THE UNIVERSITY OF MICHIGAN 7140-1-T STUDY AND INVESTIGATION OF A UHF-VHF ANTENNA Interim Engineering Report February through 30 June 1965 July 1965 Prepared by J. A. M. Lyon, N. G. Alexopoulos, C-C Chen, A. M. Kazi and G. G. Rassweiler Approved by 2/./t.M. L..yon, Prv'p sor t./Electrical Engineering Contract No. AF 33(615)-2102 Project 6278, Task 627801 O. E Horton, Project Monitor Air Force Avionics Laboratory AVWE Research and Technology Division, AFSC Wright-Patterson Air Force Base, Ohio 45433

THE UNIVERSITY OF MICHIGAN 7140-1 -T FOREWORD This report was prepared by The University of Michigan under USAF Contract No. AF 33(615)-2102. The contract was initiated under Project 6278, "VHF-UHF Antenna Study, " Task 627801. This was 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). _.iii....

THE UNIVERSITY OF MICHIGAN 7140-1-T TABLE OF CONTENTS Page LIST OF FIGURES vi ABSTRACT viii I INTRODUCTION 1 II TRAVELING WAVE ANTENNAS WITH FERRITE LOADING 2 2. 1 Conical Log Spiral 2 2. 2 Ferrite-Loaded Helical Antennas 3 2. 2. 1 Bifilar Helical Antennas 7 2. 2. 2 Monofilar Helices 16 III FERRITE SLOT ARRAYS 21 3. 1 Ferrite Waveguide Preliminary Tests 21 3. 2 Preliminary Non-resonant Array Tests 21 3. 3 Magnetic Bias Control of Ferrite Array 25 IV ENERGY TRANSFER TO FERRITE SLAB 2-6 4. 1 Analysis 26 4. 2 Experiments on Energy Transfer and Radiation 35 V SLOT ANTENNAS WITH RIDGES OR IRISES 37 5. 1 Assumptions of the Study 37 5.2 Solid Ferrite Loaded Antenna 37 5. 3 Loaded Slot Antenna with Irises 41 5. 4 Ridged Loaded Slot Antennas 46 5.5 Conclusions and Summary 49 VI FERRITE MATERIALS 56 VII FUTURE EFFORT 60 ACKNOWLEDGEMENTS 61 REFERENCES 62

THE UNIVERSITY OF MICHIGAN 7140-1-T LIST OF FIGURES Page 1 Conical Spiral (No. 200) Loaded with Solid Ferrite Bars 4 2 Impedance Diagram of Solid-Ferrite Loaded Conical Helix Antenna. Bottom Half of Cone Shell Loaded. 5 3 Impedance Diagram of Solid-Ferrite Loaded Conical Helix Antenna. Entire Conical Shell Loading. 6 4 Bifilar 4" Helix with Balsa Wood Core and Cap. 8 5 Fiberglass-Epoxy Tube Form for Helices 9 6 Loading Diagram: Bifilar Helix (No. 213) Full Core Loading. 11 7 Loading Diagram: Bifilar Helix (No. 213) Layer Loading. 12 8 Loading Diagram: Bifilar Helix (No. 213) Layer Loading Plus End Cap. 13 9 Bifilar Helix (No. 213) Antenna Patterns. Loaded vs Unloaded. 14 10 Bifilar Helix (No. 213) Antenna Patterns. Unloaded vs Loaded. 15 11 Monofilar 4" Helix with Small Tube for Center Conductor. 17 12 4" Monofilar Helix (No. 215)1E012 Linear Power. Unloaded vs Loaded. 18 13 4?" Monofilar Helix (No. 215) 1 Ev12 Linear Power. Unloaded vs Loaded. 19 14 Proposed Mechanical Configuration for Waveguide Test. 22 15 Experimental Details to Determine Insertion Loss of Waveguide. 23 16 Simplified Diagram of 9-slot Ferrite Loaded Waveguide Array. 24 17 Coupled Ferrite Slab Antenna 27 18 Energy Transfer Between Two Coupled Lines. 33 19a Impedance Diagram of Slot Antenna Loaded Entirely with Solid Ferrite. 38 19b Impedance Diagram of Slot Antenna Loaded Entirely with Solid Ferrite. Double Stub Tuner Used. 40 20a Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Iris. 42 20b Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Iris. Double Stub Tuner Used. 43..... vi

THE UNIVERSITY OF MICHIGAN 7140-1-T LIST OF FIGURES (continued) Page 20c Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Iris. 44 20d Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Iris. 45 20d1a Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Ridges. 47 2 lb Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Ridges. 48 21c Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Ridges. 50 21d Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Ridges. 51 21le Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Ridges. 52 21f Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Ridges. 53 21g Impedance Diagram of Solid Ferrite Loaded Slot Antenna with Ridges. 54 22 Q and /' For Various Ferrites. 57 vii

THE UNIVERSITY OF MICHIGAN 7140-1-T ABSTRACT This report covers the preliminary efforts on the experimental and analytical studies involving the loading of various types of antennas with ferrite material. Major emphasis has been placed upon improvements of conical log spiral antennas through the use of ferrite loading techniques. With this in mind, a series of basic studies on the ferrite loading of helices has been made. These studies indicate the effect of thickness and placement of ferrite material. Data are given showing the shifting of the operating frequency due to the introduction of ferrite material. Also some information is given on the bandwidth for these study type antennas. A preliminary effort has been devoted to the design of simple slot arrays using ferrite material with provision for magnetic control of these arrays. This technical report has been reviewed and is approved....._,,,,viii

THE UNIVERSITY OF MICHIGAN 7140-1-T INTRODUCTION The contract effort described here is a continuation of a previous effort + showing the possibility of improved performance for UHF-VHF antennas with ferrite loading. The early effort in this contract period has been to clearly show the importance of the amount of ferrite loading as well as the placement of ferrite loading with respect to traveling wave antennas such as the conical log spiral antenna. The preliminary experiments described are on helices since the study of the helix antenna is often considered to be a good analytical starting point for the study of the spiral log conical antenna. Anticipated effort on this project will include the analytical study of the loaded conical log spiral antenna. Work has been initiated on the log zig-zag antenna with ferrite loading. Also, effort has been expended which resulted in a preliminary design of a ferrite-loaded waveguide test, and a preliminary design on ferrite slot arrays using this waveguidq one of which is capable of magnetic control. Early work on previous contracts has shown that magnetic bias can shift the center of frequency of the operating band of an antenna. The magnetic control of the slot arrays will make use of the change of the incremental permeability of the ferrite material, thus providing shifts in the phasing of the various elements. + AF 33(657)-10607, Air Force Avionics Laboratory.

THE UNIVERSITY OF MICHIGAN 7140-1-T II TRAVELING WAVE ANTENNAS WITH FERRITE LOADING The analytical work so far has been to review available analysis of helices and conical log spiral antennas. Such analysis has for the most part, been on unloaded types of antennas. Extensions of this analysis to ferrite loaded conical log spiral antennas have not progressed to a form suitable for inclusion in this report. Pertinent references useful for this type of analysis are listed at the end of this report. Additions to the analysis maybe based on a mathematical model selected after detailed information upon the ferrite loading of helices is available. The conical log spiral antenna could also properly be called the conical log helix antenna throughout this report; both terminologies are used. Specific types chosen for ferrite loading of traveling wave antennas include the conical log spiral antenna and the log zig-zag antenna. These choices were made because one of them represents an often used circularly polarized antenna, whereas the other is a linear polarized antenna. 2. 1 Conical Log Spiral The conical log spiral antenna with ferrite loading is being considered both from the experimental and analytical viewpoint. Since the conical log spiral was loaded with powdered ferrite, as reported in the final report on the previous contract covering this study (Lyon et al, 1965), it was decided to ascertain how loading of a conical log spiral with solid ferrite material would affect its frequencies of operation. The difficulties of loading with solid ferrite are that the available ferrite, EAF-2, is available only in the large bars, 7"xl"x 1/2". Since the material cannot be readily duplicated without some expense, there has been some reluctance to machine these bars to fit any particular geometry desired at the moment. Therefore, the uncut bars were taped to the inside of the conical helix in the best way possible, leaving a minimum air gap

