Bimonthly Report No. 7 January 2. 1964 to March 2, 1964 554- 7-P 5549-7-P = RL-2131 STUDY AND INVESTIGATION OF A UHF-VHF ANTENNA by J. E. Herman S. B. Rhee Approved by: 4 ' John A. M. Lyon COOLEY ELECTRONICS LABORATORY Department of Electrical Engineering The University of Michigan Ann Arbor United States Air Force Air Force Systems Coimand Aeronautical Systems Command Contract No. AF 33(657-1 607 Wridht-Patterson Air torc Ia Ohio *fe -,* ' n.. A 3^t... M s *

TABLE OF CONTENTS Page ABSTRACT 1. REPORTS. TRAVEL AND VISITORS... 2 2. PERIOD ACTIVITIES............... 2 2. 1 Equiangular Spial 2 2. 2 Ferrite Loaded Ritc'*anguiar Slot 2 2.3 Log Spiral Zig Zag Antenna 3 2.4 Log Coancai Spirai Antennas 4 3. FUTURE RESEARCH EFFORT..... 4 3. 1 Equianlgular Spir}al Antonna 4 3. 2 Ferrite Loadked iRectang.lar Slot 4 3. 3 Log Conical Spirai Antenna 4 3. 4 Log Zig- Zag Atenna 5 3. 5 Electric Bias Study 5 4. SUMMARY AND CONCLUSIONS 5

ABSTRACT A comparison of theoretical and oxperimental beam patte rns for the equiangular spiril wiil h ae vailable shortly Preliminary tests of magnetic bias on the Ierr ic -filled rectanguiar sl:)t indicate that tho resonant frequency of the slot increases with increasing magnetic fields. Further tests of the effects of fer rite 1 )ldirg on VSWR and beanm patter n for the log conical and log c ig- zag antennas are beilg t onducted. An extension of the frequency range of 1he antennas is indicated.

1. REPORTS, TRAVEL, AND VISITORS During this period n,, repot s wet c issued and!-i n l- vlsited the laboratory on p:olet', husinesi. A trip was made tj Wrgh - Pa erso- Air Force Base on February 11 196i4 i jr disk usinrs with Mr E, M. Turner and Mr. 0. E. Hortonr D:-. I A, M. Lyi-,, a-it Mr. R. M Kalalus represented this proj \t: PERIOD ACTIVIT1ES 2. 1 Equliangular Spiral Test mdct.s of a thin wire equlangular spiral and Irs i omplement, the equiangular siot, are being constructed in order to check experimentally 'he results (if the theory developed in the last bimonthly report. The comp)uter proglom for solution ot the tfeld equa ions of the spiral has been freed fr.m errors and uteoretical beam patterns are being calc;lted lor the abuve antennas. Weather perrmitting experimental rt-suls should be available soor, 2. 2 Ferrite Loaded Rectangular Slot A model of the solid ferrite- fiiled rectangular slot antenna delivered to WPAFB has been cLonstructed and preliminary tests of the effect of strong magnetic bias are being conducted. First results indicate that the resonant fr equency of the antenna increases with increasing magnetic bias. These results were obtained for a nonuniform -2 -

magnetic field aligned with the "E" field and across the aperture of the antenna using a Varian magnet with pole faces 4 inches in diameter. 2. 3 Log Spiral Zig- Zag Antenna Preliminary tests have been made on the log spiral zig-zag antenna both in air and embedded in ferrite powder. The construction data for this antenna were obtained through a reference by Tang and McClelland. 1 During the same period, an aluminum cavity was constructed to fit the antenna. The purpose of the cavity construction was to investigate the flush- mounted operation of the antenna. For the preliminary tests the zig-zag antenna was loaded with a thin layer (0. 5 inches) of ferrite powder. The voltage standing wave ratio was measured for different frequencies and compared with the same structure without ferrite powder. The radiation patterns for the zig-zag antenna were also taken at several selected frequencies for the loaded and unloaded cases. The effect of the cavity was initially tested by comparing values of VSWR for both the loaded and unloaded cavity. For the ferrite loaded cavity, the powder "A" was used for a depth of approximately five inches which covered the bottom two turns only and provided a thickness of approximately 1.5 inches. C. H. Tang, 0. L McClelland, "Polygonal Spiral Antennas, " Antenna Lab. Tech. Rep. No. 57, Univ. of Illinois, June 1962. -3 -

2.4 Log Conical Spiral Antenna In previous reports several different methods of loading and their effects on radiation patterns as well as the VSWR were reported. As a final test on loading, a conical antenna with hollow center was designed to observe the effect of loading inside the antenna with the ferrite powder. The design data were the same as reported previously for the small log spiral cone. The tests are continuing at the present time. 3. FUTURE RESEARCH EFFORT 3. 1 Equiangular Spiral Antenna Theoretical and experimental patterns will be obtained and compared, including the case of a thin ferrite load. 3. 2 Ferrite Loaded Rectangular Slot Magnetic tuning experiments will continue utilizing both uniform and nonuniform bias in an effort to arrive at the optimum method of tuning the antenna. Various orientations of the magnetic axis will be used. A test will also be made to determine the effects of removing some of the ferrite material from slot. The effect on VSWR and pattern will be investigated. 3.3 Log Conical Spiral Antenna As a final experimental study of the antenna, an Amphenol "subminax", 50-ohm cable will be used as a radiating element. Also -4 -

the cavity backed antenna with a large ground plane will be used to investigate further the radiation patterns of the antenna with and without ferrite powder loading. It is noped that a final experimental model of this antenna will be obtained at the end of the period. 3. 4 Periodic Z jZag Antenna An effort will be made to study radiation patterns of the antenna with and without the ferrite powder. Also, radiation patterns for the cavity-backed antenna with and without the powder will be studied. 3.5 Electric Bias Study A preliminary study of the possibilities of shifting the operating frequency range through the use of electric bias is being made. If the effects can be made sufficiently pronounced on a practical antenna then the light weight of the electric field source could become influential. No results are now available. O course sufficient nonlinearity of permittivity must be present. 4. SUMMARY AND CONCLUSIONS Construction of test antennas and completion of the computer program indicate that a comparison between theoretical and experimental beam patterns will soon be available. It is hoped that the effect of a thin ferrite loading may be theoretically predicted. A ferrite-filled rectangular slot has been constructed and preliminary tests of the effects of nonuniform magnetic bias completed. - 5 -

A continual increase of resonant frequency with increasing magnetic bias is indicated. There are no inflections in the resulting graph. Further tests of both uniform and nonuniform bias will be made. Since, to date, only preliminary tests have been made on the log conical and log zig- zag antennas, no definite conclusions can be made. -6 —