1084-5-Q Technical Report ECOM-0547-5 December 1968 Azimuth and Elevation Direction Finder Techniques Fifth Quarterly Report 1082-5-Q - RL-2026 1 July - 30 September 1968 Report No. 5 Contract DAAB07-67-C0547 DA Project 5A6 79191 D902-05-11 Prepared by J. E. Ferris, P. H. Wilcox and W. E. Zimmerman The University of Michigan Radiation Laboratory Department of Electrical Engineering Ann Arbor, Michigan For United States Army Electronics Command, Fort Monmouth, N. J. Distribution Statement Each transmittal of this document outside the Department of Defense must have prior approval of CG, U. S. Army Electronics Command, Ft. Monmouth, New Jersey, 07703, ATTN: AMSEL-WL-S.

1084-5-Q ABSTRACT During this reporting period efforts have continued in the design and development of the quadrafilar balun, and the assembly of the components of the DF system has been 90 percent completed. Preliminary tests that have been conducted on the quadrafilar balun have shown that the amplitude variation is well behaved. However, there is some undesirable phase discrepancies in the network. In addition to these tests a preliminary evaluation of the DF system has been conducted. The results of the preliminary tests show that the system is able to direction find with an accuracy of + 5 in both the azimuth and elevation directions. ii

1084-5-Q FOREWORD This report was prepared by The University of Michigan Radiation Laboratory of the Department of Electrical Engineering under Contract DAAB07-67-C0547. This contract was initiated under United States Army Project No. 5A6 79191 D902 -05-11 "Azimuth and Elevation Direction Finder Techniques". The work is administered under the direction of the Electronics Warfare Division, Advanced Techniques Branch at Fort Monmouth, New Jersey. Mr. S. Stiber is the Project Manager and Mr. E. Ivone is the Contract Monitor. This report covers the period of 1 July through 30 September, 1968. The material reported herein represents the results of the preliminary investigation into the study of techniques for designing broadband circularly polarized azimuth - elevation direction finder systems. The authorls wish to express their thanks to Messrs. E. Bublitz and W. Henry for their efforts in the experimental work that has been performed during this reporting period, and to M. Gurney for his efforts in the mechanical design of components that are associated with the azimuth - elevation antenna system, and also to M, Wright for her contributions in the preparing of the many graphs presented in this report. iii

1084-5-Q TABLE OF CONTENTS ABSTRACT ii FOREWORD iii LIST OF ILLUSTRATIONS v I INTRODUCTION 1 II AZIMUTH - ELEVATION DF ANTENNA SYSTEM 3 III ELECTROMECHANICAL SWITCH 13 IV DATA CONVERSION SYSTEM 16 4.1 Hewlett-Packard 450A Video Amplifier 16 4.2 Micro Instruments 5201-B-1 Memory Voltmeter 16 4. 3 Texas Instruments 848 Analog to Digital Converter 16 4.4 Varian 6201 Computer 17 4.5 Other Equipment 17 V DF TEST RESULTS 18 VI FLY-BY TESTS 39 VII CONCLUSIONS AND RECOMMENDATIONS 41 DD FORM 1473 iv

1084-5-Q LIST OF ILLUSTRATIONS 2-1 Quadrafilar Output Amplitude Variations 4 2-2 Phase Relationship Between the Four Ports of the Quadrafilar Balun vs. Frequency 5 2-3 Quadrafilar Balun 7 2-4 Quadrafilar Spiral and Balun 8 2-5 15 Turn Cavity Backed Spiral with a Duncan - Minerva Balun Mounted at the Zenith of a 6 Foot Hemisphere (E-Plane Patterns for a 5:1 Frequency Band) 9 2-6 15 Turn Cavity Backed Spiral with a Broadband Stripline Balun Mounted at the Zenith of a 6 Foot Hemisphere (E-Plane Patterns for a 5:1 Frequency Band) 9 2-7 Ellipticity Data at 1. 6 GHz for 15 Turn Cavity Backed Spiral Mounted at the Zenith of a 6 Foot Hemisphere (Duncan - Minerva Balun) 11 2-8 E-Plane Pattern Data for a 15 Turn Cavity Backed Spiral Positioned Non-Symmetrically on a Dielectric 6 Foot Hemisphere (Frequency = MHz) 12 3-1 VSWR Characteristics for Maximum Switch Coupling 15 3-2 VSWR Characteristics With Switch Adjusted for One Half Coupling 15 5-1 Data Conversilor Equipment 5-2 Azimuth - Elevation System Block Diagram 20 5-3 Azimuth - Elevation Coordinate System 21 5-4 Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for 0= 90~ o o and 0= 270 x x. 22 5-5 Azimuth Angle as Generated by the DF System as a Faunction of the True Elevation Angle for 0 = 80 o o and 0 = 2600 x x. 24 5-6 Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for 0 = 70 o o and 0 = 250~ x x. 25 5-7 Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for 0= 60 o o and 0= 240~ x x. 26 v

1084-5-Q LIST OF ILLUSTRATIONS, Continued 5-8 Theoretical Calculated Elevation Angle vs. True Elevation Angle (Assuming a Cosine Element Pattern with Elements Placed at 0 = 40 and 80) 28 5-9 System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.6 GHz) 29 5-10 System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.6 GHz) 30 5-11 System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.6 GHz) 31 5-12 System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.6 GHz) 32 5-13 System Generated Azimuth Angle vs. True Elevation Angle (Frequency =1.4 GHz) for 0 = 600 o o and 2400 x x 33 5-14 System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.4 GHz) 34 5-15 System Generated Azimuth Angle vs. Frequency for a Fixed Azimuth and Elevation of Illuminating Source (0 = 900, 0 = 300) 35 5-16 System Generated Elevation Angle vs. Frequency for a Fixed Azimuth and Elevation of Illuminating Source (0 = 900, 0= 30 ) 36 6-1 NIKE Ajax Skin Tracking Antenna 40 vi

