1084 —ECR = RL-2028 1084 -8-ECR * TECHNICAL ktlitOI 0 S 0 S 0 0 0 0 0 S 0 S 0 0 S 0 0 0 0 0 S 0 0 0 0 0 0 00000000000 60000 RT ECOM- 8 - 0547 MENT COMPLIANCE REPORT VATION DIRECTION FINDER TECHNIQUES (Developmental Model) By V. B. Henry and W. E. Zimmerman January, 1969 ECOM UNITED STATES ARMY ELECTRONICS COMMAND CONTRACT DA AB07-67-C0547 DA I THE UNIVERSITY OF MICHIGAN DEPARTMENT OF ELECTRICAL ENGINEERING RADIATION LABORATORY ANN ARBOR, MICHIGAN FORT MONMOUTH, N.J. Project 5A6 79191 D902-05-11

EQUIPMENT COMPLICANCE REPORT This r t desribes the testing procedures and test resuts employed to -evlmmt the ptrlwinre of an Ai uth-Elevation Direction Finding (A-ED?) system drstopd b-y Tb. University of Michigan Radiation Laboratory. The A-DOQ system osists of an antenna system, electromechanical switch, video a er, A/D on-verter, computer and aimth-elevation display system. The AMDF systm dis yied for uwe in the detection, frequency mesuremmas, ar- determination of berlmg (asinUth and elevation) of radio frequency (RF) trsmissins rom fixed, mobile or portable airborne sets operating in the -freq;em y range of 0.6 to 3.0 GHz. Since suceossafl system operation depends on the performance of the subsystems, the desip als include specifiatio for the subsysms as well as th total system performane. t is tsb. ethTiasiled that the series of tests conducted were not designed to provide an exhaustive description of the A-EDF eqipment, but rather were oonceived as design aids during the development of the splortory model. The report diusses the testing procedures utilized to evaluate and determine the degre of omplane of the antenna array, the data processing system, and tbe overall performance of the A-EDF iystem. Two types of tests were performed for the evaluation of the A-EDF system; 1) ree space tests and 2) fly-by tests. The purpose of the free space tests was to determine stm accuracy and an ideal environment. The results of the free space tests suges that the system has an accuracy of t 5~ in both azimuth and elevation. The ff-by test were performed to determine the effect of reflections on t A-EDO ystem performane uer dynamic environmental conditions. However, it is difficult to asses the contribution of the ground reflection alone due to the electrically hostilse aironment in which the A-EDG system was operated. i

TABLE OF CONTENTS SUMMARY i 1.0 INTRODUCTION 1 2. 0 DATA ACQUISLTION SUBSYSTEM 2 2.1 Antenna Array Elements 2 2.2 Hemispherical Array 9 3. 0 DATA PROCESSING SUBSYSTEM 9 4. 0 PERFORMANCE OF THE A-EDF SYSTEM 12 4. 1 Free-Space Performance 12 4.2 Fly-By Tests 25 5. 0 CONCLUSIONS AND RECOMMENDATIONS 40 ii

AZIMUTH AND ELEVATION DIRECTION FINDER TECHNIQUES EQUIPMENT COMPLIANCE REPORT 1.0 INTRODUCTION This report describes the testing procedures and test results employed to evaluate the performance of the A-EDF system developed at The University of Michigan in terms of the design goals set forth in Contract DAAB07(67-C-0547 "Azimth and Elevation Direction Finder Techniques". Since the task described in the contract is for the development of an exploratory developmental model, there has been no officially approved test plan. It is to be emphasized that the following series of tests were not designed to provide an exhaustive description of the A-EDG system performance, but rather were conceived as design aids during the development of the exploratory model. The A-EDF system is comprized of two main ubsystems; one for data acquisition, which is the antenna array, and the other for data processing including a receiver (FE), memory voltmeter, analog-to-digital converter, and computer. Since successful system operation depends on the performance of the subsystems, the design goals include specifications for the subsystems as well as total system performance. The following chapters of this report discuss, in order, the testing procedures utilized to evaluate and determine the degree of compliance of the antenna array, the data processing subsystems, and the overall performance of the A-EDF system, At the end of the report we present our conclusions and recommendations dwnfroiths;leseats. 1

