(NASA-CR-120581) REDSHIFT ANTENNA PROJECT N75-14965

Final Technical Report (Ball Bros. Research

Corp.) 44 p HC $3.75 CSCL 09E

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FINAL TECHNICAL REPORT

For The

REDSHIFT ANTENNA PROJECT

Project 3260

Contract NAS8-29504

DRL No. 424, Line Item 2

20 November 1974

Submitted To

NASA/MSFC

BALL BROTHERS RESEARCH CORPORATIONBoulder, Colorado

Table of Contents

Section Page

A General Discussion of Antenna Design 2

B Phase/Temperature Measurements and Analysis 11

C Temperature Survivability Test 17

D Conclusions 20

A. General Discussion of Antenna Design

The program was initiated with the layout of the center frequency

2203.1 MHz antenna. The 4 to 1 taped layout was photograph re-

duced and a single antenna section (half.an antenna) was etched.

Initial impedance and frequency mismatches were corrected, first

by adding copper tape to the transform lines and trimming the

microstrip patches. The artwork was subsequently revised and

a complete 2203.1 antenna was etched. Impedance plots of each

of the two halves are shown in Figs. 1 and 2. The VSWR of the

assembled antenna was good as shown in Fig. 3.

The antenna was mounted on the ground plane mock-up used during

the proposal and a 2 dB e = 900 roll pattern was obtained (Fig. 4).

Additional effort was required to smooth out the bulges at section

joints and center feed points such that the required 3 dB varia-

tion at the other aspect angles could be obtained. An aspect

pattern of this initial antenna (Fig. 5) indicated that the gains

would be acceptable.

Using the 2203.1 MHz layout as a reference, initial layouts were

made for the remaining two frequencies 2117.7 and 2299.7 MHz, and

single sections fabricated. After encouraging VSWR results at

2117.7 and 2299.7 MHz were obtained, the artwork for the three

frequencies were combined into a single antenna system. Several

configurations were tested to obtain the best combination of gain,

phase and isolation performance. The configuration shown in

Fig. 6 was selected. BBRC drawing 46296 defines this configuration

and its associated interface requirements in detail.

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In this configuration the worst isolation is approximately 29 dB

between the 2203.1 and 2117.7 MHz terminals. The isolation test

results are shown in Fig. 7. It should be noted that the tested

configurations where the antenna/feedline positions of one of

the antennas was reversed the isolation between the antenna was

at some points as low as -20 dB.

The configuration of Fig. 6 met the gain and phase specification

for all frequencies, but the roll amplitude variation failed to

meet specifications at certain angles. Tests were conducted to

determine the sensitivity of the roll variation to the total test

configuration. Figure 8 shows the roll amplitude variation

measured as a result of the following modifications:

Configuration

Effect of -- No. Description

1. Adjacent Antennas la 3 antennas on standardground plane. Model 4-8

lb Tested 2203 MHz. Other2 antennas taped over.

2. Bumper slots in G.P. 2a Same as (lb)

2b Taped over slots withaluminum tape

3. Open aft end of G.P. 3a Same as (2b)

3b Ground plane filled withabsorber material

4. Wire mesh relativeto solid ground plane 4a Same as (3b)

4b Wire mesh covered withaluminum foil

The only significant variation occurred between la and lb when the

antennas adjacent to the center 2203.1 MHz antenna were covered

with aluminum tape.

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The measurements of Fig. 8 were made because the roll amplitude

patterns seemed to be punctuated at the feed point location and

at the seams between the two antenna sections. After various

possible causes such as antenna soundness and seam dimensions were

investigated, transformer lines were placed on the feed lines

which fed the area between the feed point location and the seam

(Fig. 9). It was thought that the proximity of the feed lines had

caused a slight unbalance of the power to this area of the antenna.

The transformers would increase the power and balance the roll

amplitude. The assumption proved to be correct and was incor-

porated into the final network.

