Bimonthly Report Noo 8 March 3, 1964 to May 2. 1964 5549- 9-P 5549-9-P = RL-2132 STUDY AND INVESTIGATION OF A UHF-VHF ANTENNA by Jo s. A. D. E. Herman B. Rhee Ij Simanyl E. Oliver Approved by,. d': ' f /^ r John A. M. Lyon ' for), COOLEY ELECTRONIC;ABORATORY Department of Elqctrical Engineering The university of MichigaA 6 AnnArbor United States Air Force Air Force SystSms Command Agronautical SyStems Division Contract No. AF 33(657)- 100Q7 Wright-Patterson Air, Force Base, Ohio May 1964

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TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS.. o o............ iv ABSTRACT..o e. e.. o o... o o... I..... v 1. REPORTS, TRAVELS, AND VISITORS.......... 1 2. PERIOD ACTIVITIE$............. 1 2. 1 Equiangular Spiral 1 2. 2 Ferrite Loaded Rectangular Slot 1 2. 3 Log Conical Spiral Antenna 6 3. FUTURE RESEARCH EFFORT.............. 8 3. 1 Equiangular Spiral Antenna 8 3.2 Ferrite Loaded Rectangular Slot 8 3.3 Log Conical Spiral Antenna 9 3, 4 Helical Antenna 9 3. 5 Electric Bias Study 9 4. SUMMARY AND CONCLUSIONS.............. 9 iii

LIST OF ILLUSTRATIONS Figure Page 1 Effect on VSWR of replacement of single cells of ferrite in a rectangular aperture~ 2 2 Effect on VSWR of replacement of horizontal rows of cells of ferrite in a rectangular aperture. 4 3 Effect on VSWR of replacement of vertical columns of cells of ferrite in a rectangular aperture. 5 4 Ferrite loaded log conical antenna in a metal cavity compared with the air filled case. 7 IV

ABSTRACT Extensions of the rectangular slot filled with ferrite and cavity backed have been made. Experiments have been performed in replacing certain rectangular prismatic regions with balsa wood in place of ferrite. The ensuing effects upon VSWR and radiation patterns have been observed and reported. In addition, numerous experiments have been performed using a log conical spiral backed by an aluminum cylindrical cavity. Ferrite has been placed in numerous locations and data have been recorded for a variety of arrangements yielding very promising, although tentative, results. V

. REPORTS, TRHAVELS, AND VISITORS During this period, 'The Rectangular Cavity Slot Antenna With Homogeneous Isotropic L.adlng,' by Mr. A. T. Adams was printed for issuance both as a technical retli f A TR 147) on this contract and as a dissertation submitted for the Dlctor of Phlilsopl)hy Degree. Distribution of Technical Report No. 147 will he effected up)on the ctnmpletion of minor alterations. No trips were mllade hb prt ject personnel in connection with the activities of this pr-ject gyroup. 2. PERIOD ACTIVITIES 2. 1 Equiangular Sp i al Prelirninary experiments weie peri frmed on the equiangular spiral having tapered ferrite loading in the form of a, conical section. The results of VSWR measurements were encourtgingo However, as yet, no radiation patterns have been obtained fo: this type of loading. 2. 2 Ferrite Loaded Rectangular Silt For the purpose of studying the effectiveness of ferrite at various locations in the aperture, a grid was made to represent the aperture with numbers assigned to the various cells in the grid as shown in Fig. 1. Each cell number then corr"esponds to a rectangular prismatic bar either of solid ferrite or of balsa w)oo:d,d as the case may be. The curves in Fig. 1 clearly show the effect of replacing a given numbered

4.0 3.0 2.0 1.0 I3 iQ 320 330 340 350 360 370 380 390 400 410 420 430 440 450 Fig. 1. Effect on VSWR of replacement of single cells of ferrite in a rectangular aperture.

3 - cell or prismatic bar with balsa wood. Results indicate that filling a cell on either of the outside edges of the aperture with balsa wood instead of ferrite will result in a shift in the frequency band of approximately 5 Me upward. The individual curves shown in Fig. 1 identify the location of the balsa wood replacement used. Figure 2 shows results obtained by tlhe replacemnent of entire rows of cells with balsa wood. For example, for one curve Cells 1, 2, 3, 4, 5 have been replaced w ith balsa wlId,, The elimination of ferrite in this region or this whole layer has resultcd in a VSWR characteristic as shown in Fig. 2. Other replacenients of whole layers are also shown in this figure. In connection with one curve the blocks of balsa wood inserted in locations 1, 2, 3, 4, 5 were taped as a flat layer with metal tape and, in addition, metal tape was placed over the face of these blocks which terminates in the physical apetrtureo In this way, the aperture and the waveguide feed were reduced with a new metal boundary forming the top ol the waveguide and the metal tape in the aperture reducing the height of the slot. It is deduced that very little energy is propagated in this horizontal layer of balsa wood. In Fig. 3 a very interesting situation is depictedo One curve shows that if the ferrite of Cells 1, 6, 11, and 16 on one side of the slot as well as the ferrite in Cells 5, 10, 15, and 20 on the other slot are replaced by balsa wood and the cells are then covered with aluminum tape, the resulting VSWR curve is moved upward on the frequency scale 9 Aez1-e