2.0 DATA ACQUISITION SUBSYSTEM This chapter describes contract design goals for the data acquisition subsystem, the tests used to evaluate the subsystem, tad the degree to which this subsystem complies with those design goals. 2.1... A r _a Elment The oontract design goals for the antenna array elements include a VSWR of no greater than 3: 1, an axial ratio of 3 dB for the circularly polarized elements, and a gain of not less than 5 dB above a circularly polarized isotropic source. All of thee specifications apply across the entire 5: 1 operating bandwidth of 600 to 3000 MHz. The VSWR of the elements was measured with a slotted line employing the equipment arrangement shown in Fig. 2-1. Care was taken to insure the antenna was in an esentially free space environment. The measurements were repeated only for a few of the 17 elements because of the excellent agreement from element to element. Typical VSWR data is shown in Fig. 2-2 for 100 MHz increments across the 5: 1 band. The maximum VSWR is 2.80 and occurred at 2800 MHz. The axial ratio of the antenna was measured by rotating the antenna about an axis normal to the plane of the element spiral in 10~ increments and rotating the spiral continuously in the plane containing the axis. This allowed the axial ratio to be measured not only at the peak of the beam, but at all other points as well. The maximum axial ratio measured at the peak of the beam of the sample of elements measured is tabulated versus frequency in Table 2. 1 for the discrete frequencies of 0.6, 1.6, 1.8 and 3.0 GHz. The maximum axial ratio is 1dB for the frequencies measured. TABLE 2.1: SPIRAL AXIAL RATIO VS FREQUENCY Frequency (GHz) 0. 6 1.6 1.8 3.0 Axial Ratio (dB) 0.5 1.0 0.5 1.0 The gain of the elements was measured by the substitution method. A pattern of an antenna with a known gain (in this case a gain standard horn) was superimposed on a pattern of the element antenna. The directive gain at the peak of the beam is then the difference in received signal levels at that point. The equipment arrangement is given in Fig. 2-3. The gain of the elements measured is 3 dB above a linearly polarized isotrope at 1.1 and 1.6 GHz. Since the gain of a linearly polarized isotrope is 3 dB above a circularly polarized isotrope, the gain of the elements is 6 dB above a circularly polarized isotrope source at these frequencies. Another important parameter of the element antennas employed in this direction finder system is squint. Pattern measurements for one antenna orientation were repeated at 100 and 200 MHz increments across the 5: 1 frequency band specified. The results appear in Fig. 2-4. 2

FIG. 2-1: VSWR Test Set (continued on next page).

VSWR TEST SET Frequency Range Legend Equipment Description Manufacturer Model Serial; -- -- -- - 1 1 1 1 2 3 4 5 5 6 7 8 a b c d a b VHF Signal Generator UHF Signal Generator UHF Signal Generator UHF Signal Generator Wide Range Oscillator 3dB Attenuator Slotted Line Bolometer Bolometer Standing Wave Indicator Test Antenna Shielded Anechoic Enclosure 10 - 480 MHz 450 - 1230 MHz 800 - 2100 MHz 1.8 -4.1 GHz 5 - 60,000 Hz DC - 3.0 KMc 500 - 4000 MHz 50 - 1000 MHz.5 - 10 GHz 1000 Hz 600 - 3000 MHz 500 - 12000 MHz Hewlett-Packard Hewlett-Packard Hewlett-Packard Hewlett-Packard Hewlett-Packard Weinschel Hewlett-Packard Hewlett-Packard PRD Hewlett-Packard 608A 612A 614A 616B 200CV 50-3 805A 476A 627A 415B 1577 299-01770 289-02172 007-00893 229-41280 D2567 226 2775 483 FIG. 2-1 (continued) Description of VSWR Test Set.

