THE UNIVERSITY OF MICHIGAN 7848-1 -Q STUDY AND INVESTIGATION OF UHF-VHF ANTENNAS Quarterly Report 1 February 1966 through 30 April 1966 May 1966 Prepared by J. A. M. Lyon, P.R. Wu, N.G. Alexopoulos, A. M. Kazi and D.L. Smith Approvedby y/.A. M. Lyon, Professor Electrical Engineering Contract No. AF 33(615)-3609 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 This document is subject to special export controls and each transmittal to foreign governments or foreign nationals may be made only with prior approval of AFAL (AVPT), Wright-Patterson AFB Ohio.

THE UNIVERSITY OF MICHIGAN 7848-1-Q TABLE OF CONTENTS Page ABSTRACT v I INTRODUCTION 1 II FERRITE LOADED ANTENNA 3 2.1 A Bifilar Complementary Helical Antenna 3 2.1.1 The Radiation Pattern 3 2.1.2 The Near Field Amplitude 3 2.1. 3 The Measurement of the Phase Velocity Along the Gap 5 2. 2 Ferrite Rod Antennas 9 2.3 Loaded Antennas Types For 30 MHz Operation 11 III ARRAYS 13 3. 1 Interdigital Array Antenna 13 3.2 Ferrite Loaded Slot Array 13 3.2.1 Theory 13 3. 2. 2 Co-ordinate Transformations 14 3. 2. 3 Experimental Work 25 IV POWER MEASUREMENT OF FERRITE LOADED ANTENNA 28 4. 1 Power Capability of Ferrite Loaded Slot Antenna 28 4.2 Loss Tangent, Qm Determination Method For Lossy Ferrites 32 V CONCLUSIONS 36 VI FUTURE EFFORT 37 ACKNOWLE DGE MENTS 38 REFERENCES 39......_ _ _ _ _ _ _ _ _ __ ~iii

THE UNIVERSITY OF MICHIGAN 7848-1 -Q ABSTRACT This first quarterly report describes the effort devoted to the four listed tasks of this project. The largest part of the effort has been devoted to two of the tasks; (1) the conical spiral antenna or the log conical spiral antenna, as frequently called; (2) array antennas utilizing loading effects on elements. The remaining tasks (3) endfire ferrite rod antenna and (4) new antenna types at 30 MHz are covered very briefly. These last two tasks have just been initiated. In addition, some effort has been devoted to electrical properties of material and the measurement of these properties. This information on properties of material will be helpful for the ferrite loading involved in the four numbered tasks. Some data are also included on the power level limitations of ferrite loaded rectangular slot antennas.

THE UNIVERSITY OF MICHIGAN 7848-1-Q I INTRODUCTION During this report period, effort was spent upon each of the four tasks included in the contract. Considerable work was done in the area of log conical loaded antennas and in arrays utilizing ferrite elements. The remaining tasks involving end fire ferrite rod antennas and new types of antennas down to 30 MHz are discussed very briefly, since work has only recently been initiated. Additional work is described which is a background for all of the tasks. This work involves the properties of loading materials and the measurement of such properties. The results on log conical antennas are encouraging. This type of antenna has been under study for some time by personnel on this project with respect to loading with dielectric materials. Now such studies are being extended to loading with ferrite materials. Some progress has been made relative to the attainment of the parameter values listed in the specifications for this type of antenna. The study of the antenna using both transmitting and receiving modes simultaneously has just been started. Various conditions under which there may be error due to intermodulation are now being considered. A complete resume of analytical studies of the loaded helix will be emphasized in a future report. These studies are important for understanding the operation of the ferrite loaded log conical antenna. The use of dielectric rod antennas as endfire radiators has been surveyed. The criteria for design of dielectric rods are being extended into criteria for ferrite rods. A detailed comparison of the operation of ferrite rod and dielectric rod radiators is under way. The use of individual ferrite loaded slots as elements in an array has been attempted. Although one design has been completed, the necessity for modifying the laboratory and the range have delayed experimental verification of the initial design

THE UNIVERSITY OF MICHIGAN 7848-1-Q of this array. However, a brief description of an array using such loaded slots is given. Considerable effort has been given to the study of the interdigital array antenna. A comparison is being made with a somewhat similar array of elements as available from a commercial supplier. This experimental check has not been completed. The analysis of the interdigital array is not presented in this report, since major steps in the analysis are yet to be made. The influence of ferrite loading on the power capability of ferrite loaded rectangular slots is given in some detail. The electrical characteristics of ferrite material are very much temperature dependent. At elevated temperatures, there can be sufficient deterioration of the electrical characteristics so that the efficiency as a radiator of electromagnetic energy is markedly lower. The deterioration of the radiation efficiency occurs at a temperature considerably lower than that required to permanently change the material. Nevertheless, such a restriction may be of great importance for antennas used on aerospace vehicles during the re-entry period.