1084-5-Q I INTRODUCTION During this, the fifth quarter, the design, fabrication and assembly of components required for the azimuth - elevation direction finder (DF) being developed by the Radiation Laboratory of The University of Michigan have continued. The function of the azimuth - elevation DF system is to collect the signals received by each of the antennas (17) associated with the DF system. The above data is evaluated by a computer and the direction of the incoming signal is computed and optically displayed by the data processing equipment. As a design goal the accuracy of the system is to be + 20 in azimuth and + 5~ in elevation. A thorough discussion of the theory of the DF system and the components associated with it have been presented in the first and second quarterly reports (ECOM-0547-1 and 2). Therefore, this report will again be restricted to the experimental results (as was the case in ECOM-0547-3 and 4) that have been obtained during this reporting period. An experimental model of the 5:1 frequency band ( 600 - 3000 MHz) quadrafilar balun has been fabricated and evaluated. The results of this evaluation show that the balun has a phase discrepancy associated with it suggt-sting that additional adjustments should be made to one of the components of the balun network. A few preliminary pattern measurements have been made employing the quadrafllar log conical spiral. Pattern results were not. as well behaved as had originally been anticipated because of the phase behavior of the balun. It i.s also felt that to optimize the pattern characltristics of the log conical spiral it would be necessary to i111i'i.ul' the effect of the shape factor and the wrap:1iogl aIssoC Mat.ed with the filaments used in its construction. 1

1084-5-Q The DF system has been assembled and is now being evaluated on one of the antenna ranges at The University of Michigan. Preliminary measurements show that the azimuth - elevation direction finder is capable of computing angular information with an accuracy of + 5 in both azimuth and elevation planes. A better accuracy figure may be obtained after some improvements are made in the range geometry. At the present time the antenna system for the azimuth - elevation direction finder consists of 17 flat planar spirals that were designed and built on a preceding contract associated with azimuth - elevation direction finder techniques (Contract DA 28-043 AMC-01499 (E)). Data is presented to demonstrate the operating characteristics of the cavity backed spiral over the 600 - 3000 MHz range, using both the modified Duncan - Minerva balun and a broadband stripline balun. Because of the poor operating characteristics of the cavity backed spirals much of the data collected has been restricted to a frequency of 1. 6 GHz where the cavity backed spirals are well behaved. Some data processing techniques have been considered on a preliminary basis. Further effort should be expended on data processing to optimize the accuracy of the system. 2

1084-5-Q II AZIMUTH - ELEVATION DF ANTENNA SYSTEM During this period the design and development of the quadrafilar spiral balun has continued. An engineering model of the quadrafilar balun has been constructed and tested. Amplitude and phase variations are shown respectively in Figs. 2-1 and 2-2. In Fig. 2-1 it is shown that the amplitude variation at the four ports is small although the phase data (Fig. 2-2) is not well behaved. The phase variations associated with port 2 relative to port 1 theoretically should have been 90, + 10, and the data of Fig. 2-2 shows that this phase variation over a major portion of the band was within these limits. However, at a frequency of 2. 0 GHz the phase has a discrepancy of approximately + 300. The cause of this variation is not understood and the problem will require further study. However, of greater concern is the data for ports 1-3 and 1-4 which have a larger discrepancy associated with them. It is of interest to note that the data for ports 1-3 relative to that for ports 1-4 shows phase differences of approximn:3f-yy 900 over the 5:1 frequency band which is desirable. The fact that. the data for pot s 1-2 agrees well with the expected 900 phase variation suggests that the three 3dB hybrids shown in Fig. 2-3 are operating as expected. This conclusion is further substanriat.ed because the amplitude variations at the four ports are also well behaved as shownt in Fig. 2-1. The linear slope associated with the curves of ports 1-3 and 1-4 relative to the data of 1-2 suggests that the broadband 900 phase shifter is not. funci!or'inrg properly. Because the two curves for the ports 1-3 and 1-4 iary in a linear fashion it suggests that the reference line of Fig. 2-3 is of the wrong length. If the bt'oadband phase shifter were properly etched it is very probable that the- curres of ports 1-3 and 1-4 relative to 1-2 would not have exhibited the linear phase discrepancy apparent in Fig. 2-2. 3

1084-5-Q ~ +1.5 0 -1.5, I 1 I 0.6 1.0 1.4 1.8 2.2 2.6 3.0 Frequency (GHz) FIG. 2-1: Quadrafilar Output Amplitude Variations. 0-0 Port 1-4 xx Port2-3 4

1084-5 -Q 360 - 270 - bf a) 90 ^ aD. —4 X X Phase of Port 2 Relative to Port 1 (1-2) Phase of Port 4 Relative to Port 1 (1-4) *-* Phase of Port 3 Relative to Port 1 (1-3) 0.6 1.0 1.4 1.8 2.2 2.6 3.0 Frequency (GHz) FIG. 2-2: Phase Relationship Between the Four Ports of the Quadrafilar Balun vs. Frequency. 5

