THE UNIVERSITY OF MICHIGAN AFAL-TR-65-64 5549-1 -F STUDY AND INVESTIGATION OF A UHF-VHF ANTENNA FINAL REPORT January 1963 through January 1965 Contract AF 33(657)-10607 Project 6278, Task 627801 O. E. Horton, Project Monitor Technical Report AFAL-TR-65-64 April 1965 Prepared by J. A.M. Lyon G.G. Rassweiler, D.M. Grimes, S.B. Rhee 'J. E. Herman and A. I. Simanyi Approved by J. A. M.. Lyon, Pessor Electrical Engineering Air Force Avionics Laboratory AVWE Research and Technology Division, AFSC Wright-Patterson Air Force Base, Ohio 45433

THE UNIVERSITY OF MICHIGAN 5549-1-F FOREWORD This report was prepared by The University of Michigan under USAF Contract AF 33(657)-10607. The contract was initiated under Project 6278, "VHF-UHF Antenna Study", Task 627801. This work was administered under the direction of the Electronic Warfare Division, Air Force Avionics Laboratory, Research and Technology Division, Air Force Systems Command at Wright-Patterson Air Force Base, Mr. Olin E. Horton, Project Engineer (AVWE).

THE UNIVERSITY OF MICHIGAN 5549-1 -F TABLE OF CONTENTS I INTRODUCTION 1 II BROADBAND ANTENNAS WITH FERRITE LOADING 3 2. 1 Ferrite-Loaded Spiral Antenna 4 2.1.1 Experimental Loading 4 2.1. 2 Theoretical Radiation of Equiangular Spiral 20 2. 2 Log Zigzag Antenna 24 2. 3 Ferrite-Loaded Helix 27 2.4 Log Conical Spiral 34 2. 4. 1 Log Conical Antenna Without Cavity 38 2. 4. 2 Log Conical Antenna Inside a Cavity 44 2. 4. 3 Evaluation and Future Work on Log Conical 52 Spiral Antennas III SLOT ANTENNA 53 3.1 Magnetic Tuning 53 3.1.1 VSWR Curves 53 3.1. 2 Antenna Patterns 64 3. 1. 3 Efficiency 64 3.1.4 Theory 64 3. 2 Changes in Slot Geometry 68 3. 2. 1 VSWR 68 3. 2. 2 Other Characteristics 72 3. 3 Temperature Effects on Efficiency 72 V FERRITE MATERIALS 78 4. 1 Temperature Dependence of Magnetic Properties of Ferrite 78 4. 2 Basic Limitations and Future Potential of Ferrites 81 V FUTURE WORK 92 ACKNOWLEDGEMENT 93 RE FERENC ES 94

THE UNIVERSITY OF MICHIGAN 5549-1-F ABSTRACT The results of a program for the miniaturization of antennas through the use of ferrite materials is described. The antennas include the log conical spirals, both within and outside a cavity, the cavity-backed log spiral, a helix, a zigzag, and the cavity-backed slot antenna. Generally speaking, linear reductions of the order of 2 or 3:1 were achieved for the wideband antennas, and above 6:1 for the slot antenna. An experimental study of ferrite material vs temperature and frequency is included as well as a theoretical review of the current status and basic limitations of ferrite materials. This technical report has been reviewed and is approved. RONALD G. STIMMEL Acting Chief Electronic Warfare Division ili I

THE UNIVERSITY OF MICHIGAN 5549-1 -F INTRODUCTION Many attempts at miniaturizing antennas have been made, usually by loading the antennas with dielectric or ferrite materials or with circuit elements. In the present investigation we have limited our attention to ferrite loading. With cavity or waveguide antennas, the advantage of loading with high A or e materials is quite obvious; the cutoff size of the cavity or waveguide is smaller due to a change in wavelength. For free-standing antennas, the advantage of loading antennas is less obvious. Repeated attempts, reported in the literature, to load a dipole antenna with material have resulted only in changes in the resonant frequency and radiation resistance; however, the resonant frequency could be shifted by circuit elements, and the increase in radiation resistance was usually due to the losses in the ferrite. The result of loading loop antennas, of course, has been much more productive. Great gains in the effective receiving aperture have been achieved, and ferrite loaded antennas in low frequency radios are common. More recently, the loading of broadband antennas, as has been done on this project, has resulted in size reduction due, apparently, to a change in the phase velocity of the wave along the antenna, and thus a shift of the 'active regions' to a smaller part of the antenna. The use of ferrite at the higher frequencies of 50-700Mc has caused losses in antenna efficiency due to basic ferrite limitations and materials manufacturing problems. These have not been entirely overcome on this project; however, size reduction has been achieved with less loss than encountered in the use of either attenuators (to lower the VSWR) or absorption of the waves at the low frequency end of the antenna (to preserve the axial radiation mode and a good VSWR). Further improvement of ferrite materials in the future may be expected. In Section II, the studies of ferrite loaded broadband antennas are reported. In Section III the investigation of the effects of magnetic tuning of a ferrite loaded Manuscript released by authors 18 February 1965 for publication as an RTD Technical Report. 1., I I.1..1. ~~~1,

THE UNIVERSITY OF MICHIGAN 5549-1 -F cavity backed slot antenna is discussed and in Section IV is presented a survey of ferrite material characteristics and some results of an experimental study of ferrite characteristics vs temperature and frequency. In Section V some brief recommendations for future work are made.

THE UNIVERSITY OF MICHIGAN 5549-1 -F II BROADBAND ANTENNAS WITH FERRITE LOADING A major objective on broadband antennas has been to utilize the benefits of ferrite loading and still retain the broadband characteristic of a given form of antenna. Some placement of ferrite may change the radiation characteristics of a given antenna type. However, it is believed that certain basic types of broadband antennas such as equiangular spirals, the log conical spiral, the helical antenna, an the zigzag antenna, and the zigzag antenna can be modified in such a way as to provide a miniature type of antenna and yet each type will retain its basic characteristics. Results to date have indicated very favorable results in regard to the retention of the radiation pattern. In addition, ferrite loading makes possible the retention of the desired radiation pattern through a greater range of frequency than was heretofore possible without ferrite loading, due to a lowering of the low frequency limit of at antenna. The desired upper frequency characteristics of the antenna must be retained by not loading the upper frequency active regions, since the present ferrite+ is very lossy above 500 Mc and future ferrites (discussed in Section IV) are high frequency limited. The ferrite-loaded spiral antenna will be discussed first (Section 2. 1), followed by the ferrite-loaded helix and log conical sprial antennas. Type "A" with composition, Ni 9696Zn 0404Co 03Fel. 84A1. 0404 9. 0 1

THE UNIVERSITY OF MICHIGAN 5549-1 -F 2. 1 Ferrite-Loaded Spiral Antenna 2. 1. 1 Experimental Loading The VSWR of the cavity-backed equiangular spiral shown in Fig. l(a) was measured with and without ferrite loading. The feed shown in Fig. l(b) is of the 'infinite balun' type. Standard 50 ohm coaxial cable was used for the feed construction. The VSWR for the simplest loading condition is shown in Fig. 2. The cavity was fully loaded with the ferrite powder. A thin layer of ferrite powder was also placed on top of the spiral. The fully loaded case produced a reduction of the lower cutoff frequency (or alternatively, of size) by a factor of approximately 2. The narrow-banding effect, due to the magnetic Q becoming small above 700 Mc, is a function of the type of material and loading used, and is not a basic limitation. Figure 3 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 4 shows the response of the bidirectional 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. Preliminary efficiency measurements for the loaded spiral without cavity indicate an efficiency of about 80 per cent. Efficiencies of unloaded spirals are typically greater than 90 per cent. Additional experiments were performed on an equiangular spiral which was mounted on the apex of a Styrofoam cone. This mounting allowed the equiangular spiral antenna to be centered in a cylindrical cavity flush with the flanges of the cavity. The space between the Styrofoam cone and the wall of the metal cavity was, in the ferrite loading situation, filled with powdered ferrite as shown in the insert of Fig. 5, which depicts VSWR with and without ferrite loading. Figure 6 shows radiation patterns for the equiangular spiral, as depicted in Fig. 5, with and without

THE UNIVERSITY OF MICHIGAN 5549-1-F ferrite loading over a range of 300 - 900 Mc, showing that the patterns of the loaded antenna are at least as good as those of the unloaded antenna,.

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THE UNIVERSITY OF MICHIGAN 5549-1-F z 0.i z 0 z 0 RX~~~~~~~~~~~~~a z.""~ ':i'"' 'i.'" {: i,... i:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~% ' '.'.' " '..'.' ".....'i.:'.' ':;.:'..:::::.... O:5:~~~~~~~~~~~~~~~~~~~:::::::1 ~ 'i.:'...:~ ~ ~ ~~~~~~~~~~~~~~~~~~~~:::... ',f:::ii?: 0 ~~~~~~~~~~~~~~ ~i............. ~......... iii~~~~~~~~~~~~i~~:{;::~ri:_::iil:~~ii;:::::::::-:~~:'::.....-.."::).... i....... ~::..'~.. '.: ".':."'..:'..: 0:.;i:..".:i'..'.ii.2:'2...:.."'..: —~J ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 4~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _" _ _ _ _ _ _ _ _..........