THE UNIVERSITY OF MICHIGAN 7848-1 -Q II FERRITE LOADED ANTENNA 2. 1 A Bifilar Complementary Helical Antenna A bifilar complementary helix (or narrow gap helix) was constructed and its property as an antenna was investigated. The specification of the antenna is as follows: Diameter: 13 cm Length: 40 cm Gap Width: 0. 1 cm Pitch Angle: 100 Construction: Bifilar, balanced or unbalanced feed. 2. 1. 1 The Radiation Pattern The radiation pattern is shown in Fig. 2-1 where it is seen that the unloaded antenna has good patterns from 600 MHz up to around 900 MHz, which is quite comparable to the equivalent wire helix (its dual) The radiation pattern of a loaded case is also shown. The EAF-2 ferrite shell of 1/2" thick was loaded inside and under the gap. The radiation pattern indicated in Fig. 2-1 seems to give a useful frequency range from 450 MHz up to around 700 MHz, which gives about 0. 75 reduction in the resonant frequency. This is also very close to the value obtained from its dual. 2. 1.2 The Near Field Amplitude The complementary antenna was placed inside an anechoic chamber for the near field amplitude measurement. Since it is a dual of the wire helix, an E-probe was used instead of the H probe that was used in the wire helix measurement. The E-probe was made from a 0. 084 cm coaxial line, the length of the protruding inner conductor was 0. 4 cm, which is bent 90~ with respect to the feeding coaxial line; and a small disk of 1. 2 cm diameter was attached to the outer conductor and 3~~~~~~~h

THE UNIVERSITY OF MICHIGAN 7848-1 -Q /W/ \ 900 MHz 800 MHz 700 MHz irN II i I 600 MHz 500 MHz 450 MIHz (S~~ to~~~~~~~~~~, Unloaded I X tl --— \-....Ferrite Loaded I I 400 MHz \ 300 MHz I I \\ / \_ / FIG. 2-1: RADIATION PATTERNS OF A COMPLEMENTARY HELICAL ANTENNA 4

THE UNIVERSITY OF MICHIGAN 7848- 1-Q perpendicular to the protruded inner conductor. This unbalanced probe was then placed X /10 above the antenna with its inner conductor parallel to the axial direction of the antenna. The near field amplitude is shown in Fig. 2-2. The general shape and the trend is very similar to those of the wire helix previously taken and discussed (Lyon et al, 1966). The best near field pattern is at 600 MHz (which also gives best far field pattern). The near field amplitude was also taken with 1/2" shell loading of K-10 dielectric, as shown in Fig. 2-3 which seems to indicate the best near field pattern at 700 MHz. This is a somewhat confusing and strange result. However, since the radiation pattern is not yet available for this type of loading, it is too early to draw any conclusion. 2. 1. 3 The Measurement of the Phase Velocity Along the Gap. The phase velocity along the gap can be measured accurately if the phase shift along the axial direction is measured by a typical phase mneasurement arrangement. However; it is a very time consuming and painstaking measurement. Therefore, a very crude and easy method was devised. The set-up is shown in Fig. 2-4. The antenna is fed through a PRD standing wave detector with a standard VSWR measurement set-up. The shorting copper ring was moved to obtain a minimum reading on the amplitude meter. Then the ring was moved to obtain a second minimum. The distance between the two minima was recorded for several trials and the average value taken. This should be a halfwave length along the axial direction. This value was then converted to the distance along the gap by dividing by the sine of the pitch angle. With the frequency known, it is then possible to obtain a phase velocity along the gap for different types of loadings at different frequencies. The measurement at or near the resonant frequency is very difficult (if not impossible) because most of the energy is radiated before traveling too far down the helix. Therefore, the phase

0 -.I X 500 MHz 0- 600 MHz ---- 'i700 MHz — \ 800 MHz 900 MHz Z.r 3 O 900 500 r —4 —00X I ~a \\ 4 x 3t Ix I 450C800, 7 6 0 0 a)8 x 5 800 no 9 a)~~~~~~~~~~~ A 10 N, x~~ 0 0 10 20 30 40 Feed Point 1 (cm) End of Antenna FIG. 2-2: NEAR FIELD AMPLITUDE OF A COMPLEMENTARY HELICAL ANTENNA WITHOUT LOADING.

Q0 600 MHz 0 --- - 650 MHz 700 MHz:)8~~~~~~~~~ ~800 MHz 1 pi\\ d\600 C Probe Position: X/10 Above 0 -4 l / < 4I \__ 650 6d — 800 7 8 70 \ 9 FIG. 2-3: NEAR FIELD AMPLITUDE OF A COMPLEMENTARY HELICAL ANTENNA WITH DIELECTRIC LOADING. W7ITH DIELECTRIC LOADING.

rl i Amplitude 1 KHz I Meter Modulator +-2 _ t f_ _i~i_ L PRD Signal Feed Point4 571 - Standing. ~ Generator Wave Detector Shorting Ring Antenna FIG. 2-4: SET-UP FOR THE PHASE VELOCITY MEASUREMENT. Z