Figures 10 and 11 show the fabrication of the deliverable antenna

S/N 001 antenna. S/N 002 was fabricated in a like manner. The

final measurement data on these antennas was sent with the delivered

units. The performance of the delivered antennas was quite satis-

factory and well within specifications.

B. Phase/Temperature Measurements and Analysis

During the development phase and amplitude measurements were taken

over the temperature range from 200 C to -10°C. Results showed

that the relative phase variation in each conical cut were within

the specified 450 limitation, and that the relative phase varia-

tion changes very little with temperature. However, the absolute

phase changed significantly over the 300 temperature range. As

expected, the magnitude of the phase variation is directly pro-

portional to the amplitude variation. The absolute phase varia-

tion was magnified somewhat by the fact that the test chamber

rotary joint and test cable also experienced some cooling. In

addition, the antenna surface probably had some condensation build-up

during the test. The condensation would affect the radiated phase.

Figure 12 illustrates the temperature test chamber. Since the

thermal enclosure had no window, we could not observe how much

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Fig. 12 Phase/Amplitude 300 Temperature Test Chamber

16

condensation was present during the test.

In a related effort, tests were made for the analysis effort to

predict the total system phase change from -100 0 C to 125 0 C.

Separate tests were performed to measure the phase change in the

power dividers, cables and connectors, feed networks on the PC

board and a radiating patch by itself. During the testing of the

section of the radiating antenna, as in the full antenna tests,

some condensation formed on the antenna surface at temperatures

close to 00 C. Coincidentally, the rate of phase change increased

significantly around the O'C range. The rate of change of phase

remained quite linear over the rest of the temperature range. The

system phase analysis report titled "Analysis of the Phase Varia-

tion Resulting from Temperature Variation of the Redshift Antenna",

is attached as an addendum to this report.

C. Temperature Survivability Test

Temperature survivability test were performed on a development

antenna and the results were presented at the CDR. There was

essentially no change in VSWR between the pre and post temperature

tests. However, the roll pattern amplitude variation at one

conical cut (0=1350) at 2117 MHz increased from a 3.25 dB variation

to 4.5 dB from the pre to post temperature tests. This antenna

was not mounted in the flight configuration. This situation was

discussed at the CDR and it was decided to rerun the test.

Figures 13 and 14 illustrate the variation of the roll patterns

and VSWR of the antenna SN 001 before and after the repeat of the

temperature survival test (-80 0 C to +50 0 C). The VSWR showed a

minor shifting of the impedance curve. The roll pattern varia-

tion versus aspect angle seemed to become smoother. The temper-

ature.cycling seemed to set the antenna to the curvature of the

model and reduce the peak variation of the roll pattern variation.

17

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D. Conclusions

The majdr items which affected the successful completion of this

antenna within specification can be listed as follows:

* Accurate and symmetrical feedline lengths such that

the antenna is fed with very uniform and equal phase.

a Roundness. The roll amplitude variation patterns are

affected by the roundness of the ground plane and

the conforming of the antenna to the ground plane.

* Isolation. Best isolation is dependent upon the

radiating elements and separation. Therefore, the

feedline - radiator, feedline - radiation etc.,

arrangement maximizes the isolation.

o The proximity of feedlines and weak coupling be-

tween feedlines may cause an unbalancing of the

amplitude around the antenna. This unbalancing

may be compensated for by transforming sections

which increase the power to areas of the roll

pattern which show reduced power.

Additionally, the phase variation of the antenna system with tem-

perature is quite linear. The phase variation of the microstrip

feedlines tended to decrease in slope at temperatures above 500 C.

Since the microstrip lines are a primary phase determining factor

in the antenna system, the slope of the phase variation of the

antenna system also tends to decrease at the temperatures above

500 C. A phase step occurred in the phase analysis measurements

for the radiating antenna between the temperatures of +100 C and

-100 C. This step was caused by the condensation of water on the

antenna surface. This condition should not occur in a flight

environment.

