Bimonthly Report No. 4 July 2, 193 to Septembr 2, 1963.549-4-P STUDY AND INVESTIGATION OF A UHF-VHF ANTENNA by A..T. Adams J. E. Herman S. B. Rhee Approved by \k / y o? L-. I/ I John A. M. Lyon COOLEY ELECTRONICS LABORATORY Department of Electrical Engineering The University of Michigan Ann Arbor 5547-4-P = RL-2128 United States Air Force Air Force Systems Command Aeronautical Systems Division Contract No. AF 33(657)-10607 Wright-Patterson Air Force Base, Ohio September 1963

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tNT o0 ILtTWaAfo ABWTRACT 1. REPORTS, TRAVEL, VISITORS 2. FACTUAL DATA 2. 1 Rectangular Cavity Slot Antennaa 2.2 Equiangular Spiral Antenna 2.3 Log Conical Spiral Antenna 3. FUTURE EFFORT 4. SUMMARY AND CONCLUSIONS

' -,1... *.:;,I0.-, I C'#t;i. X, _LJr gctdlCbl# TlUt i — Nn amhn 1 ure 3 Figure 4 Figure Figure Figure Figure Figure Figure Figure Figure 5(a) 5(b) 6 7 8 9(a) 9(b) 10 Comparison of rectangular slot antennas. VSWR for air filled rectanular slot antenna. V8WR for ferrite powder filled rectangular slot antenaL VSWR for solid ferrite filled rectangular slot antenna. VSWR for dielectric loaded rectangular slot antenna. Equiangular spiral. Construction showing feed and loading. VSWR for fully-loaded spiral. V8WR for single-filar loading. VSWR for loaded spiral with no cavity. Models of log conical antennas. Cavity-back log conical antenna. VSWR for log conical spiral antenna. Page 3 4 5 6 7 8 9 10 11 12 14 15 17 iv

ADITRACT Construction of final models of the loaded rectangular cavity slot antennas was completed, final tests were conducted, and delivery made. Experimental results show the lower cutoff frequency of the equiangular cavity-backed spiral may be reduced by a iactor of 2 with ferrite loading. Broad-banding possibilities are indicated. Preliminary results on the cavity-backed log conical spiral indicate the antenna resonant frequency can be reduced by ferrite loading by a factor of 2. v

1 - 1. REPORT TMYVZL, AND VIITOMS On Jtf4 9, 10 ad 11, 1903, Dr. John A. M. Lyon attended the 1963 Interatlol Syotsuam on Space Telecommunications at Boulder Colorado. During tI Syposium he discussed with Mr. Edwin M. Turner, Chief Ai- Section, ARDC, WPAFB, the use of ferrite antennas for space vehicles. Al-d-io to the future efforts on this project were outlined. uring this period no reports were issued, and no one visited the project. *

-2 - 2. FACTUAL PTA ~ { Hie.^Mul C~avity Slot Antennas Comtruction of final models of the solid ferrite and solid dielectric -mus was completed. Final models of the air loaded slot, ferrite powder, loaded slot, and solid ferrite loaded slot were delivered. The dielectric loaded slot is scheduled for delivery by October 1, 1963. Table 1 shows the relative characteristics of the four antennas. The solid ferrite loaded slot was the smallest and the dielectric loaded slot the most efficient, although it had the narrowest bandwidth. VSWR (voltage standing wmve ratio) curves for the slot antennas are shown in Figures 1 2, 3, and 4. 2.2 Equiangular Spiral Antenna The VSWR of the cavity backed equiangular spiral shown in Figure 5(a) was measured both with and without ferrite powder loadingo The feed, shown in Figure 5(b), is of the "infinite balun" type used by Dyson.* Standard 50 ohm coaxial cable was used for the feed construction. The VSWR for the simplest loading condition is shown in Figure 6. The cavity was fully loaded with the ferrite powder. A thin layer of powder was also placed on top of the spiral. The fully loaded case produced a reduction of the lower cutoff frequency by a factor of 2. Figure 7 shows that approximately the same result can be obtained by loading only one arm of the spiral. This method has the advantage of using less ferrite material. Figure 6 shows the response of the bi-directional spiral without a cavity in both the loaded and unloaded conditions, The curves have the same general shape as the cavity backed spiral. Thus the cavity introduces little basic deterioration of the antenna response. * J. D. Dyson, "The Equiangular Spiral Antenna, " IRE Transactions on Antennas and Propagation, April 1959, pp. 181-187.

OOMARISON 0F PZC~TAhUIAR SwrT AVZCUNAS Size Vol. - W with Y3Ange. VBW=3.0 V9M-6 0 Air loaded Power loded.e3ol~id loaded Dielectric loaded 50" ix 7-1/2"t x 10 3."x 5" 5"I x 2"l 1-1/2" 122"t x 5"t x 14" 2250 cu. in. 1144 cu -in.15 cu -in 1)44 cu -in. 14W-No YSWE-5.0 614 mc 2O mc 19 Mc 8 Mc Fla nge VSWR.6.0 9O Mc 36 mc 52 mc 16 mc Err. 22 mc 19 Mc 10 Mc 50 mc 54 mc.8 Mc 90 percent 65 percent 30 percent 85 percent Kr. vt,. 5.8 5.0 5.0 5.0 16-3/4!be.3.6 lb.. lM.-1/2 lb.. C* I TLb la 1

8.0 7.o 604 5. Ut 4. 3. 2. 1. I I 260 270 280 290 300 310 320 330 340 350 Freq. in Mc/sec. Fig. 1. VSWR for air filled rectangular slot antema

I 8.0 6. 0 5.0 to 3.0 2.0 1.0 1 290 300 310 320 330 340 350 300 370 Freq. in Mc/sec. Fig. 2. VSWR for ferrite powder filled rectangular slot a-sm