THE UNIVERSITY OF MICHIGAN 7848- 1 -Q velocity at the resonant frequency must be obtained approximately by extrapolating the results of other frequencies. The measurement was taken for the unloaded, the metal (cylinder of 4" diameter) loaded, the K-10 dielectric shell (1/2" thick) and the EAF-2 ferrite shell (1/2" thick) loaded cases. The results are shown in Fig. 2-5. The resonant frequency can be read out from the intersection of the zero phase shift axis and the straight lines connecting measured points, i. e. 630 MHz for the unloaded, 650 MHz for the metal loaded, 500 MHz for the K-10 dielectric loaded and 520 MHz for the ferrite loaded cases. 2.2 Ferrite Rod Antennas A study has commenced on the use of high quality ferrite material for rod radiators. An attempt is being made to utilize the previously developed theory regarding dielectric rod radiators. It is expected that the analytical and experimental studies will include the HE11 mode as well as the two higher modes, TE01 and TMO1 modes. The latter two modes will produce a null in the endfire direction. It is also expected that the study of ferrite rods will use a variety of feed structures. Using a helix as a feed structure, it is expected that a rotating HE11 mode can be studied. This mode would correspond to the usual circularly polarized mode of the helix, often designated as the n = -1 mode. Of course, simple circular cylindrical shapes will be studied. In addition, a ferrite panel guide will be used as a radiator excited in the HE11 mode with a vertical polarization. This and other shapes that make use of the image properties of ferrite on a metal sheet will be explored. Some analysis will be made of traveling wave antennas utilizing ferrite rods. It is expected that the field analysis commonly available for the dielectric rod for the HEMN mode will be extended to include the effects of permeability as well as permitivity. The determinantal equation obtained by matching tangential components at the cylindrical interface of ferrite and aid should be solvable utilizing a computer.

K-10 0,5 0.3 / / z 0C 3 / ~ 0.1 -WT300 400 V/ 700 800 900 1000 -0.v4 FIG. 2-5: AXIAL PHASE SHIFT OF A COMPLEMENTARY HELICA ANTENNA WITH VARIOUS LOADINGS.

THE UNIVERSITY OF MICHIGAN 7848-1-Q It is expected that the loss characteristics of the ferrite will be incorporated in this solution. In studying ferrite rod radiators, the effect of metal walls and plates in the vicinity of the ferrite material will be thoroughly studied. Also, the use of hollow shells of ferrite instead of solid ferrite rods will be considered. 2. 3 Loaded Antennas Types For 30 MHz Operation Considerable planning has been done during this period so that antenna measurements may be performed down to 30 MHz. This group has available a ground reflection range located near Hangar No. 2 at Willow Run Airport. This range operates reasonably well down to 50 MHz at present. It appears feasible to extend this range down to 30 MHz with some alterations. This range is used on a time sharing basis and its location is somewhat inconvenient. At the present time, this group is setting up a new UHF-VHF range on the roof of the Fluids Building on the North Campus of The University of Michigan. This range is designed to operate down to 100 MHz. In addition, a feasibility study is under way to use a large tract of flat land near the Fluids Building for a ground reflection range operating from 20 to 100 MHz. Such a use of land must be compatible with other activities of the university. Careful scrutiny is being given to the plan. It is expected this plan will be approved by the University Administration. If this range can be built, it will enable data to be taken more conveniently in the lower VHF range than would be possible at the Willow Run range. At the present time, consideration is being given to loading both a log conical helix and a log periodic dipole antenna with toroids of Q-3 ferrite. The idea is that the toroids would act as lumped inductances for the transmission mode of each antenna and also tend to shorten the length of the radiating elements. Hence, the physical dimensions of the antenna would be reduced. Q-3 is an excellent material 11

THE UNIVERSITY OF MICHIGAN 7848-1 -Q for these experiments since it has a high permeability and has a high Q below 200 MHz. 12

THE UNIVERSITY OF MICHIGAN 7848-1 -Q III ARRAYS 3.1 Interdigital Array Antenna The exploratory experiments conducted have shown the feasibility and some significant advantages of the interdigital array antenna. The structure is interesting for the following reasons: 1) A compact, flush mount is possible. 2) The construction and feed are simple. 3) The antenna is wideband and relatively high gain. 4) The elements may be loaded. The theoretical investigation has been under way. A systematic experiment on a uniform interdigital array is expected to continue along with the theoretical analysis. 3. 2 Ferrite Loaded Slot Array 3.2.1 Theory The preliminary design and test procedures are discussed in detail in previous report (Lyon et al, 1966). The brief theory of the ferrite loaded slot array is given below. The usual symbols for array analysis will be used throughout: R (O, 0) = E (0, 0) S (O, 0). R (0, 0) - antenna pattern. E (0, 0) - element pattern. S ( 0, 0) - array factor. On a power basis this is: IR(, 0) 2 = IE(0,0) ~ S ((0, 0)