1084-5-Q It is believed that the faults in the balun indicated by the data of Figs. 2-1 and 2-2 were not serious and can be corrected with some additional effort. However, because of the lack of time and funds available in the present contract, further work on the balun and antenna network for the quadrafilar configuration has been discontinued and the remaining time and funds will be devoted to the evaluation of the DF system. The quadrafilar balun is shown in Fig. 2-3. This balun consists of three broadband 3dB directional couplers and a broadband 90 phase shifter. For the purposes of this program, broadband is defined to be a 5:1 frequency band that covers the range of 0. 6 - 3. 0 GHz. To minimize coupling between adjacent components, it is necessary to use screws throughout the balun network as can be seen in Fig. 2-4. For this particular balun configuration, a total of approximately 600 screws were required to minimize coupling between components. Spacing between the screws must be X/8 or less at the highest frequency of interest. It has been found that the spacing between the screws and the stripline center conductor can be as small as X/8 at the highest frequency of interest without affecting the impedance characteristics of the stripline. Pattern data for the quadrafilar spiral antenna has not been encouraging. The cause for the poor pattern behavior is believed to result both from the poor phase response of the balun network and the inaccuracies associated with the winding of the quadrafilar spiral elements. A further discussion of the quadrafilar spiral will be presented in the recommendation of this report. To provide some comparison as to the desirability of employing a well behaved (electrically) balun network, two sets of data are presented for a cavity backed spiral antenna, one fed with a modified Duncan - Minerva balun and the other by a broadband stripline balun network. Typical pattern data is shown in Figs. 2-5 and 2-6. The two 6

I UO'-k2 0 *1 -4 4 0 ~>, (0 DL() ] r r kk Ad 0 I I 0 I I 'AF I I I - - - - - - - I I I I I I L- - - - - - - - - -. I, El p - - - - - - - - - - -.i I I -M q w Input I -MMJ 16 - FIG. 2-3: Quadrafilar Balun. 7

Co2 FIG. 2-4: Quadrafilar Spiralan Bam 0 to

1084-5-Q 600 600 \\^ 700,II 0ll A j - At'S 800 I 900 1000 1100 1200 1300 1400 2000 I --- r 1, Q 1600 1800 2200 2400 2600 2800 3000 Frequency (MHz) FIG. 2-5: 15 Turn Cavity Backed Spiral with a Duncan - Minerva Balun Mounted at the Zenith of a 6 Foot Hemisphere (E-Plane Patterns for a 5:1 Frequency Band). 600 I k' > i-l:, / Q0 700 800 900 1000 1100 1200 Q 1300 1400 2800 3000 1600 1800 2000 2200 2400 2600 Frequency (MHz) FIG. 2-6: 15 Turn Cavity Backed Spiral with a Broadband Stripline Balun Mounted at the Zenith of a 6 Foot Hemisphere (E-Plane Patterns for a 5:1 Frequency Band). 9

1084-5-Q sets of data noted above were recorded at several frequencies in the 0. 6 - 3. 0 GHz frequency range. It will be observed from this data that at several frequencies the Duncan - Minerva patterns show some deterioration in comparison with the data for the bifilar stripline case. There are some anomalies noted in the bifilar stripline data and this is felt to be caused by the higher order modes that may be radiated by the bifilar spiral configuration as noted in the first quarterly report (ECOM-0547-1) dated October, 1967. Because of the poor pattern response at several frequencies in the 0. 6 - 3. 0 GHz band for the Duncan - Minerva cavity backed spiral configurations, evaluation of the azimuth - elevation DF system has been limited to a frequency of 1. 6 GHz. This frequency was chosen because of the well behaved pattern characteristics as a function of antenna orientation. Typical ellipticity data is shown in Fig. 2-7 for a cavity backed bifilar spiral fed with a Duncan - Minerva balun. Additional data has been recorded for spiral elements located at 0 = 400 and 800 and is shown in Fig. 2-8. The 0 angles of 40 and 80 were selected because two rings of 8 antenna elements each were located at 0 = 40 and 80. This data is shown to demonstrate the pattern characteristics of the spirals when located unsymmetrically on the hemisphere surface. The 17 antennas associated with the antenna system of the azimuth - elevation direction finder are mounted on a non-metalized fiberglas surface possessing a hemispherical contour 6 feet in diameter. The gain of the Duncan - Minerva cavity backed spiral antennas measured at 1. 1 and 1. 6 GHz has been found to be approximately 3dB above a linearly polarized isotropic source. If the antennas are assumed to be reasonably well behaved insofar as the ellipticity is concerned, an additional 3dB may be added to the linearly polarized gain suggesting a gain of approximately 6dB above a circularly polarized isotropic source. However, no measurements have been made to confirm this assumption. 10

1084-5-Q 0, 0~ 10 10~ / N %: _4Q X) 'A Q QL 20~ 30~ 400 50~ 60~ 70~ 80~ 90~ I. i: ~: I I i) =! \ rj:,31,- vo,.e 100~ 110~ 120~ 130~ 140~ 150~ 160~ 170~ 180~ (1600 MHz) FIG. 2-7: Ellipticity Data at 1. 6 GHz for 15 Turn Cavity Backed Spiral Mounted at the Zenith of a 6 Foot Hemisphere (Duncan - Minerva Balun). 11

1084-5-Q 600 700 800 900 1000 1100 1200 1300 1400 1600 1800 2000 2200 2400 2600 2800 3000 0 = 80~ 600 700 800 900 1000 1100 1200 1300 1400 1600 1800 2000 2200 2400 2600 2800 3000 = 40~ FIG. 2-8: E-Plane Pattern Data of a 15 Turn Cavity Backed Spiral Positioned Non-Symmetrically on a Dielectric 6 Foot Hemisphere (Frequency = MHz). 12

