lilat

PB 161579

^o.78

OBLIQUE INCIDENCE RECEIVING ANTENNA ARRAY

FOR

A RELATIVE IONOSPHERIC OPACITY METER

BY

A. C. WILSON

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in PubUc Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing materials, devices,

and structures; advisory services to government agencies on scientific and technical problems; in- vention and development of devices to serve special needs of the Government; and the development

of standard practices, codes, and specifications. The work includes basic and applied research,

development, engineering, instriunentation, testing, evaluation, calibration services, and various

consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the

Bureau's unique competence is required. The scope of activities is suggested by the listing of

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's work take the form of either actual equipment and devices or published papers. These papers appear either in the Bureau's own series of publications or in the journals

of professional and scientific societies. The Bureau itself publishes three periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Scries,

}Iandbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's publications can be found in NBS Circular 460, Publications of the

National Bureau of Standards ($1.25) and its Supplement ($1.50), available from tlic Superintendent

of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS

No. 78

OBLIQUE INCIDENCE RECEIVING ANTENNA ARRAY FOR A

RELATIVE IONOSPHERIC OPACITY METER

A. C. Wilson

November, I960

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

DISTRIBUTED BY

UNITED STATES DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WASHINGTON 25, D. C.

Price $ . 50

CONTENTS

PAGE

Abstract ------------------ 1

1. INTRODUCTION 1

2. EXPERIMENTAL PROCEDURE 3

3. RESULTS 4

4. CONCLUSIONS 6

5. ACKNOWLEDGMENT -- 6

6. REFERENCES -7

OBLIQUE INCIDENCE RECEIVING ANTENNA ARRAY FOR A

RELATIVE IONOSPHERIC OPACITY METER

by

A. C. Wilson

Abstract

Experimental measurements incidental to the design of an antenna for a relative ionospheric opacitymeter (RIO Meter) are described.

The frequency of operation is 50 Mc. The antenna

requirements are that the main lobe of the antenna is

directed at 23* above the horizon, the half-power beamwidth in the vertical plane does not exceed 10°, the

minimum front-to-back ratio is at least 13 decibels, and

the side-lobe levels are at least 10 decibels below the

naaximum response in both the E- and H-planes. Since

the antenna is for use in Alaska, it is to be of sinnple

design and physically able to withstand any anticipated

wind and ice loads.

The final antenna design is an array of three stacked

horizontal dipoles with two optimally spaced reflectors

behind each dipole to obtain the required directivity.

The narrow main lobe of the antenna directed at an angle

of 23** above the horizon is obtained by properly spaced

and phased dipoles above the groiind. The half-power

beamwidth in the vertical plane is computed to be 7-1/4*,

The front-to-back ratio over the rear 180* sector is not

less than 20 decibels, and the half-power beamwidth in

the E-plane is 74*.

Two complete receiving antenna arrays w^ere constructed, adjusted, and tested. These antennas were

installed in Alaska w^here they are now in use by an

auroral transmission loss project.

1. INTRODUCTION

In connection w^ith an antenna requirement for the Auroral

Transmission Loss Project of the Radio Propagation Physics Division of the National Bureau of Standards Central Radio Propagation

Laboratory, a series of measurements were carried out to obtain a

suitable antenna design to meet the specific requirements. The
2

antenna is to be used as a receiving antenna at 50 Mc for a relative

ionospheric opacity meter used for cosmic noise absorption measure1 2

ments. ' The polarization is horizontal.

The requirements of the antenna are that the main lobe of the

antenna be 23' above the horizon, the half-power beamwidth in the

vertical plane not over 10", the front-to-back ratio at least 13 decibels, and the side-lobe levels at least 10 decibels or more below the

maximum response in both the E- and H-plane. The gain of the antenna

is of secondary importance. The antennas are for use in Alaska, so

the physical design requirements are that they be as simple a design

as possible and able to w^ithstand any anticipated w^ind and ice loads.

It is also believed to be desirable to complete all impedance adjustments and measurements prior to installation in Alaska because of

the difficult field working conditions and temperatures.