THE UNIVERSITY OF MICHIGAN 7848-1 -Q These relations are true for a "parallel array"; which is defined as an array where any element can be made to coincide with any other element by translation without rotation. It is generally assumed that the "magnetic current" distribution in a radiating slot is sinusoidal (analogous to sinusoidal electric current distribution on a dipole)..This assumption is supported by experiments (Adams, 1964). Note that the slot antenna is a magnetic dipole (analogous to electric dipole) having He(0) and E (0) fields. At resonance, the slot antennas used are half wave magnetic dipoles and the fields of each dipole are given by: -jkR N (max)e cos( cos0 ) H (0) j 2 n o0. 2wR [ sin0 I V (max)e cos ( cose ) E0(0) = j 2TrR [ sin n The slot can radiate only on one side of the ground plane, hence the pattern for E (0) and H (0) is a half of the usual "doughnut" pattern. 3. 2.2 Co-ordinate Transformations In the x-z plane 0= 0 2 x cos(2 sin 0) H (0) = K 0 cos 0 cos ( 2 sin 0) E (0) = K,_ _ _ _ _ _ _ _ _ _ _ _ __,,1 4

THE UNIVERSITY OF MICHIGAN 7848-1-Q Therefore, cos2( ( sinO0) E(O,) = K", 2 l cos 0 For array factor calculations in the x - z plane; a Dolph and Tschebycheff distribution was assumed. Thus: (00) = S(O ) = 2(A +A cos+ A2 cos 2d) where = kd cos 0 = kd sin 0 (in x-z plane) (see Figs. 3-1 and 3-2) The amplitude coefficients turn out to be: 2 A = 6.02 0 2 A = 9.5 2A = 4.48 See the final report of the previous contract (Lyon et al, 1966) for the calculations (Kraus, 1950). In the following Table III-1 the far field pattern is predicted in the tabular form for several values of 0. The steps in the calculations are included. As far as the loading of the waveguide slot array is concerned, it has been already established that the length of the array is unchanged though the cross section of the waveguide is reduced to a considerable extent, by approximately through the use of the loading material. r r

THE UNIVERSITY OF MICHIGAN 7848-1-Q x (I) CD z 0 1 0 H o 16

O - ~~~~250H lb Far Field 26db C 0o Axis of Array x0 =kdcos x 2 co Ferri/ / / z FIG, S F C O ARA W 15fi/ r /4,1,, ~ ~ ~ ~ ~~~~~~,,, Loo FS5 /S4 /3 2 FIG. 3 -2: SIMPLIFIED FINAL CONFIGURATION OF ARRAY WITH SHUNT SLOTS,

THE UNIVERSITY OF MICHIGAN 7848-1-Q TABLE HI-1 S (0) = 6.02 + 9.5 cos (z sin 0) + 4.48 cos (2w sin 0) 2 = 6.02+ 9.5 cos (v sin 0)+ 4.48 2 cos (w sin 0) - 1 2 = 1.57 + 9.5 cos (r cos 0)+ 8.96 cos (z sin 0) i S(0) 2 = 2.37+ 29.22 cos (w sin 0)+ 117.8 cos (z sin 0)+ 170 cos (r sin 0) + 80.35 cos (z sin ) _. Cos sin2 ) 0 2 sin0 cos 0 x=cos(wsine) x x x ()2 (Degrees) cos 0 10 0.955 0.1737 0.9848 0.855 0.73 0.625 0.534 251 12 0.939 0.2079 0.9782 0.794 0.63 0.5 0.397 203 12.5 0.934 0.216 0.976 0.78 0.609 0.475 0.37 199.3 15 0.891 0.2588 0.9659 0.687 0.471 0.324 0.223 133.2 20 0.835 0.342 0.9397 0.477 0.227 0.109 0.05 55 30 0.667 0.5 0.8660 0 0 0 0 1.572 45 0.394 0.707 0.707 -0.614 0.377 -0.232 0.142 0.205 60 0.1729 0.8660 0.5 -0.92 0.846 -0.779 0.715 0.06 80 0.02275 0.9848 0.1737 -1 1 -1 1 0.0273 90 0 1 0 -1 +1 -1 +1 0

THE UNIVERSITY OF MICHIGAN 7848-1-Q Other workers (Jones 1965 and Cheo 1965) have studied waveguide loaded with a dielectric material and the slots cut in the broad face of the waveguide with the goal of achieving a very directive beam pattern with a very low side lobe level. The frequency used (Jones 1965) was around 5.4 GHz for an array of 7 slots in the broad face of waveguide loaded with a dielectric material. A power pattern had a 160 half power beamwidth and 22 db side lobe level. The slots were not loaded with material. Oliner's formulas are used here for calculating individual slot properties with certain modifications to take into account the magnetic characteristics of the loading material. In addition, the slot is filled with the ferrite. This problem differs from that of Jones and Cheo as follows: 1) The operating frequency is much lower (200 MHz). 2) The slots are loaded with ferrite. 3) The goal is to determine the efficiency of the system. The design has only five slots. This is because at 200 MHz, the length of the array is quite large and it woul.d be very cumbersome to handle longer lengths. The distance between the slots, for either a loaded or unloaded waveguide array, has to be approximately X0/2. It should be possible to achieve a 250 half power beamwidth and 26 db side lobes with the present design. The design of (an individual) slot proceeds in much the same way as given by Oliner for an air filled waveguide, except for the modification of the wave number (Cheo 1965). 2 2 2 2 k = k -(-) was modified to k = - (- E r0 a ~e rrO a A slot can be considered as an impedance in the waveguide. The impedance is either a shunt or series impedance depending upon the location and orientation of the slot with respect to the central line of the waveguide. (The slots are in the broad 19