1084-5-Q III ELECTROMECHANICAL SWITCH The electromechanical switch has been fabricated and tested and is presently being employed with the DF system to collect DF data. The photo-diodes for the switch have been installed which provide the interrupt information to the computer to designate which antennas are being interrogated as a function of time. A few problems were encountered with the interrupt circuit necessitating some modifications to the pulse circuitry associated with the photo-diodes. These problems appear to have been corrected and the circuitry is now being wired for delivery. The VSWR characteristics of the switch are shown in Figs. 3-1 and 3-2. The data of Fig. 3-1 is for maximum coupling between one of the antenna switching ports and the output port. It will be observed that at approximately 2. 4 GHz the unit exhibits a high VSWR. This may be explained as follows: each switching port has associated with it a characteristic impedance. A similar impedance is associated with the rotary junction because both coupling junctions are mePrhamrcadly identical. The transmission line or stripline interconnecting the rotary jcint ai.-^d switchiig port has a length that results in an addition of the impedances to produce a high VSWR. at 2 4 GHz. The data of Fig. 3-2 is for the case when the switch is rotated to a po.-snt.cn where the switching port is adjusted for half coupling. Here again i.t will be (not.d that the VSWR characteristics are quite well behaved across the wide band of fre — quencies, however, a high VSWR is noted at the high end of the freque..ncy band. The loss through the switch has been checked at several frequencies in the operating band and found to be 0. 5dB or less. To protect the switch from dirt and dust during field operation, a dust cover has been attached to enclose the switch rotor and precision spindle employed to accurately acdliu St the spacing between the rotor and stator of the switch. It is 13

1084-5-Q recommended that this cover be kept in place at all times and only be removed in the case of emergency or malfunctioning of the switch. It will also be recalled that the spacing between the rotor and stator of the switch is approximately 0. 004 inches and therefore it is extremely important that the switch be handled with care to minimize the possibility of changing the spacing between the stator and the rotor. 14

1084-5-Q 5 3 1 0.6 1.0 1.4 1.8 2.2 2.6 Frequency (GHz) 3.0 FIG. 3-1: VSWR Characteristics for Maximum Switch Coupling. 5 3 1 0.6 1.0 1.4 1.8 2.2 2.6 Frequency (GHz) 3.0 FIG. 3-2: VSWR Characteristics With Switch Adjusted for One Half Coupling. 15

1084-5-Q IV DATA CONVERSION SYSTEM Below is a brief description of each of the components that make up the data conversion system (Fig. 5-1) employed with the azimuth - elevation direction finder. Each of these components will be described more completely in the operator's manual now being prepared. 4. 1 Hewlett-Packard 450A Video Amplifier (Not Shown in Fig. 5-1) The output from the receiver is passed through this amplifier and then to the memory voltmeter. A switch on the front panel allows the selection of either 20dB or 40dB gain. A DC restoring network has been added to the amplifier so that its output is always positive. 4. 2 Micro Instruments 5201-B-1 Memory Voltmeter The memory voltmeter (peak detector) is used to detect the highest signal level picked up by each of the antenna elements as the antenna switch passes by the corresponding switch position. It is capable of registering all signals from DC to pulses as short as 50 nanoseconds. The voltmeter is activated by the computer during the time when the antenna switch is coupling one of the elements to the receiver. At the end of this period, the voltmeter output continues to record the magnitude of the largest signal present during the interval. 4. 3 Texas Instruments 848 Analog to Digital Converter The analog to digital converter (A/D) transforms the voltage output of the memory voltmeter into a digital form acceptable to the computer. On command from the computer, the converter samples the voltmeter output and forms the digital representation of it. This process takes about 29psec after which the computer may read the result into its memory. 16

1084-5-Q 4.4 Varian 6201 I Computer The computer function is to control and coordinate the whole system. It can turn the memory voltmeter on and off, trigger the A/D converter, read data from the A/D converter and display results (angles) on the NIXIE tube registers. Also, it has interrupt lines from the antenna switch and A/D converter which allow these devices to interrupt the normal operation of the computer to inform it that some external event has occurred. Available for use by the computer is a clock which can be turned on and off, and which interrupts at 100 psec intervals after it is turned on. Also connected to the computer is a model 33ASR teletype through which the operator can communicate with the computer either by the use of the keyboard or punched paper tape. Likewise the computer can punch or print information for the operator. The core memory of the 6201 has 4096 words, each 16 bits long and a full cycle time of 1. 8,usec. 4.5 Other Equipment In addition to the components described above, the main equipment rack also houses logic circuitry which interfaces the computer with the varioas external devices and contains the 100 pusec clock. The NIXIE tube displays, along with their high voltage power supply, and some logic cards are mounted on.h3 front parcel. In back is a separate power supply used to run the logic circuits. 17

1084-5-Q V DF TEST RESULTS A photograph of the data conversion equipment is shown in Fig. 5-1. The complete system has now been assembled and is being evaluated at the Radiation Laboratory of The University of Michigan. A block diagram of the system is shown in Fig. 5-2. Initial data that has been collected for the azimuth - elevation direction finder have some system errors associated with it. The prime system error is the inaccuracy associated with the alignment of the azimuth - elevation DF antenna system. Initial data is being collected for a frequency of 1. 6 GHz. The pointing errors for the present data appear to be in the range of + 50 for both azimuth and elevation. At the present time data is being collected to determine the system repeatability. Initially the azimuth - elevation DF antenna was oriented such that data would be presented for a constant azimuth angle ( 0 = 90 or 270 ) while the elevation angle was varied through 1800. To aid in the understanding of the azimuth - elevation angular data, a coordinate system is shown in Fig. 5-3. A typical set of azimuth data that has been obtained from the azimuth - elevation system is shown graphically in Fig. 5-4. The data of Fig. 5-4 shows the calculated azimuth information as a function of elevation angle at a frequency of 1. 6 GHz. Ideally the azimuth data should read either 900 or 2700 depending upon which side of the hemisphere (east or west) data is being collected from. It will be observed that the data near the pole position of the hemisphere (i. e., data looking straight above the hemisphere, 0 = 00) is of least accuracy. However, if one considers that the elevation data is accurate to within + 5, this is a rather small solid angle over which the ambiguity exists. A cause for the errors near the polar region ( 0 = 0 ), is the inaccuracies or imperfections associated with radiation patterns of the antenna. Further, it is to 18

1084-5-Q Digital Display (NIXIE Tubes) A/D Converter -- -|Peak Detector Computer (Varian 6201) FIG. 5-1: Data Conversion Equipment. 19

RPM 100 10 -L 1000 Rate,/ Switch 0O3 0 0 00 I 01n k FIG. 5-2: Azimuth - Elevation System Block Diagram.