THE UNIVERSITY OF MICHIGAN 7140-1-T between the bars and the windings of the helix. The conical helix selected for this study was No. 200, the characteristics of which were detailed by Lyon et al (1965). A photograph of No. 200, loaded, is shown in Fig. 1. The lowest operating frequency of this conical helix when unloaded is approximately 360 MHz. Figures 2 and 3 show the input impedance due to a partial and full loading of the bars. Figure 2 shows the effects when bars cover only the bottom half of the conical helix and Fig. 3 shows the effects for loading over the entire interior. In each case, the bars are loaded only one bar deep, i. e. the loading was approximately a one-half inch shell. It is apparent from the figures that even at frequencies down to 280 MHz (partial loading) or 245 MHz (full loading) a VSWR of approximately 3 or less is maintained. The results indicate that the reduction in the lower operating frequency of 80 - 100 MHz may be achievable with solid bar loading, if radiation patterns also show this reduction. The results further indicate that the ferrite bars, even though they have much greater and e than the powdered form, do not appear to cause a greater decrease in the lowest operating frequency of the conical helix than the powder causes. Further studies of impedance are planned. The antenna patterns of this loaded conical helix were less satisfactory than the impedance behavior. The beamwidths were greater and the patterns fragmented. The presence of discrete ferrite bars may hopelessly complicate ferriteair boundary effects. The higher /t and c may emphasize such boundary effects. Further tests using much smaller strips of the Q-3 ferrite may allow a more uniform solid ferrite loading, within the acceptable frange of frequency (below 200 MHz) for this material. 2. 2 Ferrite-Loaded Helical Antennas The experimental study of the conical log spiral is being preceded by a series of experimental efforts on ferrite-loaded helical antennas, since the basis for analysis for the conical log spiral antenna is that each active region behaves approximately as an equivalent bifilar helical antenna with the same pitch angle

THE UNIVERSITY OF MICHIGAN:i o00)::: V = FEf E B RS FIG. 1: CONICAL SPIRAL (No. 200) LOADED WITH SOLID FERRITE BARS 4

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 \ 9 ~\&g20 / 150 ~7 0100 2808 9)~~~ 0~~~290 ~~~~~430 \~ 1600 3 0240 420 0 VSR 0200 0, ~ ~ ~~340~070 o175 060 310160 ~~420~~o220 200200 90 070 3320 I 070 o175 / r~ so ANTENNA. Bottom Half of Cone Shell-Loaded, Freqluencies in MHz.

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 120 60 o 1 00 1 150 150 30 ~180 33t 0 ~240 0 130 / FIG. 3: IMPEDANE DIAGRAM OF SOLID FERRITE LOADED CONICAL 6/~~~~~~160 140 VS R 300 ]. o....... 4 20 10 5 120 2 1.5 0230 350 190 2 400 360 210 410260__ 330 310 ~ 210 0240 o 130 24~ 0170 300 HEIJX ANTENNA. En~tire Conical Shell Loading. (Freqluency M/liz).

THE UNIVERSITY OF MICHIGAN 7140-1-T and diameter. Several turns of the log conical spiral actively participate in the radiation phenomena. It is assumed that the analysis of the loaded helix will apply at least as a preliminary step in the analysis of the log conical spiral loaded with ferrite. In the last final report (Lyon et al, 1965) there was a section on the ferrite loaded helix in which a brief analysis was made. Also, there were some simple radiation patterns given and a description of the relevance of the K - 1 diagram for the unloaded helix. In recent work, considerable effort is being made to extend the interpretation of the K- 3 diagram with the objective of finding more precisely the dependence of the propagation constant of the phase velocity around the turn upon the ferrite loading. A series of experiments have been designed for various types of helical antennas. Monofilar and bifilar antennas with various diameters and pitches are used in these experiments. A number of the most informative situations are depicted in the descriptions of the experimental effort which follow. 2. 2. 1 Bifilar Helical Antennas. A 4"11 dia. bifilar helical antenna was tested with various loadings of EAF-2 ferritepowder. The parameters of the basic antenna are listed in Table I. Figure 4 shows the basic antenna and the balsa wood insert used for retaining ferrite layers. The bifilar antenna was fed with an infinite balun set-up similar to that used in conical log spiral antennas. The validity of using this balun was partially checked by observing variations in antenna pattern as the coaxial feed was manipulated. Less than twenty percent variation in signal amplitude was noted due to such changes, indicating that antenna currents had decayed sufficiently by the end of the helix to justify using an infinite balun feed arrangement. The form upon which the helix was wound was fiberglass (Fig. 5). The effect of the fiberglass and balsa wood is presently being studied. In general the effect is expected to remain constant for the 'with' and 'without' loading cases.

THE UNIVERSITY OF MICHIGAN 7140-1-T FIG. 4: BIFILAR 4" DIA. HELIX WITH BALSA WOOD CORE AND CAP. 8

THE UNIVERSITY OF MICHIGAN 7140-1-T FIG. 5: FIBERGLASS-EPOXY TUBE FORM FOR HELICES.

THE UNIVERSITY OF MICHIGAN 7140-1-T TABLE I: ANTENNA NO. 213 Helix Diameter 4.15" Helix Length 10" (6. 5 turns) Feed Type Infinite balun, bifilar, no ground plane. Pitch 1. 5" (6. 6~ pitch angle). Conductor RG58U cable stripped of outer insulation. Form Fiberglass-epoxy tube, three layers ( 1/16" thick, 11" long). In measuring antenna performance, patterns were first taken without material loading and then the core inside the helix was entirely loaded with ferrite powder as shown in Fig 6. Patterns were taken on this antenna to observe the frequency of axial radiation and the change of this frequency with loading. Finally, the loading was reduced to an interior layer or shell by placing an insert of balsa wood, assumed to be essentially equivalent to an air core, inside the helix and placing ferrite powder between this insert and the fiberglass retaining tube (Figs. 7 and 8). One shell loading shown is with a powder 'cap' or layer at each end of the antenna; the other shell loading was without this cap. The Eo patterns of the 4" bifilar helical antenna are shown in Fig. 9 and the E0 patterns are given in Fig. 10. Results are given for various frequencies and both the ferrite-loaded and the unloaded axial patterns are displayed. The solid patterns are for the unloaded cases, the dashed patterns are for the 1/2" powdered ferrite layer and the dotted patterns are for the ferrite powder in the entire core. The figures show that the unloaded helical antenna had an axial mode frequency at approximately 710 - 720 MHz whereas the loaded antenna, both with the full core loading and with the 1/2" layer loading, show an axial mode frequency approximately 550 - 600 MHz. Therefore, the powder loading causes a reduction of approximately 110 - 160 MHz in operating frequency. 10

THE UNIVERSITY OF MICHIGAN 7140-1-T 4" Dia. Fiberglass Tube, 11 3/8" Long Ferrite Powder 1/2" Balsa Wood Plugs Side View Ferrite Powder FIG. 6: LOADING DIAGRAM: BIFILAR HELIX (No. 213) FULL CORE LOADING. 11.

THE UNIVERSITY OF MICHIGAN 7140-1-T 4" Dia. Fiberglass Tube, 11 3/8" Long. 1/2" Layer Ferrite Powder 3" dia Balsa Wood Core 1/2" Balsa Wood Plugs Side View 1/2" layer Ferrite Powd End View FIG. 7: LOADING DIAGRAM: BIFILAR HELIX (No. 213) LAYER LOADING. 12

THE UNIVERSITY OF MICHIGAN 7140-1-T 4" Dia. Fiberglass Tube, 11 3/3" Long. Ferrite Powder 3" dia. Balsa Wood i3/8 Core 1/2" Balsa 11 3/8?" 8?" Wood Plugs Side View Ferrite Powder Balsa Wood Core End View FIG. 8: LOADING DIAGRAM: BIFILAR HELIX (No. 213) LAYER LOADING PLUS END CAP (Ferrite Powder Thickness: Ends 1 3/46", Side 1/2" ). 13

THE UNIVERSITY OF MICHIGAN 7140-1-T ~~~~~~~~1.0 -~~~~~~~~1.0 - 1.0 550 M HZ -/.. (d) (e) () I.0 1.0 I 5 5 ''~ Ii 550 MHz ',. ' ]~ (c) 710 MHz 500 M Hz (a) (h) ( p11.0 1.0 I(~ ~ ~ -..Tr II1 I - A -% -N"- -vr IIv r%-,vi r, v w, - 600 MHz 680 M'Hz, = LINEAR POWER. 0 = POLAR ANGLE, P = POWER RECEIVED, F9I- AIR LOADED, HFULL CORE FERRITE POWDER LOADING, - - -. 5" INTERIOR LAYER FERRITE POWDER LOADING. 14