THE UNIVERSITY OF MICHIGAN 7848-1-Q wall of the guide, Fig. 3-3) Use is made of shunt type slots. The design is based on Oliner's formulas in which the thickness of the wall of the slot is a very important and critical factor in determining slot impedance variations. The Oliner formulas are for an air filled waveguide with air filled slots. The modification of these formulas for a dielectric loaded waveguide has been suggested (Kay 1956) and verified (Larson et al, 1966). These references considered unfilled slots. In this work the slots are filled flush with ferrite. This appears to be a way of achieving negligible coupling between elements. The filling of slots with ferrite reduces the resonant length of the slot to almost one third of that for an unfilled slot. Since the distance between two neighboring slots is fixed at X0/2, loading of the slots increases the edge to edge distance between two neighboring slots, andthus the mutual coupling, which is a function of this distance, is reduced considerably. The procedure for calculation of slot impedance from Oliner's formula for a dielectric filled waveguide (with unfilled slots) is in the form of a computer program by Maldups and Larson of this laboratory. Modifications have been made to take into account the magnetic character of ferrite. The modified computer program was given the code name "Oliner SLIME IB". Details of the computation effort are shown in previous report (Lyon et al 1966). Design data curves are plotted in (Figs. 3-4, 3-5 and 3-6). Since the mutual coupling between two slots can be neglected, the impedance properties calculated above for an individual slot can be used in determining the power radiated by each slot. The power radiation required from different slots is then calculated. To achiev this power distribution by the individual slots, appropriate conductance values (symbolizing radiated power) must be chosen. The control variable is the displacement of the slots from the central line of the waveguide. As can be seen from the curves of impedance properties of an individual slot (Figs. 3-4, 3-5 and 3-6), the 20

Series Rotated Type Shunt Displaced Type e x a X - cCo Series Displaced Rotated and Displaced Type - FIG. 3-3: TYPES OF SLOTS AND THEIR PARAMETERS. z1

THE UNIVERSITY OF MICHIGAN 7848-1-Q 0.006 I Ferrite Filled Slot 0.3 cm T T T x 0.1-cm 0.005 0.2 0.004 B 0.003 G G I |0 I I 0.1 0.002 0.08 0!j G Y -0.06 0.001 0.04 I _ 0.02 ~~!0 I0 7.0 cm g ~ I | T Z7.1 cm 7.11 cm a' - I Resonant Leigth FIG. 3-4: SLOT NOT FILLED WITH FERRITE 22

THE UNIVERSITY OF MICHIGAN 200 7848-1-Q 180 160 140 -120 100 -_ L 60 40 20 Resonant Length of Slot = 7.0774 cm. 7.07 1 2 3 4 5 6 7 8 9 7.08 a' — slotlength (cm) FIG. 3-5: SLOT FILLED FLUSH WITH FERRITE. 23

THE UNIVERSITY OF MICHIGAN 7848-1-Q 0.000170 9 = 50 0.19 ro o 0 -R for 0 30 0.000002 - 0.07 11 cm 1 'cm. 13cm 1, cm 15 cm Slot length(cm) FIG. 3-6: SHUNT SLOT PROPERTIES 24

THE UNIVERSITY OF MICHIGAN 7848-1-Q conductance is a very sensitive function of the displacement and slot length and it is hardly feasible to achieve the proper displacement within reasonable mechanical tolerances. Another method to control the conductance would be to put the slot on the central line of the waveguide and perturb the field in the guide by means of a screw probe, using one for each slot. This experimental method will be tried. Arguments for this are based on the sketch Fig. 3-7. When the field is unperturbed, the slot does not intercept any current lines, and hence does not radiate. When the field is perturbed, the symmetry of the distribution is disturbed, as shown in Fig. 3-7, and the current lines are no longer parallel to the slot. The slot starts radiating. The depth of the screw will determine the angle of the current lines with the slot, increasing the angle with increased depth and hence increasing radiation. Thus the required power distribution could be achieved. A radiation sensing device will be needed to sense power from the slots. 3. 2. 3 Experimental Work The properties of the Q-3 ferrite material were determined for the proper design of the waveguide. A VSWR of 1. 95 was achieved by designing an appropriate feed loop and a pattern was taken keeping the other end of waveguide open as an aperture. Attenuation due to ferrite filling was determined for frequencies from 160 MHz to 220 MHz. The experimental set-up is shown in Fig. 3-8. Verification of the calculated impedance and the predicted pattern as well as determination of the efficiency remain to be done. 25