VSWR Air caseFerrite loaded cavity 8.01 --- Loaded cavity; 1/4" ferrite-on top 7.0 Z Cavity depth 2-3/16"1 6.0 5.0 c,1 -4.0 ~T1 3.0 2.0 *0 1.0 100 200 300 400 500 600 700 800 Frequency (Mc) FIG. 2: VSWR FOR FULLY LOADED SPIRAL

10.0.t Air case_ 9.0 -Coax fed arm loaded from cavity side, 2-3/16"deep VSWR ~ 8.0 / i-\ - Coax fed arm loaded from both sides, 2-3/16" deep C / \ 7.0o -- 7 t~~~~~~~~~ 05 \ Cavity depth 2-3/16", 6.0, \ 4.0 I \\ 3.0 \ 2.0 \ /\ K 2.0 300 400 500 600 700 800 900

Air Case VSWR r I Loaded 1-1/4" on one side; air on cable side, Loaded 1-1/4" on both sides 8.0 1M 7.0 No cavity 6.0 \ I ' 5.0 I 40, / / \ 3. \\~~~~~~ o Ir J 100 200 300 400 500 600 700 2.0 ' 0 100 200 300 400 500 600 700 Frequency (Mc) FIG. 4: VSWR FOR LOADED SPIRAL WITH NO CAVITY

VSWR - Air loaded ---- Ferrite loaded | \ Equiangular spiral H 6 |. \.. Fer/ iFlange C | powde X Styrofoam Cavity cone O'1 \ 4 x X U x/ 200.I, I J 200 300 400 500 600 700 800 9)00 1000 Frequency (Mc) FIG. 5: UNIDIRECTIONAL EQUIANGULAR SPIRAL (No. 301) WITH TAPERED FERRITE LOADING..,..,,,,,. S,......~i

THE UNIVERSITY OF MICHIGAN 5549-1 -F o z o 1q 2 e 2 _4 _1 N N 5~~~ 71 n 1 11

THE UNIVERSITY OF MICHIGAN 5549-1-F "10 20 t0 25 25 400 Mc E 400 Me E db db 25 ' 25 E E 500 Me c 500 Me FIG. 6b: NO. 301 AIR LOADED ____ ____ ___ ____ ____ ___ ____ ___ 13 i

THE UNIVERSITY OF MICHIGAN 5549-1 -F db 10 - 15 'o 20 25 25 600 Mc Ee 600 Mc E db db 14 - 15 15 20 20 25 25 700 Mc 700 Me FIG. 6c. NO. 301 AIR LOADED 14

THE UNIVERSITY OF MICHIGAN 5549-1 -F db 10 -10 800 Mce E 800 Me E db db -510 - 15 15 - 20 900 Mc Ee 900 Mc E 15

THE UNIVERSITY OF MICHIGAN 5549-1 -F O L co CD co CO.1 q CC - ~16

THE UNIVERSITY OF MICHIGAN 5549-1 -F db db.10 15 15~~~~~~~~15 20~~~~~~~20 25 400 Mc Ep 409 Mc E0 db db ~'/ ~ 1 t0 0 / 2~~~10 FIG. 6f: NO. 301 FERRITE LOADED ____ ____15______17

THE UNIVERSITY OF MICHIGAN 5549-1-F db 10 db 10 15 15 '20 20 25 25 600 Mec E 600 Me E db 10 db 10 -,.____ 185 15

THE UNIVERSITY OF MICHIGAN 5549-1-F db / 4 ~~~10 X (db 110 15 15 80090 E FIG. 6h NO. 301 FERRITE LOADED _ _ _ _ _ _15 2_______ 19 _[ -I.6h O 20 FRI LAE

THE UNIVERSITY OF MICHIGAN 5549-1-F 2. 1. 2 Theoretical Radiation Pattern of Equiangular Spiral A mathematical expression for the radiation fields of the equiangular spiral thin-wire (or slot) antenna is now presented which is adaptable to solution using the IBM 7090 computer, if the current distribution and mode of excitation are specified. Consider the planar monofilar spiral shown in Fig. 7, where (r', 0') are source coordinates, (r, 0, 0) are field coordinate, and r" = r-r'j. The magnetic vector potential for a thin current distribution in space is given by (1)r,, I(g,)er spiral +jwt where the e time dependence is understood. In the radiation field phase variations are taken into account by r" = r-r' sin0 cos (0 - '). (2) The equation of the equiangular spiral is r' =r' e (3) 0 whence d~'= (dr?)2+(r 2d ') 2 a+' |2 +da r' ea do' (4) 0 and 1 aB' ' = i d2'=d 1+ r'(e -1). (5) 0 a 0 The direction of the segment di' as shown in Fig. 7 is given by | = sin('/ -X ')x+ cos('- ')y (6) where |__________ 20tan ' _ = r'd' = a. (7) l 20

THE UNIVERSITY OF MICHIGAN 5549-1-F ~~~~~z \ r" y \ 0 Y',x in x-y plane FIG. 7: SPIRAL COORDINATES

THE UNIVERSITY OF MICHIGAN 5549-1 -F A rather crude approximation to the current is that of a curved two-wire transmission line with no coupling to surrounding elements. This gives a current depending only on the distance (i') along the line from the feed point, i. e. a traveling wave, IQ(') =IeL' + re e,1; (Y= -+jiA3) (8) where Q' is given by (5) and F is the reflection coefficient for current. Thus the vector potential may be written as P eI -jkr, A (r, 0,)= 0 * exp(jkr' sino cos(0-0)ea ] Lsin(Q'-0)x+cos-0)y r= e2; -2L= /1+ a1)) 1+ -- r' (- (10) where L and 4 correspond to the remote end of spiral. In spherical coordinates, the radiation field is related to the magnetic vector potential by Eo -jwA0; E — jwA0 (11) where AO A cosOcos0+A cos 0sin l A = -A sin 0+A cos0 * (12) Thus, if A is known the field can easily be found from (11). - _ _ _ _ _ _ _ _ _ __ ~22

THE UNIVERSITY OF MICHIGAN 5549-1 -F Consider the bifilar spiral with the currents in the two wires out of phase by an angle A at the feed. Then the total magnetic vector potential will be given by (1)(1) A A(r,O,0,t) A( (r,O,0,t)+A (r,O,+r, t+ ). (13) Thus for balanced excitation (A=: r) the total magnetic vector potential will be 00l 2 -jkr A(r 0,0) — 01+a r' — exp r'I -exp(-a-I3)1 a- ( 2eaea0)). a21 ao'l -exp + —2o +2 rl (2._15 cos kr sin cos(09ej)e e Isin(r 1-09coso+cos/ir.l0?sino]coso 0 For convenience the following substitutions may be made: 1~~( 1 z'=aoI Z=a0 a &=o 1+ r' fr =/31+- rt' kl=kr3, a a xp -I 2 -jkr B=- 00 a r' (15) 27~ra o r cos Besincos(~'-ez] eo'[sin(-i'-)cosoo+cos(in ~? a 1}dz' (16) A~~r, 0, 0) =2Be 0~

THE UNIVERSITY OF MICHIGAN 5549-1-F Equation (16) gives a set of integrals which may easily be evaluated by numerical methods on the computer. Whence, the magnitude and phase of the field components may be tabulated for each set of parameters. The application of this method to a ferrite loaded antenna presents a difficult boundary value problem. However, it is hoped that a thin layer loading may be simulated by merely assuming the current propagates in a 'slow-wave' mode, i. e., by assuming 1 =\-3 k. A computer program was written but results did not compare well with experimental patterns, probably because the current assumed is not that observed or predicted in the 'active region' concept. 2.2 Log Zigzag Antenna A log zigzag antenna was designed to take advantage of its reduced volume with frequency independent characteristics similar to those of the log conical spiral. The dimensions used (Tang, 1962) are shown in Fig. 8. An initial test of the VSWR for a 1/4" thick uniform layer of type "A" powder was made and compared with the air loaded case (Fig. 9). An aluminum cavity was constructed to fit the antenna, to investigate the flush-mounted operation of the antenna. The effect of the cavity was initially tested by comparing values of VSWR for both the loaded and unloaded cavity. For ferrite loaded cavities, the powder "A" was used for a depth of approximately 5", which covered the bottom two turns only and provided a thickness of approximately 1. 5" However the cavity was too small to allow adequate radiation. Further tests may be made in the future. 24

THE UNIVERSITY OF MICHIGAN 5549-1-F I 8cm tc 170 22 cm. I I I 74t" FIG. 8: LOG SPIRAL ZIGZAG ANTENNA CONSTRUCTION DETAILS..............i" '-' -'.... ---- 25 5.

THE UNIVERSITY OF MICHIGAN 5549-1-F 10 VSWR 9. Ferrite filled ------ Air filled 7 6 I I 4 3 I 2 1 l l l 200 400 600 800 1000 Frequency (Mc) FIG. 9: FREQUENCY VS VSWR FOR LOG SPIRAL ZIGZAG ANTENNA. 26

THE UNIVERSITY OF MICHIGAN 5549-1 -F 2. 3 Ferrite-Loaded Helix A ferrite-loaded helix (Fig. 10) was constructed in order to test the size reduction obtainable with such a structure. The helix was wound of No. 14 copper wire on a balsa wood cylinder of 4" diameter and 20" length. For a six-turn helix wound on this core, the pitch angle A, defined by tan (diameter) (turn-to-turn spacing) is 140. As shown in Fig. 10, this structure is loaded around the perimeter of the cylinder, just inside of the helical winding, with 1" x 1/2" ferrite bars. The ferrite bars extend over the total length of the antenna; they are spaced 900 apart around the perimeter of the cylinder. The reason for choosing a moderate pitch angle of 140 was that most of the measurements by other workers had been concentrated in this region, and therefore data were available for comparison. The helix is fed by the center conductor of a type N connector, which is mounted on the axis of the cylinder. Figure 11 shows the measured voltage standing wave ratio for both the unloaded (balsa wood core) and the loaded (ferrite bars embedded in the surface of the basa wood core) case. The values of VSWR are quite reasonable for both cases, especially when one considers that no attempt was made to obtain a better match between the 50 ohm coaxial feeding line and the helical antenna, by any kind of an impedance transforming network. Generally, VSWR's of about 2. 5 are obtained in the useful radiation regions. For the unloaded antenna, the VSWR reaches very high values at 600 Mc and below, whereas for the ferrite-loaded structure this cutoff is reduced to 450 Mc. In Fig. 12 radiation patterns are presented for the ferrite-loaded helix from 300 - 1000 Mc. The patterns were taken with the helix being mounted on a 4' x 4' aluminum ground plane. The patterns are quite unidirectional for both Ee 27

No. 14 Copper Wire Ferrite Bars 2 2 Balsa Wood Core 5, IL1" cr n4 D~~~~Cc S: 3.14" D~ 4 SFerie ar Pitch =Tan -rD.25 Type N Connector Ferrite Bars 1kI40 C) FIG. 10: HELUIX ANTENNA LOADED WITH FERRITE BARS C) z