THE UNIVERSITY OF MICHIGAN 7140- 1-T,, 1.o0.1.0, ' Ir! I!' _ I,5\ J,/, c- 90 t~, '~ +900 I x 'I 500 MHz 550 MHz (a) (b) 1.0 t0 t.0 1.0 iI ',~2.3 vertical 600 MHz 620 MHz (c) (d) - 700;.MHz (e).o.0 0.0 710 MHz 750 MHz (f) (h) (g) FIG. 10: BIFILAR HELIX (No. 213) ANTENNA PATTERNS. UNLOADED VS LOADED E- LINEAR POWER, 0 = POLAR ANGLE, P = POWER RECEIVED, AIR LOADED, ---- FULL CORE FERRITE POWDER LOADED, --.- 5" INTERIOR LAYER FERRITE POWDER LOADED

THE UNIVERSITY OF MICHIGAN 7140-1-T It should be noted that relative amplitudes between different frequencies or polarizations are not comparable due to normalizations made in drawing the patterns. The only relative amplitudes that are comparable are those appearing on one sub-plot, i. e. the same frequency and polarization. These comparisons within subplots were plotted relative to a constant matched power in and therefore indicate relative radiation efficiency. There are certain discrepancies in Figs. 9 and 10. For example, at 600 MHz, one polarization shows an on-axis pattern and the other polarization shows an offaxis pattern. Furthermore, at 500 MHz, one polarization indicates that full core loading has a larger amplitude, whereas the other indicates a larger amplitude from the partial core or shell loading. Even though amplitudes between plots are not comparable, one expects a conclusion as to the best loading method to be the same for both polarizations of a circularly polarized antenna. This anomaly in results is probably due to pattern asymmetry, indicated by a measured axial ratio of approximately 1. 3 in both loaded antennas. Also, at 500 MHz, one polarization indicates that full core loading is more effective, whereas the other polarization indicates that neither loading is very effective due to an off-axis main lobe. It is apparent that more comparison data is necessary for air core helical antenna. Such anomalies of data will be removed or clarified in the final report. 2. 2. 2 Monofilar Helices In order to determine the effects of ferrite powdered loading on monofilar helices, several tests of 4" and 5" dia. helices were fabricated. The specifications for Antenna No. 215 (Fig. 11) are given in Table II and antenna patterns are presented in Figs. 12 and 13. Several conclusions may be drawn from these figures. First, a reduction of the center operating frequency due to loading, of about 150 MHz, (approx. 650 MHz to 500 MHz) is seen. Second, the radiated powers for the ferrite loaded case are 16 -

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THE UNIVERSITY OF MICHIGAN 7140-1-T.5.5.5 \DIR P~~~~~~~~~~ / I 151 \ - 1.s -1.0~~~~~~~~~~~~~ x-1.0 [~~~~!/ I \/ ( 5- ~ ~ 1 ~5 - (d) (e)~~~~~~~~~~~~- I ~~~~~~~/5 (a) (b) - (c)" 250MHz 300MHz 400MHz -- 1., —4.5 / 1000 1.0. I.8~ I~~~~~ ~ 1 / I \G 1 4 /" /H (. 1 T-M 2n \ P/ /P/ '~ ~ ~ ~ ~ ~ ~ ~ ~ ~~/ \ P/ (d) Y;(e) t-''f '" 450MNH z 500 M~Hz 550Mz 1.5 1.5 1.5 ~ P/10 -1.0 1C / I 'I~~~~~~~~~~~~~~~~~ -.5 / I -.2 / J I f\~~~~~~~ \ x/ / %! (g) (h) (i) 600MHz 6O0MHz \ \ 700MHz \ \ \ ) FIG. 12: 4" DIA. MONOFILAR HELIX (NO. 215) 1E012 LINEAR POWER. - UNLOADED, --- FULL CORE FERRITE POWDER LOADED. P = POWER RECEIVED. 18

THE UNIVERSITY OF MICHIGAN 7140-1-T 1.5 1.5 T1.5 I..5 "-, Y"'~/lo 10 (a) b) t (c) 250MHz 300 MH2 400 MH; 1.5 1.5 - -15 (d) (e) (f) 450MHz 500 MHz 550 MHz 1' —. ' — i1.51 I 5 (g) (h) ( 600 MHZ 650 MH 700 H FIG. 13: 4" DIA. MONOFILAR HELIX (NO. 215) IE I2 LINEAR POWER. UNLOADED --- FULL CORE FERRITE POWDER LOADED. P = POWER RECEIVED.

THE UNIVERSITY OF MICHIGAN 7140-1-T much greater than for the air loaded case (the notation P/N, referring to the ferrite case on the figures, indicates that the power received divided by N was plotted). Since the plots are relative to a constant net (matched) power input, the greater received power is apparently due to increased radiation efficiency. This result will be re-checked. TABLE II: ANTENNA NO. 213 Helix Diameter 4" Helix Length 5 turns Pitch 3" (130 pitch angle) Conductor 7 strand, 14 guage, copper stranded antenna wire. Form Fiberglass tube, 14" long 3 layers thick ( 1/16") Feed Ground plane, type N connector........ 20...

THE UNIVERSITY OF MICHIGAN 7140-1-T III FERRITE SLOT ARRAYS In order to study the effects of magnetic fields on ferrite radiators, a preliminary design for an array of slots placed in a waveguide filled with ferrite material has been made. The array has not been fabricated; plans for the investigation are being worked out. 3. 1 Ferrite Waveguide Preliminary Tests The waveguide filled with ferrite is shown in Figs. 14 and 15. This waveguide will be used for preliminary tests; transmission characteristics will be measured with emphasis on insertion loss. One objective will be to find out whether the ferrite filling composed of small sticks of ferrite is adequate. There is some question as to whether the interstices associated with this assemblage of sticks offer a detrimental influence. Hopefully, the interstices effect has been minimized by aligning the long dimension of the sticks with the direction of propagation of energy in the waveguide. This preliminary experiment should serve as a check on the coupling arrangements from the coaxial cables used to feed power to the waveguide and extract power from the waveguide. 3. 2 Preliminary Non-resonant Array Tests A preliminary design of an array of several slots with an array length somewhat over three wavelengths in free space for operation in the vicinity of 200 MHz or less is shown in Fig. 16. This array has been designed so that it is a nonresonant array making use of the traveling wave from right to left in Fig. 16. Although the array has several slots,its directivity will be quite low since this depends on the array length in air. Each of the slots of the array is filled with ferrite material; otherwise, these slots would be below cut-off frequency. This array can be modified by having an additional 1/8l layer of ferrite caused by having one stick of ferrite placed on top of the ferrite in the slot. The slots have been designed

+ + + + IIThick Aluminum Plate H Insulated Feed Loop Insulation 0 Coaxial feed ferrite ferrite from the side piece piece 0.3 cm,* ~17.5 cm Earthed to the bottom plate FIG. 14: PROPOSED MECHANICAL CONFIGURATION FOR WAVEGUIDE TEST.