1084-5-Q Zenith 0=0 0= 90 0= 90~ E 0 = 00 0-00 N 0= 90 FIG. 5-3: Azimuth - Elevation Coordinate System. 21

1084-5-Q %0 fc QQ *ibo 0.,, Cd C) 370 280 190 100 350 260 170 80 330 240 150 60 310 220 130 40 290 200 110 20 270 180 90 0 X-X 0-0 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for 0 = 90 0- and 0 = 270~ x-x. FIG. 5-4: 22

1084-5-Q be noted that the errors that have been observed in the polar region had been determined theoretically prior to the tests now being conducted. Again the theoretical work was performed taking into account the inaccuracies associated with the antenna patterns. One will also observe that there is an increase in the error near the horizon (at elevation angles of + 90 ). This error is caused because of the inaccuracy in the positioning of the antenna with respect to the illuminating antenna. Efforts are now being made to improve the position of the antenna so as to be able to more accurately evaluate the accuracy of the azimuth - elevation DF system. Additional azimuth data has been collected at 1. 6 GHz for azimuth angles of 800, 700, and 600 and this data is shown in Figs. 5-5 through 5-7. Here one will observe similar errors for the azimuth data as for the data for 0 = 900. Little has been said about the errors present in the elevation data. In the first quarterly report (ECOM-0547-1) dated October, 1967, it was theoretically determined that there would be an error in the elevation data. The cause for the error in the elevation data comes about because of the non-symmetry in the location of antennas in the 0 plane of the antenna system, i. e., antenna elements are only employed in the upper hemisphere of the spherical coordinate system. Therefore, since the data employed to calculate the elevation angle are from a nonsymmetrical system, the errors noted above are expected. Further, in the first quarterly report (ibid) it has been shown that the errors associated with the elevation angle are predictable and therefore can be corrected for in the computer. As of the present time, we have not inserted the necessary correction factor in the computer since further experimentation will assist in optimizing the correction factor. 23

1084-5-Q 370 280 190 100 0 -U2 a) a) bD.,4 C) 0 o 350 260 170 80 330 240 150 60 310 220 130 40 290 200 110 20 270 180 X ---X 90 0 0-0 0 20 40 60 80 90 True Elevation Angle in Degrees (eT ) FIG. 5-5: Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for 0 = 800 0-0 and 0 = 260~ X —X - 24

1084-5-Q 370 280 190 100 Cl -e -r bD *-4 CT a) -- Cd C) -s 3) +o 350 260 170 330 240 150 310 220 130 290 200 110 270 180 X-X 90 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) FIG. 5-6: Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for = 70~ o and 0 = 250~ X-x. 25

1084-5-Q 370 280 190 100 P. aO EID 8 S4 cd a N C) 350 260 170 80 330 240 150 60 310 220 130 40 290 200 110 20 270 180 90 0 X-X 0-0 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) FIG. 5-7: Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for 0 = 60~ 0-0 and 0 = 240~ X-X. 26

1084-5-Q For the purposes of comparison we have included the theoretically computed elevation angle versus the actual elevation angle assuming a cosine antenna pattern for the individual elements in Fig. 5-8. Referring to Fig. 5-8, it is to be noted that the data varies in a piecewise linear fashion such that the correction factor to be inserted in the computer will be a relatively simple expression. Referring now to the elevation data in Figs. 5-9 through 5-12, it will be observed that the system generated data does not agree with the true elevation data. However, the data does agree well with the theoretical data of Fig. 5-8. Therefore, the system elevation data should be easily corrected for as noted above. To illustrate the importance of having antenna patterns that are well behaved both as a function of frequency and orientation, an additional set of azimuth - elevation data has been plotted for an azimuth angle of 0 = 600 at a frequency of 1. 4 GHz in Figs. 5-13 and 5-14. The reader is referred to the pattern data shown in Fig. 2-5 for a frequency of 1. 4 GHz. Here it will be observed there is considerable non-symmetry in the element pattern for this frequency. It is because of this non-symmetry in the element pattern that the large errors shown in Figs. 5-13 and 5-14 are present both in the azimuth and elevation data. To gain some insight as to how the azimuth - elevation data may vary as a function of frequency, the orientation of the illuminating antenna was held fixed (with respect to azimuth - elevation system) and the data plotted in Fig. 5-15 and 5-16 was collected as a function of frequency. This data was collected for several frequencies in the range of 0. 6 - 3. 0 GHz.- It will be observed that there are some large errors associated with the data as a function of frequency. The cause for the errors is related to the symmetry associated with the antenna element patterns both as a function of frequency and orientation. 27

1084-5-Q 90 m - / ~) / 0 / 60 40 0b20 0 / a) 0 / 10 I / - / 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) FIG. 5-8: Theoretical Calculated Elevation Angle vs. True Elevation Angle (Assuming a Cosine Element Pattern with Elements Placed at = 40~ and 800). 28

1084-5-Q 90 q) Q q) 2 0.4 4D q) cU c) C) P-3 80 60 40 20 0 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) FIG. 5-9: System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1. 6 GHz). 29

1084-5-Q 90 80 - ~ / E) /.0 40 / -.- 20 0-"0 j 800 C-8 - / x 260 True Elevation Angle in Degrees ( T) FIG. 5-10: System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1. 6 GHz). 30

I UOs-D-w (1) bl) Q) r. -4j ro r- l 90 80 60 40 20 0 0 20 40 True Elevation Angle in 60 80 90 Degrees ( T ) FIG. 5-11: System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1. 6 GHz). 31