3.0 2.5 -2.0 -1.5 -1.0- I 0,6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2, Frequency (GHz) FIG. 2-2: Spiral VSWR versus Frequency. 4 2.6 2.8 3.0 5

- - - -0 ~ - ~~- ~ ( ---- - @I -i FIG. 2-3: Pattern nd Gain Meaeurement Test Set (continued on next page).

GAIN AND PATTERN MEASUREMENT TEST SET Legend Equipment Description Frequency Range Manufacturer Model Serial 1 2 3a 3b 3c 4 5 6 7 8 a 8b 9 10 11 a 11 b 12 13 Regulated Power Supply Fork Modulator Unit Oscillator Unit Oscillator Microwave Oscillator Directional Coupler Bolometer Standing Wave Indicator 40' Transmitting Tower 15' Parabolic Dish 10' Parabolic Dish 200' Transmitting Dist. 40' Receiving Tower Test Antenna L band Gain Standard Horn Bolometer Antenna Pattern Recorder 1000 Hz 250 - 920 MHz 900 - 2000 MHz 1.7-4.1 GHz 1.0 -4.0 GHz 50 - 1000 MHz G.R. Antlab G.R. G.R. G.R. Narda H.P. H.P. 1201B 2707 1209B 1218A 1360B 3022 476A 415B 1451 158 486 110 483 500 - 1500 MHz 1500 - 2500 MHz 1.12 - 1.70 GHz.5 - 10 GHz Built to NRL Spec. PRD Antlab 627A 2375A 2775 301 FIG. 2-3 (continued) Description of Pattern and Gain Measurement Test Set.

600 700 800 1600 1800 FIG. 2-5: 900 1000 1100 1200 1300 14C 2000 2200 2400 2600 2800 30( Frequency (MHz) 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). )0 00

The oertrat desip Is covering the array smsts that the array shall onBsist of a mMM-TUn oi 16 bwm-e-Bm, ravty-baekd, flat spiral ae-am elements, m-end en a 6' - hemisph al gsronBd plmn. The acal arry delivered o ss of It b0reband. eav tysbaeksd, flat spiral antenna ele=*ens Deied on a o f 1 t -, owsbt, tlat -ra.l - ilz- -. 0 a 8' ladmetr hrd__Shria l rd pla. A t a the omplet ar is hms in rig. 2-5. Also p- i r trat to array ihall be capable of beraind a.lotrm y. b0 tw ot aNad sopl y e velopi a broad prly eletr ( e dg. darrata eletrom aaeal U it has bn uttutd. Tiab u it prervj rteiabte upra iena tor the stire 5:1 opu a l band, dirplays low Iwrtio a s ad h prsia for varying the soandl h rat. The annlng roor, l b wnt h to aocommodate all manner of signal modulatio. The Matin rat has en optimised at 1000 scans per soond, with prrl i for uvarying e tl ra at the o perator. 3.0 D&TA PBOCEMiNQ SJUB5YSTEM Thlt chapter deasrlbe o the dt design pals for the data procesing bem ad te deee to whioh ti subsystem oomplies wfth those specfiaatlons. Th o ra deign goal inlue a system which shall obtain the relative amplgitde inarmation mfrom the elements of the antenna array. Ths information shall be processed and preseted in a form to the visual bearing indicator unit suitable to permit the visual preseatatien of the alimuth and elevation direction of artival of the received signals. Additionally, the information fed to the visual bearing indeator unit shall be read out in numerical form. The data processing subsystem is shown in block diagram in Fig. 3-1. The relative amplitude information is received, amplified, measured and processed. The asimuth and elevation informaton is preseated in visual numerical form by a NIXIE tube presentation on the front of the cabinet. The information can also be aitomatieally printed out on the system teletype at the discretion of the operator. A CRT visual bearing ibdioator was rejected as providing only redundant information at a low precision and high eost. 9