Lossy load termination Output Fee 6.55 cm _ /.55 cm / (~, _ t — r-~ —~-, ---------- 100 cm - '| 0.3 cm r, FIG. 15: EXPERIMENTAL DETAILS TO DETERMINE INSERTION LOSS OF WAVEGUIDE. Thickness of one ferrite strip = 0.3cm. Dimensions of one ferrite piece= 2. 82"x0. 49"x0. 12". Fourteen pieces lengthwise = 100cm. 14 pieces width-wise = 17.5cm. ~ z

THE UNIVERSITY OF MICHIGAN E-i II 0 cli~~~~~~~~~~~~~2 ><~~~~. ~~~~~ o c'J.C_ t6 0E - 0~. O 0 ~~~~~~~~~~~~CI) I! pcWE'~ I 4% E 0 24 24~E F~

THE UNIVERSITY OF MICHIGAN 7140-1-T with a dimension of 0.5"x2.83"x0.125". The ferrite to be used in this design is Q-3, manufactured by Indiana General Corporation. This ferrite is relatively new to this project; more information on the material is given in Section IV. 3. 3 Magnetic Bias Control of Ferrite Array The array shown in Fig. 16 has been designed to demonstrate the usefulness of ferrites in such an antenna. The use of ferrite material offers a possible method for controlling beam shape or position by the application of a magnetic field. For the purpose of demonstrating magnetic control, a still simpler array is contemplated. For this purpose an array having only three slots may be used. The space between adjacent slots will be such that a magnetic field can readily be produced by pole faces placed in these regions. The most convenient arrangement for pole pieces is to have a magnetic field which will line up with the direction of the E-field in the waveguide. The application of a magnetic field in this direction offers the possibility of control by causing a phase shift in the transmission mode between each two slots. For the 3-slot array, there are two such intervals for the application of magnetic field. At each of these two locations,the extent of the magnetic pole piece in the direction of propagation would be important. It is through the active width of the magnetic field pole piece that the permeability of the ferrite can be changed (reduced). An important advantage of this simple design is that it allows the magnetic pole pieces to be very close together. In previous experiments on the magnetic control of slot radiators, the distance between the pole pieces was much greater. The arrangement discussed here should make possible the use of magnetic fields greatly in excess of those previously used; fields as high as 1500 Gauss may be obtained. 25

THE UNIVERSITY OF MICHIGAN 7140-1-T IV ENERGY TRANSFER TO FERRITE SLAB Studies have been made of continuously excited (i. e. excited over a large portion of the antenna length) traveling wave antennas (Spitz, 1962; Walter, 1965; Weeks, 1957; Rumsey, 1953). Recently, this laboratory began studies of such antennas using ferrite materials. Specifically, a mathematical study of the energy transfer process from the exciter (in our case, a helix) to the ferrite slab (the intended radiating mechanism ) has been made. In a study of energy transfer into a ferrite slab one can start with the proposition that with two transmission lines coupled together, energy fed into one line will be transferred optimally to the second, under certain conditions. The voltage and current differential equations for each of the two transmission lines have been written. A consideration of the coefficients involved in these transmission lines indicates the dependence upon mutual coupling factors. When the second transmission line is to serve as a radiator, it is expected that the energy transferred to this line will be radiated at the far end in the end fire direction. 4. 1 Analysis In order to cause a strong coupling between the feeding electric circuit and the receiving ferrite slab the phase velocity of the electric circuit in the axial direction must be adjusted to be approximately the same as the wave phase velocity in the ferrite slab. The phase velocity of the helix of the electric circuit is approximately: vp= csin ~ where ~ is the pitch angle and c is the velocity of light. Treating the helix as a transmission line with distributed L and C, the ferrite slab may be considered to be another transmission line. The arrangement of lines is shown in Fig. 17. Due to.........~ >26

THE UNIVERSITY OF MICHIGAN 7140-1-T V1(x) I1(x) ----!\\\\\0t\\ \\\tt \ \\\ \\ Helix F g\\~_ ////////////////Ferrite Slab V2(X) I2(X) ~ Ground Plate FIG. 17: COUPLED FERRITE SLAB ANTENNA the excitation of the helix,there is mutual coupling between the helix and the ferrite slab. The circuit equations are Circuit No. 1: Helix: dV1 dx= z1I1+z2IZ (1) d{ dx YlVl+Y12V2 (2) Circuit No. 2: Ferrite dV2 =z212+z 2111 (3) dx 2I2 Z211 (3) dI2 dx Y2V2+Y 21V1 (4) Let z 1/y1, Z2 =z2/y2. (5) Multiply equation (2) by + Z1 and add the result to (1), dX (V1 1 -J(V1 1 )+zl2 -Y12Z2 1 2 Multiply (4) by + Z2 and add the result to (3), d (V2 +I2Z2)= -Z J 2 (2 -+I22)+ z21I1 +Y21Z2V1 27

THE UNIVERSITY OF MICHIGAN 7140-1-T Define the following modes. V -+I1 Z V -+IZ Al+ 47Zl A2~ 422z2 (8) There are two modes (+ = forward, - = backward waves) propagating in each circuit. All modes mentioned are a subclassification within the TEM mode existing on each line. V1 = 2 1 (Al++Ai_) [= 2 I A+A for Circuit No. 1 (9) Ii=-(Al+-Al_) V2=2I22 (A2++A2_) ( 2 for Circuit No. 2 (10) I2= Z(A 2+-A2-) Substituting (8), (9) and (10) into (6) and (7) yields |(d +Y)A1= 2Z 2+ 2-1- -2 (A2++A2) d z21 Y21 2 2qA A(A +A (12) ( ~ I / 2 1+1 -Next, equations (11) and (12) upon regrouping coefficients can be written, ~. _ z12 + Y12 Y121 dx 2 2+ - 2\2 -(13) + 1 )A2(z21 - Y21 Z 1Z2\. (14) - - 2 2 2 Y2 Z):2 z + Y21ZZ + 22 28

THE UNIVERSITY OF MICHIGAN 7140-1-T Note that A1+ means Al+(x). This simplified notation is used from here on. The above equations of specialized forms are the more general set of equations for the coupling of physical systems in terms of modea a1, a2, etc. da1 dx cllal+12a2+13a3+... (15) da2 dx c21al+c22a2+c23a3+ ''. (16) da3 dx= C31al+c32a2+c33a3+ (17) Note that each of the above equations applies for each of the lines; the numerical subscript used in these is a mode designation much like the + and - used heretofore. Now: Ai+ = forward mode in Circuit No. 1 A2+ = forward mode in Circuit No. 2 A = backward mode in Circuit No. 1 A2 = backward mode in Circuit No. 2. From equations (11) and (12) there are four possibilities of coupling among these four modes and these are (1) coupling between Al+ and A2+ (2) coupling between Al+ and A2_ (3) coupling between A and A2+ (4) coupling between A_ and A2 The total or net power of the two lines at any plane located a distance x from the origin is given by 29

THE UNIVERSITY OF MICHIGAN 7140-1-T V (x)Ii'(x) V (x)I' (x) P(x) =Re + Re (18) Expressing P in terms of modes, this becomes P(x)=2 Al+(x)I _A1(X) +1A2 (x)12 A2_ (X) 2j (19) Evaluating P at x = 0 yields P(0)= 2[Al+(0)2 -LAl (0) 2] (20) Consider each of the four possibilities or cases of coupling in turn. Coupling between two forward modes A1+ and A2+ Jz1 ~+ Y12 Z+c2~ Kz 2)r-gA2K-2IZ 2 12 (21) (22) to Line 2, I z 12 Y12 2Z'Z12 12 Yl1 21..12,+ 21 12 Then equations (21) and (22) simplify as d( z1 2 y12_Z1Z22 Y1 1 2 ( dx-+l2)Ai+= (2 / 2+ (23) d ( Z21 Y21Z1Z (24) 2 - 2,~2)A +(... A A24) 2+ /ZZ' 2 1+2 (22) Using the following inerality holds trcouplinge for the greatesult power transfer from Line No. 1 d d 2 12 2 ( +JCll)A1 C12A2 j) (= 2 -1..d 0d d1= +j 11 )A1 C12 222 and 2 )A2=C21A1 30

THE UNIVERSITY OF MICHIGAN 7140-1-T The above equations are correct for either forward or backward waves. Assume Al and A2+ vary ase ex (T+ j Cll)Al+ C12A2+ (25) (T+ j C22)A 2+=C21A+ (26) For a nontrivial solution, the determinant of (25) and (26) must be zero; this yields T' =- -12 22 ( ) (27) 112 i- C12 C21- 2 (27) Equations (25) and (26) are solved for a pair of values y and PyI which apply only for coupling between Al+ and A2+ modes A () - Me X+ Ne (28) 1+ If the -y 'Is are imaginary, the coupling is called passive; if they are complex, the coupling is called active. Then the solution for each of the two lines must be A+(x)=Me X+NeTX (29) dA 1+(x)x dx (30) Az2+ W) - dx +jCA +(x) (30) 12 Initial conditions are: Al +(x)=A+ (0) (31) A 2+(x)= 0 at x =0. (32) The resulting values of the coefficients M and N are, A1 +(0)7 +jCll M j26 (33) A +( ) 2+ J ll N = - 31(34) j26 31

