UNITED STATES EPARTMENT Of 8MMERCE

UBUCATION NBS TECHNICAL NOTE 647

MICROWAVE ATTENUATION

MEASUREMENT SYSTEM

ISERIES SUBSTITUTION)

U.S. :partment

OF

COMMERCE

National

Rnrpaij

100

U5T53

1974

« 9
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government. (3) a technical basis for equity in trade. and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs. THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Nuclear

Sciences = — Applied Radiation = — Quantum Electronics a — Electromagnetics 3 — Time

and Frequency " — Laboratory Astrophysics ! — Cryogenics ". THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; provides advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of

technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute consists of a Center for Building Technology and the following divisions and offices: Engineering and Product Standards — Weights and Measures — Invention and Innovation — Product Evaluation Technology — Electronic Technology — Technical Analysis — Measurement Engineering — Structures, Materials, and Life Safety * — Building Environment * — Technical Evaluation and Application * — Fire Technology.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective

utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Pan of the Center for Radiation Research.

> Located at Boulder, Colorado 80302.

* Part of the Center for Building Technology.
IL 1 4 1974 £»' MICROWAVE ATTENUATION

,5753

y MEASUREMENT SYSTEM

,5- (SERIES SUBSTITUTION]

Wilbur Larson

Eugene Campbell

Electromagnetics Division

Institute lor Basic Standards

,5' National Bureau of Standards

Boulder, Colorado 80302

»*<"

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS Richard W Roberts. Director

Issued February 1974
National Bureau of Standards Technical Note 647

Nat. Bur. Stand. (U. S.), Tech. Note 647, 28 pages (February 1974) CODEN: NBT1NAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D. C. 20402

(Order by SD Catalog No. CI 3.46:647) $0.35
Contents

Page

1. Introduction 1

2. The Measurement System 3

3. The Standard Attenuator 6

4. Errors of the Measurement System 9

5. Attenuation Measurements of Transfer Standards 11

6. Conclusion 12

7. References 2 3

List of Figures

Figure 1. Block diagram of microwave attenuation calibration system. 14

Figure 2. Detailed block diagram of microwave attenuation calibration system. 15

Figure 3. Schematic diagrams of pin diode modulator

driver and power supply. 16

Figure 4. Schematic diagram of the circuit for the null

preamplifier 17

Figure 5. Estimated limits of systematic errors for the

optical-rotary-vane attenuator. 18

Figure 6. A recording showing the system stability at

30 dB measurement level. 19

List of Tables

Table I . Insertion loss measurements of fixed attenuators A and B by the i-f and series substitution methods at 9.0 GHz. 20

Table II. Attenuation difference measurements of a variable attenuator by the i-f and series substitution methods at 9.0 GHz. 21

Table III. Insertion loss measurements of a fixed attenuator by the i-f and series substitution

methods at 9.0, 9.8 and 11.2 GHz. 22

iii

MICROWAVE ATTENUATION MEASUREMENT SYSTEM*

(SERIES SUBSTITUTION)

A dual detection microwave bridge circuit has

been incorporated in a series substitution system for

the measurement of microwave attenuation devices.

The use of an optical rotary-vane attenuator in the

system yields practical resolution and stability

of 0.00005 dB from zero to 30 dB . The dual detection

system has several favorable features: (1) it

employs a single microwave source which reduces cost,

(2) measurements are obtained without power stabilization of the microwave signal source, and (3) this

waveguide configuration enables measurements of

attenuation devices at any length with minimum of

effort and movement of waveguide components.

The system configuration is convenient for both

attenuation difference, and insertion loss measurements from zero to 70 dB over the WR90 waveguide band

of 8.2 to 12.4 GHz.

Key words: Attenuation; measurement; rotary-vane

attenuator; series substitution.

