing electronics for the WVR. It is analuminum enclosure with both weather and RFI gasket seals, and a sealed armor cable to protect powerand data connections. The module mounts via cooling plate and offset wedge to the main feed arm truss
at the correct point to place the feed phase center at the focal point of the WVR antenna.
Inside the module (Figure 5), RFI-tight compartments separate the feed, LNA, switched-power system,
and receivers from the power supplies and thermal control boards. All RF components are mounted to athermally stable plate that is kept at 30.00°C +/– 0.01°C by a control system driving Peltier-effect heatpumps. The heat pumps are thermally connected to the module wall that is thermally connected to theantenna cooling system. Thermal insulation around the thermal plate reduces thermal transfer from theenclosure walls, and an external heat shield reduces solar heating on the exposed module walls.

Page 8 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

Figure 5 - WVR receiver module schematic.

4.2.3

WVR Junction Box

WVR power and fiber are connected at the WVR junction box located inside the main feed arm truss
along the electrical conduit leading from the Pedestal Room to the IRD module. The junction box is acommercial weather-sealed electrical box specified for all-angle exposure. Sealed armor cable is used toconvey –48 V power and M&C fiber to the WVR.

4.2.4

Alignment Wedge

A manually adjustable hinged wedge is mounted to the main antenna feed arm truss, and provides themounting point for the cooling plate and WVR electronics module. The wedge provides the necessary
feed angle relative to the WVR antenna in order to allow adjustment of the WVR beam to be parallel tothe main antenna beam. The wedge contains a fine-adjustment mechanism to allow the feed angle to beprecisely aligned during the WVR pointing/alignment procedure performed during installation and major
maintenance. Adjustment bolts are locked after alignment with safety wire.

4.2.5

Cooling Plate

The WVR cooling plate is similar to the main IRD module cooling plate. Fluid cooled by refrigerators on
the antenna pedestal is circulated through lines leading to the cooling plate, through channels in the coolingplate, and back to the pedestal room. Coolant temperature is maintained at 20°C +/– 5°C by a control
system in the pedestal room. The WVR cooling plate contains channels for circulating fluid, and isremovable for maintenance. Mounting holes allow attachment to the alignment wedge on one side and of
the electronics module on the other.

Page 9 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

Thermal transfer to the module is facilitated by flat-machined surfaces and silicone thermal-transfer gasket.
Fluid connections are high-reliability drip-free quick-connects and fluid lines are nitrile-based hydraulichoses protected by steel armor cable.

4.2.6

Feed

The wide-band feed is an mWave FPP1-222-S linear feed for K band 18.0–26.5 GHz. It is flange-mounted
to the aft end of the receiver module with RFI and environmental gaskets. The feed terminates in an SMAK female connector, and is protected from ultraviolet radiation and physical damage by a PTFE window.

4.2.7

Feed Heater

A radiant feed heater coil is mounted to the main feed arm aft of the feed and facing it. Power connections
to the feed heater are supplied from the WVR junction box. Current is supplied to the heater through asolid-state relay in the WVR junction box which is controlled by the WVR processing module in thepedestal room. Feed heat is commanded by the antenna supervisor, which determines if conditions arenecessary for feed heat based on weather data, feed temperature, and WVR data output. The supplied
heat is sufficient to clear condensation from the window without damaging the window material.

4.2.8

Front EndA single polarization is taken from the K-band feed. A switched noise diode source is coupled to the feedsignal, and a low-noise amplifier provides initial gain. A power divider provides the signal to the two
Integrated Receiver/Digitizer modules, which amplify and filter, downconvert, and digitize the signals.

4.2.9

Integrated Receiver/Digitizer

The NRAO CDL has developed an Integrated Receiver/Digitizer (IRD) module to be used for ngVLA. The
WVR will use two IRD modules, each of which consists of two independent receivers and digitizers. In
total, four subbands covering K band will be sampled, with 32 100 MHz channels for each subband being
produced by the WVR processing module.
To ensure precise calibration, one channel of each subband will overlap one channel of the neighboring
subbands. The IRD digitizers will be configured to provide 8-bit samples to better handle RFI, an increasein which is expected over the array lifetime. Data is streamed over a custom transmit-only fiber link using
QSFP28 transceivers directly to the processing module in the pedestal room.

