1962 IRE TRANSACTIONS ON MILITARY ELECTRONICS 359

Multiple-Target Data Handling with a Monopulse Radar*M. KORFFt, MEMBER, IRE, C. M. BRINDLEYt AND M. H. LOWEt, SENIOR MEMBER, IRE

Summary-Recognition and application of fundamental signal- as range and target cross section. The amplitudes of thegain relationships inherent to monopulse radars provide the means offset signals are also functions of the input signalfor determining the angle offset pattern and hence, angular position g . .of all targets within the beam of a monopulse radar. With this se t bution aiti dep end u o thetare'method some 20 to 40 targets can be tracked with dynamic accuracies angular position with respect to the axis of the radarthat approach the static accuracy of the radar, thus permitting precise beam. An example of a ten-target complex with relativedeterminations of their individual trajectories and cross sections. indications of reference and angle offset channel videoThese determinations can be made in real or nonreal time, as de- signals is shown in Fig. 2. Normalizing the ofset signalsired, by using a small portion of the storage capacity of the digital signa in Fig. 2. No rm ng e s etigacomputer normally utilized with range instrumentation systems to amplitudes with respect to the reference signal elim-calibrate, store and process information in accordance with the data mates their dependence on input signal strength, mak-operations described herein. The main advantage of this digital ing them functions of target beam position only.data processing scheme lies in the elimination of a number of com- In many texts and in practice the normalized azimuthplications which characterized earlier methods. and elevation offset signals are commonly referred to as

INTRODUCTION the azimuth and elevation error signals, and the termsazimuth error pattern and elevation error pattern have

mHEBit coIDa bhndpthe oration ra been defined as the relationship of these error signaljLamplitude-comparison monopulse tracking radar

is illustrated in Fig. 1. Each of four horns receives amplitudes to the respective angular positions of thetarget in the radar beam. In this paper the terms offsettarget signal-return energy proportional to the relative .gnal and offset pattern are used because "untracked"

location of the target within the beam. Within the horn testructure the signal return is processed to form a left- metote principl o onopde Ad maynbe foundright (or azimuth) offset signal, an up-down (or eleva- in the literature"o2tion) offset signal and a sum (or reference) signal, eachof which is applied to separate radar IF amplifiers. Thereference signal amplitude depends upon the total input TARGET CLOUD EL. AXISsignal only, and thus, is a function of parameters such X8 Xl