Perturbing Screw Normal Unperturbed Field Distribution Slot / Perturbed Field Distribution 03e ar- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - - FIG. 3-7: FIELD DISTRIBUTION OF A SLOT C) C)

Power Supply and Modulator ~T1 VS'WR Meter slot z CrT Frequency Isolating Slotted Generator Attenuator Line -c - Waveguide Meter Horn Antenna I ~~~~~~~~C) FIG. 3-8: EXPERIMENTAL SET-UP Radiation Detector

THE UNIVERSITY OF MICHIGAN 7848-1-Q IV POWER MEASUREMENT OF FERRITE LOADED ANTENNA 4. 1 Power Capability of Ferrite Loaded Slot Antenna Since it is anticipated that ferrite loaded transmitting antennas may be operated at high power input levels, an investigation was made of the limitations which may be imposed on allowable power levels due to excessive heating of the loading material and possible deterioration of its inherent magnetic and electrical properties. As a preliminary investigation, a cavity slot antenna filled with EAF-2-A powdered ferrite was tested at 10, 50, 100 and 150 watt inputs. The temperature distribution was measured by means of a series of thermocouples placed along the broad center line of the cavity (see Fig. 4-1). The dimensions of the slot antenna tested are 12"x 3" backed by a cavity 5" deep. The thermocouples are Copper-Constantan probes inserted 2. 5" into the aperture face of the cavity. After a typical temperature versus thermocouple location curve was established (Fig. 4-1), only the thermocouple located at the point of maximum temperature rise (center of antenna) was retained. The rest were removed in order to eliminate the perturbations of the electromagnetic field. The data points for the curves of Fig. 4-1 were taken after thermal equilibrium was reached. The block diagram of the experimental set-up is shown in Fig. 4-2. This arrangement was decided upon as the most appropriate, after several schemes were tried. The frequency of operation for the tests was 312. 5 MHz where the VSWR was 1. 16 and 1. 47, respectively, with and without thermocouple No. 4 in position. Some of the results of the experiments are shown in Figs. 4-3 and 4-4. Of particular interest is the graph of temperature versus time which appears in Fig. 4-3. This graph corresponds to 150 watts input. The 150 watt curve covers an abrupt 28

THE UNIVERSITY OF MICHIGAN 7848-1 -Q 0F 100 / 95- / 50 watts 90 -- - N~' --— ~ 85 -80 -75 -70~ - 10 watts -70 ~- I.ok_>==)~~ == _- _ P i_. 69 F 650 1 2 3 4 5 6 7 8 Thermocouple number (Distance along length of equity 1. 5" /division) 1 2 3 4 5 6 7 Thermocouple Positions rectangular slot antenna FIG. 4-1: TEMPERATURE VERSUS POSITION IN CAVITY AT THERMAL EQUILIBRIUM 29

THE UNIVERSITY OF MICHIGAN 7848-1-Q I 2I8 1. High Power transmitter 2. 40 db Directional coupler 3. 10 db Attenuator 4. Incident power meter 5. Reflected power meter 6. Antenna 7. Temperature bridge 8. Anechoic chamber FIG. 4-2: EXPERIMENTAL SET-UP 30

F C 500 - 400 - 300 v "co 200 - 100 0 20 40 60 80 100 '120 140 100 180 200 220 240 - Minutes FIG. 4-3: INCREASE IN TEMPERATURE VERSUS TIME ( 150 watts).

THE UNIVERSITY OF MICHIGAN 7848-1-Q change of the characteristics of the ferrite at temperatures ranging between 120 - 150~ F. If this change is attributed to the deterioration of m' and pm" at these temperatures, then from Fig. 4-4 the power limitation of the ferrite loaded, slot antenna is about 50 watts. However, before any definite conclusions are reached one must determine the exact dependence of ml and I" on temperature for the EAF-2-A powdered ferrite. For this investigation measurements can be taken using modified techniques as given in the references (Rado, 1955 and Lax 1962). Also, measurements for the determination of the performance of ferrite loaded antennas, at elevated temperatures showing any deterioration of radiation pattern or efficiency should be made. 4.2 Loss Tangent, Qm Determination Method For Lossy Ferrites The loss tangent and magnetic Q-factor of lossy ferrite materials can be accurately measured by employing a short-circuited coaxial transmission line technique. The short circuited impedance of a coaxial line is given by Z = Z tanhky. (4.1) If the line is loaded by ferrite material in a length (f (as shown in Fig. 4-5) then Eq. 4.1 is modified as Zsc Zftanh ff If (4.2) 32

THE UNIVERSITY OF MICHIGAN 7848-1-Q oF 500 400 300 - 200 - / 100 50 100 150 watts FIG. 4-4: F VERSUS WATTS. sc ______ ' __ _ _ FIG. 4-5: COAXIAL LINE WITH SPECIMEN IN POSITION 33