20

ADDENDUM 1

ANALYSIS OF THE PHASE VARIATION RESULTING FROMTEMPERATURE VARIATION OF THE REDSHIFT ANTENNA

A-i

ANALYSIS OF THEPHASE VARIATION RESULTING FROM

TEMPERATURE VARIATIONOF THE REDSHIFT ANTENNA

Project 3260

18 June 1974

Contract NAS8-29504

Submitted to

NASA/MSFC

By

BALL BROTHERS RESEARCH CORPORATIONBOULDER, COLORADO

PHASE/TEMPERATURE ANALYSIS OF THE REDSHIFT ANTENNA

1.0 INTRODUCTION

The phase/temperature analysis of the Redshift Antenna consists

of actual measurements of individual components of the antenna.

The phase/temperature measurements were separated into four (4)

separate tests:

o A0/AT of coaxial cables

* A /AT of coaxial cables and power divider

* A4/AT of microstrip transmission line

e At/AT of microstrip antenna segment

These measurements are backed by computation where the pertinent

information is available. The total value of phase change versus

temperature is calculated by summation of the separate values.

The effects of the temperature on the radiating cavity were

measured by varying the temprature of an antenna segment and

recording the transmitted phase. The major problem in the measure-

ment of the radiating cavity is the phase change caused by con-

densation on the face of the antenna.

2.0 TEST RESULTS

2.1 A6/AT OF COAXIAL CABLES

The test setup for coax cables for both the high and low tempera-

ture ranges is shown in Fig. 1. During the high temperature test

the coaxial cables were placed in an enclosed oven and the cable

temperature monitored by a thermocouple. The low temperature

range phase variation was measured by placing the coaxial cable

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Fig. 1 Coaxial Cable A/AT Test Setup for Highand Low Temperature Ranges

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length above an insulated receptacle of liquid nitrogen. The

phase variation was monitored as the temperature decreased.

However, since the downward temperature change was quite rapid,

the cables were placed in an insulated box and the phase/tempera-

ture monitored as the temperature rose. This procedure allowed

more data points to be obtained.

Figure 2 shows the recorded phase variation of the 34-inch length

of coaxial cable. Between plus and minus 400 C the slope of the

phase change with temperature was the most rapid-approximately

10 degrees phase per 80 degrees centigrade for 34-inches of coax

(.0037 0 '/C/inch). The slope of the phase change was much less

for temperature extremes beyond these temperatures. Figure 2

also relates the calculated cable phase change using the manu-

facturers representative numbers of -15 ppm/oC for the high

temperature range and -55 ppm/oC in the low temperature range to

-400 C. It is important to note that both curves demonstrate a

similar change in slope.

2.2 A4/AT OF COAXIAL CABLES AND POWER DIVIDERS

Figure 3 illustrates the test setup for the measurement of the

phase/temperature variation of the coaxial cables and power

divider. The test procedure was similar to that of the coaxial

cable except for the addition of the power divider and a length

of cable with a matched load. Energy was fed into the power

divider in a fashion similar to the flight operation. The

additional coaxial cable and matched load provided a matched

load to the unused power divider port. During the temperature

test the coaxial cable allowed the matched load to be placed

outside of the temperature variation.

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Figure 4 shows the results of the phase/temperature measurements.

The results are quite similar to those obtained in Section 2.1

for the coaxial cables alone. This result is quite logical since

the same coax cable was used and the only difference is the

additional small length of the power divider. Figure 5, the

difference between the results in Figs. 4 and 2 is the change

due to the power divider alone.

2.3 A /AR OF MICROSTRIP TRANSMISSION LINE

The test setup for the phase/temperature testing of the micro-

strip transmission line is the same as the coaxial cable in

Fig. 1. The physical length of the microstrip transmission line

was nine inches. This line was an actual Redshift transmission

line printed on the pcb with a connector attached at each end.