10 8 8 I | FERRITE LOADED HELIX C ---- AIR LOADED HELIX Z.4-1 d C 4 - \ ~~C/24d~~ _. 2 400 500 600 700 800 900 1Q00 Frequency (Mc) FIG. 11: VSWR FOR LOADED AND UNLOADED HELIX

THE UNIVERSITY OF MICHIGAN 5549-1-F 00 00 100 I00-3 80 80 60 60 40 \40 /) 20,,~90 270- 900 / 400 Mc --- Ee 300 Mc180~ 180~ 30 00 80 '0 20 90' 2700 900 ~500 Mc --- Ee 600 Mc Ee 30

THE UNIVERSITY OF MICHIGAN 5549-1-F 00 00 10 100 80 60/ -— 0 700 Mc/ / / 40 N EE 18:/ FI 20 20 2 270o 90 27090 2700x 1_-~ 90 90 000 Me 7080 M 0Mc --- Ee --- E E E9, 1800 1800 ~-900o - 80 N " /80 FG. 1 / F 31

THE UNIVERSITY OF MICHIGAN 5549-1 -F and E0, with little back radiation except at the low end (300 Mc) where the wave is not properly launched yet and at the high end (800 - 1000 Me) where the phase velocity along the helix is below that required for a single beam unidirectional pattern. The beamwidth of the ferrite bar loaded antenna is about 800 at 400 and 500 Mc, 70~ at 600 Me, and 450 at 700 Mc; these values compare well with the electrical length versus beamwidth relationship expected. For the lengths involved (.80X at 500 Mc, 1.07k at 600 Mc and 1.24X at 700 Mc), Kraus (1950) arrives at beamwidths of approximately 700, 600 and 500, respectively. The unloaded antenna should operate with a well-formed beam for:.77< C < 1.3, where Ck is the helix circumference measured in free space wavelengths. For this 10. 1 cm diameter helix, the operating range should be between 727 and 1230 Me without loading. The ratio of the upper to lower frequency is 1. 69 and this is the same ratio as obtained for the ferrite-loaded helix, where f. =400 and min f = 700 are the two limits. The lowest usable frequency is reduced by a factor max of 1. 8. This is the ratio by which the diameter of the helix has been reduced. The solid ferrite used was measured to have p = 6. 2 and c = 12. 6 at 600 Mc, where j c-= 8. 9. In an infinite ferrite medium, the phase velocity and antenna lengths would be reduced by this factor. The actual reduction of 1. 8 in helix s ize rather than 8. 9 is mainly due to the lack of enough ferrite material: only one-third of the perimeter is loaded, and only 16 per cent of the total internal volume is loaded with ferrite bars. A size reduction of around 3. 5, or 40 per cent of the theoretical limit indicated by the material parameters, seems quite feasible by using more ferrite inside the antenna. From the k-13 diagram shown in Fig. 13, drawn for a 14~ pitch unloaded helix, one can deduce the frequency band for which the helix could be an effective 32

.5 0 */ 14.4 C ka - /- B Cot4C - -- 0.5 1.0 1.5 0o,oa Cot 2 FIG. 13: k-3 DIAGRAM FOR A 140 PITCH ANGLE UNLOADED HELIX

THE UNIVERSITY OF MICHIGAN 5549 -1 -F radiator. The region AB is a linear region and so is BC, however, the slope AB is suitable for realizing the Hansen-Woodyard condition whereas BC is not (Maclean, 1959). Therefore, the upper cut-off for ka= C = perimeter of helix in wavelengths, is located around B, from which point the helix wave velocity, V, is not increasing sufficiently fast with frequency to maintain a directive beam. Therefore, above this point, a breakup of the main lobe occurs. The studies on ferrite loaded helices were very encouraging as the data which have been acquired and presented here indicate. Actually, a thorough study of the data such as presented in Fig. 11, VSWR for loaded and unloaded helices, show show that there has been considerable improvement with ferrite loading. However, the advantage of ferrite loading is even greater than shown in this figure. The ferrite material which has been used for loading deteriorates rapidly at frequencies over 600 Mc so that the full benefit of loading at frequencies over 600 Mec cannot be seen. The low frequency limit of the antenna has been reduced by approximately 100 Mc. The VSWR studies, the radiation pattern studies and efficiency studies should be made in the frequency range from 100 to 500 Me by redesign of the helix, The trends shown for the ferrite loading of helices are encouraging. 2.4 Log Conical Spiral-Antennas Since the log conical spiral antenna has a very large inherent bandwidth, it was decided to load this antenna with ferrite in hopes that a large bandwidth would be maintained, in contrast to the very narrow bandwidth of the ferrite loaded rectangular slot antenna. The free standing log conical antenna was loaded with layers of ferrite; in addition, attempts at placing the log conical antenna in a cavity were made in order to allow flush mounted operation. Table I gives the specifications of the antennas and their identification numbers. Figures 14 and 15 are photographs of these antennas. 34

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THE UNIVERSITY OF MICHIGAN 5549-1 -F TABLE I: LOG CONICAL SPIRAL ANTENNA SPECIFICATIONS Identification Number 200 201 202-202a 204 208,209 Base Diameter 26.5cm 17.5cm 12.5cm 1 cm 13 cm Apex Diameter 10. 5 5. 5 6 5 3 Height 39 47 30 27.5 27.5 Apex Angle 100 10~ 70 6~ 10~ Pitch Angle 73~ 730 800 730 730 Outer Conductor 1/4 " 1/4" 50Q2 50Q 3/16" copper copper bare cable bare copper tube tube RG141U cable tube RG141U Inside of Cone hollow hollow balsawood hollow hollow 37

THE UNIVERSITY OF MICHIGAN 5549-1-F 2. 4. 1 Log Conical Antenna Without Cavity Two log conical antennas, with loading (No. 208) and without loading (No. 200) are depicted in Fig. 16, along with the' VSWR characteristics. The unloaded antenna was actually larger than the loaded one, rather than being the same size as shown. It is seen that the lower bound of operating frequency has been reduced from above 300 Me to below 200 Mc, as judged by the VSWR characteristics even though size reduction was also achieved. Figure 17 shows radiation patterns of the log conical antenna without cavity and shows that the lowered operating frequency range is maintained in radiation characteristics as well as VSWR curves. The loading of the smaller log conical antenna (No. 208) was by a ferrite powder everywhere inside the log conic l1 antenna and 1/8" beyond the conductors, retained by a thin polyethylene sheet. The efficiency of this free standing loaded log conical antenna (No. 208) was approximately 23 per cent. Loadings other than the solid core loading above are possible. Initial attempts at loading were with layers. Figure 18a shows Antenna 201 loaded with a layer of ferrite, and Antenna 202 unloaded. Figure 18b shows various partial loadings that were attempted with the large log conical spiral antenna (No. 201). The type "A" ferrite material of Fig. 18b(a) is the least lossy available (Q -30) and mag could be used in a thin layer loading only, since there was not a sufficient amount of this material available for loading with thick layers. As a result a more lossy type "B" material was used for the thicker loadings. With the more lossy material, VSWR curves would mean little; however, it was determined from numerous radiation patterns (see Bimonthly 5549-6-P on this contract) that at the higher frequencies, the thickness of loading did not effect the radiation pattern shapes significantly. At low frequencies, the thicker layers significantly improved the radiation patterns, whereas much less improvement was obtained when using the thin layers of material. Use of a thick layer resulted in a lower minimum possible operating frequency by a factor of. 08 based upon constant VSWR level, or by a factor of 0. 7 based upon maintaining the radiation pattern. No efficiency measurements were ____I_.__________ 38

8.0 Air Ferrite Loaded.7 Powder "A" 7. o- H 6.0 -, ~T1 18"x 18" Ground Plane Z < Air Loaded rl 5.0 - - -Ferrite Loaded U,~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~U > 4.0 - 2 I I \ I / I 2.0 ro V z 1., III 300 400 500 600 700 800 900 1000 Frequency (Mc) FIG. 16: VSWR VS FREQUENCY. ANTENNA NO. 208.

THE UNIVERSITY OF MICHIGAN 5549-1-F E SON. 80 8 I0 \ I 60 40!40 ' I 20 / 2 /20 270' - 90' 270- 90' 400 Mc 500 Mc -— FERRITE --- ERRITE 1800 180 0000 0 60 O~60H \ 40 / 40 9 'I.fI I -.20 20, 2z 970 - / 27 600 Mc 700 Me z 0 O -AIR AIR ~ --- FERRITE -— FERRITE 180" 180o - s'o 880, 60 r 60 4 -- [..40 2701," 90 2' 900 800 Mc 900 Mc V --- FERR-FERRITE 180' 1800

THE UNIVERSITY OF MICHIGAN 5549-1-F ______ > oo Es ('Woo ( 60 60 40 1 40 20..70*1 900 270 90. 400 Mc./ 500 Mc - AIR AIR --- FERRITE R --- FERRITE Q 180 180- 100 _ 80_ 80 /60 60, / I. —[,.o ~) 40 -, 2'7 -90 ': 0,,-e -00 600 Mc 700 Me -— AIR -— FERRITE AIR f, — -— FERRITE 180 0 180 00o 0o 0 / 80. -..80,/ )\.' / —..40 - 20 / 20 n2c-0-4 u9o. 270-f: _,_. 800 Mc -AIR 900 Mc --- FERRITE - AIR --- FERRITE 41

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THE UNIVERSITY OF MICHIGAN 5549-1-F Ferrite -q +8 " — q 2" b — Thin uniform layer, type A material. Tapered thick layer, type B material. (a) (b) 81/2" 8 1/2,, Uniform thin layer, bottom half. Uniform thick layer, bottom half. FIG. 18b: FERRITE LOADING FOR LARGE LOG CONICAL SPIRAL ANTENNA. 43