FIG. 2-5: Complete Hemispherical Array. 10

FIG. 3-1: Block Diagram of Data Processing Subsystem. 11

4.0 PERFORMANCE OF THE A-EDF SYSTEM This chapter describes the contract design goals for the entire A-EDF system, the tests used to evaluate system performances, and the degree to which this subsystem complies with the specifications. The design goals for the A-EDF system include a t2~ bearing accuracy in azimuth over 360~ of azimuth coverage and t 50 bearing accuracy in elevation for 90~ of elevation coverage. It is desirable to hold these tolerances over a frequency range of 600 - 3000 MHz for signals containing pulse, CW, AM and FM modulation waveforms. Also, environmental requirements are supplied in the contract (i. e. temperature, wind load, etc) but no effort was expended to determine if this exploratory developmental model conformed to those specifications. 4. 1 Free-Space Performance The first series of tests with the A-EDF system were made under simulated free space conditions by installing the array on the general purpose antenna range shown in Figs. 4-1 and 4-2. The electromechanical switch used for scanning the array is located on the tower near the array in Fig. 4-1. The data processing equipment is housed in the building at the lower left of the photo. With a CW signal source operating at 1.6 GHz, the array was scanned in elevation at a constant azimuth. The coordinate system used to describe this data is shown in Fig. 4-3. Figures 4-4 through 4-7 are plots of the variations in recorded azimuth as a function of the true elevation angle. For example, referring to Fig. 4-4, the scan starts at an elevation of 90~ and an azimuth of 90~, corresponding to the circle in the lower right hand side of the graph. As the scan progresses, the elevation decreases in the direction of the arrows until the elevation passes through zero and the azimuth jumps to 270~. The scan is completed as the elevation continues to decrease from zero to 90~. Ideally the azimuth data should read either 900 or 2700, depending on the side of the hemisphere (east or west) data is being collected from. The data near the pole position of the hemisphere (i. e. data looking straight above the hemisphere, 0=00) is least accurate. Additional data collected at 1.6 GHz for azimuth angles of 80~, 70~ and 60~ is shown in Figs. 4-5 through 4-7. Figures 4-8 through 4-11 are graphs of the calculated elevation angles as a function of the true elevation for azimuth angles of 900, 800, 70~ and 600. The cause for the deviation of the calculated elevation angles from the true elevation is the non-symmetrical location of antennas in the 0 plane of the antenna system. That is, the antenna elements are only employed in the upper hemisphere of the spherical coordinate system. These deviations are predictable and the necessary corrections have since been programmed into the computer. For purposes of comparison, the theoretically computed elevation angle versus the actual elevation angle, assuming a cosine antenna pattern for the individual elements is included in Fig. 4-12. Note that the measured elevation does indeed conform well to the theoretical data of Fig. 4-12.

FIG. 4-1: Photograph of Antenna Range used for A-EDF System Free Space Measurements. 13

vc.4-2: P~hotoo-raph. of ANtitnna Pangeo- use [oir~i~)?Ivstem FeeSpace Mleasuremient s. 14

Zenith 0 = 00 Z - 900 Y 600= E N 0 = 900 FIG. 4-3: Azimuth - Elevation Coordinte System 15

370 280 190 100 P4 4) E: -C) Cd Q I.:3 N 4) Cd:1 350 260 170 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.ngle in Degrees (0 ) Azimuth Angle as Generated by the DF System as a Function of the True Elevition.\ngle for i- 90~ 00 and = 270~ x-x. FIG. 4-4: 16

370 280 190 100 Is,_ U (2) C.);-.4 U Z,. I 4 -j all -r-I rl!11 IN., 1-11 (D 4 1 -j,- 4 -0.-j C) u 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 (0 ) FIIG. 4-5: Azimuth Angle as Generated by the DF System as a Function of tile True Elevation Angle for 0 80 0-0 and 0 = 260~ X-'X. 17