Figure 6 shows the phase variation with temperature. The

phase/temperature variation is somewhat larger than the coax cable

.0098/°C/inch versus .0037/oC/inch for the plus 400 C to minus

400 C range. However, similar to the coaxial cable, the slope

of the phase/temperature decreases at the temperature extremes.

At the high temperature extreme (+80 - +125 0 C) the phase change

reversed direction.

2.4 A4/AT OF MICROSTRIP ANTENNA SEGMENT

Figure 7 illustrates the test setup for the phase/temperature

testing of a section of the antenna. The antenna and receiving

horn were surrounded with absorber to assure that the phase was

not affected by exterior reflections. The antenna was mounted

on an aluminum plate which acted as a heat sink to provide a

slow transition of temperature of the antenna. The temperature

7

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..... ... IT _L -I-LL : - jil -ill' 4- 11 H l'

i +H+H+H-H±Lit-- 4111 T-TIHmHwlI - 4+HIT 1"!

Fig. 5 AO/AT of Power Divider (Fig. 4 minus Fig. 2)

10 X 10 TO 1/2 ]Ncm 46 1323K-E 7 X 1 0 INCHES MADE IN U.S.A.

KEUFFEL & ESSER CO.

+Hi ±H±

±H± ±i± ±H± 4_1

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r4- 4 -FF -- J#

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fig

Tam a## 44+44 - -H 1 ++"44-H+[+f++jt +H-l ISMS "Tan

a

+H±

4[+

_4TFFFl+t'W4A4 "m+H4+ +H+

++H++H+-I AL

gR # I TM

W HHH! -

.................

Fig. 6 Measured A /AT of 9-inch Acrostrip Line

SA /75.e A

A I A1

C, 414 c

4eA Or ¢ooi "

Fig. 7 Test Setup for Measurement of Ap/AT of Antenna Segment

11

thermocouple was placed on the antenna front surface. The high

temperature range was measured by applying a heat gun to the

surface of the aluminum plate. The antenna. was cooled by placing

the antenna over the surface of a receptable of liquid nitrogen.

A prime difficulty in the measurement of the phase/temperature

variation of the antenna was a step variation of phase which

occurred as the antenna was cooled. As the temperature was lowered

from 24 to 100 C, a dew formed on the surface of the antenna and

a rapid change in phase occurred. The test continued down to

-100 0C, and the phase/temperature measurements were repeated

as the antenna was allowed to return to ambient room temperature..

The final phase at 240 C did not agree with the initial phase

measurements. The dew was removed from the surface of the antenna

with a soft paper towel and the phase changed by 190 returning to

the initial phase measurement. Attempts to set the antennain the

fumes of the liquid nitrogen to prevent condensation were not

successful. Figure 8 shows the phase versus temperature variation

with the condensation. The slope of the phase/temperature curves

are basically the same for the high and low temperature ranges

outside of the region where the frost or dew occurred on the antenna.

Figure 9 is a phase/temperature curve of Fig. 8 with the 190 phase

step removed. In the absence of an air/water atmosphere it would

be correct to. use the phase/temperature curve of Fig. 9 for the

system phase calculations.

3.0 CALCULATED SYSTEM A /AT

The calculated system A4/AT is a summation of the phase change

with temperature of the individual components. The At/AT of the

antenna (Fig. 9) and the power divider (Fig. 5) are representative

of the actual components. The Ac/AT' for the coaxial cable and

the microstrip transmission line were calculated from the 34-inch

and 9-inch length samples tested.

12

0, X 10 TO 1/2 INCH 46 1323WE1 X 10 INCHES AlDE IN U.S.A.

KEILIFFEL & ESSER CO.

rr

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_p

4-H+4+-_+J4- F -iFp_ i J ## :44

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---- 4j--H

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10 X 10 TO 1/2 INcH 46 13237 X 10 INCHES IiIADE IN U.S.A.