THE UNIVERSITY OF MICHIGAN 7140-1-T where '-y= j 2 6 (35) 6=/lc12c2 +( C2 (36) A (O)Qy+ A1+ (X)= - j 2 6 '+jCll)e X-(Ty+jCll)e (37) A1+(0) (+ jCell) (TY' +j Cll) A (x)= 1jC)(yTjC)(eYXe 'X) (38) 2+ j26 C12 Assume that -y's are pure imaginary quantities (lossless). Then T = -j (p+6), ' = -j (/- 6) (39) where (CllC22) (40) 6 1 [C12C21 1+( 2 ) (41) J2 (X)~(41) P + power in Al+(x) mode = 2 A +(x) 2A +(x)A'+(x) 1+ 1+ 1+ c 1+ 1+ 12.1+ Define F12 as the power transfer between modes Al+ and A2C21 1 (43) 12 1l-c22) 1 \2/, C12 21 32

THE UNIVERSITY OF MICHIGAN 7140-1-T Then the powers in Al+ and A2+ are Pl+=2 [A1+(X)j2=2[ A1+(0) 2 [-F12sin2 6 (44) P2+2FA+(X)2=2 =IA1+(o)2HA+(X) 2=I +(0) F12sin2 6x. (45) Figure 18 shows the variation of power on the two lines for the forward mode. Note that power is first transferred from Line 1 to Line 2 beginning at 6x = 0. Then from 6 x = r /2 to -x = power is coupled back to Line 1. P 1+ 21 A1+(0)2 6x=r/2 (a) P2+ 2F121A1+(0)12 6X=7rf/ (b) FIG. 18: ENERGY TRANSFER BETWEEN TWO COUPLED LINES..........- ~33

THE UNIVERSITY OF MICHIGAN 7140-1-T Comparing equations (15), (16), (23) and (24) yields Cll=jJzlYlF (46) z12 YlffZ1Z2 2 C 3- (47) C12 2 + 2 (47) C22 = jJZ2y (48) F (49) F12 ( zYi- 1z2Y1 2 1 z12 Y12~Z12_2 z! -j2L if Z1= -jwL z2=-jwL2 Z1 - L/-CC y=-jwC1 Y2=-j1C2 z 2=-jM Y =-jwN Z 2/ where L1, C2, M and N are line parameters per unit length of 1 meter. Then = (50) 12 -+(W2-2CI/L C2 2 1 1+ 2 ( / j tM jwN ]LL2 / CIC2' Optimum coupling occurs if w Vm=CwL2C and F12 equals one. This means total power transfer occurs. _ 34 _34

THE UNIVERSITY OF MICHIGAN 7140-1-T Pl+=2[2LA1+ x )2=2A1+(o)2 L-sin2 2L1 2C / + cC2 2 (51) P 2A2 (x)1 =2IAl+(0)I2sin 2(L Lj/CC Cj + 27 2M 2~NJ2L2 / lcC2 (52) The coupling of the other mode combinations mentioned on page 29 is not given here but will be included as an appendix to the final report. There is very low coupling for Cases (2) and (3) involving, in each case, opposite modes. The coupling for Case (4) involving backward modes only on the 2 lines, is formulated in the same general manner as Case (1) 4.2 Experiments on Energy Transfer and Radiation The experimental program will be used to confirm the energy transfer conditions prevailing for a ferrite radiator which is fed in a manner corresponding to one transmission line being coupled to another. To date, the experimental data acquired have not been sufficient to confirm the mathematical relations. Certain definitive experiments were run using a spiral transmission line for Line No. 1, and various pitches and diameters of such a transmission were used. Also, measurements were used at various spacings of the transmission to the ferrite slab. Radiation from spiral transmission line was not wanted and therefore shielding was introduced so as to make measurements upon the radiation field of the ferrite slab alone. This meant that an objective was to study the ferrite slab as an end fire radiator, knowing that all energy so radiated had to be coupled at the second transmission line from Line No. 1. It is expected that the optimum coupling situation will take place when the phase velocity along the axis of Line No. 1 is very near, or slightly in excess of the phase velocity for a wave traveling in the ferrite 35

THE UNIVERSITY OF MICHIGAN 7140-1-T slab. This criterion is one similar to that commonly used in traveling wave tubes. The results of this experimentation are not entirely conclusive at the present time. It is expected that in the final report itwillbepossible to summarize worthwhile results of this experimental program. It is possible that a test set-up such as used in this study may be used to devise a method of accurately ascertaining the produce of /A and E, since the optimal point for energy transfer may possibly be used as an indicator for the matching of phase velocities. 36

THE UNIVERSITY OF MICHIGAN 7140-1-T V SLOT ANTENNAS WITH RIDGES OR IRISES In continuing the research on ferrite loaded slot antennas that was initiated by this laboratory on earlier contracts, it was decided to modify the slot antenna, if possible, to allow a wider bandwidth or lower frequency of operation for the same given outside dimensions of the slot antenna. Well-known properties of the ridged waveguide, as well as preliminary experiments performed last year, indicated a possible potential for broadbanding or lowering the frequency of operation of the slot antenna. The following study was entirely experimental and consisted of inserting various ridges and metal irises into the ferrite-filled slot antenna and noting the changes and impedance as shown in the Smith Chart of the impedance to the antenna. To reduce the complexity of the data presentation, all Smith Chart grids have been suppressed except for a VSWR scale. 5. 1 Assumptions of the Study Several assumptions were made in processing the impedance data for a 'bandwidth. 1) Tuners were usually not used experimentally. 2) A VSWR circle = 3 was placed about each desired grouping of impedance points to obtain bandwidth (equivalent to the use of a wideband phase shifter and a wideband impedance transformer). 3) No further distortion of the impedance plots by compensation tuning was allowed. Actually, with compensation tuning, somewhat larger bandwidths might well be obtained. 5. 2 Solid Ferrite Loaded Antenna Figure 19a shows an impedance Smith Chart diagram of the input impedance to the slot antenna entirely filled with solid ferrite blocks. All ferrite is solid 37

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 all ferrite blocks 120 60 1 290 310 ~270 150/ \ \30 210 330 \/~ ~ ~ ~ ~ " 360 I0250 ~~~~38~~380!~~~~~~~~~~7! I.1a ~PDNEDAEA FSO NEN ODDETRL!~~~~IHSLDF]EIE(rcunyMz #~~~~~~~~~~3

THE UNIVERSITY OF MICHIGAN 7140-1-T EAF-2 material, the properties of which are summarized in Section IV of this report This slot antenna, entirely filled with solid ferrite, has been thoroughly analyzed by Adams (1964) The operating frequency of this antenna is 352 MHz and the bandwidth is 18 - 20 MHz for a VSWR below 3, as may be seen by drawing a circle (VSWR=3) about the origin of the Smith Chart. Nevertheless, this antenna, if its impedance would be transformed properly, could operate from approximately 333 MHz to 383 MHz (50 MHz bandwidth), as may be seen by shifting the loop located in the upper right-hand portion of the Smith Chart clock-wise to the real impedance axis (e. g. by a wideband phase shifter) and then drawing a VSWR=3 circle about this loop, keeping in mind that the diameter of this circle changes with position on the Smith Chart. The 50 MHz bandwidth is therefore roughly the optimum bandwidth that could be achieved by this antenna with a wideband impedance transformation, but without other optimizing circuits. In order to show the effect of a simple, but very narrowband transformer in the form of a double stub tuner, this solid ferrite loaded slot antenna was tuned with a double stub tuner in an attempt to move the upper right-hand loop to the central region. Figure 19b shows the resulting input impedance,and indicates a drastic change has taken place in the shape of the curve due to the additional phase shift of the double stub tuner. The phase reference for the original solid ferrite loaded slot antenna was at the input to the 'N' connector mounted directly on the antenna. The phase reference for the antenna shown in Fig. 19b with the double stub tuner attached, was at the input to the double stub tuner, a considerable distance from the actual antenna. This caused an additional phase shift down by a more rapid rotation of the input impedance with change in frequency. This second curve (Fig. 19b) has much less optimized bandwidth (approximately 23 MHz) for only slightly lower center frequency. One can conclude that transformation of the input impedance with this particular setting of the double stub tuner, and probably with most other settings, would not be satisfactory for transforming the input impedance in the manner desired for increasing bandwidth or lowering frequency of operation. 39