1. Introduction

A substantial amount of work has been done to develop

various techniques for measuring attenuation in the microwave

region. Each method has definite properties that enhance its

choice for the measurement of a given range of attenuation

or a specific interl aboratory standard. The i-f substitution [1] system has been developed to a high degree of

*Presented at the Technical Applications Sessions of the IEEE

Interlaboratory Convention, New York, March 22, 1971. This

work was completed at the National Bureau of Standards,

Boulder, Colorado, under the sponsorship of the Calibration

Coordination Group of the Department of Defense.
excellence for the measurement of attenuation over a wide

dynamic range. A major disadvantage of this system is the

requirement of two microwave signal sources. The af system

requires but one microwave signal source. Both of these advantages are combined in the attenuation systems known as the

modified dc substitution [2] and the modulated sub-carrier [3]

techniques

A microwave series substitution attenuation system has

been developed in the Electromagnetics Division of the National

Bureau of Standards at Boulder, Colorado. Two advantages of

the microwave series substitution technique of attenuation

measurement are: (1) knowledge of the response law of the

detectors is not required because the signal power in the

detectors is constant for each null in the measurement process and (2) the resolution of the system remains constant

through the entire range of measurement. The systems' reso- lution of measurement is several orders of magnitude greater

than is necessary for calibrating commercially available

attenuators

This calibration system utilizes the NBS designed precision rotary vane attenuator as the reference standard [4].

The stability and resolution of this system is consistent

with the 0.00005 dB resolution of the reference standard at

1 dB and exceeds that of the reference standard at values

above 1 dB . The system uses a single microwave signal source

and does not require a high degree of amplitude stability.

The range of attenuation measurement for fixed or variable

2
devices is to 70 dB for this system in the frequency band

of 8.2 to 12.4 GHz. Sources of error in the microwave attenuation measurement system and devices under test for attenuation

difference and insertion loss measurements are discussed.

2. The Measurement System

This microwave attenuation measurement system employs

two waveguide channels in a bridge network. Each channel has

a waveguide detector and a low frequency (1 kHz arm) . The

standard attenuator and the attenuator under test are inserted

in the same waveguide channel, and a reference attenuator in

the other waveguide channel. A block diagram of the microwave

attenuation calibration system is shown in figure 1. Fixed or variable devices may be used as the standard or reference

attenuators

With this microwave measurement system, a change in the

attenuator under test is equal to the change required in the

standard attenuator to rebalance the bridge. In order to

make an attenuation measurement the following steps are

required: (1) initially balance the bridge for a reference

null, (2) make the desired change in the attenuator under

test, and (3) rebalance the bridge with the standard

attenuator.

The dual detection technique offers several unique

features: (1) it employs a single source at the microwave

frequency which reduces cost, (2) measurements are obtained
without power stabilization of the microwave signal source,

and (3) this waveguide configuration enables measurement of

attenuation devices of any length with a minimum of effort

and movement of waveguide components.

Figure 2 provides a more detailed block diagram of the

system components that are used in NBS microwave attenuation

measurement systems. The source of microwave power utilizes

conventional isolation and frequency measuring auxiliary com- ponents, but the usual power stabilization required for precision measurement is not necessary. The main arm of directional

coupler (A) connects to a level set attenuator and an isolator.

These components are followed by a pin-diode modulator

that is driven by an audio signal source. The modulated

signal feeds into directional coupler (B) which separates

the signal to the two microwave arms of the bridges. The other

arms of the bridge are the two dc biased detectors. The

shorter microwave arm of the bridge contains the reference

rotary-vane attenuator (for initial balance of the bridge),

and an additional isolator before the waveguide detector.