370 280 190 100 cr - r qJ - - -..) c -0 - Wj 350 260 170 330 240 150 310 220 130 290 200 110 270 180 X-X 90 0 20 40 60 80 90 True Elev'ition Angle in Degrees ( 0 ) FIG. 4-6: Azimuth Angle as Generated by the OF System as a Function of the True Elevation Angle for 0 = 70 00 and = 250 X-X. 18

370 280 190 100 Pco Ca c) 4-, Ca c4 - 350 260 330 240 310 220 290 200 270 180 x 170 80 ' 150 60 -130 40 ' 110 20 ' 90 0 -0-0 0 20 40 60 80 90 True Elevation Angle in Degrees (0T) FIG. 4-7: Azimuth Angle as Generated by the DF System as a Function of the True Elevation Angle for 0 = 60 0 -and 0 - 240~ X-X. 19

90 z - 80 60 o 60 *.Q< "-4 I 40 2 c) 6. 2 cd 0 20 40 60 80 90 True Elevation Angle in Degrees (T ) FIG. 4-8: System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.6 GHz). 20

90 C/.20 80 60 / x- 0 / 20 - J ~ o~ 0 20 40 60 80 90 True Elevation Angle in Degrees (0 ) FIG. 4-9: System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.6 GHz). 21

90; 80 / Q / / / 0 /: c. 60 -/ / 20 0 20 40 60 80 90 True Elevation Angle in Degrees (0 ) FIG. 4-10: System Generated Elevation Angle vs. True Elevation Angle (Frequency =1.6 GHz).

-- r-l a) C) -1 ca > rd rC) 90 80 60 40 20 0 0 20 40 60 80 90 True Elevation Angle in Degrees ( T ) System Generated Elevation Angle vs True Elevation Angle (Frequency = 1.6 GHz). FIG. 4-11: 29:

90 / 8 80 / I / o / 6 X 60 40- / 20 0 O 1 — -- / 0 20 40 60 80 90 True Elevation Angle in Degrees (0T) FIG. 4-12: Theoretical Calculated Elevation Angle vs. True Elevation Angle (Assuming a Cosine Element Pattern With Elements Placed at 0 = 40~ and 80 ). 24

The system response as a function of frequency is graphed in Figs. 4-13 through 4-16. Figures 4-13 and 4-14 are azimuth and elevation data collected at 1.4 GHz with an azimuth angle of p=60~. Figures 4-15 and 4-16 show the variations of the calculated azimuth and elevation angles as a function of frequency. Note that this data was collected at a fixed azimuth and elevation angle. The data presented above has been collected employing a CW source. In addition, some tests have been made employing pulsed signals. The pulse data employed a pulse width of approximately 4 microseconds duration and a repetition rate of 1000 pulses per second. This data agreed well with the CW data presented above. The results of the experiments described above suggest that the A-EDF system has a pointing accuracy of at least ~ 5~ in both elevation and azimuth at an operating frequency of 1.6 GHz. The system response with respect to frequency is not constant. Errors as large as 30~ have been measured in azimuth at some frequencies. For this reason most of the preliminary investigation was limited to a single frequency. Since these tests were run, the computer program has been modified to include the elevation correction factor as shown in Fig. 4-12. Subsequent tests were performed to insure that the correction factor functioned properly. However, these tests were not documented and no data is available for presentation. Other program modifications include an averaging subroutine to reduce the effects of random variations in the data, and a subroutine which limits the amount of data used by the computer to make a direction decision. These modifications are discussed in more detail in the System Operation Manual (Section 3. 1. 2 "Variable Instructions) which was prepared under Contract DAAB07-67-C-0547. 4.2 Fly-By Tests The fly-by series of tests were designed to evaluate the effect of ground reflections on the A-EDF system performance under dynamic environmental conditions. To conduct these tests the A-EDF system was installed at The University of Michigan's NIKE-Ajax radar site. A photograph of the radar site and sketch of the A-EDF system installation appears in Figs. 4-17 and 4-18 respectively. A 1.6 KHz CW source was installed in a DC-3 aircraft and the aircraft tracked simultaneously by the A-EDF system and the NIKE-Ajax radar. The aircraft maneuvered in a random fashion around the vicinity of the test site at an altitude of approximately 10, 000 feet and ranges from two to ten miles. The NIKE-Ajax radar coordinates were correlated with the A-EDF system by the use of a data multiplex switch which read the radar coordinates into the A-EDF system computer. This data was then printed out on the A-EDF system teletype. The data multiplex switch and voltage scaling networks are described in the Appendix of the Final Report prepared under this contract (ECOM-6-0547, 1084 -6-F). 25