THE UNIVERSITY OF MICHIGAN 7848-1 -Q where Zf - Zo f = af+jf, af = attenuation constant in the ferrite, Of = phase constant in the ferrite. Using an impedance bridge, a reference for the shorted air-loaded line is established by employing (4. 1) and a Z- 0 chart. When the ferrite specimen is placed in the line, the readings taken by the use of the bridge are transformed through an I -f rotation in the Z -0 chart, in degrees. This then gives the correct Z for the ferrite material. If the length of the ferrite sample is very, SC small relative to the wavelength (I < X /70) one can approximate relation (4. 2) by l Z Z Tff. (4.3) Also, for ferrites assuming the lossy component of the permittivity constant negligible and writing Z = R + jX, one obtains: R+jX Z.f (4.4) E ~ From the above relation by squaring both sides, rearranging terms and then separating real and imaginary components one obtains: '(f2 2) +,"(2f f) (r2 2) ~ (4 5) Of f -x 2(4.5) If and 'I(2f -3f)- -(( 2 f)=(2r (4. 6) If with r =R/Z, x= X/Z. Solving (4. 5) and (4. 6) for -u', I" and taking the ratio there results: 34.

THE UNIVERSITY OF MICHIGAN 7848-1 -Q 22 2 2 r -xf f 2rx 2a f Of 1tan (4. 7) In r 2-f2 _ f2_ f2 m - 2 (4.8) 2rx 2af Of m22 2 2 2rx 2crf of where the parameters r, x, a f f 2rx 2a f f3 where the parameters r, x, a f, of can be experimentally measured. 35

THE UNIVERSITY OF MICHIGAN 7848-1 -Q V CONCLUSIONS The phase velocity on a helical structure at a given frequency has been shown to be readily attainable through the use of a shorting ring on the complementary helix. As described in the body of the report, the measurements are actually standing wave measurements at the feed-end of the antenna. The measurements on ferrite loaded log conical antennas are sufficiently encouraging so that all of the objectives for this type of antenna seem to be obtainable at least in part. In now appears that the most difficult part will be the requirements on physical size. The design study on array antennas using ferrite loaded rectangular slots of small dimensions is encouraging from the consideration of the reduction of mutual coupling due to the small elements. The variation of the port impedance of a phased array will be much improved if the viewpoint expressed here on mutual coupling is substantiated. The interdigital array study has not been carried to the point where a firm evaluation can be made. Similar statements apply to the ferrite rod task and the task for a ferrite loaded antenna operable down to 30MHz. 36

THE UNIVERSITY OF MICHIGAN 7848- 1 -Q VI FUTURE EFFORT In the near future, possibly by the end of the next quarterly report period, it is anticipated that the analysis of the conical spiral treated as a helix boundary value problem with loading material will be completed. It is planned to present the detailed analysis of this type of antenna. Arrangements will be made so that the power handling capability of the conical spiral can adequately be tested. Generators, together with amplifiers, capable of producing 100 watts cw power, will be made for a few spot frequencies. It is still hoped that a high power generator capable of delivering in excess of 100 watts, over a frequency range of 200-600 MHz will be made available by the contracting agency. It is expected that experimental work on the radiation properties of the small slot array with ferrite loading will be available at the end, of the next report period. The newly improved range facility should be usable within the next few days to allow this work to proceed. Work is continuing on the interdigital array and considerable analytical effort is already under way. Some preliminary results of an experimental nature should also be available in the very near future. The study of endfire ferrite rod antennas for the frequency range from 300-1000 MHz has been initiated. In the next quarterly report, a detailed comparison of ferrite rod radiators with dielectric rod radiators will be made from an analytical viewpoint. It is expected that some of the future experimental work will also give detailed comparisons of these types. The task involving the feasibility of new types of antennas capable of operating with ferrite loading down to 30 MHz has been barely started. However, the direction of effort will be to consider types on two bases: 1) the utilization of 37

THE UNIVERSITY OF MICHIGAN 7848- 1 -Q existing types previously good only for higher frequency but with ferrite loading capable of operating at lower frequencies; 2) the creation of entirely new types of antennas which with ferrite will give radiation efficiencies comparable to prevailing efficiencies at frequencies down to 30 MHz. Immediately after a survey of types, it is anticipated that a great deal of experimentation will take place on selected types which offer the greatest promise. It is anticipated that this task will be attacked primarily on an experimental basis. ACKNOWLE DGE ME NTS Contributors to this report include; T. B. Lewis and U. E. Gilreath. 38