1084-5-Q PI 04 m *4) 4.) $4. 0 U r-4 0) Cd~ 4) 4) 90 80 60 40 20 0 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) FIG. 5-12: System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.6 GHz). 32

1084-5-Q l — a c C) *-I C) -) r-4 U 370 280 190 100 350 260 170 80 330 240 150 60 310 220 130 40 290 200 110 20 270 180 90 X-'X 0 e-oj 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) FIG. 5-13: System Generated Azimuth Angle vs. True Elevation Angle (Frequency = 1.4 GHz) for 0 - 60~ O- and 240 XX. 33

1084-5-Q 90 80, 60. 40 20 -0 //s I 20 / / I 1 0 20 40 True Elevation Angle FIG. 5-14: System Generated El 60 80 90 in Degrees (T ) levation Angle vs. True aquency = 1.4 GHz). Elevation Angle (Fre 34

1084-5-Q 100 0 — bfl 0 Q>..r. N r-4 z C. 80 60 40 20 0 0.6 1.0 1.4 1.8 2.2 2.6 3.0 (Frequency = 1. 6 GHz) FIG. 5-15: System Generated Azimuth Angle vs. Frequency for a Fixed Azimuth and Elevation of Illuminating Source ( = 90, 0 = 30). 35

1084-5-Q 90 80 - 0) D 5 60 - 60 --).2 40 - 0 P-4 m 20 -Z 0o r —4 X-X 15 Foot Illuminating Source *- - * 10 Foot Illuminating Source -,. ~ /,',,/" 'f.S 0.6 1.0 1.4 1.8 2.2 2.6 3.0 (Frequency = 1.6 GHz) FIG. 5-16: System Generated Elevation Angle vs. Frequency for a Fixed Azimuth and Elevation of Illuminating Source ( =90~, 0 =30~). 36

1084-5-Q The data presented above has been collected employing a CW source. In addition, some tests have been made employing pulse data. In this test a pulse width of approximately 4 microseconds duration and a repetition rate of 1000 pulses per second was used. This data agreed well with the CW data presented above. The results presented above have been collected without benefit of any data processing techniques. Some preliminary work has shown that data processing can improve the accuracy for those cases where the element patterns are not well behaved both as a function of frequency and orientation. In one of the data processing schemes only a limited amount of the data collected by the computer was processed. This method simply required that the computer scans the data collected from the 17 antennas and determines the maximum signal received, so that the remaining data can be normalized with respect to the pattern maximum. Only data within a specified limit of the pattern maximum is employed in the calculation of the alZimlthL - elevation angles. Typically, data has been limited to that within 15, 10, and 6dB of the data maximum. Essentially, one is discarding all data below the specified limit. Through this method one hopes to limit the data used by the computer to that region where the antenna element patterns are well behaved both as a function of frequency and antenna orientation. A second method of processing required the averaging of data. Employing this technique the azimuth and elevation is calculated and stored (in the computer) for several revolutions for the antenna, typically 10 revolutions. This data is then averaged and the average displayed to the operator. The purpose for using this technique is to provide a large number of data points which have random variation due to anomalies in the DF system from which to calculate the azimuth and elevation direction of arrival. 37

1084-5-Q More effort is required to properly evaluate data processing techniques that may be applicable in improving the accuracy and reliability of the data displayed by the DF system. 38

1 084-5-Q VI FLY-BY TESTS Preparations are now being made to conduct a series of fly-by tests with the azimuth - elevation direction finding equipment. In these tests the aircraft flies in the vicinity of the azimuth - elevation direction finder while radiating a 1. 6 GHz CW or pulse signal. The aircraft will be tracked with a NIKE Ajax (Fig. 6-1) skin tracking radar system to provide an accurate azimuth - elevation location of the aircraft as a function of its flying time. At the present time, it appears that the data from the NIKE Ajax system can be placed in a format such that it can be inserted into the azimuth - elevation direction finder computer system and printed out on the teletype along with the azimuth and elevation data from the DF equipment. This will provide a real time comparison between a known azimuth - elevation system (the NIKE Ajax system) and the system under test (Azimuth - Elevation Direction Finder). Presently one of two aircraft are being considered for use. They are a C-131 Air Force aircraft or an Army C-46 aircraft. Either of the aircraft has the capability of being flown at an altitude of 10, 000 feet for a minimum of one hour testing time. 39

1084-5-Q FIG. 6-1: NIKE Ajax Skin Tracking Antenna. 40

1084-5-Q VII CONCLUSIONS AND RECOMMENDATIONS The fabrication of the quadrafilar balun network has been completed and the phase data is not as well controlled as desired. However, it is felt that with some additional effort, the balun can be optimized to operate in accordance with the design criteria. It is recommended that this effort (optimization of the balun network) be continued, so as to obtain the proper amplitude and phase chalacttle istics required for the quadrafilar spiral. As noted in Chapter II, some preliminary radiation patterns recorded for the quadrafilar spiral were unsatisfactory. The cause for the poor pattern characteristics is the improper phase distribution associated with the balun, and the wrap angle of the spiral and perhaps irregularities in the winding of the spiral elements. The present quadrafilar spiral was hand-made and some errors in the manner in which the elements were wound are apparent. Therefore, it is recommended that the study of the quadrafilar spiral configuration be continued so as to optimize the element design, thus enhancing accuracy of the direction finder system As a part of the optimization of the elements, consideration should be given to the cone angle and material, element conductor and wrap angles. Although several investigators are working with the multifilar spiral configuration, no sa:;tactoryl antennas are available commerically. Because of the unavailability of multifilar spirals the authors have given consideration to the use of the bitflar cavity backed spirals as advertized by many commercial organizations. However, as a result of extensive (.t sclIssioIs with the manufacturers representatives, it has been learned that. most of the spirals are inefficient and therefore have low gains. One cause for the poor efficiency associated with commercially available cavity backed spirals is that the manufacturer employs resistive material (microwave absorber, etc. ) to minimize moding and to improve the radiation characteristics of the antenna. 41