370 280 190 100 I.-I Ll "'ZI I. U) I, f) 1-1 I-.1 7 I'll I= e"I -1 I:j -t 1= -— 4 71, u 350 -260 170 330 240 150 310 220 130 290 200 110 20 270 180 90 X-X 0 20 40 60 80 90 True Elevation Angle in Degrees (0 ) FIG 4-13: System Gencraited( Azimuth Angle vs. True Elevation \nles (Frequency 1. 4 G(Hz) for 0 ()~ 0- and 24() X-X. 26

Cl U) C) 0 a) ~rl" 0 -4 1-4 U SZ1 O -4-, Q) 7i) I i 4-) w0 U) 90 80 60 40 20 0 0 20 40 60 80 90 True Elevation Angle in Degrees ( 0T) FIG. 4-14: System Generated Elevation Angle vs. True Elevation Angle (Frequency = 1.4 GHz). 27

100 -- 80 4 \/ \ X,,, ' F X \,- 60- " 40 =s 1 20 0 _ X — X 15 Foot Illuminating Source.. -.. 10 Foot Illuminating Source ii 0. 6 1.0 1.4 1.8 2.2 2.6 3. 0 (Frequency = GHz) FIG. 4-15: System Generated Azimuth Angle vs. Frequency for a Fixed Azimuth and Elevation of Illuminating Source (0 - 90, 0 = 300). 28

90 80 0 X —X 15 Foot Illuminating Source a) ) * --- 10 Foot Illuminating Source 60. 40 C) - 0 I Td ~5 —~ L~~ I --- —-------- 0.6 1.0 1.4 1.8 2.2 2.6 3.0 (Frequency = GHz) FIG. 4-16: System Generated Elevation Angle vs. Frequency for a Fixed Azimuth and Elevation of Illuminating Source ( = 90, = 30~). 29

FIG. 4-17: Photograph of Test Site for Fly-By Tests. 30

N 14 -— l. 1 ----J I i ( I. I_. J Aj t L- —. _.. - - -,. _ I Generator Pad A-EDF System Array A-EDF System Van 1-I L I Tracking Radar Van r Tracking FIG. 4-18: Sketch of A-EDF System/Nike Radar Site During Fly-By Tests (not to scale). 31