The output port of the side arm of the directional

coupler provides a 20 dB power loss to the reference attenuator. This reduction of the modulated signal enables

the reference attenuator to be set at a lower value where

higher resolution aids the resettability . In addition, the

reduction of signal level prevents possible damage to the

diode in the detector at small dB attenuation measurements.
In the longer arm of the bridge an isolator is followed

by a tuner, a directional coupler, and a second tuner. These

components make up the basic portion of a reflectometer as shown in the schematic diagram. The secondary arm of the

directional coupler in the reflectometer [5] contains an isolator and a waveguide detector. The output of the detector is connected to a VSWR indicator for use in reducing the

mismatch error [6] at the insertion point of the measurement

system. One side of the insertion point for the standard

attenuator is connected to the reflectometer by a precision

waveguide section. The other side is connected to another

precision section of waveguide and other waveguide components

which isolate the standard attenuator from the attenuator under

calibration. In order to obtain the isolation and matching

desired, this fabricated section has a stub tuner and a precision section of waveguide at each end. The second

port of the above fabricated waveguide section is used as one

side of the matched insertion point for the attenuator under

test. On the other side of the attenuator under test is

located another precision section, a tuner, isolator, and

another detector to complete the output of the longer arm

of the microwave bridge.
The output signal of each detector in the microwave bridge

couples to the input transformer of the null preamplifier.

The output of the null preamplifier is coupled to a synchronous

detection circuit [7] which provides the readout indication

for the measurement of attenuation.

This attenuation measurement system can be constructed

with commercially available waveguide components and instrumentation equipment. However, some of the instrumentation

equipment used in this system was designed by NBS. The schematic drawings of two such components, the modulator driver

and the null preamplifier, are shown in figures 3 and 4,*

respectively

3. The Standard Attenuator

The rotary-vane attenuator is a device which when fabricated with high precision can meet the criteria essential

for an attenuation standard [8,9,10]. It operates at the same frequency as the device under test and has very low

insertion loss at zero setting. This low insertion loss

enables one to make a measurement of attenuation to 50 dB

with less difficulty than is encountered with an i-f series

substitution system employing a 30-MHz piston attenuator [1]

as a standard.

*Replacement of designated parts by others may affect system

performance or the reproducibility of the results reported,

and hence should be made with caution.
Three high resolution rotary-vane attenuators with

optical readouts have been constructed at the NBS, and were tested over the range of zero to 50 dB. The tests were accomplished using three independent methods for making attenuation difference measurements [2,3,4]. The results of

this testing indicate the three rotary-vane attenuators described have a realizable accuracy of 0.002 dB or better from

zero to 20 dB. The estimated error from 20 to 50 dB is 0.002

to 0.025 dB , respectively.

Three errors related to the standard rotary-vane attenuator are incorrect vane alignment, resettability , and

transmission errors. Incorrect vane alignment in the rotor

causes a systematic error that is inherent in the rotary-vane

attenuator. In addition, resettability of the attenuator dial

by the operator must be included in the error analysis. In

making an attenuation difference measurement with the (standard)

rotary-vane attenuator the errors at the final setting may

be written as cos(e

£ +e £o +e £I ) fo

+ £ fi

= - 40 10 §io COS Or

where 9 f is the vane-angle at the final setting to obtain

the calculated attenuation, r is the vane -angle error made

to ° by the operator at the final setting, and 6 £ j is the

inherent vane-angle error [11,12].
The estimated rotor vane-angle alignment error (6 fT ) is

about 18 seconds and the operator resettability angle error

(9.C ) is about 2 seconds. Figures 5a and 5b show the

estimated limits of attenuation error due to alignment and

resettability for dial settings of 10 to 70 dB . These errors

are 0.03 and 0.003 dB , respectively, for the 50 dB dial

setting at 9.0 GHz. Total attenuation error due to alignment and resettability at the initial or zero dial setting

is estimated to be less than 0.01 microbels or 6.8 nanobels

2 The transmission error or deviation from cos law caused

by insufficient maximum attenuation in the center vane can

be determined by measuring the maximum attenuation of the

standard. The transmission error is given by [10]

e = -20 log(l + e'

al tan 2 0)

where e

' is determined from the maximum attenuation, and

9 angular value of the center vane at given dial setting.

The transmission or internal leakage error is estimated to be

about 0.003 dB at the 50 dB dial setting for a maximum attenuation value of 120 dB . Refer to figure 5c for the

estimated limits of the transmission error of the optical

attenuator at dial setting from 10 to 70 dB.