THE UNIVERSITY OF MICHIGAN 5549-1-F made on these early models. 2.4.2 Log Conical Antenna Inside a Cavity In order to achieve flush mounted operation, the free standing log conical antenna as discussed in the last paragraph, could be mounted on a missile nose cone, r other conical aerodynamic shape. Another way of flush mounting is to place the antenna (No. 209) mounted in a cavity (5. 5" dia., 15" deep). The figure also dislays VSWR characteristics vs frequency. The ferrite loading is seen to improve hese VSWR characteristics considerably, although much of the improvement may be ue to ferrite losses. However, as seen in Fig. 20, the radiation patterns of the errite loaded antenna with cavity are vastly superior to those without cavity, probably due to the fact that the ferrite loading allows the lowest dominant mode in the avity whereas cutoff characteristics of the air loaded cavity appear to dominate elow 900 Mc. It would seem that the ferrite loading allowed operation down to 300 Mc. rather than 900 Me, which is a tremendous improvement. The cavity and antenna No. 209 are shown in Fig. 21. For loading, the ntire cavity was filled with ferrite powder. A considerable decrease in efficiency as noted over the free standing air loaded conical antenna in a cavity with loading. The loading of the log conical antennas with a completely filled cavity was he final of a long series of experiments attempted at loading these antennas. Other inds of loading are possible. The log conical antenna originally used is No. 202 (Fig. 15). The results of early tests using a cast cavity are shown in Fig. 22, as a lot of VSWR vs frequency for the ferrite-filled and air-filled cavity with log conical spiral antenna (No. 202). A reduction in more than 2: 1 is seen in the lower perating frequency due to the ferrite loading. Figure 23 shows several types of oading used with this original log conical antenna wound on a balsa wood core. The esults shown in Fig, 22 were from loading as in Fig. 23b. In addition, partial oadings (Figs. 23c and 23d) were tried, with the results as shown in Fig. 24. It is 44

8. 0 Air Loaded Ferrite Ferrite Ferrite Loaded (Powder "A" Air a. ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~~~ 7.0 Cavity -. ~..-... -.,. ~... 6. 0... ~r~ ~ ~ C 1 '2 2 5.0 o"11 4.0 0 3.0 iA \ VP c, r" I x / — ~~- ^% ~ / 2. 0 V V ~ I 1.0 300 400 500 600 700 800 900 1000 Frequency (Mc) FIG. 19: VSWR VS FREQUENCY. ANTENNA NO 208 WITH CAVITY ~~\Ix/,~~~ ~ i/ v C

THE UNIVERSITY OF MICHIGAN 5549-1-F 100 co0 BK. ---- E0 ~~..-' -..... ---_ N _ 4 0~ 270 1 ) 7 70 900270- 900 0/,' ', /,,,- /. 300 Mc 400 Mc F00 Mc - AIR AIR FERRITE FERRITE 11 --- FERRITE 1130~ 1100 -- 80%,/ 80 -' 60' / 60 2 190 270- 900 2700 9 00 600Mc 00 Mc | M 800Mc AIR AIR AIR - AIR --- FERRITE FERRITE --- ~- FERRITEE IT ~1800~~80 -AI --- FERRITE --- FERRITE 1808 180~ FIG. 20a RADIATION PATTERNS OF LOG CONE WITH CAVITY t~o 4~;bo ~fO00 46

THE UNIVERSITY OF MICHIGAN 5549-1-F / 860 s8 80 / \ 4 1890 180 llK)- FERT20 'i /.'6 300 Mc AIR 400Mc 500 M FERITEAI- -AIR 180'~"'90~- F._ERRITE - FERRITE lter ISOO 80' 000s -.40 0M4 FIG. RADIATION PATERNS OF LOG CONEWI —H FERRITECVT 20~ 2 o. 270, go"z 600M9c 700MM 800MM FERRITE -- FERRITE-AIFR 0'90' 270- 90 300 7 O0 Me 8000 M0 -, —.. 47

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VSWR* Ferrite filled Air filled 70cavity cavity 7.0 6.0 - I~ I \ 1 z 5.0 Frequency (M ~4 ~o=100 a73 b=.053. 3.0 C\ O =l100, au = 730, b =0. 053.

THE UNIVERSITY OF MICHIGAN 5549-1-F FAir Ferrite X avity (a) (b) (c) (d) FIG. 23: FERRITE LOADING FOR SMALL LOG CONICAL SPIRAL ANTENNA IN A CAVITY. 50

10 9 L Cavity filled with ferrite |H - -- Uniform thin layer ferrite (cavity backed) 8 - - - Cavity with air ----- Tapered layer (thick on top part) 7Z M 6 o WTH CAVITYC ~a ~\ 1/ 1 i I I I iC) 400 600 800 1000 1200 1400 Frequency (Mc) FIG. 24: FREQUENCY VS VSWR FOR SMALL LOG CONICAL SPIRAL WITH CAVITY.

THE UNIVERSITY OF MICHIGAN 5549-1-F interesting to note that the various ferrite loadings appeared to make little difference in VSWR. The original cavity with an aluminum cast cavity was finally replaced with a superior, machined cavity (Figs. 19 - 21 apply to the machined cavity). 2.4.3 Evaluation and Future Work on Log Conical Spiral Antennas Numerous experiments were designed and tests were made involving this type of antenna. The experiments so far performed do not completely cover the hole range necessary. However, results have been sufficiently encouraging so that more critical experiments are being designed. Unfortunately the range of experiments with and without a metal cavity are not sufficiently complete. It was found that there was considerable deterioration of efficiency when the log conical spiral was mounted in the cavity. Different arrangements of the ferrite material should be tried in order to more fully determine what is he most appropriate arrangement of material. Also, there appears as a result of he experiments performed so far, the need for possibly* using more than one type of absorbing material just inside the curved cavity wall. It would be informative to use the log conical spiral inside a metal cavity with the ferrite material concentrated entirely inside of the cone formed by the active antenna conductors. In view of the experimental results found so far, certain types of partial loading of the log conical spiral should be attempted. In the early experiments some partial loading was attempted. It is now believed that the more methodical program with two or more layers of ferrite inside the conical structure may yield results far better than any shown in this final report. There is the distinct possibliity that such an arrangement will increase efficiency through two possibly changes; a) the smaller amount of core material and thereby a smaller amount of magnetic loss associated ith the volume of material, and b) a smaller amount of loss due to additional reflection present at an air-ferrite interface. Appropriate design of this last interface may result in improved radiation.,_ _ __ _ _ __ _ __ i_ 52

THE UNIVERSITY OF MICHIGAN 5549-1-F III SLOT ANTENNA The ferrite-filled rectangular slot antenna was the major subject of the report by Adams (1964). Since then, additional studies have been made of variations in the slot antenna, particularly those due to magnetic tuning, slot geometry (changes by the addition on metal or air in place of some of the ferrite), and changes due to temperature of the ferrite. 3. 1 Magnetic Tuning Since the ferrite-filled slot antenna has a rather narrow bandwidth (16 - 20 Me) it has been expected that some tuning of this slot antenna would be achieved by the application of a d - c magnetic field. Originally, experiments were carried out with a permanent magnet as the source of a unidirectional magnetic field. More recently, an electromagnet was fashioned so that continuous changes in magnetic field can be achieved. Since the three characteristics of the antenna, VSWR, antenn patterns and efficiency, were studied as the unidirectional magnetic bias field was varied, these three characteristics will be discussed separately. 3.1.1 VSWR Curves The first attempt at shifting the resonant frequency of the ferrite-filled slot antenna was with permanent magnets as shown in Fig. 25. Figure 26 shows the effect of applying a permanent magnet to the back of the slot antenna. In order to get a variation in the intensity of the applied magnetic field, the magnet was applied both with and without an aluminum plate as shown in Fig. 26. A shift in the resonant frequency of 70 Mc was achieved with the strongest magnetic dield. In addition, no marked change in the bandwidth occurred. Figure 27 shows a more extensive set of measurements made with two magnets placed in various combinations on the side of the slot antenna. Most of the configurations are seen to produce only a small change in the resonant frequency of the antenna. However, in using Configuration No. 7, where the applied magnetic field is along the wide dimension of the aperture, the 53 _

THE UNIVERSITY OF MICHIGAN 5549-1-F H z z.......?~iii*~i:iiiii:!~::~i~?~......................................................:i!........:;i;~::.iiii ~!;;i: C!i? 4..... Hii i 5&~~~~~~~~~~C z/:~ w: E~~~~~::-:: ~~W~~~~~ tiU:"::::::::ii;iii-.:l:i::ils:li:;:~~i:i::::i::::::; i:: ---;;:i::z:: r Fc1 &n:1 __________________________________ 54 ___________________________________~~~~~~~~~~~~~~~~~

Ferrite Blocks. _ H j~ D Magnetron Magnets 3/8" Aluminum Plate 6 Z (No Magnet < a ( i Magnet and Aluminum Plate ( % 200 Gauss) bD ( With Magnet (~ 300 Gauss) B 4 b(t 3 O O 3alU \ i(1 ~/ / 2 / 300 350 400 Frequency (Mc) 450 500 FIG. 26: VSWR VS FREQUENCY FOR RECTANGULAR FERRITE SLOT ANTENNA NO. 101 WITH PERMANENT MAGNETS

TH1VERS OFY 0O MlCnIGAk **o 0 V 1Zso-go~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~* 4.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~7 560 O O O ZOCI~ );ZC/0 10 ~ d~~~~~~~~~IZ