Computations were carried out to obtain the radiation pattern

for an array of three dipoles stacked one above the other. Figure 1 presents the array design and Figure 2 presents the computed radiation

pattern in the vertical plane. A main lobe at an elevation angle of 23'

above the horizon is obtained by using a height of 0, 64X for the low^est

dipole and odd multiples of 0. 64X for the other two dipoles. The center

dipole is 180' out of phase with respect to the top and bottom dipoles.

Other antenna arrays w^ere considered for this application, but the

stacked array of three dipoles was chosen as being the most suitable,

both practically and economically.

These computations provided an array design which would

fulfil the requirements for the desired 23' angle of arrival and the

directivity and side -lobe levels in the vertical plane. The remaining

problem then was to design an antenna utilizing dipoles with reflectors

in place of the dipole used in the computations, which would give the

desired directivity in the E-plane and still meet the physical requirements previously stated.
3

A dipole with a single reflector, with the reflector length optimized for maximum gain, has only an approximate Sg-db. front-toback ratio. A more complex antenna, such as a Yagi, has directivity

characteristics not suitable for this application. It was necessary

then to obtain a design for a reflector of simpler construction having

better reflecting properties than a single reflector.

A series of measurements w^ere carried out to obtain the design

for a suitable antenna. The results of these measurements and the

design configuration and parameters are described in this report.

Z. EXPERIMENTAL PROCEDURE

For the purpose of determining the best reflector design, a

half-wavelength folded dipole was constructed for a measuring frequency of 400 Mc (a scaling factor of 8). The dipole w^as then mounted

on an insulated supporting structure approximately three wavelengths

above the ground at the NBS Antenna Range on Table Mesa near Boulder, Colorado. The dipole with its reflector was used for receiving.

The target transmitter -was approximately 1000 w^avelengths away.

A series of measurements was carried out using different receiving antenna reflector configurations, and repeatedly measuring

the radiation patterns in the E- and H- plane in order to determine the

front-to-back ratio and side-lobe levels. A 20-db front-to-back ratio

was set as the design goal instead of the minimuin 13-db requirementc

The first series of measurements was carried out to determine

the best front-to-back ratio "which could be obtained by the use of a

single reflector behind the dipole. Radiation patterns were recorded

for different combinations of reflector spacing from the dipole and reflector lengths. The highest front-to-back ratio was measured to be

approximately 11 decibels.

Further measurements consisted of considerable experimentation with different reflector configurations and reflector lengths. The

reflector spacing from the dipole was then set at 0, 2\, which seemed

to be generally optimum. The reflectors were then alw^ays kept in the

same vertical plane for simplicity of design. The experimentation
4

then settled down to be a systematic check of the effect of the number

of reflectors, the vertical spacing, and the length combinations.

3. RESULTS

The experimental measurements which w^ere carried out

suggested a configuration which would give the required results of a

20-db front-to-back ratio and side-lobe levels at least 20 decibels

down from maximum. The design parameters are presented in Figure 3. The resultant E- and H-plane radiation patterns are shown in

Figure 4. An additional 0. 5 decibel was added to the front-to-back

ratio by the use of two additional reflectors of the same length, one

spaced 0. 4 wavelength above the top reflector and one spaced 0. 4

wavelength below the bottom reflector. However, the 0. 5 decibel

gained is considered to be worth the additional two reflectors required.

An additional increase in the front-to-back ratio was obtained with

some of the reflector configurations studied, but the side-lobe levels

w^ere too high.

It was found that, when an additional reflector was installed

directly behind the dipole, between the tw^o reflectors, the radiation

patterns deteriorated rather than improved. It was also found that,

when an aluminum sheet reflector was installed between the two reflectors, the radiation patterns deteriorated considerably.

Measurements w^ere made to compare the front-to-back

ratio obtained by use of the two-reflector configuration shown in

Figure 3 with that w^hich can be obtained by the use of an aluminum

sheet reflector having a dimension of one w^avelength on each side

and spaced the same 0. 2\ behind the dipole. The front-to-back ratio

obtained by the use of the solid sheet reflector is only 16 decibels.

This would indicate that a reflector sheet or grid should w^ell exceed

one w^avelength in order to provide maximum suppression of signals

to the rear.