80 -- 7.0 \ / Without lge 8.0 - I i 1 1 I ith 4.0 3.0 2.0 1.0 290 300 310 320 330 340 350 360 371) Frequency in megacycles per second. Fig. 3. VSWR for solid ferrite filled rectangular slot ainta

9 6. /I o / No 5.0 \\ flange /flange 400 3.0 /1 (4, / 200 2.0 y 1.0 _______ _ ____ 300 310 320 330 Freq. (Mc) Fig. 4 VSWR for dielectric loaded rectangular slot anteam

-8 - P —4 Cld k.P4 (n k cd P-4 Z bl) sz Cld.0.4 z v w Cld U-5 tD.r4 PL4

* *>; i /:......e?'?fiti^ i~i: m ~ ~ A i~Cii~?~~"/f!l:~c(:'!^iS^ N'!..1.^.:,J... Fig. 5(b) Construction showing feed and loading

VSWR 8. 0 7. O 6. 0 5.0 4. 0 3. 0. 0 1.0 I I 100 z00 300 400 500 600 700 Freq (Me) 800 Fig. 6. VSWRfor fully-loaded spiral

t 10.0 Aircase 9.0 - Coax fed arm loaded from cavity side, 2-3/l16"eep 8.0 /\ Coax fed arm loaded from both sides, 2-3/16" de / \ 7.0 - i \ Cavity depth 2-3/16" 6.0 \ 5.0 / 4.0 / 3. 0 \ \ \.-_ 0 /, 1.0 ' 100 200 300 400 500 600 700 800 900 Freq (Me) Fig. 7. VSWR for single-filar loading

VSWR 8. 0 L — JuLut I — — / 61 X lA UULJ II LUb C 7. 0 \ 1 7.0 _' * No cavity 0 I 5.0 l, 3\\ / 3. \ / I \ 1. 0 /\, 100, 400 00 600 700 Freq (Mc), — -, I J*....,1 iI...L. A....A 100 zO0 300 400 500 600 700 Freq (Mc) Fig. 8. VSWR for loaded spiral with no cavity

- 13 - Preliminary efficiency measurements for the loaded spiral indicate an efficiency of about 80 prcento Efficiencies of unloaded spirals are typically greater than 90 percent. Although miniaturization of the spiral has been achieved, the introduction of the ferrite powder introduces a narrow-banding effect. This is due to the fact that the magnetic Q of the powder becomes small above 70C mc This causes the efficiency of the spiral to fall above 700 me. This is a superficial effect, however, since it is a function of the type of material used It is expected that with the development of wideband, high Q ferrites moderate widebanding of the spiral antenna can be achieved; some reduction in efficiency may have to be accepted. 2. 3 Log Conical Spiral Antenna Preliminary tests have been made on the log conical spiral antennas shown in Figures 9(a) and 9(b), both in air and embedded ii- ferrite powder. For testing purposes two models were constructed according to desirlgns based upon Dyson's work. * The physical dimensions of th:e antenlna were 4 - 7/8 inches in base diameter and 11 - 1/4 inches in height, A 93 ohm cable (RG62/U) and a 50 ohm cable (RG 141/ U) were separately used as radiators. An apex angle of 10 degrees with a pitch anrgle of 73 degrees was chosen in order to compare with the known results with the same parameters; The cone was made with balsa wood which has a dielectric constant close to that of airo The choice of a solid base for the antenna was made due to the limited amount of ferrite powder available for the experiment. The cavity backing was an aluminum casting of cylindrical form with 5 - 1/2 inches in the base diameter and 15 inches in height. VSWR was measured as a function of frequency for the antenna backed with an air-filled cavity and a ferrite-filled cavity, The results obtained * Jonn D. Dyson, 'The Unidirectional Equiangular Spiral Antenna," IRE Transactions on Antenna and Propagation, po 329, October 1959,

I IP Fig. 9(a) Models of log conical antennas

Fig. 9(b) Cavity-back log conical antenna

- 16 - fpem the m-a-weiMMts are given in Figure 10. Due to the limited amount of available Information on construction details, the design of the aMs"mM was not sufficiently close to produce results comparable to pblished data. However, the effect of ferrite powder on the low frequency cutoff was encouraging. 3. FUTURE EFFORT It appears that considerable time should be devoted in the future to: 1. Power limitations of ferrite filled antennas 2o Magnetic bias of ferrite antennas for improvement of frequency e bandwidth 3o Extent of validity of reciprocity relations 4, Assessment of possibilities of ferrite changing mode of operation 5. Assessment of possibilities of ferrite being used to achieve new and different radiation patterns 6. Extension of work to frequencies of 100 Mc and below; reduced efficiency may be tolerable. 4. STUMMARY AND CONC LUSIONS Three final models of the rectangular cavity slot antenna have been delivered and the fourth has been constructed and is being readied for delivery. Experiments on the equiangular cavity-backed spiral show a decrease in lower cutoff frequency by a factor of 2. Efficiency seems to be about 80 percent as compared to over 90 percent for the unloaded case. Broadbanding possibilities are indicated, Preliminary results from the study of the cavity backed log conical spiral indicates miniaturization possibilities. Further modifications in design will be made.

- — `- - -- -.,. 7.0 5.0 4.0 3.0 20 1.0 I Air filled cavity Ferrite filled cavity -100 Log conical spiral "uuteana O = 10~ a = 73~ b = 0.053 A / A> /N / i I i I i I I I. IA I I I \ \ V / / / I I I I I I I I I I.. I.. I. I 100 200 300 400 500 600 700 800 m3W Freq. in Mc Fig. 10. VSWR for log conical spiral mti