THE UNIVERS 59Y1 FOF MICHIGAN hift is again quite large (about 60 Mc). Again, there were no major changes in the andwidth about the resonant point of the slot antenna. Figure 28 shows the effect pon VSWR of using an electromagnet to provide a unidirectional bias field along the ide dimension of the aperture. In this case, a shift of 120 Mc in the resonant frequency of the antenna was achieved with the largest bias field of 1100 gausses. The andwidth of the antenna was again substantially unchanged. Figure 29 shows the uning curve of magnetic bias vs shift in the resonant frequency for the same magnet configuration as in Fig. 28. In order to achieve greater magnetic bias, it appeared ecessary to fabricate wot electromagnets, because severe heating effects were encountered with one magnet at field strengths greater than 1000 gausses.. Figure 30 shows the VSWR curve with two magnets along the wide face of the antenna aperture. Little additional tuning shift over that for the single magnet was observed because the ferrite was saturating; thus, a higher magnetic flux in the ferrite was not achievable. Figure 31 shows a different electromagnet configuration with the resulting VSWR curves vs frequency. It was noted in the permanent magnet configurations that magnetic fields across the short face of the aperture did not cause large shifts in resonant frequency. The experimental results shown in Fig. 31 confirm these results for the electromagnet case. However, it is noticed that a second minimum occurred with this configuration that did not occur in the unbiased slot antenna (Fig. 31) for B = 0. Figures 32 and 33 show configurations with the electromagnet biasing fields on opposite sides of the aperture opposing each other. Note that the biasing in Fig. 33 differs from that in Fig. 30 because of the top bias field in Fig. 33 opposing that bias on the bottom. In Fi. g 30, the two bias fields are both in the same direction. Again significant shifts in the resonant frequency did not occur. A second minimum VSWR occurs as in Fig. 31, but only for a very large magnetic bias. An attempt was made to wind the electromagnet directly around the cavity part of the slot antenna so that the plane of the coils was parallel to the aperture face and directly behind it, causing the magnetic field to be normal to the aperture. This attempt failed to affect the resonant frequency, possibly due to a weak magnetic field. Heating was also a severe problem. 57

3.5 3.0 VSWR 2.5 No Magnetic Magnetic Magnetic co 4- Magnetic Bias -Bias Bias lC Bias 640 gausses 975 gausses 1100 gausses 2.0 1.0 330 350 400 Frequency (Mc) 450 500 FIG. 28: VSWR VS FREQUENCY FOR MAGNETIC TUNING I 1~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

THE UNIVERSITY OF MICHIGAN 5549-1-F 0 I 00 o0 200 400 600 800 1000 1200 1400 1600 1800 2000 Tuning Bias Flux (Gausses) FIG. 29: TUNING BIAS VS RESONANT FREQUENCY,,_ _ _ _ _ _ _ _ _ __,5 9

Magnetic No MagnetBiagnetic Magnetic Bias Bias 3: Bias 630 gausses 50 350 gausses gausses 0 ~..C~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~C 0 ' I I I III I I I I 330 340 350 360 370 380 390 400 410 420 430 440 Frequency (Mc) FIG. 30: VSWR VS FREQUENCY - ELECTROMAGNET TUNING

oole Frequency (Me)I 300g350 400450-B=l800gausses FG3:VWVFRUNYELCOAN TUI / Il / / 'I "1 ~~~ ~ ~~~B=O I - V C) (U ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~C) s~~~o ~~350 Frequency (Mc) 4 450Z FIG. 31: VSWR VS FREQUENCY - ELECTROM~AGNET TUNINGI

500 I I ~~~~~gausses rd vl vl~~e / = ~~~~~~~~~I. \ CID~~~~~~~~~~~~ I~~~~~~~~~~~~~~~~~~~~~~~ (P~~ ~ ~ ~ ~ I 11ae-.\0 rg / t,..- ~ ~ ~~~~~~I t I~~~~~~~~~~~~~' lv) Unbiased-c100guse Slo I r 300 350 Frequency (Mc) 0 450 FIG. 32: VSWR VS FREQUENCY - ELECTROMAGNET TUNING

I I. 1000 gausses tX~ '// Fs//zt t~,,,1 Inisd G clot \ \ /// - I,,,.,I Z F.- /O TN ~~~~~~~~~~I I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Unbiased —~ Slot -0 I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~:z ~300 350 Frequency (Mc) 400 450 FIG. 33: VSWR VS FREQUENCY - ELECTROMAGNET TUNING

THE UNIVERSITY OF MICHIGAN 5549-1-F 3. 1.2 Antenna Patterns It is important that the magnetic tuning should not impair the ferrite slot antenna patterns. Figure 34 shows a series of antenna patterns taken for the original ermanent magnet tuning experiments shown in Fig. 26. It is seen that the backlobes are somewhat affected by magnetic tuning and that the essential dipole pattern of the errite slot is preserved. No pattern deterioration occurred for bias in any other direction, since only the TE10 mode can exist in the slot cavity. Changes in the lobe irection have been reported in the literature for situations where higher modes exsted. 3.1.3 Efficiency It is essential that the magnetic tuning of the ferrite slot antenna not reduce he efficiency of the slot antenna. Efficiency measurements have been made for both ermanent and electromagnet biasing. The efficiency changed from the original uniased 30 percent efficiency to a biased efficiency of 25 per cent for the permanent agnet on back and 22 per cent for the electromagnet aligned as in Fig. 29. Thus, appears that the effect of magnetic tuning on the efficiency of the ferrite-filled lot antenna is not intolerable. 3.1.4 Theory More extensive derivations of the effect of unidirectional magnetic bias on a ferrite rectangular slot antenna are planned in the future. However, it is felt that he results just presented may be explained. The ferrite is a highly anisotropic edia, which means that if a unidirectional magnetic bias is in the direction of the hort dimension of the aperture, the i in the long direction of the antenna aperture ill not be effected. Since the dominant mode in the cavity is with the H vector along he wide dimension of the aperture, it is to be expected that the only significant effect n P in this wide direction will be when the magnetic bias is in the wide direction. n addition, the wide dimension of the aperture determines cut-off frequency and reonant cavity size. Therefore, when the bias is in this wide direction, the effective ize of the cavity is altered; when it is not in this direction, the effective size of the *gvitv is essentially unaltered. 64

THE UNIVERSITY OF MICHIGAN 5549-1 -F db 410 Mc db 420 Me -10 430 Mc. -~~~~~ 10 ~-25-15 I-20 1 ~ 0-20 V[ —25 (c) FIG. 34a-c: RADIATION PATTERNS (E ) FOR ANTENNA NO. 101 WITH MAGNET. RESONANT FREQUENCY = 420 MC 65 _

THE UNIVERSITY OF MICHIGAN 5549-1 -F db - 20 \ -20 MGE -25 AN (d) (e) db 400 Me -10 410 Me 6 ~-6 -15 -20 Xf~~~-2 -/25 (f) FIG. 34d-g: RADIATION PATTERNS (E) FOR ANTENNA NO. 101 WITH MAGNET AND ALUMINUM PLATE. RESONANT FREQUENCY = 395 MC 66

THE UNIVERSITY OF MICHIGAN 5549-1-F 340 MC3 M 350 Me ~.-15..-15!20o _-20 -25 1 t-25 (h)(i) db 360 Mc /-15 -20. -25 (j) FIG. 34h-j: RADIATION PATTERNS (EF) FOR ANTENNA NO. 101 WITHOUT MAGNET. RESONANT FREQUENCY - 350 MC.....- 67

THE UNIVERSITY OF MICHIGAN 5549-1-F 3. 2 Changes in Slot Geometry From observations on the ridged waveguide it may be anticipated that configurations other than the rectangular slot will give far greater bandwidth of operation. Some measurements of the ridged waveguide, ferrite-powder-filled slot antenna were taken two years ago on this project. Initial experiments were recently performed on the solid-ferrite-filled slot antenna with various segments of the ferrite replaced with low dielectric material (balsa wood) or with metal segments replacing the ferrite. 3. 2. 1 VSWR Figure 35 shows the effect of replacing single cells of ferrite with balsa wood (essentially air). Curve A shows the original VSWR curve for a completely filled ferrite slot antenna. Curve B represents the effect of replacing a single outer cell with balsa wood. Curve C depicts the effect of replacing an interior cell with balsa wood. It is evident that an interior cell is more important than an exterior cell in shifting the resonant frequency. However, no significant change in bandwidth occurs. Figure 36 shows the effect of replacing horizontal rows of cells with combinations of solid metal and air. Unfortunately, this curve was not extended down to 300 Me for comparison with the original resonant frequency minimu on the VSWR curve. In the frequency range 500 to 800 Mc the ferrite in the slot becomes quite lossy and low VSWR curves are probably caused by this loss rather than a well matched radiating antenna. The VSWR of the completely ferrite-filled slot antenna is shown for comparison and the low VSWR effect above 500 Me is observed. Figure 37 shows the effect of replacing vertical columns of ferrite cells with balsa wood. In this curve, the crucial 300 to 500 Mc frequency range is covered. The most significant effect is seen in Curve B of Fig. 37, which shows a very large increase in bandwidth occurring when the outer vertical columns of cells are replaced with balsa wood and then blocked off at the aperture with a metal iris. Effects such as shown in Curve B will be much more thoroughly explored in future work. |__ _ _ _ _ _ __ - 68

A - All blocks ferrite. B - Block 1, 6,11,16, 5, 10, 15 or 20 replaced with balsa, one at a time 1 2 3 4 5 C - Block 7 or 9 replaced with balsa. 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 4.0 A B Z A B ~~~~~~CC Cy 3.0- \ 2.0 - C) i1.0 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 Frequency (Mc) FIG. 35: EFFECT ON VSWR OF REPLACEMENT OF SINGLE CELLS OF FERRITE IN A RECTANGULAR APERTURE.

7.0 ~.... Original all-ferrite slot antenna, for comparison Blocks 1 - 5 replaced with solid metal and 6 - 10 replaced with balsa. H 6.0 60 -_ _ Blocks 6 - 10 replaced with balsa. 1tr - Blocks 1 - 10 replaced with balsa. 5. 0 I - 4.0- c 2.0 - 400 500 Frequency (Mc) 600 700 800 Z FIG. 36: EFFECT ON VSWR OF REPLACEMENT OF HORIZONTAL ROWS OF CELLS OF FERRITE IN A RECTANGULAR APERTURE.