6.0 5.0 4.0 3.0 2.0 1.0 40 Blocks 6, 7, 8, 9, 10 replaced with balsa 1, 2, 3, 4, 5 replaced with solid metal. a Blocks 6, 7, 8, 9, 10 replaced with balsa Blocks 1 2, 3, 4, 5, 6, 7, 8, 9, 10 replaced with balsa qllezlft 10 F \ N.-. I "", I 1% 1 I I 500 600 700 800 Fig. 2. Effect on VSWR of replacement of horizontal rows of cells of ferrite in a rectangular aperture. / I I i I I I II x / -,,,;-, I I 4. t -- /, i -, I" / I /. / 'I /K'JIP x.4 IV i ft t I "'w. f, I I.il, jf,, , -.1 1

Curve A - Blocks 1, 6, 11, 16, 5, 10, 15 and 20 replaced with balsa Curve B - Blocks 1, 6, 11, 16, 5, 10, 15 and 20 replaced with balsa Balsa section of slot blocked off with metalic iris Curve C - Blocks 16 and 20 replaced with balsa 5.0 A A C 4.0 B B C 3.0 o 2.0 1.0 1 1 1I I I l I l l.l ll. l l l 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 480 490 500 510 Fig. 3. Effect on VSWR of replacement of vertical columns of cells of ferrite in a rectangular aperture.

-6 - and is wider. One of the curves shows the VSWR for the aperture completely filled with ferrite. Another curve also useful for comparison is the VSWR curve taken for the replacement situation just described except that the aperture has not been reduced by the use of the metal tape irises covering Cell Nos. 1, 6, 11; 16. 5, 10, 15, and 20. Many radiation patterns have been recorded for the cases discussed in the three figures already mentioned. However, it can be said that the replacement procedures so farl have not resulted in any significant change in the shape of the radiation pattern i of the rectangular slot. So far, no measure of changes in radiacion efficiency have been measured. 2.3 Log Conical Spiral Antenna The physical situations which were tested are shown schematically in the upper right-hand corner ut Fia e 4, The basic log conical antenna (No. 207) used in these tests utilized subminax coaxial cable No. RG196. The antenna was wound on four supporting balsa wood strips. The two cuives shown in Fig. 4 enable a Ltomparison to be made of the VSWR for this antenna when mounted (as shown in Fig. 4 ) in an aluminum cavity of cylindrical shape with air broth surrounding the antenna conductor elements and filling all remaining space in the cavity. In the second situation, the antenna was again miunted in the cavity, but in this case, ferrite powder "A" filled a.l of the intervening space both inside and outside the conical antenna and of course, inside the

6.0 5.0 4.0 3.0 o 2.0 \ V 1.0 LI I I I l l I 300 400 500 600 700 800 900 1000 1100 Fig. 4. Ferrite loaded log conical antenna in a metal cavity compared with the air filled case. I.... I

- 8 - cylindrical cavity The level of ferrite was made to be flush with the outside flange of the cavity and was just suffic tent to cover the top of the conical antenna together with its feed. The improved VSWR characteristic with ferrite is quite apparent from the curves. In the air case a typical axial beam radiation pattern was observed over a frequency range of 700 to 1100 Mc. In the ferrite powder case a typical axial beam radiation pattern was observed over a frequency range of 250 to 1100 Mc. A comparison of the efficiencies of the two cases is not available. 3. FUTURE RESEARCH EFFORT 3. 1 Equiangular Spiral Antenna Radiation patterns for the various types of loading with cavity backing will be taken in the near future. 3. 2 Ferrite Loaded Rectangular Slot Although magnetic tuning experiments on ferrite filled slots have been started, additional physical arrangte ments are necessary before any radiation pattern work can be done. Several practical difficulties still remain and it is hoped that simple solutions can be found so that initial results can be reported soon. Spot measurement of efficiency corresponding to some of the experiments mentioned above will be made shortly. Such information is necessary for a correct evaluation of any benefits to be obtained for the arrangements studied.

-9 - 3. 3 Log Conical Spiral Antenna It is anticipated that efficiency measurements will be made utilizing a substitution method for this type of antenna. Possible modifications of the reflection or "hat" method of measuring efficiency to be used in the case of circular polarization will be given consideration. 3.4 Helical Antenna A study on the periodic loading of a helical antenna has been started. Initial data on related experiments should be available soon. 3. 5 Electric Bias Study Electric Bias using electric polarization may be helpful in antennas operated over a very narrow frequency range. The means of producing the bias are attractive since it is expected that a light weight high voltage supply could be utilized. In the near future simple experiments to assess the amount of nonlinearity of permittivity will be made. The problem is to obtain sufficient nonlinearity of a ferroelectric powder. 4. SUMMARY AND CONCLUSIONS The further results described here concerning the log conical antenna continue to be encouraging with respect to improvement of the broadbanding quality. VSWR and radiation pattern measurements are reassuring. Final conclusions with respect to broadbanding must be drawn only after sufficient data have been obtained upon the radiation of efficiency.

- 10 - Oni the basis ot the ftew exp.lenis rep.rt:d, general conclusions cannot yet be tmiade of the effects ti p)sitlonlIng of ferrite of the aperture. Some of the experiments have not been sufficiently sensitive to demonstrate effects tJxpec(ed.