The results of the fly-by tests appear in Table 4. 1. For the 60 data samples collected, the average azimuth error and standard deviations were 1.55~ and 5.9~ respectively. If the error distribution were normal (Gaussian) the average error would be zero. Assuming the distribution is normal, one would expect the error on 68 percent of the data points to lie within the standard deviation. Of the data collected, 77 percent of the points were within t 6~, suggesting that the assumption of a Gaussian distribution is acceptable and conservative. The averageelevation error and standard deviations were 0. 53~ and 7. 5~ respectively. Seventy-two percent of the elevation data points collected had an error of less than or equal to 8~. The error distribution is slightly skewed from the normal, but conforms well to the results predicted by assuming a normal distribution. It should also be noted that the radar data presented in Table 4.1 has associated with it a random uncertainty of t 1~ due to the processing of the data through the multiplexer and scaling amplifier. Referring to Figs. 4-17 and 4-18 one can easily see that the possibility of multiple signal paths is high. An example is diagrammed in Fig. 4-19. Due to the irregular nature of the positions and geometries of the reflecting objects and the irregular flight paths of the aircraft, little correlation exists between a specific azimuth or elevation angle and the error experienced at that angle. It is highly improbable that the contribution of the reflections to the A-EDF system output can be quantitatively evaluated from these tests. A second known source of uncertainty is the low signal-to-noise ratio of the signals received during these tests. Knowing the output power of the airborne source, the transmitting and receiving antenna gains and the signal path attenuation, one can calculate the magnitude of the received signal. With the aid of the path length versus attenuation graph in Fig. 4-20, the computations indicated above are performed in Table 4.2. The results of the computations, which are graphed in Fig. 4-21, indicate that for a range of two miles, the signal power into the receiver is a maximum of -62 to -72 dBm. Previous experience with the A-EDF system has indicated that a minimum signal power of -70 dBm into the receiver (Micro-Tel WR-200) is necessary for a 6 dB signal-to-noise ratio into the peak reading voltmeter which is the very minimum signal-to-noise ratio for meaningful system operation. An input signal of -55 dBm is the minimum desirable input level. The signals received during these tests were seldom more than the absolute minimum required for system operation, and could at times be observed receding into the noise. It should also be noted that the signal levels in Fig. 4-21 are somewhat optimistic since the airborne antenna was a monopole, vertically polarized with respect to the wings of the aircraft and exhibited somewhat less than 0 dB gain at elevation angles near the zenith. As a result of these tests, the computer program has been modified to reject data below a minimum signal-to-noise ratio selected by the operator. 32

TABLE 4-la Results of Fly-By Tests Azimuth (degrees) Elevation (degrees) Sample A-EDF System 0 Radar A A A-EDF System Radar o A E ' ' ' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 204 269 172 32 173 289 164 195 274 307 198 329 331 16 12 18 50 276 285 353 16 14 218 318 338 325 352 352 41 43 208 267 173 40 172 287 159 195 282 316 201 319 325 10 8 23 46 278 284 347 7 7 228 329 331 329 349 351 35 38 -4 +2 -1 -6 +1 +2 +5 0 -8 -9 -3 +10 +6 +6 +4 -5 +4 -2 +1 +6 +9 +7 -10 -11 +7 -2 +3 +1 +6 +5 51 21 69 30 54 40 40 57 46 36 59 31 42 42 42 15 22 25 18 28 40 33 33 40 49 40 52 57 54 62 65 31 61 21 61 44 29 64 61 37 58 30 38 30 27 17 11 24 23 30 29 34 31 38 50 49 65 63 66 66 -14 -10 +8 +9 -7 -4 +11 -7 -15 -1 +1 +1 +4 +12 +15 -2 +11 +1 -5 -2 +11 -1 +2 +2 -1 -9 -13 -6 -8 -4

TABLE 4-la (continued) Sample A-EDF Svstem 0o Radar AA A A-EDF System Radar AE E 31 32 33 34 35 3 (; 37 38 39 40 41 42 43 44 45 4 6 47 48 49 50 51 52,- h 53 54 55 56 57 r- 8 58 59 60 58 71 75 10( 144 198 26 (; 344 (37 151 200 5 84 154 14 25 15 14 322 317 325 333 331 35 176 183 194 19 (; 60 65 72 107 144 188 266 335 68 141 191 16 77 154 17 22 10 23 317 310 315 325 3'27 331 11 31 175 181 197 197 -2 +6 +3 -1 0 +10 0 +9 -1 +10 +9 -11 +7 0 -3 +3 +5 -9 +5 +7 +10 +8 +4 -6 -4 +4 +1 +2 -3 -1 55 54 62 62 64 55 21 15 1 7 31 34 51 43 39 43 45 37 18 19 31 36 36 40 52 31 60 69 66 71 56 58 58 58 68 54 26 19 2 8 33 24 36 44 24 30 49 30 10 23 31 37 40 43 61 17 59 63 71 72 -1 +4 +4 +4 -4 +1 -5 -4 -1 -1 -2 +10 +15 -1 +15 +13 -4 +7 +8 -4 0 -1 -4 -3 -9 +15 +1 +6 -5 -1