4.2.10 Monitor and Control
Monitor and control in the receiver module is provided by a standard ngVLA M&C board. The board isconnected to the M&C fiber network and provides control over the IRDs, switching diode, feed heaters,
and all other electronics. All sensors, including feed and cold plate temperatures, system voltages, andsystem currents, are read by the M&C board and reported to the M&C network. The antenna supervisor
software in the pedestal room analyzes conditions in the WVR and elsewhere and provides control overWVR power-up, operation, and safe shutdown.

4.2.11 Thermal Stabilizer
To determine water vapor column density, the amplitude of each spectral channel must be determinedwith an accuracy of about one part in 10,000. Fluctuations in gain and other parameters of the Front End
electronics make this specification impossible to meet unless thermal stability is maintained to within about
0.01°C. To achieve this stability, the RF components and the digitizers are mounted to a thermal mass—
the “cold plate”—which is maintained at a specified temperature to that accuracy.

Page 10 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

Date: 2019-07-26
Version: A

The cold plate is manufactured out of 6063 aluminum, picked for its superior thermal conductivity.
Through aluminum load plates, the cold plate is thermally connected to Peltier effect devices, which canpump heat through themselves in either direction based on supplied electrical current. The Peltier devices
are thermally connected to the enclosure, then to the antenna cooling plate. The cold plate has thermal
sensors mounted to it. The processor on the Monitor and Control board (details below) implements acontrol system to maintain the cold plate at the specified temperature.

4.2.12 Processing Module
The processing module is a Dell PowerEdge C4130 1U rack-mount server located in the pedestal roomelectronics rack, hosting a Bittware XUSP3S processing card. Four QSFP28 modules accept fiber datafrom the WVR receiver module. This server is also the host for the antenna supervisor processing board.
RFI Shielding is provided by the pedestal rack.

4.2.13 Firmware
Data from the two IRDs is received via the QSFP link and read by the FPGA logic. A 32-channel polyphasefilter (PPF) channelizes the data from the four subbands. Integration of 100–1000 ms is performed perchannel. Detection algorithms flag channels affected by RFI. Calibration routines join the subbands andnormalize the bandpass. An ARM processor soft-core is then triggered to process the channel data to
determine the water vapor column density in the WVR beam, and the data is emitted onto the M&C
network. The processor board also networks M&C data for itself, IRDs, temperature controller, power
supplies, and all other electronics in the module.

4.3 WVR Locations
All 18-meter antennas in the array will be equipped with a WVR.

4.4 Interfaces with other Subsystems
4.4.1

Antenna Feed Arm Truss

The antenna will mount to the feed arm truss, and therefore must induce no undue loads from wind or
thermal stress.

4.4.2

Antenna Liquid Cooling

The WVR receiver will use 20 W of cooling from the antenna cooling system, and will require one line
each for outbound and return cooling fluid.

4.4.3

Antenna Air Cooling

The WVR processor will use 100 W of cooling, supplied by the common rack cooling air.

4.4.4

Local Oscillator

Four LO clocks are provided to the WVR electronics module via fiber from clock synthesizers in thepedestal room.

4.4.5

Time

Accurate observation time will be provided to the data processing module by the array’s Time Distribution
System.

Page 11 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

4.4.6

Date: 2019-07-26
Version: A

Monitor and Control

The WVR processor will use 100 kB/s on the M&C Ethernet over a single fiber connection.

4.4.7

Power

The WVR receiver will consume 20 W of power from the antenna supply. The WVR processor will use
100 W of power from the common pedestal rack supply.

Page 12 of 13

Title: Water Vapor Radiometer
Design Description

Owner: Erickson

NRAO Doc. #: 020.45.00.00.00-0002-DSN-AWATER_VAPOR_RADIOMETER_DSN_DESCR

5 Appendix
5.1 Abbreviations and Acronyms
Acronym
AD
CDL
DBE
DTS
IF
LNA
LO
LRU
M&C, M/C
NES
ngVLA
NSF
PLL
PFB
RD
RF
RFI
TBD
VLA
WVR

Description
Applicable Document
Central Development Laboratory, NRAO
Digital Back End
Data Transmission System
Intermediate Frequency
Low-Noise Amplifier
Local Oscillator
Line Replaceable Unit
Monitor and Control
Near Earth Sensing
Next Generation VLA
National Science Foundation
Phase Locked Loop
Polyphase Filter Bank
Reference Document
Radio Frequency
Radio Frequency Interference
To Be Determined
Jansky Very Large Array
Water Vapor Radiometer

Page 13 of 13

Date: 2019-07-26
Version: A