The gain of the dipole w^ith the two reflectors was not

measured. How^ever, during the measurements, a gain of at least

5 decibels over a half-wave dipole at the same height was indicated.
5

Of considerable iiTiportance is the frequency bandwidth of the

dipole with two reflector elements. While the experimental measurements described did not have the frequency sensitivity as an important

item, some measurements were made to determine the deterioration

of the pattern (loss of front-to-back ratio and increase in the levels

of the side lobes). If the design parameters are held constant and

only the frequency changed, a ±2% change in frequency caused a maxi - mum loss of 4 decibels in the front-to-back ratio. However, by either

lengthening or shortening the length of each reflector and not changing

the other dimensions, a ± 10% change in frequency causes a maximum

loss of 4 decibels in the front-to-back ratio.

In order to make the model antenna more compatible with the

full-scale antenna to be constructed using parameters based on the

model measurements, a scaled model antenna was constructed w^ith a

l"-wide (0. 0339X) vertical metal strap betw^een the tw^o reflectors and

a l"-wide (0. 339X) horizontal raember to support the folded dipole.

Measurements w^ere made which indicated a required increase in the

overall reflector lengths from 0. 517\ to 0. 529X. in order to obtain the

same exact patterns as obtained previously w^ithout additional straps

or supporting members.

A scaled model of one antenna array, consisting of the three

dipoles and their reflectors, has been constructed for measuring the

radiation pattern in the vertical plane at a frequency of 1000 Mc. It

is anticipated that these measurements will be raade w^hen a planned

antenna range is constructed which will provide a facility for the highangle-of-arrival vertical pattern measurements. Figure 5 presents

the conaputed pattern in the vertical plane for the three stacked horizontal dipole units.

Dipole units for two complete antenna arrays w^ere constructed

to dimensions based on the measurements on the scaled model antennas.

The dipole reflectors w^ere mounted on their supporting members, and

the impedance of each dipole unit w^as individually adjusted to be 52

ohms. The 180° phase shift required for the center dipole unit in the

array w^as obtained by the method of balun and coaxial cable connection. Each set of dipoles and reflectors w^as then movinted at the
6

required heights on a tower on Table Mesa for the final impedance

measurements. Each dipole was connected by equal lengths of

RG-17B/U coaxial cable to a junction box. The output impedance of

the junction box (approximately 17 ohms) was matched to a 52-ohm

coaxial lead-in cable by means of a shorted stub and impedancematching cable length.

Figures 6 and 7 show different views of the dipole units. The

construction material is entirely aluminum alloy. The method of construction of the dipole units is such that they can be conveniently

packed for shipment, and assembled and installed with a minimum

amount of field work. After the final impedance measurennents and

adjustments, the dipole units were coded for ease of reassembly and

dismantled and shipped to Alaska where they have been installed and are

in use for the project.

4. CONCLUSIONS

The antenna array, consisting of the dipole units with the two

optimally spaced reflectors behind each dipole, provides a simple,

durable and practical antenna type meeting the specific requirements

previously described for this antenna. The 20-db side-lobe level and

20-db front-to-back ratio make the antenna practical for uses where

these electrical characteristics are more important than gain. The

dipole unit may be conveniently used as a component in an antenna

array. The physical design configuration is such that it can be motinted on the face of a pole or steel tower. The compact size reduces

the w^ind and ice load areas for w^eather extremes.

Other uses for this antenna design would be single -channel

high-band TV reception and communication antennas w^here only a

single frequency of transmission is used and the bandw^idth is sufficient. While the antenna, as designed, is for receiving purposes only,

it is also usable as a transmitting antenna type.

5. ACKNOWLEDGMENT

The experimental measurements were carried out w^ith the

assistance of Mr. W. L.Martin, the final impedance measurements and

adjustments with the additional assistance of Mr. W. B. Hogwood.
6. REFERENCES

1. C. G. Little and H. Leinbach, The riometer - a device for the continuous measurement of ionospheric absorption, Proc. I. R. E. , vol. 47, pp 315 - 320, Feb. 1959.