KEUFFEL IN ESSER CO,

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+

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44+1+j+f-4#_ 41114 1 1 1 11

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Irld" ------

H-H+ -+ ff ±H±-H±E

-- w- HHH!-F ttt14 7 4-FA

_++I-F +H+ +±

# ........... +H+±

Fig. 9 Modified A /AT of Antenna Segment

Figure 10 shows the Ac/AT of the 20.5 inch (longest) length coaxial

cable. The Redshift microstrip transmission line length from the

coaxial terminal to the point where the antenna segment was tested

is 17.95 inch and the extrapolated Aq/AT is shown in Fig. 11.

Figure 12 is the summation of Figs. 5, 9, 10 and 11 which is the

calculated system At/AT with the modified antenna segment AA/AT.

The Ap/AT slope is approximately 0.286 0 /°C from -100 0 C to

+100 C and approximately 0.6250 /0 C from +100 C to +500 C. The phase

tends to be almost constant for the temperature variation above

+500 C. Although Section 2.4 explained the reason for the modified

antenna A /AT curve, the system Ac/AT with the unmodified curve

is shown in Fig. 13. Figure 14 relates the modified Ap/AT with

17-inch cables.

4.0 COMPARISON WITH FULL-MODEL TESTS

The phase changes predicted above appear to correlate quite well

with the test data obtained by testing the complete antenna over

a 300 C range.

The enclosure used in the full-model phase tests was designed

so that no moisture would condense on the enclosure. However,

immediately following the temperature tests on the 2203 MHz

frequency, it was noted that considerable condensation existed

on the antenna itself. The actual amount of condensation on

the antenna during test could not be observed because of the

construction of the thermal enclosure. The phase meter was

zeroed prior to taking each roll pattern, and the average phase

difference between 200 C and -10 0 C for each of the three pairs

of roll patterns taken at 2203 MHz was 360 .

15

_, 10 X 10 TO 1/2 INCH 46 1,323

W E 7 X 10 INCHES MADE IN U.S.A.

KEUFFEL &ESSER CO.

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10 X 10 TO 1/2 INcH 46 1323W E 7 X 10 INCHES MADE IN U, S.A.

KEUFFEL & ESSER CO.

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Fig. 11 Extrapolated A /AT of 17.95-inch Alcrostrip Transmission Line

10 X 10 T0 1/2 INCH 46 1323W E 7 X 10 INCHES M DE IN Ei. A.

KEUFFEL & ESSER CO.

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AH9H

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46 --- ---- --- ... fitJ ...... ...... . .......

FF L

Him - 7 -4 U

Fig. 12 System A /AT with Modified Antenna Segment A /LT for 20.5-inch coaxial Cable Lenth

'0 X i0 TO 1/2 INCH 46 1323"7 X 10 INCHES MADC IN U.S.A.

KEUFFEL & ESSER CO.

I I-

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10 X 10 TO 1/2 INCH 46 13237 X 10 INCHES -DE 114 U. S. A.

KEUFFEL& ESSER CO.

H +

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HH +H+L_ 4A

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+ ii± 4+Fi+4+H++ f- -4Fft4+H+

;+H+hH+w+-. .444R,

Fig. 14 System W AT with Modified Antenna -Segment A /LT for 17-inch Coaxial Cable Length

The test chamber was purged for a longer time prior to testing

the 2117 MHz antenna in an effort to minimize the condensation.

Again the actual condensation could not be observed, but the

average phase change between temperatures for 2117 MHz was

14.30

Correspondingly, if we estimate the phase change from 200 C to

-100 C on Fig. 12 (no condensation) and Fig. 13 (with condensa-

tion) we get 8.5 and 21.00 4 respectively.

It should be noted that during the phase test the cable length

between the crystal detector and the antenna and to some extent

the crystal itself were cooled. The inclusion of their addi-

tional AW/AT due to the feed cable would provide closer agreement

between the phase test A4/AT and the A /AT predicted by analysis.

21