6.0 A = Blocks 1, 6, 11, 16, 5, 10, 15 and 20 replaced with balsa. B = Blocks 1, 6, 11, 16, 5, 10, 15 and 20 replaced with balsa - balsa section ID of slot blocked off with metallic iris. I C = Blocks 16 and 20 replaced with balsa. I H D = Original all-ferrite slot antenna. I 5.0 A I d I~C 010 501 ', RECTANGULARI A-U 1.0- I I I I I 310 330 350 370 390 410 430 450 470 490 510 Frequency (Mc) FIG. 37: EFFECT ON VSWR OF REPLACEMENT OF VERTICAL COLUMNS OF CELLS OF FERRITE IN A RECTANGULAR APERTURE

THE UNIVERSITY OF MICHIGAN 5549-1-F 3. 2. 2 Other Characteristics The other antenna characteristics have not been well investigated as yet. Several antenna patterns taken for the case of balsa wood replacement of ferrite showed that no large change in the dipole-like pattern of the antenna occurred. No measurements on efficiency were taken. 3. 3 Temperature Effects on Efficiency In Section IV the effect of temperature on ferrite characteristics will be discussed, and it is apparent that high temperatures lead to greatly increased losses in ferrite materials. In this section, a theoretical study of the effect of a change in material Q on the efficiency of the slot antenna is reported. Figure 38 shows a plot of the magnetic Q of the material vs temperature for the ferrite presently being used to load antennas. These curves come from dividing the experimentally determined loss permeability /A4" into the permeability, '. It will be shown that the parameter magnetic Q is the most important parameter in determining slot antenna efficiency. It can be seen from Fig. 38 that magnetic Q deteriorates very rapidly above 1000C. The effect on efficiency of the slot antenna is shown in Fig. 39 for a ferrite powder filled cavity. It is seen that for temperatures above 1000C, the efficiency deteriorates quite rapidly at most frequencies, although for 300 Mc, good efficiency is maintained up to 150 C. These curves are theoretically calculated values and were obtained as follows. The loaded ferrite cavity antenna has been fully investigated theoretically (Adams, 1964). Formulas from this reference give efficiency as 4 1 = r (17) 1+PL/P where sin 2d10 d k2 2 2d) 22 2 (k2a2- (18) ~r (1-R) k a -Rr 72

35- 300 mc 30 25 500 mc Q mag o0m 15 -Ci 200 m \ Mc.0 20 -0 100 Temperature 0C 200 300 FIG. 38: Q VS TEMPERATURE FOR C02Z mag

100 90 z so 70 300 Mc ~, 60 C 50 0 Mc.5 40 400 me 40 PTI 30 30200 mC-~C~ 300 0 200 0 100ao30z Temperature OC FIG. 39: EFFICIENCY VS TEMPERATURE FERRITE-POWDER-FILLED CAVITY ANTENNAS. ka/Ir= 1.8.

THE UNIVERSITY OF MICHIGAN 5549-1-F and PL' r are power lost and radiated, respectively /I', pt" are components of permeability k= in the cavity d, a are the depth and long aperture dimension of the cavity, respectively,B10 is the phase propagation constant in the cavity R is the absolute value of the voltage reflection coefficient of the aperature for the incident dominant waveguide mode. The following assumptions were made in this formula: a) The perturbation approach was used in calculating losses, thus limiting accuracy at low efficiencies. b) The cavity was assumed resonant. c) Wall losses and dielectric losses were assumed negligible. d) The entire cavity was considered as one region for the boundary value problem. e) The ferrite was homogeneous and isotropic. More complex formulas without these assumptions were also derived in Adams (1964). Equation (18) may be simplified to L ~ 2kd r —~~~~~: ~~~(19) Pr 1 2 Q(1-R2) 1 k a where Q=p,'/lt? The second numerator term ofi 18) is small except very near cutoff, and has been neglected. Since in the region far from cutoff, R and k are not too 75

THE UNIVERSITY OF MICHIGAN 5549-1-F ~~1 ~2kd (20) r7- 1K/Q, where K= (20) 2 _ _ (1-R) - k2a2 K is almost constant and room temperature values are used in the computations. Equation (20) is useful to obtain first-order loss effects on a slot antenna. Nevertheless, since Mu' changes considerably with temperature (19) should be used in any exact computations. Note that while (19) appears simple, the variable R is available only be extrapolating graphs in Adams (1964) and the numerator, kd, must be computed from R in order to give caivty resonance. This calculation is tedious. Note also that for a given cavity antenna in resonance at room temperature, a rise in temperature detunes the cavity, thus violating assumption (b). In the computations, a termperature compensating tuner was assumed. Figure 38 shows the plots of Q for various solid ferrites vs temperature. Figure 39 indicates the effect of this Q on powdered ferrite slot antennas using the crude approximation (20). Note that, in the case of the powdered ferrites, it has to be assumed that Q was the same as for solid ferrites at a given temperature. This was found approximately true at room temperature. In addition, if equation (19) were used, scaling of Mu' and Mu" would have to be assumed. Figure 40 shows a comparison between calculations using (19)+ and its approximation (20). The efficiencies of the example slot antennas are very low for T> 2000 C. Actually, to find the optimum size and balance between E', El", M' and 1A" a computer study should be made; this is tentatively planned. A new method of calculating the reflection coefficient R other than the numerical integration given by Adams (1964) appears to make such an optimization feasible. The MA' and /A" measurements appear to be consistent and correct. The same instrumentation was used for 200, 300 and 400 Mc; however, no explanation is yet offered as to why the efficiency drops at 200 Mc. The result of (18) is then substituted in (17), of course...... _ 76

100 90 80 z 70 -ow-300 mc L 60 C More exact Eqs. (19) and (17) '50 40 Approximate Eq. (2O)Y % w 30 20 10 0 0 100 200 300 Temperature OC FIG. 40: EFFICIENCY VS TEMPERATURE. RESONANT SLOT FERRITE POWDER FILLED ANTENNA. b/a=. 255. ka/w=1. 805 at 270C.

THE UNIVERSITY OF MICHIGAN 5549-1-F IV FERRITE MATERIALS 4. 1 Temperature Dependence of Magnetic Properties of Ferrite The ferrite antenna characteristics described throughout the report have been obtained at very low power levels and at room temperature. In anticipation of the use of ferrite antennas at high power levels and possibly high ambient temperatures, studies have been made on the magnetic properties of the ferrite at various temperatures and frequencies. The type "A" ferrite used is that previously described in other reports by the following formula: Ni Zn Co Fe Al 0 N9696Zn 0404Co 03Fe 1.84.04 4. Figure 41 shows the apparatus used for permeability measurements at elevated temperatures. This equipment provides the means of heating a sample to a specified temperature. The sample is in the form of a toroid which fills a small coaxial cavity. Measurements are taken on the two components of permeability p ', the rea] component of relative permeability, and u" the loss component of relative permeability, using the techniques of Rado (1953) and Lax (1962). Figure 42 shows a plot of /' and u" vs temperature. From these measurements of characteristics it is apparent that the temperature may impose a severe restriction on the use of ferrite antennas. The heating of aerospace vehicles upon re-entry is an example where a severe temperature may limit the use of a ferrite antenna unless special provisions are made to shield the ferrite material. However, in initial tests with moderate (10 watts) transmission power th the antenna, no significant change in slot temperature was noted; thus, internal heating may not be a problem. 78

THE UNIVERSITY OF MICHIGAN 5549-1-F 3e~~~~~~~~~~~~~~~~~~~~o min z ii'~ ~ ~ ~ ~ ~ L z...........il::~~~~~~~~~~~~~~~~d.77~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-..................................~~~~~~~~~~~~~~~~................

THE UNIVERSITY OF MICHIGAN 5549-1-F 14 12 300 Mc 8s~~~~~8~~ 200 Mc. o 26 400 Mc C02z. 4 500 Mc 600 Mc 700 Mc Temperature oC FIG. 42a: RELATIVE PERMEABILITY @"') VS TEMPERATURE FOR 12 ~10 / 200 Mc o 6 2 o~ 500 Me 600 Mc 0 '00 200 300 400 Temperature ~C FIG. 42b: RELATIVE PERMEABILITY (4")VS TEMPERATURE FOR 80

THE UNIVERSITY OF MICHIGAN 5549-1 -F 4. 2. Basic Limitations and Future Potential of Ferrites 4. 2. 1 Introductory Comments A magnetic dipole of moment m, in the presence of an external magnetic field, H, is subject to a torque T: T=uL mxH (21) The torque equals the time rate of change of angular momentum L, or: dL T= - dt ' (true either for a whole or unit volume) and M ge (22) L 2m' where M is the magnetic moment per unit volume, g is the spectroscopic splitting factor m is the mass of an electron (scalar) e is the change on an electron. Putting these three equations together and using y=Upge/2m, the gyromagnetic ratio, the result is dm =dm =ym x H. (23) In a magnetic material with magnetization M, not only the effective value of H inside the material must be considered but also the torques produced through interactions between the separate dipoles. The interaction can be phenomenologically substantiated through the expedient of a power series expansion for the magnetization in terms of the applied field, i. e. aM X = yMxHt - - Mx(M x H) (24) 81.