Leakage of the standard rotary-vane attenuator used

in this system was more than 120 dB [4] below the incident

power due to liberal use of microwave absorbing material in the
design of the housing and rotating joints. Leakage in the

waveguide system can be kept to a minimum by using waveguide

components that have flat, smooth surfaces and well mated

flanged joints

In order to reduce what appeared to be a ground loop

problem, mica was placed between the flanges of each detector

mount and adjacent isolator. The increase in space between

the flanges of the detector introduced another problem of

leakage. However, both problems were finally resolved by the

use of mica at the flanges of the pin diode modulator.

4. Errors of the Measurement System

Prior to each calibration the waveguide insertion points

of each system are tuned with a ref lectometer to reduce

possible mismatch errors. The series substitution system

requires the tuning of two insertion points as one includes

the working standard (refer to figure 2) . The tunable reflec

tometer [5] included in the waveguide system provides a means

for matching the insertion points. Thus, the mismatch error

[6] causing uncertainty in the measurement of attenuation can

be minimized by these tuning techniques. The mismatch error

is estimated to be 0.002 dB for a system VSWR of 1.01 at the

insertion point and an attenuator VSWR of 1.05.

To insure reliable matching of the open ports at the

insertion points, the ports should be aligned prior to tuning
so that excess movement or re-alignment is not necessary.

In addition, the waveguide components should be mounted on laboratory benches [13] that hold the waveguide in a rigid

position and provides the stability required for precise

measurement

The device under test may be connected in cascade with

the standard attenuator at the same insertion point. Then,

cascade mismatch errors [14,15] must be considered in addition

to the mismatch errors at the insertion point.

Instability of the signal source can cause deviations

that appear on the output recording chart as system drift. In

figure 6 the stability of the NBS microwave measurement system

is illustrated by the recording of the null detector output

for a 12 -minute run at a nominal value of 30 dB in each

microwave arm. Full scale deviation on the strip chart cor- responds to 0.002 dB and each line is 5 microbels (10 decibels). The maximum deviation is shown to be ± 10 microbels

from the reference during the 12 minute run. A preliminary estimate of the random uncertainties for

the microwave attenuation measurement system is based on ex- perimental data taken on five transfer standards. An average

estimate of a is 0.0010 dB for 125 determinations made during

the interval of twelve months. The estimate of a for the 75

determinations of insertion loss of the fixed transfer standards

was 0.0013 dB and the estimate of a for the 50 determinations of

attenuation difference of the variable transfer standards was 0.0006 dB.

10
It has been demonstrated with this microwave attenuation system that amplitude changes of 10 dB at the signal

source resulted in deviations of less than 0.001 dB at the

null detection output.

5. Attenuation Measurements of Transfer Standards

Direct comparison was made in attenuation measurements

between the series substitution method using the optical

rotary-vane attenuator as a standard, and the i-f substitution method employing the 30 -MHz piston as the standard.

In order to obtain a comparison in both insertion loss and

attenuation difference, fixed and variable waveguide attenuators were used as transfer standards.

To compare the insertion loss measurements, two NBS

designed fixed attenuators [16] were measured for insertion

loss in each system. Table I presents a comparison of the

insertion measurements obtained by the microwave series

substitution and the i-f substitution methods. The table

shows that the difference between the insertion loss meas- urements are 0.004 dB for attenuator (A) and 0.003 dB for

attenuator (B) . A commercially available rotary-vane attenuator was calibrated for attenuation difference between the values of

5 to 50 dB by each method at 9.0 GHz. The measured values

11
of attenuation difference for the dial settings of 5, 10,

15, 20, 30, 40 and 50 dB are shown in table II. The deviation in the measured values of attenuation difference between the two methods varied from 0.002 to 0.013 dB for the

dial setting of 5 to 50 dB

In order to evaluate the microwave series substitution

system at high attenuation, a fixed waveguide standard of a nominal value of 70 dB was measured. Previously this fixed

waveguide standard was measured in the microwave attenuation

calibration system by the i-f substitution method at three

frequencies in the X-band region. Table III gives the insertion loss results obtained between the series substitution

and the i-f substitution systems at 9.0, 9.8, and 11.2 GHz.