1084-5-Q A general review of the preliminary results that have been obtained for the azimuth - elevation direction finder substantiate the feasibility of employing the vector analysis technique for direction finding in both azimuth and elevation. Present results show that the system accuracy is + 5 for both azimuth and elevation planes. The chief limiting factor to the system is the antenna elements. To overcome this limitation additional effort is needed on the optimization of the elements and further consideration on improved data processing techniques is in order. In the event there is interest in employing the present azimuth - elevation DF system with higher gain elements, it would be desirable to store the element pattern in the computer. It appears that this would require a more sophisticated computer than the one now in use. This is another area of study worthy of future consideration. 42

1084-5-Q DISTRIBUTION LIST FOR REPORTS UNDER DAAB07-67-C0547 U of M Project 01084 Destination Number of Copies Technical Library, Rm. 3E-1039, Pentagon Dir., Defense, Research and Engineering Washington, DC 20301 1 Defense Intelligence Agency ATTN: DIARD Washington, DC 20301 1 Director, National Security Agency ATTN: C31 Ft. George G. Meade, MD 20755 20 Naval Ships Systems Command ATTN: Technical Library 20526 Main Navy Bldg., Rm. 1528 Washington, DC 20325 1 Dir., U. S. Naval Research Laboratory ATTN: Code 2027 Washington, DC 20390 1 Rome Air Development Center ATTN: EMTLD, Documents Library Griffiss AFB, New York 13440 1 Electronic Systems Division, ESTI L. G. Hanscom Field Bedford, Mass. 07130 2 Hq., AFSC ATTN: SCTSE Bolling, AFB, DC 20332 1 CG, U. S. Army Materiel Command ATTN: R and D Directorate Washington, DC 20315 1 Redstone Scientific Information Center Attn: Chief, Document Section U. S. Army Missile Command Redstone Arsenal, Ala. 35809 1 CO, USASA, Test and Evaluation Attn: IAOTR Ft. Huachuca, Ariz. 85613 1

1084-5-Q U of M Project 01084 Distribution List (continued) CO, Aberdeen Proving Ground Technical Library, Bldg. 313 Aberdeen Proving Ground, MD 21005 1 CG, U. S. Army Combat Developments Command CDCMR-E Ft. Belvoir, VA 22060 1 CO, U. S. Army Combat Developments Command Communications-Electronics Agency Ft. Monmouth, NJ 07703 1 CO, U. S. Army Security Agency Combat Developments Activity Arlington Hall Station Arlington, VA 22212 1 U. S. Army Secuirty agency OAC of IS, DEV (IARD-EW) Arlington Hall Station Arlington, VA 22212 3 U. S. Army Security Agency Processing Center IAVAPC- R and D Vint Hill Farms Station Warrenton, VA 22186 1 CO, U. S. Army Nuclear Defense Laboratory Attn: Library Edgewood Arsenal, MD 21010 1 Harry Diamond Laboratories Attn: Library Connecticut Ave and Van Ness St Washington, DC 20438 1 CG, U. S. Army Electronic Proving Ground Attn: Technical Information Center Ft. Huachuca, Ariz. 95613 1 Assistant Secretary of the Army R and D Department of The Army Attn: Deputy Assistant for Army R and D Washington, DC 20315 1 CO, U. S. Army Limited War Laboratory Aberdeen Proving Ground, MD 21005 1

1084-5-Q U of M Project 01084 Distribution List (continued) CO, U. S. Foreign Science and Technology Center Attn: AMXST-RD-R, Munitions Bldg. Washington, DC 20315 1 Office, AC of S for Intelligence Department of the Army ATTN: ACSI-DSRS Washington, DC 20310 1 CG, U. S. Army Electronics Command Attn: AMSEL-MR 225 South 18th Street Philadelphia, PA 19103 1 Director, Electronic Defense Laboratories Sylvania Electronic Products, Inc. ATTN: Documents Acquisition Librarian P. 0. Box 205 Mountain View, Calif. 94040 Chief, Intelligence Materiel Development Office Electronic Warfare Lab., USAECOM Ft. Holabird, MD 21219 1 Chief, Missile Electronic Warfare Tech Area EWLab., USAECOM White Sands Missile Range, NM 88002 1 HQ, U. S. Army Combat Developments Command Attn: CDCLN-EL Ft. Belvoir, VA 22060 1 USAECOM Liaison Officer Aeronautical Systems, ASDL-9 Wright-Patterson AFB, Ohio 45433 1 USAECOM Liaison Office U. S. Army Electronic Proving Ground Ft. Huachuca, Ariz. 85613 1

1084-5-Q U of M Project 01084 Distribution List (continued) CG, U. S. Army Electronics Command Ft. Monmouth, NJ 07703 ATTN: AMSEL-EW 1 AMSEL-IO-T 1 AMSEL-RD-MAT 1 AMSE L-RD-LNA 1 AMSE L-RD-LNJ 1 AMSE L-XL-D 1 aMSEL-NL-D 1 aMSEL-HL-CT-D 2 AMSEL-WL-S 6 NiSA Scientific and Technical Info. Facility Attn: Acquisitions Branch S-AK/DL P. 0. Box 33 College Park, MD 20740 2 Battelle-Defender Info. Center Battelle Memorial Institute 505 King Avenue Columbus, 0. 43201 1 Remote area Conflict Info. Center Battelle Memorial Institute 505 King Avenue Columbus, 0. 43201 1 TOTAL 72