THE UNIVERSITY OF MICHIGAN 7848-1 -Q RE FERE NCES Cheo, B.R. and Pelish, L. (1965), "Radiating Slots on a Dielectric Filled Waveguide, " Technical Report 400-118, New York University. Jones, H.S., Jr. (1965), "Dielectric-Loaded Waveguide Slot Arrays," USAMC Harry Diamond Laboratories, Technical Report TR-1269. Kay, A. F., (1965), "Mutual Coupling of Shunt Slots in the Broad Face of a Rectangular Waveguide, " Scientific Report No. 3, AD 98799, TRG, Inc. Kiryushin, V. P. (1957), "The Influence of Dielectric on the Phase Constants of the Space Harmonics of a Helix," Radiotekhnika i elektronika, 2, No. 7, pp. 901 - 911. Kraus, J.D. (1950), Antennas, McGraw-Hill, New York. Larson, R.W. and V. M. Powers (January, 1966), "Slots in Dielectrically Loaded Waveguide," Radio Science, 1, No. 1, pp. 31 - 35. Lax, B. and K.J. Button (1962), Microwave Ferrites and Ferrimagnetics, McGrawHill Book Company, New York. Lyon, et al (1966), "Study and Investigation of a UHF-VHF Antenna," 7140-1-F, The Radiation Laboratory, The University of Michigan. Oliner, A. A. (January, 1957), "The Impedance Properties of Narrow Radiating Slots in the Broadface of Rectangular Waveguide, " Part I and II. Rado, G.T. (1953), "Magnetic Spectra of Ferrites," Rev. Modern Phys, Vol. 25, No. 1. Ramo, S. and J. R. Whinnery (1953), Fields and Waves in Modern Radio, JohnWiley and Sons, New York, pp. 351, 370 and 371. Sensiper, S. (1951), "Electromagnetic Wave Propagation on Helical Conductors," Technical Report No. 194, Research Laboratory of Electronics, Massachusetts Institution of Technology,, Cambridge, Massachusetts.

UNCLASSIFIED Security Classification DOCUMENT CONTROL DATA- R&D (Security cleaalflcatlon of title, body of abstract enc Indexing annotation must be entered when the overall report is classilied) 1. ORIGINATIN G ACTIVITY (Corporate author) a. REPORT SECURITY C LASSIFICATION The University of Michigan Radiation Laboratory Unclassified Department of Electrical Engineering 2b GROUP 3. REPORT TITLE Study and Investigation of UHF-VHF Antennas 4. DESCRIPTIVE NOTES (Type of report and inclusive datee) Quarterly Report- 1 February 1966 through 30 April 1966 5. AUTHOR(S) (Leat name, first name, Inti'el) Lyon, John A. M., Alexopoulos, Nickolas G., Kazi, Abdul M., Smith, Dean L. and Wu, Pei-Rin 6. REPORAT 6*T.. 7a. TOTAL NO. OF PAGES 7b. NO. OF REFI 39 May 1966 12 ea. CONTRACT OR GRANT NO. 41. ORIGINATOR'S REPORT NUMBER(S) AF 33(615)-3609 7848-1-Q b. pROJECT NO. 6278 c.9b. OTH R Rf PORT NO(S.9) (4 ny other number that may be aesln ed thia report) 627801 thstl d. 0. AV A IL ^elLITY/,MlrTAT,'oNN No T!C, Qualified requestors may obtain copie s of this report from DDC. This document is subject to special export controls and each transmittal to foreign governments or foreign nationals maybe made onlywith prior approval of AFAL (AVPT), WrightPatterson AFB Ohio. 11. SUPP.EMENARY NOTES... 1.SPONSORiNG Ml.ITAMY ACTIVITY Air Force Avionics Laboratory AVWE Reserach and Technology Division, AFSC Wright-Patterson AFBS Ohio 45433 13. ABSTRACT This first quarterly report describes the effort devoted to the four listed tasks of this project. The largest part of the effort has been devoted to two of the tasks; (1) the conical spiral antenna or the log conical spiral antenna, as frequently called; (2) array antennas utilizing loading effects on elements. The remaining tasks (3) endfire ferrite rod antenna and (4) new antenna types at 30 MHz are covered very briefly. These last two tasks have just been initiated. In addition, some effort has been devoted to electrical properties of material and the measurement of these properties. This information on properties of material will be help ful for the ferrite loading involved in the four numbered tasks. Some data are also included on the power level limitations of ferrite loaded rectangular slot antennas. DD,1JAN 4 1473 UNCLASSIFIED Security Classification

UNCLASSIFIED Security Classification 14. LINK A LINK B LINK C KEY WORDS ROLE WT ROLE WT ROLE i 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 SECUI~TY CLASSIFICATION: Enter the over2a..REPORT SECUTY 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-authozed. 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 Directive 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 PDC 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 classifica- tion, 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 incluive 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 1L SUPPLEMENTARY NOTES: Use for additional explanaor in the report. Enter last name, first name, middle initial. tory notes. If -.ilitary, 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, ie., 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, Bc, & 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, etc, or 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 NUMB ER(S): If the report has been words but will be followed by an indication of technical conassigned any other reprt mbers either by 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 lim-I itations on further dissemination of the report, other than those UNCLASSIFIED Security Classification

UNIVERSITY OF MICHIGAN 111111 03465 839II1111 116111111111111 3 9015 03465 8396