TABLE 4-1 (b) iSummary of Statistical Results Average A'zimuth Error N A n 'A n = 1 N + 1.55 Azimuth Standard Ieviation N 2 1/2 z A n (A A dN-1 n -- I N - i 5. 9 Average Elevation Error N n nN E +.53 Elevation Standard Deviation N 2 1/2 AE n (E E n -- 1 N - 1 7.5~

N l ~- -- -. — ---- - -- - — ~ - --- —.. i I Generator -._ i ' Pad _-j _ _.. ii \1 X II -- I! A-EDF System Array -- A-EDF System Van ii I r" - -.-, iTracking I 1 Radar Van I I.. f 'he, I Sj, Xi \R Tracking Radar FIG. 4-19: Example of Multiple Path Reflection 36

-120 -+ -110 - -100 / F.- 1 i ( Ilz - I I I I I I I 1 0 '2 4 6( 8 10 1 2 Path Length (Milves) FIG. 4-20: Path Loss versus ePath Length.

-1 00 -r (B O 70 - 6/ 7t t - (G 21 ( }t -50 - _ _ _ _ 0 24 81 0 1 IT ath Length ( Miles I FIG'. 4-21: Rjeceived Power versus P~ath Length.

TABLE 4. 2 Computations for Received Power P = Pt+ Gt+ G -+ N r t t r r where P = Received Power (dBm) r P Transmitted Power (dBm) - +36dBm (4 watts) t N = Path Loss (dB) r G = Receiving Antenna Gain (dB) - +3dB Above a Linearly Polarized Isotrope G Transmitting Antenna Gain (dB) = +0 to -1OdB above a Linearly Polarized t Isotrope such that P = 39dBm + N r r 39

5. 0 CONCLUSIONS AND RECOMMENDATIONS From the results presented in this report, it has been concluded that the A-EDF system approaches the bearing accuracy performance goal at discrete frequencies (i. e. 1.6 GHz) under free space conditions, but is adversely affected by frequency variations and a severe electrical environment. The free space bearing accuracy at 1.6 GHz is approximately ~ 50 in both azimuth and elevation. However, there is nothing inherent in this technique for azimuthelevation direction finding which limits the bearing accuracy to ~ 5~. A quantitative evaluation of the system accuracy and accuracy degradation due to imperfect component performance is given in the Final Report under this contract (Chapter m., System Error Analysis). The system bearing accuracy during the fly-by tests was about ~ 60 in azimuth and ~ 80 in elevation. It is felt that the performance degradation from the free space condition was due to the hostile environment. Low signal amplitude and the resultant high signal-to-noise ratio of the data and the high probability of multiple path reflections are felt to be major sources of error. As a result of the A-EDF system tests described in the preceding chapter, the computer program has been modified to include several improvements. These modifications include an averaging method which allows the operator to select the number of data points to be averaged before the display is changed, a command which limits the amount of data used to make a given bearing computation, and a routine that inhibits the display if sufficient signal is not present to provide accurate results. A more detailed description of these modifications can be found in the A-EDF system Operator's Manual prepared under this contract (ECOM-7-0547, 1084-7-OM, Section 3. 1. 2 "Variable Instructions"). The results of the tests documented above are not to be construed as a complete description of the A-EDF performance. These tests were designed primarily as design aids to compliment the system development. It is recommended that a much more complete testing program be initiated. Such a program might include: 1) a complete series of free space tests utilizing CW modulation at a single frequency where the antennas perform well (e. g. 1. 6 GHz), 2) free space tests employing other modulation types, 3) free space tests at other frequencies, and finally, 4) dynamic environmental tests with the system installed at the testing site as recommended in Chapter II of the A-EDF system Operator's Manual. 40