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 slot loaded entirely 120 o 250 250with ferrite blocks 0450 270 0 150/ \ 30 440 180 _ /i VSWR 42 u 1X 36~~~80~~~~ / 385 \ X 3 V 310 29 330 210 335 330 310 o 425 40 356 320 27o 40

THE UNIVERSITY OF MICHIGAN 7140-1-T 5. 3 Loaded Slot Antenna with Irises Earlier studies by this laboratory indicated that partial blocking of the loaded antenna aperture significantly changed the input impedance of the antenna such that the bandwidth (as measured by magnitude of VSWR) was improved. Figure 20a shows the effect of two irises which are actually aluminum tape covering the front ends of several of the ferrite blocks used in loading the slot antenna. The actual input impedance (referenced to 50 ohms) is poor by any standard. Nevertheless, the loop on the left is interesting since it occurs at such low frequencies. A circle for VSWR corresponding to three indicates a possible transformed bandwidth of 16 MHz centered at approximately 259 MHz. Another attempt at transforming the impedance chart with a double stub tuner had the effects shown in Fig. 20b where the lower frequency of operation loop has clearly been moved closer to the center of the Smith Chart. Although the loop is larger in radius, the bandwidth of 20 MHz around 261 MHz is approximately preserved. The reason that the lower frequency of operation loop has not been placed at the center of the Chart is an experimental difficulty in controlling the placement of this loop with the double stub tuner (which is after all, essentially a narrow band device) In summary, the possibility of operating at a frequency approximately 100 MHz lower than the original frequency of the ferritefilled antenna by simply using an iris, is interesting and potentially useful, but it is accomplished at the expense of bandwidth. Another iris experiment Fi g. 20c) involved covering the lower row of ferrite blocks. This produced practically no impedance changes in the lower frequency of operation; a bandwidth of 42 MHz around 356 MHz is shown and this iris was therefore discarded. In the final iris experiment (Fig. 20d) the iris covered the lower three blocks of the center column. The low frequency loop in the upper left diagram has a potential VSWR = 3 bandwidth of 13 MHz centered around 273 MHz, which is again potentially useful in decreasing the operating frequency, although it drastically reduces the bandwidth. _ 41..

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 covered with aluminum 120 60 tape 260//310 330 \2390 l 3 350 280 150 30 255 270 370 265 258 410 180 1 _ VSWR I -- I97 FIG. 20 10 5 IMPEDANCE3 2DIAGRAM 15OF SOLID FERRITE LOADED SLOT 395 420 390 210 330 0440 42

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 [ _ covered with aluminum 120 60 tape 250 270 VSW o 440 150 / 30 21070255 265 3FIG. 20b IMPEDANCE DAGRAM OF SOLID FERRITE LOADED SLOT ANTENN57 30043 30 _I__ ' VSWR 0o 20 ~t00 325 385:05 210 380 330 340 43

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 covered with aluminum I tape 1200 5 3 160 1 g VSWR ~ 310 0290 330 15o /0270 370'0'~' 3o \ ---4060 0250 FIG. 20c: IMPEDANCE DIAGRAM OF SOI.5 FERRITE LOADED SLOT ANTENNA 210' /33044,2T /0 /~~~~~~~~~~7 lI.2c MEAC LLGI~I F OI ERT ODDSO NEN l~~~IIH II Fejec ~)!~~~~~~~~4

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 covered with aluminum tape 120 0 60 ~21~0/\ /~ 33033 310 3 265 150 60 270 30 285 2! ~~~~~~370 250 FIG. 280 IMPEDANCE DGRAM73 405 410 I I WITH IRIS (Frequency MHz).80 [ 275 395 20 i30 210 330 440 45

THE UNIVERSITY OF MICHIGAN 7140-1-T Experiments attempted using side irises, were unsuccessful. In conclusion, irises appear to act as very narrow band tuners since reflections from the iris (sensitive to frequency) are being used; nevertheless, lower frequencies of operation are achievable with apparently greater bandwidths than would be obtained by using an external tuner. 5. 4 Ridged Loaded Slot Antennas Because of the increased bandwidth and lower operating frequency of the ridg waveguide, a series of slot loaded antenna experiments was initiated with various ridges created by steel or aluminum blocks replacing the ferrite blocks usually used in loading the slot antennas. It is important to note that the ridges were used without regard for possible improvement in matching the input probe impedance, even though the input probe was specifically designed only for the fully filled ferrite slot antenna. Figure 21a (inset) shows two metal ridges extending down to the lower side of the antenna where upper and lower are distinguished in this antenna by the fact that an electric monopole probe feed is used to excite the slot antenna and is inserted in the center of the antenna from the top. Figure 21a also shows the effect of the ridges on the input impedance and indicates again a substantial lowering in the lowest operating frequency obtainable from the slot waveguide. A bandwidth of 35 MHz around 291 MHz is achieved. This is felt to be a significant improvement in antenna performance. The second set of ridges used (Fig. 21b) consists of two sets of two steel block or ridges substituted for the center ferrite blocks. Figure 21b shows then the effect on the input impedance of these center ridges and indicates an operating bandwidth of 50 MHz around 330 MHz. The resulting 50 MHz is essentially unchanged from the completely loaded ferrite slot antenna and the center frequency of 330 MHz is not much different from the original 350 MHz. This loading, therefore, it not considered to be particularly useful....._46..........46.

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 aluminum blocks 120/30 60 150 300 30!0 295 290 80 \VSWR 0 4 20 10 5 3 2.0 1.5 410 0 210 330 o430 240 300 FIG. 21a: IMPEDANCE DIAGRAM OF SOLID FERRITE LOADED SLOT ANTENNA WITH RIDGES (Frequency MHz). 47

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 steel blocks 120 60 250 260 270 150 / \30 290 440O~~~~~~440 I20 10 5 3 2.0 1.5 i 280~ \ O400 _<,, / /!~>; /~ ~ ~ IHRDE (rqec ~)

THE UNIVERSITY OF MICHIGAN 7140-1-T Another double ridge slot antenna (Fig. 21c) shows significant improvement in the lower operating frequency with a possible transformed bandwidth of 44 MHz around 317 MHz. This is a shift downward of 41 MHz in operating bandwidth, a small but possibly useful shift. Figure 21d shows an asymmetrical ridged arrangement used in the loaded slot antenna and the resulting impedance diagram. Again, an important lowering in the operating center of frequency is noted. The resulting bandwidth of 27 MHz around 292 MHz may be useful. The higher frequency loop on the Smith Chart (around 360 MHz) is not considered valuable. Many somewhat less successful experiments were attempted using ridged slot waveguide. Figures 21e, 21f and 21g show such loadings. Although the curves all appear single-looped and reasonably simple, they do not appear to have value either in lowering the center of operating frequency or increasing the bandwidth even when impedance transformations to the center of the Smith Chart are considered. Ridges extending down from the top and ridges covering all (or almost all) of the height of the slot were unsuccessful. Finally, various schemes of replacing ferrite blocks with balsa wood were attempted, the balsa acting essentially as free space or air. Such schemes invariably ended in raising, rather than lowering, the center of the operating frequency. 5. 5 Conclusions and Summary Table III summarizes the results of the ridged slot antenna studies. Figures 20a, 20b, 21a, 21c and 21d showed configurations which were useful in lowering the operating frequency while maintaining a reasonable bandwidth. In all of these, it is noted that a single or double arm iris or ridge in the waveguide is used, extending to the bottom of the waveguide and partially to the top. Most irises or ridges are three blocks high (out of the four) and arranged in a central column. A decrease in center frequency of 60 MHz is not difficult to attain. Ridges appear to have potentially a wider bandwidth than irises. 49......