THE UNIVERSITY OF MICHIGAN 5549-1-F where Ht is the sum of applied H and internal fields, H. and X is the loss constant. The magnetic energy in the absence of an external field, must be produced by and have the symmetry of the magnetic material. This can be introduced by expanding the magnetic energy density for a single crystal in a power series expansion as: 12 2K2 3+2 14 2 4 34 6 U=Ui 0 (Kba1 +Ka2 +Kba3)+(Kea+ K a2 + Kc a)+0(ca) (25) where the K's are constants of the material at a given temperature and the ac's are direction cosines. Those materials with a large value of U. the exchange energy density, are ferrimagnetic. Of interest are hexagonal and cubic structures, and only the lowest trivial value of K will be considered. For hexagonal material 2 3 it follows that K = Kb and U =U +K sin 0 (26) i o 1 while for cubic material, U.=U +K (ca 4+a4+a (27) i o 1 1 2 3 22 2 remembering that al+a2+ a3 = 1. The four cases of interest are: cubic and hexagonal each with K1 <0 or K >0. Table II lists the anisotropy category of many room temperature ferromagnets. Referring back to Eq. (25), the exchange energy density U produces an effective torque which aligns the magnetic moments of each atom to be nearly parallel. The subsequent terms produce torques which are dependent upon crystalographic direction. These torques are describable as effective magnetic fields Han and result in the magnetization being oriented along certain preferred or "easy" directions in the crystal. The effective magnetic fields produced are given in Table III. Turning to a nonoriented polycrystalline sample, the maxi mum value of magnetization possible for the different symmetries is also listed. 82

THE UNIVERSITY OF MICHIGAN 5549-1-F TABLE II: CONPOSITIONS BY ROOM TEMPERATURE ANISOTROPY Cubic, K1 < 0 Cubic, K1 > 0 NiFe204 CoFe204 MnFe204 Fe (metallic) FeO Fe304 Ni (metallic) MgFe204 Very small anisotropy — >Y3Fe5012 Lil/2Fe2 1/204 Hexagonal, K1 < 0 Hexagonal, K1 > 0 Ba2Mg2Fe2022 (g2Y) BaFe12019 Ba2Ni2Fe 12~22 Co (metallic) Ba2Zn2Fe 12022 BaFe18027 Ba2Co2Fe 12022 (Co2Y) BaNi2Fe 16027 Ba3Co2Fe 24041 (Co2Z) TABLE III: Mg is the spontaneous magnetization in each single crystal. M max is the maximum magnetization for a non-oriented polycrystalline material. Cubic Hexagonal K1> 0 K1< 0 K1> 0 K1< 0 H an 2Kl/oMs -4K1/3p M 2K1/PoM 2K2/poM M 0.831 0.866 0.500 0.785 s -__ _ __ _ _ __ _ _ __ _ _ ___ |83

THE UNIVERSITY OF MICHIGAN 5549-1 -F The Curie temperature is that temperature at which the thermal energy density is essentially equal to UO. Above that temperature thermal disorder predominates and there is only a magnetic moment in the presence of an applied field. Magnetic material is useless, as such, more than a few degrees above that temperature. The Curie temperature of many substances is listed in Table IV. 4. 2. 2 Permeability Spectrum The frequency dependence of the permeability is determined from equation (24). It is necessary in all cases to account not only for the fields listed in Section I, but also fields due to discontinuities in magnetizations both at the surface of the magnet and internally to it. These discontinuties produce fields which at times completely cancel the driving field and at other times become essentially infinite. These effects produce a shift in the effective resonant frequency of the sample. To avoid such complexities the discussion here will apply to an infinite sheet of material magnetized perpendicular to the plane. Under these circumstances the field is H=H ejWt+H (28) - -o -an which must be substituted into (24). It is assumed that I Han ~HJI and IMIl IH I The results, for cubic symmetry, or for hexagonal symmetry with K2> 0, are; t = ~,_j),, dM wM w[ )+ (222 2 w2+X 2 2 -= - - _L + t Li-jXWo +Li t1 +,. dH D o o o o D=[ 2-w2(+X)] +4w2w2X2- (29) O O where wM = yMs and wo = YH. Equation (29) for low loss material (i. e., X<<1) becomes: 84

THE UNIVERSITY OF MICHIGAN 5549-1-F TABLE IV: CURIE TEMPERATURES ~C Material T Fe 770 Co 1131 Ni 358 +NiFe204 585 2 4 +MnFe20 300 +Fe304 585 +MgFe204 440 +Li5Fe 2.504 670 +CoFe204 520 BaFe 2019 450 BaFe 18027 455 BaNi2Fe 0 > 520 Ba2Mg2Fe 12022 Ba2Ni2Fe 12022 390 Ba2Zn2Fe 12022 130 Ba2Co2Fe 12022 340 +++Ba3 Co 2Fe 240 410 Y3Fe501 287 +The Curie temperature can be decreased from this value towards absolute zero by partially replacing the divalent cation with Zn or Cd. * Undergoes an anisotropy change at about 280~C. ++A sample of composition Me2Y where Me = Mg. +I A sample of composition Me2Z where Me = Co. -_ ~85 _......

THE UNIVERSITY OF MICHIGAN 5549-1-F (W2 2 XWM~Wo(2o+,2) ) (2 2)2 2 2 2 Xw t (o2 +w2) 222 222 (30) (W + 2XtW + W The real part of the susceptibility resonates at w=w, i. e. the frequency corresponding to the anisotropic field. In the limit of low frequency, the susceptibility is: toM M (31) H (31) o an or to oM (32) where to is the resonance frequency. Equation (32) contains a basic limitation r upon the use of nonsaturated ferrites. The product of the magnitude of the low frequency susceptibility and the resonant frequency is parabolic. The factor WM varies only slightly from material to material while to varies widely from about 0. 1 to 20, 000 Mc. From (30) it is evident that J(" will be substantially small only if t < w, so if the usable frequency range is to be increased o must be increased but this can only be done by decreasing A' ' A very large value of tM is 2r x 8400 Mc, so an initial susceptibility of 10 can, at best, have a resonant frequency of 840 Mc, and a usable frequency range to about 300 Me. The situation is altered for hexagonal structures with K <0. The real part of the susceptibility turns out to be, at very low frequencies. 86

THE UNIVERSITY OF MICHIGAN 5549-1-F X o iv (33) 3w 3~~~0~1 an equation similar to (32) except that in this case w is the resonant frequency within the Basal plane and is independent of the value of K1 of equation (26). On the other hand, the resonant frequency is: 1 w Wr m(w2 -wo)w |Uo0 (34) where 02 is proportional to the anisotropy constant K1 and: 2 2ww X ow =o 2 (35) o0 3 determines the limiting values of X for a fixed value of w O r A good material exhibiting these anisotropy characteristics is Co 2Z (see Tables II and IV). Using Co2Z, an initial permeability of about 50 and a resonant frequency of 800 Me results at room temperature. 4.2.3 Permittivity Spectrum The polarizability of all electron clouds within the material gives rise to a relative permittivity of about 10 to 15 for ferrites. This value is essentially constant and extends at least down through the millimeter wavelengths. The loss associated with this permittivity is, in general, very low. In addition, the multivalent atoms can produce a finite conductivity (and thus imaginary permittivity) through the relation: e =e' - j-. (36) +2 +3 +2 This is particularly relevant for the cases where either Fe and Fe or Mn and +3 Mn are present in the same sample. A slight excess of iron in a sample will produce an increase of up to 8 orders of magnitude in conductivity. It follows that the d - c conductivity is a strong function of the oxygen pressure present during the firing of the sample. 87

THE UNIVERSITY OF MICHIGAN 5549-1-F sample will produce an increase of up to 8 orders of magnitude in conductivity. It follows that the d-c conductivity is a strong function of the oxygen pressure present during the firing of the sample. Another source of permittivity separate from a d-c conductivity is due to a difference in conductivity between the interior of a single grain of material and the surface layer. In many cases an insulating surface layer separates conducting grains. This produces a permittivity with a relaxation frequency equal to the mean transport time of the conducting charge across a grain. A typical relaxation frequency is from 100 Kc to 1 Mc. Below the relaxation frequency, permittivities on the order of 10 exist. Above 10 Mec the permittivity is between 10 and 20. These effects are particularly evident in the MnFe204 compounds, but exist in all ferrites. 4. 2.4 Complex Susceptibilities It is clear from the form of equation (30) that the real and imaginary parts of the susceptibility are related. Although the equation describing the dielectric susceptibility differs slightly from that for the magnetic susceptibility, the real and imaginary parts are also related. It is also clear that i 2 1 (37) U. j(/'-f')H + 2 (E -j ~")E (37) where U is the energy density in the system. The real part of (37) is the energy density stored in the system while the imaginary part is the energy lost. The functional relationship between real and imaginary parts has the result that one cannot arbitrarily increase the real part without an increase in the imaginary part. For a single oscillating system the relationship is: 88

THE UNIVERSITY OF MICHIGAN 5549-1-F 1 =r 22 2 0 W -~ (38) 2 o WX, (1) 2 1 From the first of equations (38) putting Z" ( 1) = 6(w -w1) where the 6 represents the Dirac delta function, then V"(w) becomes: aw 2 L0 ', (0) - 2 2 (compare with (30) for X= ). (39) O -w 0 Equations (38) are for single oscillators only. They must be applied with caution to a solid where the separate oscillators are dependent and the resonant frequencies are not uniquely determined but averaged over the sample. Nonetheless, the relations (38) above, the Kramers-Kronig relations, are useful even when used for the average values. The result is that loss must always exist. Its magnitude is proportional to X and the form of the spectrum can be controlled but the loss can never be eliminated without, at the same time, eliminating the real part as well. The dielectric loss is due predominately to conduction effects, usually local currents. The magnetic loss is due to (1) magnetostrictive coupling, (2) spin wave effects, (3) eddy current losses, and (4) electron level changes. All usable antenna materials have a sufficiently high resistivity so that item (3) is negligible. Item (1) is determined by the magnitude of the magnetostrictive constants. It is subject to optimization through the original choice of material but is only a slowly varying function of composition of the sample and is in the class of structure insensitive properties. Item (2), on the other hand, is structure sensitive with an irreducible minimum. Item (2) can be understood as follows. Referring to equation (30), a resonant frequency wo exists with a particular value of wave number 2. The 89

THE UNIVERSITY OF MICHIGAN 5549-1-F exchange field that produced the magnetic alignment can also be put into an equation of the form of (30). The result is a separate resonance in the exchange field at the same frequency! There is, however, a very much shorter wavelength This represents a magnetic wave traveling through the medium at a lower velocity than that of electromagnetic propagation. Thus there is always the possibility of energy transfer from the electromagnetic to the spin wave modes and the transfer can only be prevented by the elimination of coupling mechansims and this is a structure sensitive property of the material. The coupling centers, on the other hand, occur whenever V M is large within the sample; i. e. abrupt changes in the local magnetic fields. Thus impurity grains, rough surfaces, etc., must be eliminated insofar as possible. Item (4) involves a shift in the energy level of an electron due to the electromagnetic field. After the field maximum passes, the electron decays to its original energy level. (It is interesting to note that the spontaneous magnetic moment, in general, decreases with increasing temperature. This is due to thermally generated spin waves. ) 4. 2. 5 Temperature Effects The anisotropy, in most cases, is very strongly temperature dependent and decreases with increasing temperature. So it follows that wo of equation (30) decreases rapidly and therefore the maximum operating frequency of a given material decreases with increasing temperature. The anisotropy constant K1 for the case of Co2Z decreases until it passes through zero at about 2800C. A factor of importance in antenna material is the magnetic Q=P ' XC", by definition. From Eq. (30) 2 1 dQ 4o Qdto 4 4 ' (40) 0 to -to 90

THE UNIVERSITY OF MICHIGAN 5549-1 -F and in the usable frequency range the denominator is greater than zero and the Q decreases with decreasing w. Thus results can only become worse as the temperature goes up. It then appears that the temperature should be lowered for better results. However, the factor 1'Q is also important, and 2 2 -t i d o 1X da (XQ) - 2 2 (41) XQ dw (o ) O O The left side of Eq. (41) increases with decreasing w. The possible range of operation is limited to a certain temperature range by Eqs. (40) and (41). 4. 2. 6 Conclusions Antenna material could probably be made that would be usable to about 700 Mc, using the hexagonal compounds. At present the lower Q at higher frequencies is the governing limitation. There is now an effort being made in Europe (but none in the United States) to better control the loss and improve the Q. An operating temperature over a broad frequency band in excess of 2250C seems improbable. A lower frequency (200 Me) material could probably be made operable to a temperature up to 350~C.