2. C. G. Little and H. Leinbach, Some measurements of high-latitude

ionospheric absorption using extraterrestrial radio waves, Proc.

I.R. E. , vol. 46, pp 334-348, Jan. 1958.

lO

II

l>5 -P•H

?^

cd Ho

ft

-pa

(1) fH ^ s o

-p ^ a <] 03 < •H o o ra f^ •H H •H 'd EH +

•H > m CM• r< , a -4--d- •H VX) vo

CQ • • ^ O o 1

11 II

a

X

H

XlM + ^

•H

CQ ^—

0)

HH

h^

pi

UnHW

<;^ o

CO ^ OH

<;onhOUQ

CO

QWWhO

>^

<^<QW

O

W

Q§n

COWP

U

. 1 t-H l^ U

Q

M h-i /v!

8338930 'iVAId^V 30 319NV

COO

H

U

w

w

O

H

H

W

O

ft

(U

14

;:! GO H

U. U

CO

<;w

Eho

COon

CO

iz; an

COW

Q

(U

US •H

ol-l CO<

W

H

o

w

Q

I W

COO

H

O

W

W

o

Kg^^r—

f

coW

^n

^5

<5

PL. ol-H

Q

51381330 '3SN0dS3a a3znvwyoN

lO

<

U CO

w

o

^3

S33d93a 'iVAiyyV jo 319NV

Figure 6

A VIEW OF THE THREE DIPOLE UNITS MOUNTED ON A TOWER

FOR IMPEDANCE MEASUREMENTS AND ADJUSTMENTS

u

w

o

CO

<^ W

COIDQ

Q

<

O

Q

W

H

O

co^

w w

^S

^<;

w Q

H ft

1—

I

tS. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary

ITIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

ilder, Colo., is suggested in the following listing of the divisions and sections engaged in technical work. In

leral, each section carries out specialized research, development, and engineering in the field indicated by its A brief description of the activities, and of the resultant publications, appears on the inside of the front cover. k.SHINGTON, D.C. "electricity. Resistance and Reactance. Electrochemistry. Electrical Insti-uments. Magnetic Measurements.

Dielectrics. METROLOGY. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering

Metrology. Mass and Scale. Voiumetry and Densimetry.

HEAT. Temperature Physics. Heat Measurements, Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Research. Equation of State. Statistical Physics. Molecular Spectroscopy.

RADIATION PHYSICS. X-Ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological

Equipment. Nucleonic Instrumentation. Neutron Physics.

CHEMISTRY. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances. MECHANICS. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Combustion Controls. ORGANIC AND FIBROUS MATERIALS. Rubber. Textiles. Paper. Leather. Testing and Specifications.

Polymer Sti'ucture. Plastics. Dental Research.

METALLURGY. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics.

MINERAL PRODUCTS. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and

Microstructux-e. BUILDING RESEARCH. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. APPLIED MATHEMATICS. Numerical Analysis. Computation. Statistical Engineering. Mathematical

Physics.

DATA PROCESSING SYSTEMS. Components and Techniques. Digital Circuitry. Digital Systems. Analog

Systems. Applications Engineering.

ATOMIC PHYSICS. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics.

Atomic Physics.

INSTRUMENTATION. Engineering- Electronics. Electron Devices. Electronic Instrumentation. Mechanical

Instruments. Basic Instrumentation.

Office of Weights and Measures. BOULDER, COLO.

CRYOGENIC ENGINEERING. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas

Liquefaction.

IONOSPHERE RESEARCH AND PROPAGATION. Low Frequency and Very Low Frequency Research. Ion- osphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. RADIO PROPAGATION ENGINEERING. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

RADIO STANDARDS. High frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave

Materials. Atomic Frequency and Time Standards. Electronic Calibration Center. Millimeter-Wave Research.

Microwave Circuit Standards.

RADIO SYSTEMS. High Frequency and Very High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Space Telecommunications.

UPPER ATMOSPHERE AND SPACE PHYSICS. Upper Atmosphere and Plasma Physics. Ionosphere and

Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

usco»«-Nes.8L
-^.-.itie:i%iss

NBS