The differences between the measured values of 70 dB do not

exceed 0.07 dB

6. Conclusion

The NBS microwave attenuation measurement system provides

stability, resolution, accuracy, and ease of operation in the

measurement of attenuation difference and insertion loss.

The null detection employed in this system has a unique

feature in that the signal power at the detector is constant

for each null in the measurement process. Thus, exact knowledge of the response law of the detector is not required, and

resolution remains constant over the range of the measurement.
The NBS microwave attenuation measurement system permits

qualified metrologists to make an intrinsic evaluation of

the standard rotary-vane attenuator without additional attenuation standards. Details of this method of evaluating

the rotary-vane attenuator will be presented in a forthcoming paper.

13
MICROWAVE

SIGNAL

MODULATOR

1 kHz

REFERENCE

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POINT"

ATTENUATOR

UNDER

TEST

CRYSTAL

DETECTOR

NULL

DETECTOR

CRYSTAL

DETECTOR

Figure 1 Hock diagram of microwave attenuation calibration system.

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18
Figure 6.

A recording showing the system stability at 30 dB

measurement level. 19
Table I. Insertion loss measurements of fixed attenuators A

and B by the i-f and series substitution methods

at 9.0 GHz.

Nominal Value

dB

Average

Measured

Insertion

Loss

dB

Estimated

Limits of

Systematic

Error

dB

Computed

Standard

Error

dB

3.000 (i-f sub.)

3.000 (ser. sub.)

Fixed Attenuat

3.087

3.091

or A

0.011

0.005

.0024

0.0012

Fixed Attenuator B

4.600 (i-f sub.) 4.620 0.011 0.0012

4.600 (ser. sub.) 4.622 0.005 0.0008

20
Table II. Attenuation difference measurements of a variable

attenuator by the i-f and series substitution methods

at 9.0 GHz.

Nominal Value

dB

Average

Measured

Attenuation

Difference

dB

Estimated

Limits of

Systematic

Error

dB

Computed

Standard

Error

dB

5 (i-f sub.) 5.005 0.011 0.0004

5 (ser. sub.) 5.001 0.005 .0004

10 (i-f sub.) 9.997 .011 0.0014

10 (ser. sub.) 9.992 0.005 0.0008

15 (i-f sub.) 15.013 0.014 0.0014

15 (ser. sub.) 15.015 0.005 .0010

20 (i-f sub .) 20.014 0.014 0.0016

20 (ser. sub.) 20.012 .010 0.0010

30 (i-f sub.) 30.024 .018 .0016

30 (ser. sub .) 30 .030 .012 .0014

40 (i-f sub.) 39.991 0.024 .00 30

40 (ser. sub.) 39.996 .020 .0012

50 (i-f sub.) 49.981 .043 0.0 36

50 (ser. sub.) 49.994 0.038 .0032

21
Table III. Insertion loss measurements of a fixed attenuator

by the i-f and series substitution methods at 9.0,

9.8 and 11.2 GHz.

Frequen

GHz

cy

Insertion Loss in dB

i-f s ub . ser

.

sub

.

9 .0 6 8.39 68,,32

9.8 70.24 70,,29

11.2 71.77 71,,79

22
7. References

[I] R.E. Grantham and J.J. Freeman, "A standard of attenuation for microwave measurements," Trans. AIEE 67, 329-

335, June 1948.

[2] G. F. Engen and R.W. Beatty, "Microwave attenuation

measurements with accuracies from 0.0001 to 0.06 decibel

over a range of 0.01 to 50 decibels," J. Res. NBS, Vol.

64C, 139-145, April-June 1960.