THE UNIVERSITY OF MICHIGAN 7140-1 -T 90 steel blocks 120 60 270 150 \30 300 360 / 250 320 305 VSWR 315 180~~~~~ I I I *_310 380 i20 10 5 3 2.0 1.5 314 o 400 210 330 o 440 o 420 240 300 FIG. 21c: IMPEDANCE DIAGRAM OF SOLID FERRITE LOADED SLOT ANTENNA WITH RIDGES (Frequency MHz). 50

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 90 steel blocks 120 606 310 280 30O 33 285 295 150/ \ 288 \ \30 ~/~25 ~~~29 290 350 361 3 0'~- -355 30 g VSWR 0 41~~~~~~~~~~0~ 1 I 1 1 1380 120 0 5 3 2.0 1.5 210 40330 0420 240 300 270 FIG. 21d: IMPEDANCE DIAGRAM OF SOLID-FERRITE LOADED SLOT ANTENNA WITH RIDGES (Frequency MHz). 51

THE UNIVERSITY OF MICHIGAN 7140-1-T steel blocks 90 120 ----- 60 290 310 / 270\4 150 / - h320 \ 30 360 ~~~~~~~~~~~/ / ~~380\ 0250 330 40 10 5 3 2.0 1.5 400 420 210 330!~ ~ ~ ~ ~ ~~~~7 l I.2e nPDNEDARr~ FSTI ERT ODDSO NEN!~~~IHIIGS(r~unyNz!~ ~ ~~~~~~~~5

THE UNIVERSITY OF MICHIGAN 7140-1-T 90 v steel blocks 120 60 270 310 35 150 330 320 I340 53 [~~~~~~~~~~7 I I.2f MEAC IGA FSLDFR~~ ODDSO NEN I~ ~~WT IGS(rqec ~) I~~~~~~~~~~5

THE UNIVERS l _i0YlTOF MICHIGAN 90 steel block 120 310360 0270 320 150 / \ \30 i 345 0250 380 [ 210 4 /330 341 340 VSWR 20 10 5 3 2 0 1.5 400 2104 330 o 440 240 300 FIG. 21g: IMPEDANCE DIAGRAM OF SOLID FERRITE LOADED SLOT ANTENNA WITH RIDGES (Frequency MHz). 54

THE UNIVERSITY OF MICHIGAN 7140-1-T TABLE III: SUMMARY OF RIDGE SLOT ANTENNAS Figure Center Frequency Bandwidth Remarks No. (MHz) (MHz) 19a 352 18 No tuner 19a 358 50 Optimum tuning 19b 344 23 Optimum tuning 20a 259 16+ Optimum tuning 20b 261 20+ Optimum tuning 20c 356 42 Optimum tuning 20d 273 13 Optimum tuning 21a 291 35+ Optimum tuning 21b 330 50 Optimum tuning 21c 317 44+ Optimum tuning 21d 292 27+ Optimum tuning 21e Not potentially useful Optimum tuning 21f Not potentially useful Optimum tuning 21g Not potentially useful Optimum tuning + Indicates potentially useful results. Although the impedance diagrams for various configurations of ridges and irises appear useful, the efficiency of the antenna as a radiator must yet be investigated. It is assumed that the antenna patterns will be the usual dipole patterns since the antennas are much smaller than 1 X. Attempts at measuring efficiency with the usual that reflector? method were unsuccessful. It is planned to use direct field strength measurements to determine efficiency. In order to achieve the necessary impedance transformation to make the ridges or irises useful in transforming antenna impedance, a better backing cavity should be designed for each ridge or iris configuration so that a real impedance is faced by the probe rather than the imaginary or partially imaginary impedances now seen. As mentioned, the probe was designed for a fully loaded cavity rather than the partially loaded cavities tested. In addition it may be necessary to specifically design the ridges or irises such that excessive energy concentrations are avoided, since energy concentrations lead to great losses in ferrite structures. 55

THE UNIVERSITY OF MICHIGAN 7140-1-T VI FERRITE MATERIALS During this reporting period attention has been given to extending the use of ferrite loading to lower frequencies (down to 30 MHz). With this in mind, additional ferrite material has been purchased (e. g. Q-3, from Indiana General). Some of the experiments in preliminary design are based upon forms of this material which have been readily available. This material appears to have reasonably good electrical and magnetic characteristics. Some of the designed experiments have been limited because of the availability of ferrite material in proper form. The Q-3 material has been ordered in three forms: 1) Stick (2.85"x0.5"x0.12"); 2) Cylindrical Rod (1.937"x0.25"), and 3) Circular Toroids (0.5" OD x 0.28" ID x0.25" thick). The restriction on the form of the material has resulted in certain experiments being scheduled before others. Ultimately, it is expected that powdered type Q-3 ferrite will be available. This will be obtained by using some of the solid forms mentioned above and pulverizing them through the use of a ball mill. Ferrite type Q-3 appears to have excellent characteristics below a frequency of 200 MHz. Available information on this ferrite, as obtained from advertising circulars, is somewhat controversial. The characteristics are shown in Fig. 22 and will be discussed later. It is anticipated that measurements by this laboratory on the characteristics of the material will supplant the reported values with verified data. In addition to Q-3, a considerable study has been made of other available ferrites. Table IV gives names and manufacturer for several selected high-Q ferrites. The first ferrite, EAF-2, is the one presently used in our ferrite-loaded antenna studies. Its properties have been thoroughly measured by this laboratory. All of the work involving experimental tests of antennas loaded with powdered ferrite have used this material either in powdered or solif form. Its formula is Ni 9696Zn 0404Co. 03Fel.84A. 044 56

THE UNIVERSITY OF MICHIGAN - 7140-1-T EAF-2 SOLID 200- "~ — RCCA 15569-29E 100 -70 -100 - RCA 15569 -29B 10- %\. \ "X RCA15569-63E 7- Q 3 -50 100 200 300 500 700 1000 Frequency (Mc) 30 Q-3 20- RCA 15569-63E tL 10 IZ -EAF2) (different measurements and 7 _* __ — ) samples of same batch) 5 Ferrotron — RCA 5569 - 29 3- RCA 15569- 29E 2- EAF-2 Powder 50 100 200 300 500 700 10000 Frequency (Mc) FIG. 22: Q AND a FOR VARIOUS FERRITES. DOTS AND X's TINDICATE U OF MICHIGAN MEASUREMENTS. 57

THE UNIVERSITY OF MICHIGAN 7140-1-T TABLE IV: SELECTED HIGH-Q FERRITES Ferrite Manufacturer Remarks Production not repeatable. No longer available. Tested at U of M, Several sizes on order. To be Q-3 Indiana General tested. tested. Not a ferrite. Iron impregnated Ferrotron Polymer Corp. plastic. Excellent at high temperatures. Qm and /' measured at U of M. Measured resonance in c' at IZ3 Ferroxcube 100 MHz. 100 MHz. Tested for USAEC by RCA. RCA does not produce. Formula said to be reproducible. The EAF-2 material (designated in previous reports as type A) has been satisfactory for experiments on earlier contracts. It is the same material which was used in the detailed studies of the rectangular cavity-backed slot. The temperature dependence of this material has been reported in Lyon et al (1964). Attempts to purchase more of this material have failed. This may be due to the difficulty experienced in reproducing the high quality of the first batch. The second ferrite, Q-3, has already been discussed. The third ferrite, Ferrotron, has been recently tested by this laboratory. The tests did not substantiate its advertised high-Qproperties at 300 MHz and above. The fourth and fifth ferrites have not been tested by this laboratory except for brief dielectric tests on IZ3. The RCA materials (1963) are experimental and were developed for the U S Army Signal Corps. Currently, RCA is not manufacturing this ferrite, although sufficient information is available for others to manufacture it. Figure 22 shows the Qm (magnetic Q) and.' properties for the various ferrites 58

THE UNIVERSITY OF MICHIGAN 7140-1 -T investigated. It can be seen from the Q curves that the present EAF-2 ferrite from Motorola is better than any other available ferrite except for the RCA experimental ferrite shown. In these curves, the large dots indicate experimental points measured by this laboratory for the EAF-2 and Ferrotron materials. Other curves and parts of curves are from descriptive advertising circulars. Note that the RCA ferrites with very high Q at high frequencies also have very low p properties. This is a common characteristic of ferrites -a very low loss factor usually is accompanied by a low permeability. Nevertheless, it does appear that several of the RCA ferrites are worth investigating for future application in antenna loading. It would be most helpful to have a manufacturing source for some of the RCA ferrites. 59