- - - Security Classification DOCUMENT CONTROL DATA - R&D (Security classification of title, body of abstract and indexing annotation must be entered when -the overall Report in classified) 1. ORIGINATING ACTIVITY (Corpor REPORT SECURITY CLASSIFICATION The University of Michigan, Radiation Laboratory UNCLASSIFIED Department of Electrical Engineering, 201 Catherine St. 2b ROUP Ann Arbor Michighin 4108. NA 3. REPORT TITLE AZIMUTH AND ELEVATION DIRECTION FINDER TECHNIQUES 4. DESCRIPTIVE NOTES (Type of report and inclusive dates) Fifth Quarterly Report 1 July - 30 September 1968 5. AUTHOR(S) (Last name, first name, initial) Ferris, Joseph E., Wilcox, Peter H., and Zimmerman, Wiley E. 6- REPORT DATIE 7a. TOTAL NO. OF PAGES 7b. NO. OF REFI December, 1968 42 8a. CONTRACT OR GRANT NO. 4. ORIGINATOR'S REPORT NUMBER(S) DA AB 0767C-0547 1084-5-Q b. PROJECT NO 5A6 79191 D902 0511 c. Sb. OTHER REPORT NQ(S) (Any other numbers that may be aauined this report) ECOM-0547-5 d. 10. AVA ILABILITY/.IMITATION NOTICES Each transmittal of this document outside the Department of Defense must have prior approval of CG, U. S. Army Electronics Command, Fort Monmouth, New Jersey, 07703, ATTN: AMSEL-WL-S. 11. SUPPL.EMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY U.S. Army Electronics Command AMSEL-WL-S F__t. Monmouth, N. J. 07703 13. ABSTRACT During this reporting period efforts have continued in the design and development of the quadrafilar balun, and the assembly of the components of the DF system has been 90 per cent completed. Preliminary tests that have been conducted on the quadrafilar balun have shown that the amplitude variation is well behaved. However, there is some undesirable phase discrepancies in the network. In addition to these tests a preliminary evaluation of the DF system has been conducted. The results of the preliminary tests show that the system is able to direction find with an accuracy of + 5~ in both the azimuth and elevation directions. DD JAN 64 1473 Security Classification

Security Classification I 14. LINK A LINK B LINK C KEY WORDS - KEY WOS ROLE WT ROLE WT ROLE WT Azimuth - Elevation Direction Finder Quadrafilar Spiral Quadrafilar Balun Cavity Backed Spiral i i i INSTRUCTIONS 1. ORIGINATING ACTIVITY: Enter the name and address of the contractor, subcontractor, grantee, Department of Defense activity or other organization (corporate author) issuing the report. 2a. REPORT SECURITY CLASSIFICATION: Enter the overall security classification of the report. Indicate whether "Restricted Data" is included. Marking is to be in accordance with appropriate security regulations. 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 authorized. 3. REPORT TITLE: Enter the complete report title in all 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 immediately following the title. 4. DESCRIPTIVE NOTES: If appropriate, enter the type of report, e.g., interim, progress, summary, annual, or final. Give the inclusive dates when a specific reporting period is covered. 5. AUTHOR(S): Enter the name(s) of author(s) as shown on or in the report. Enter last name, first name, middle initial. If military, show rank and branch of service. The name of the principal author is an absolute minimum requirement. 6. REPORT DATE; Enter the date of the report as day, month, year; or month, year. If more than one date appears on the report, use date of publication. 7a. TOTAL NUMBER OF PAGES: The total page count should follow normal pagination procedures, L e., enter the number of pages containing information. 7b. NUMBER OF REFERENCES: Enter the total number of references cited in the report. 8a. CONTRACT OR GRANT NUMBER: If appropriate, enter the applicable number of the contract or grant under which the report was written. 8b, 8c, & 8d. PROJECT NUMBER: Enter the appropriate military department identification, such as project number, subproject number, system numbers, task number, etc. 9a. ORIGINATOR'S REPORT NUMBER(S): Enter the official report number by which the document will be identified and controlled by the originating activity. This number must be unique to this report. 9b. OTHER REPORT NUMBER(S): If the report has been assigned any other report fiumbers (either by the originator 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 imposed by security classification, using standard statements such as: (1) "Qualified requesters may obtain copies of this report from DDC." (2) "Foreign announcement and dissemination of this report by DDC is not authorized." (3) "U. S. Government agencies may obtain copies of this report directly from DDC. Other qualified DDC users shall request through (4) "U. S. military agencies may obtain copies of this report directly from?DC. Other qualified users shall request through (5) "All distribution of this report is controlled. Qualified DDC users shall request through.. If the report has been furnished to the Office of Technical Services, Department of Commerce, for sale to the public, indicate this fact and enter the price, if known. 11. SUPPLEMENTARY NOTES: Use for additional explanatory notes. 12. SPONSORING MILITARY ACTIVITY: Enter the name of the departmental project office or laboratory sponsoring (paying for) the research and development. Include address. 13. ABSTRACT: Enter an abstract giving a brief and factual summary of the document indicative of the report, even though it may also appear elsewhere in the body of the technical report. If additional space is required, a continuation sheet shall be attached. It is highly desirable that the abstract of classified reports be unclassified. Each paragraph of the abstract shall end with an indication of the military security classification of the information in the paragraph, represented as (TS), (S). (C), or (U). There is no limitation on the length of the abstract. However, the suggested length is from 150 to 225 words. i I 14. KEY WORDS: Key words are technically meaningful terms or short phrases that characterize a report and may be used as index entries for cataloging the report. Key words must be selected so that no security classification is required. Identifiers, such as equipment model designation, trade name, military project code name, geographic location, may be used as key words but will be followed by an indication of technical context. The assignment of links, rules, and weights is optional. I CI --- _ Security Classification