[3] G.E. Schafer and R. R. Bowman, "A modulated sub-carrier

technique of measuring microwave attenuation," Proc. IEE

(London) 109, Pt. B, Suppl. No. 23, 783-786, May 1962.

[4] W.E. Little, W. Larson, and B.J. Kinder, "A rotary-vane

attenuator with an optical readout," J. Res. NBS, C. Engr

and Instr. , Vol. 75C, No. 1, January 1971.

[5] W.J. Anson, "A guide to the use of the modified re

flectometer technique of VSWR measurement," J. Res. NBS,

Vol. 65C, No. 4, 217-223, Oct. -Dec. 1961.

[6] R.W. Beatty, "Mismatch errors in the measurement of

ultrahigh- frequency and microwave variable attenuators,"

J. Res. NBS 52.7-9, January 1954.

[7] Joseph M. Diamond, "A double phase -sensitive detector

for bridge balance," IEEE Spectrum, Vol. 6, No. 6, 62-70,

June 1969.

[8] R. W. Beatty, "Microwave attenuation measurements and

standards," NBS Monograph 97, April 3, 1967.

[9] P.F. Mariner, "An absolute microwave attenuator," Proc.

IEE, 415-419, September 1962.

[10] Allan V. James, "A high-accuracy microwave attenuation

standard for use in primary calibration laboratories,"

IRE Trans, on Instrumentation, Vol. 1-11, 285-290,

December 1962.

[II] Wilbur Larson, "Analysis of rotational errors of a wave- guide rotary- vane attenuator," IEEE Trans, on Instrumentation and Measurement, Vol. IM-12, No. 2, 50-55,

September 1963.

23
[12] W. Larson, "Table of attenuation error as a function of

vane-angle error for rotary-vane attenuators," NBS Tech.

Note 177, May 20, 1963.

[13] D.W. Schulze and W.J. Foote , "Adjustable instrumentation

bench for physical laboratories," The Review of Scientific

Instruments, Vol. 33, No. 12, 1467, Dec. 1962.

[14] R.W. Beatty, "Cascade connected attenuator," Proc. IRE,

Vol. 38, No. 10, October 1950.

[15] G.E. Schafer and A.Y. Rumfelt, "Mismatch errors in

cascade-connected variable attenuators," IRE Trans.

MTT 7, 447-453, October 1959.

[16] W. Larson, "In-line waveguide attenuator," IEEE Trans.

MTT (correspondence), Vol. MTT-12, 367-368, May 1964.

24
^mNBS-IHA 11-71)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-647

2. Gov't Accession No.

4. TITLE AND SUBTITLE

Microwave Attenuation Measurement System

(Series Substitution)

7. AUTHOR(S)

Wilbur Larson and Eugene Campbell

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, Boulder Labs , DEPARTMENT OF COMMERCE

Boulder, CO 80302

12. Sponsoring Organization Name and Address

Same as #9.

15. SUPPLEMENTARY NOTES

3. Recipient's Accession No.

5. Publication Date February 1974

6. Performing Organization Code

8. Performing Organization

10. Project/Task/' Work Unit No. 2724460

11. Contract/Grant No.

13. Type of Report & Period Coveted

14. Sponsoring Agency Code

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) A dual detection microwave bridge circuit has been incorporated in a series substitution system for the measurement of microwave attenuation devices . The use of an

optical rotary-vane attenuator in the system yields practical resolution and

stability of 0.00005 dB from zero to 30 dB. The dual detection system

has several favorable features; (1) it employs a single microwave source which reduces

cost, (2) measurements are obtained without power stabilization of the microwave signal

source, and (3) this waveguide configuration enables measurements of attenuation devices

at any length with minimum of effort and movement of waveguide components

.

The system configuration is convenient for both attenuation difference , and insertion loss

measurements from zero to 70 dB over the WR90 waveguide band of 8.2 to 12.4 GHz.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Attenuation; measurement; rotary-vane attenuator; series substitution

,

18. AVAILABILITY STATEMENT

1^1 UNLIMITED. 3 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

28

22. Price

$ . 35

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