THE UNIVERSITY OF MICHIGAN 7140-1-T VII FUTURE EFFORT A complete analysis of the ferrite-loaded log conical spiral antenna will be attempted. It is expected that the ferrite loading of helices will enable a more accurate representation of the parameters to be made. These parameters will then be introduced in the mathematical formulation for the log conical antenna. The loaded zig-zag antenna will be studied in less detail. Further emphasis will be placed upon magnetic bias control of ferrite antenna elements and upon power handling capability of ferrite antenna elements. Degradation of ferrite antenna radiation characteristics as power level is increased will be considered. Resumption of the ferrite measurement program is planned for the near future. In order to properly assay the role of ferrite materials, it is necessary to know accurately the critical parameters at the actual operating frequencies. A continuation of this program has been held up, due in part to the unavailability of suitable sizes and shapes of ferrite material. Such shapes have been on order for a considerable time and it is hoped that delivery will be made soon. In continuing the studies of the loading of traveling wave antennas, it now appears that the prior work can be supplemented by further experimentation on the thickness and placement of ferrite layers. Studies are contemplated on the use of coaxially placed spirals allowing appropriate loading on each spiral. Segmented spirals which are at the same time both coaxial and coplanar allowing independent loading of each segment will also be studied experimentally. One of the contemplated experiments on the conical log spiral is an inverted spiral used over a ground plane. The intervening space between the ground plane and the spiral will be at least partly filled with a ferrite material. This, in effect,..... 60

THE UNIVERSITY OF MICHIGAN 7140-1-T will give a graduated filling of ferrite material and it will be possible in this way to make a design where the effective distance to the bottom of the cavity (which is the ground plane) will correspond to the optimum distance of the active region at any frequency (i. e. the distance of the active region to the ground plane). In this way it is hoped that it will be possible to make the active region approximately 1/4X above the conducting ground plane or the bottom of the cavity which backs the spiral. Other loadings will be made on the conical log spiral using the spiral in the more conventional mode of operation rather than as an inverted spiral as just described. Experiments to show the variation of performance of antennas over large and small ground planes will be made. These experiments will deal with antennas which should yield information useful in mounting antennas on the edges or flush mounted in aircraft surfaces. Emphasis will be placed on practical antennas such as slots, slot arrays, conical log spirals and planar spirals. Some attention will be given to the effect of non-planar ground planes. Some of the planned future work would extend beyond the end of the present contract. ACKNOWLEDGEMENTS Contributors to this report include; Chong K. Rhee, U. Edward Gilreath and R. L. Baker. - N 61..

THE UNIVERSITY OF MICHIGAN 7140-~-T REFERENCES Adams, A. T. (1964), "The Rectangular Cavity Slot Antenna with Homogeneous Isotropic Loading, " The University of Michigan Cooley Electronics Laboratory Report No. 05549-7-T. Allen, J. L. (1964), "Array Antennas: New Applications for an Old Technique, " IEEE Spectrum, 1, pp. 115-130. Bevensee, R. M. (1964, Electromagnetic Slow Wave Systems, John Wiley and Sons, New York. Bulgakov, B. M., V. P. Shestopalov, L. A. Shiskin and I P. Yakimenko (1960), "Symmetrical Surface Waves in a Helix Waveguide with a Ferrite Medium," Radio. i. elek., 5 pp. 102-119. Bulgakov, B. M., V. P. Shestopalov, L. A. Shiskin and I. P. Yakimenko, (1961), "The Irreversible Propagation of Waves in a Helix Waveguide Placed in a Ferrite Medium," Radio Eng. and Electronics, 4, pp. 118-134. Chatterjee, J. L. (1953), "Radiation Field of a Conical Helix, " J. Appl. Phys., 24, pp. 550-559. Jasik, H. (1961), Antenna Engineering Handbook, McGraw-Hill, New York, Ch. 9. Jones, H. S., Jr. (1965), "Dielectric-Loaded Waveguide Slot Arrays, " USAMC Harry Diamond Laboratories Technical Report TR-1269. Kornhauser, E. T. (1951), "Radiation Field of Helical Antennas with Sinusoidal Current," J. Appl. Phys., 22, pp. 887-891. Kraus, J. D. (1950), Antennas, McGraw-Hill, New York. Louisell, W H (1960), Coupled Mode and Parametric Electronics, John Wiley and Sons, New York Lyon, J. A. M., et al (1965), "Study and Investigations of a UHF-VHF Antenna, " The University of Michigan Radiation Laboratory Report 5549-1-F, AFALTR-65-64. Pierce, J. R. (1950), Traveling Wave Tubes, D. vanNostrand, Inc., New York, Radio Corporation of America (1963), "Hexagonal Magnetic Compounds, " RCA Report No. 8, AD 420 336. Ramo, S and J. R. Whinnery (1953), Fields and Waves in Modern Radio, John Wiley and Sons, New York. pp. 351, 370 and 371. Ramsay, J. F. and B. V. Popovich (1963), "Series-slotted Waveguide Array Antennas,' IEEE International Conv. Record, t. pp. 30-55.

THE UNIVERSITY OF MICHIGAN 7140-1-T Rumsey, V. H. (1953, " Traveling Wave Slot Antennas, " J. Appl. Phys., 24, pp. 1358 -1365. Shestopalov, V. P., A. A. Bulgakov and B. M. Bulgakov (1961), "Theoretical and Experimental Investigations of Helix-dielectric Aerials," Radio.i elek., 6, pp. 159-172. Spitz, E. (1962), "A Class of New Type of Broadband Antennas," Electromagnetic Theory and Antennas, URSI Symposiun, Copenhagen, (Ed. E. C. Jordan) Pergamon Press, pp. 1139-1148. Thourel, L. (1960), The Antenna, John Wiley and Sons, New York. Walter, C. H. (1965), Traveling Wave Antennas, McGraw-Hill, New York. Watkins, D. A. (1958), Topics in Electromagnetic Theory, John Wiley and Sons, New York. Weeks, W. L. (1957), "Coupled Waveguide Excitation of Traveling Wave Slot Antennas, " University of Illinois Technical Report No. 27. Yakimenko, I. P. and V. P. Shestopalov (1962), "An Experimental Investigation of a Helix Ferrite Waveguide, " Radio Eng. and Electr. Phys., 7, pp. 1047-1054. 63

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 is classified) 1. ORIGINATING ACTIVITY (Corporate author) 2a, REPORT SECURITY CLASSIFICATION The University of Michigan Radiation Laboratory Unclassified Department of Electrical Engineering 2. GROUP 3. REPORT TITLE Study and Investigation of a UHF-VHF Antenna 4. DESCRIPTIVE NOTES (Type of report and inclusive dates) Interim Report - February through June 1965 5. AUTHOR(S) (Last name, first name, initial) Lyon, J. A M. N. G. Alexopoulos, C-C Chen, A. M. Kazi and G. G. Rassweiler 6. REPORT DATE 7a. TOTAL NO. OF PAGES 7b. NO. OF REFS July 1965 63 24 8a. CONTRACT OR GRANT NO. 9a. ORIGINATOR'S REPORT NUMBER(S) AF 33(615)-2102 7140-1-T b. PROJECT NO. 6278 c. TASK 627801 9b. OTHERdREPORT Nq(S)(Any other numbers that may be assigne this report) 10. AVAILABILITY/LIMITATION NOTICES Qualified requestors may obtain copies of this report from DDC. 11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY Air Force Avionics Laboratory AVWE Research and Technology Division AFSC Wright Patterson AFB, Ohio 45433 13. ABSTRACT This report covers the preliminary efforts on the experimental and analytical studies involving the loading of various types of antennas with ferrite material. Major emphasis has been placed upon improvements of conical log spiral antennas through the use of ferrite loading techniques. With this in mind, a series of basic studies on the ferrite loading of helices has been made. These studies indicate the effect of thickness and placement of ferrite material. Data are given showing the shifting of the operating frequency due to the introduction of ferrite material. Also, some information is given on the bandwidth for these study type antennas. A preliminary effort has been devoted to the design of simple slot arrays using ferrite material with provision for magnetic control of these arrays. DD FORM 1473 1 JAN 64 UNCLASSIFIED Security Classification

UNCLASSIFIED _ Security Classification 14. LINK A LINK B LINK C KEY WORDS ROLE WT ROLE WT ROLEL WT Antennas UHF-VHF Ferrite Loading Techniques 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 SECURTY CLASSIFICATION: Enter the. over- (2) "Foreign announcement and dissemination of this all security classification of the report. Indicate whether "Restricted Data" is included. Marking is to be in accord- report by DDC is not authorized. ance 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. Enter 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 publicatin 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 REFERENCEfS 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, 8c, & 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 repcrt 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 3 901 5 03125 90321111111 3 9015 03125 9032