THE UNIVERSITY OF MICHIGAN 5549-1-F V FUTURE WORK + The future program of the ferrite antenna project should include: 1. An extension of the frequency coverage down to 50 Mc. New materials will have to be acquired and measured, and then employed. 2. Consideration will be given to different types of antennas, particularly the continuously excited traveling wave antennas with and without taper. 3. Additional efficiency measurements on loaded antennas vs frequency of operation will be made allowing more accurate comparisons to conventional antennas. This will include antennas studied in the past as well as the new antennas to be studied. 4. An increase will be made in maximum rf power used in ferrite-heating tests from 10 - 50 watts if possible. 5. Studies of the near fields of broadband ferrite-loaded antennas will be made to determine the phenomenon causing the miniaturization and to compare with theoretical predictions. Particularly important is a determination of current densities and phase velocities. The study of UHF-VHF antennas loaded with ferrite and dielectric materials is continuing at The University of Michigan Radiation Laboratory under Contract Nr. AF33(615)-2102. 92

THE UNIVERSITY OF MICHIGAN 5549-1-F ACKNOWLEDGMENT Contributors to this work include D. M. Oliver and S. Sigman. 93

THE UNIVERSITY OF MICHIGAN 5549-1-F RE FERENCES Adams, A. T. (March 1964), "The Rectangular Cavity Slot Antenna with Homogeneous Isotropic Loading, " The University of Michigan Cooley Electronics Laboratory Report No. 05549-7-T. Dyson, J.D. (October 1959), "The Unidirectional Equiangular Spiral Antenna, " IRE Trans. PGAP, Vol. AP-7, pp. 329-341. Kraus, J. D. (1950) Antennas, McGraw-Hill Book Company, New York. Lax, B. and K. J. Button (1962), Microwave Ferrites and Ferrimagnetics, McGraw Hill Book Company, New York, p. 442. Maclean, T. S.M. and R.J. Kouyoumjian (December 1959), "The Bandwidth of Helical Antennas, " IRE Trans. PGAP, Vol. AP-7, pp. 379-386. Rado, G.T. (1953), "Magnetic Spectra of Ferrites, " Rev. Modern Phys., Vol. 25, No. 1, p. 81. Tang, C. H. and 0. L. McClelland (June 1962), "Polygonal Spiral Antennas, " University of Illinois Technical Report No. 57. 94

Unclassified Security Classification DOCUMENT CONTROL DATA- R&D (Security classification of title, body of abstract and indexing annotation must be entered when the overall report i's classified) i. ORIGINATING ACTIVITY (Corporate author) 2a. REPORT SECURITY C LASSIFICATION The University of Michigan Unclassified 2 b GROUP 3. REPORT TITLE STUDY AND INVESTIGATION OF A UHF-VHF ANTENNA 4. DESCRIPTIVE NOTES (Type of report and inclusive date) Final Report January 1963 through January 1965 5. AUTHOR(S) (Last name, first name, initial) Lyon, J. A. M,; Rassweiler, G. G.; Grimes, D. M.; Rhee, S. B.; Herman, J. E.; Simanyi, A.I. 6. REPO RT DATE 7a. TOTAL NO. OF PAGES 7b. NO. OF REFS February 1965 100 7 8a. CONTRACT OR GRANT NO. 9a. ORIGINATOR'S REPORT NUMBER(S) AF33(657)-10608 5549-1-F b. PROJECT NO. 6278 c. 9b. OTHER REPORT NO(S) (Any other numbers that may be assigned 627801 thIs report) d. 10. A VA ILABILITY/LIMITATION NOTICES Agencies of the Department of Defense and other Government agencies may obtain copies of this report from DDC. Other persons and organizations should apply to U. S. Department of Commerce Office of Technical Services. 11. SUPPL.EMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY Air Force Avionics Laboratory AVWE Research and Technology Division, AFSC Wright-Patterson Air Force Base, Ohio 13. ABSTRACT The results of a program for the miniaturization of antennas through the use of ferrite materials is described. The antennas include the log conical spirals, both within and outside a cavity, the cavity-backed log spiral, a helix, a zigzag, and the cavity-backed slot antenna are described. Generally speaking, linear reductions of the order of 2 or 3: 1 were achieved for the wideband antennas, and above sxil for the slot antenna. An experimental study of ferrite material vs temperatur and frequency is included as well as a theoretical review of the current status and basic limitations of ferrite materials. FORM D D 1 JAN64 1473 Unclassified Security Classification

Unclassified Security Classification 14. LINK A LINK B LINK C KEY WORDS ROLE WT ROLE WT ROLE WT Antennas Ferrite loading of antenna UHF-VHF frequency Miniaturized Antennas Log-conicaLAntennas, ferrite loaded Slot cavity-backed antennas, ferritelloaded _i i,, _ _ _ INSTRUCTIONS 1. ORIGINATING ACTIVITY; Enter the name and address imposed by security classification, using standard statements of the contractor, subcontractor, grantee, Department of De- such as: fense activity or other organization (corporate author) issuing (1) "Qualified requesters may obtain copies of this the report, report from DDC." 2a. REPORT SECURITY CLASSIFICATION: Enter the over- (2) "Foreign announcement and-dissemination of this all security classification of the report. Indicate whether report by DDC is not authorized. " "Restricted Data" is included. Marking is to be in accordance with appropriate security regulations. (3) "U. S. Government agencies may obtain copies of this report directly from DDC. Other qualified DDC 2b. GROUP: Automatic downgrading is specified in DoD Di- users shall request through rective 5200. 10 and Armed Forces Industrial Manual. Enter the group number. 'Also, when applicable, show that optional, markings have been used for Group 3 and Group 4 as author- (4) "U. S. military agencies may obtain copies of this ized. report directly from DDC Other qualified users 3. REPORT TITLE: Enter the complete report title in all shall request through capital letters. Titles in all cases should be unclassified., If a meaningful title cannot be selected without classification, show title classification in all capitals in parenthesis (5) "All distribution of this report is controlled. Qualimmediately following the title. ified DDC users shall request through 4. DESCRIPTIVE NOTES: If appropriate, enter the type of," report, e.g., interim, progress, summary, annual, or final. If the report has been furnished to the Office of Technical Give the inclusive dates when a specific reporting period is Services, Department of Commerce, for sale to the public, indicovered. cate this fact and enter the price, if known. 5. AUTHOR(S): Enter the name(s) of author(s) as shown on 11. SUPPLEMENTARY NOTES: Use for additional explanaor in the report. Entel last name, first name, middle initial. tory notes. If military, show rank and branch of service. The name of the principal author is an absolute minimum requirement; 12. SPONSORING MILITARY ACTIVITY: Enter the name of the departmental project office or laboratory sponsoring (pay6. REPORT DATE Enter the date of the report as day, ing for) the research and development. Include address. month, year; or month, year. If more than one date appears on the report, use date of publication. 13. ABSTRACT: Enter an abstract giving a brief and factual summary of the document indicative of the report, even though 7a. TOTAL NUMBER OF PAGES: The total page count it may also appear elsewhere in the body of the technical reshould follow normal pagination procedures, i.e., enter the port. If additional space is required, a continuation sheet shall number of pages containing information. be attached. 7b. NUMBER OF REFERENCES: Enter the total number of It is highly desirable that the abstract of classified reports references cited in the report. be unclassified. Each paragraph of the abstract shall end with 8a. CONTRACT OR GRANT NUMBER: If appropriate, enter an indication of the military security classification of the inthe applicable number of the contract or grant under which formation in the paragraph, represented as (TS), (S), (C), or (U). the report was written. There is no limitation on the length of the abstract. How8b, Sc, & 8d. PROJECT NUMBER: Enter the appropriate ever, the suggested length is from 150 to 225 words. military department identification, such as project number, 14. KEY WORDS: Key words are technically meaningful terms subproject number, system numbers, task number, etcor short phrases that characterize a report and may be used as 9a. ORIGINATOR'S REPORT NUMBER(S): Enter the offi- index entries for cataloging the report. Key words must be cial report number by which the document will be identified selected so that no security classification is required. Identiand controlled by the originating activity. This number must fiers, such as equipment model designation, trade name, military be unique to this report. project code name, geographic location, may be used as key 9b. OTHER REPORT NUMBER(S): If the report has been words but will be followed by an indication of technical conassigned any other reprt numbers (either by the originator text. The assignment of links, rules, and weights is optional. or by the sponsor), also enter this number(s), 10, AVAILABILITY/LIMITATION NOTICES: Enter any limitations on further dissemination of the report, other than those Unclassified Security Classification

UNIVERSITY OF MICHIGAN 1111113 111111111 1 0 8111119 3 9015 03465 8719