TARGET ECHOX7 X2

~~~~~~3'13

4 2 X5 X1O 9 AZ.AXIS

NO ELEVATIONERROR OFFSET

X4

X6

3 3

4 "-2- 4 2

AZIMUTHAZIMUTH AZIMUTH AND OFFSETOFFSET ELEVATION OFFSET VIDEO

Er=E+E2+E3+E4 REFERENCE ECHO SIGNAL ELEVATIONVIDEO

ee =(E +E2)-(E3+E4) LEFT- RIGHT OFFSET SIGNAL

eo = (EZ+E4)-(EI+E3) UP-DOWN OFFSET SIGNAL REFERENCE

e (EI+E2)-(E3+E4) VIDEO

er (EI+Eg E3+Ed) NORMALIZED LEFT-RIGHT OFFSET SIGNAL

TARGET N°- 2 3 4 5 6 7 8 9 105 J(E2+E4)-(El+E3) NORMALIZED UP-DOWN OFFSET SIGNALFi.2Rfrneadostchnlvdoe r IE +E2+E3+E41 i.2Rfrneadofe hne ie

of a ten-target complex.Fig. 1-Target echo signal distribution within thebeam configuration of a four-horn aperture.

1 D. Rhodes, "Introduction to Monopulse," McGraw-Hill BookCo., Inc., New York, N. Y.; 1959.

* Received June 7, 1962; revised manuscript received August 10 2 W. Cohen and C. M. Steinmetz, "Amplitude and phase-sensing1962. monopulse system parameter," Microwave J., vol. 2, pt. I, pp. 27-

t Radar Systems Group, RCA Laboratories, Moorestowrn, N. J. 33; October, 1959.

360 IRE TRANSACTIONS ON MILITARY ELECTRONICS October

The determination of the offset patterns would be DATA OPERATIONSsimplified if the normalized offset signals eeoer and AGC Receivere,ler were, respectively, functions only of the azimuthan elvto copnet of th anua seaato For the simplified AGC-type tracking receiver shown

bndetweenthe bempoaxitsoan thetargelo sight.ain in Fig. 3 the following notation is used in addition tobetween the beam axis and the target line of sight. In. . 1 . ~~~~~~~~~thatgiven previously:general, however, some cross coupling may exist. This t

means that the azimuth component of separation is E0 =Output voltage of the azimuth offset channelnot uniquely determined by the value of eajer but also EO=Output voltage of the elevation offset channeldepends on the elevation component of separation and E,=Output voltage of the reference channelthe converse is also true. Go=Gain transfer function of the azimuth offsetThe offset pattern functional relationships for a four- channel

horn monopulse system can be written as follows: G¢=Gain transfer function of the elevation offsetchannel

-eo( C =Gain transfer function of the reference channeler v=AGC voltage.

and

= g(; 0) (2) ver

A , er _| -F-I RANGEwhere A - SR

6=azimuth angle separation between the antenna v

beam axis and the target line of sight, EL

=elevation angle separation between the antenna 0 SERVObeam axis and the target line of sight, Fig. 3-AGC-type tracking receiver.

eo = input signal to the azimuth offset channel,e¢,=input signal to the elevation offset channel, The following relationships exist:e.= input signal to the reference channel.

If these functional relations could be determined, they E0 = Goeo (3)subsequently could be used to establish target beam Er = Grer (4)position. A problem arises in that the desired input sig- Eo rGC1 eo 1nal ratios cannot be measured directly. The ratios of the E = LI L- (5)output signals, which can be measured, are different r r r

from the input ratios because of the nonlinear receiver E _ K] (6)gain characteristics. Attempts to design economical re- Er LGrj Ler jceiving systems which either are linear over wide dy-namic ranges or which provide outputs proportional to A design goal has been the attainment of equal Gr,input signal ratios have not been resoundingly success- GC and GC, and constant Er over the entire range of inputful. The data processing techniques presented in this signal levels. If this could be achieved, then [by (1),paper do not require special or elaborate equipment (2), (5), (6) ] Eo and E4 would be directly proportionaldesigns as they utilize the equipment's inherent char- to the target beam position only. In practice, however,acteristics instead of fighting them. the gain ratios G0/Gr and G/CGr may vary by several db

It will be shown that the receiver gain characteristics due to design limitations and Er will vary due to im-can be measured and utilized to obtain a normalized perfect AGC action. This results in the output voltagesangle offset pattern independent of input signal level. EB and E<, being functions of target beam position,It also will be shown how the normalized angle offset input signal strength and target scintillation frequency.pattern is used in conjunction with output signal meas- This is not detrimental to a closed-loop servo systemurements to obtain the beam position of each target in where Eo and E. drive the angle servos; however, use ofthe radar beam. The mathematical relationships and Ee and Es (by themselves) for open-loop offset patternsignal processing methods used to obtain this data vary determination would require angle offset pattern cali-slightly depending upon the particular receiver con- brations for many values of input signal strength. Thefiguration that is being utilized. Typical data operations time required to perform these calibrations and the re-consisting of mathematical relationships and data proc- quired storage would be excessive.essing for two types of wide dynamic range receivers In the presentation that follows it is shown that nor-(i.e., a conventional tracking receiver utilizing AGC mnalized angle offset patterns independent of signaland a logarithmic receiver) are presented next. strength can be obtained even with unmatched gains

1962 Korff et al.: Multiple-Target Data Handling with a Monopulse Radar 361

and imperfect AGC action. The azimuth channel is dis- tion of Table II,cussed first and all comments and derivations are fO; 4) (v, 0 )equally applicable to the elevation channel. = - vs 0;4,The effect of the AGC loop can be eliminated by a f(60; 4)0) y(v, G0; 40))

simultaneous measurement of Eo and Er, and by utiliz- which also is stored in the computer.ing the digital computer to perform the division E0 Er. In a similar manner one can obtain and store TableThus, the AGC action now serves solely to provide the III, q(v)g(40; Oo) = z(v, 4o; Go) vs v and Table IV,capability for handling a wide dynamic range of inputsignal level for the tracked target. g(O; 0) _z(v, 4; 0)

It will be recognized from the earlier discussions and g(4o; 60) Z(V, )00; Go)Fig. 3 that the first term on the right-hand side of (5) isa function of the AGC voltage v and not of target beam whereposition, while the converse is true for the second term. EoTherefore, (5) can be expressed as z(v, E;6) =E

y(v, 0; 4) = h(v)f(6; 4), or (7) (

y (v, 0; 0) q (v) ==__AO )()Gr

h(v) eowhere l4g (; 6) e=Gr

= ha(v7) Multiple- Target DeterminationGr

Use can now be made of the tabular information= f(6. 4) stored in the computer to determine the beam position

er (6 and 4) of each observed target in a cloud of targets.Es For each target, measurements are made of v, y(v, 0; 4)

= y(v, 0; 4). and z(v, 4); 0). The measurement of v and Tables I andEr III provide y(v, Go; Oo) and z(v, q5o; 6o), respectively. En-

Although h(v) is not known and cannot be measured tering Table II with the value ofdirectly because the input signals are not directly meas- y(v, 0; 4)urable, this problem is overcome by normalizing f(0; 4) ( )with respect to some arbitrary constant f(0o; Oo). Y( X ; oo)

Dividing (8) by f(0o; Oo) provides values of 0 within limits set by the boundaries of they(v, 6; 4)) _ f(6; 4)) curves are found. Similarly, entering Table IV with the

h(v)f(6o; 4o) f(o; ) (9) value of z(v,h4); 6)The quantity h(v)f(Go; 4)o) is determined empirically.

The procedure is to place a target at a fixed offset 6o, z(v, 4); 60)4o and vary v over the entire operating range. For each values of 4 within limits set by the boundaries of thevalue of v the receiver outputs are measured. Dividing curves are found. More exact values of 0 and 4) can beE0/Er in the computer yields y(v, Oo; 4o), which by (7) converged upon by successive approximations. Thisis equal to iterative process on an arbitrarily chosen pattern is

illustrated in Fig. 4. The number of iterations dependh(v)f(6o; 4)o) = y(v, do; 4)o) (10) upon the spread of the family of curves and the accuracy

Thus, Table I, y(v, Oo; Oo) vs v, can be compiled and required. Measured offset patterns have disclosed thatstored in the digital computer. From (9) and (10) the cross-coupling effect is small and a single iteration

is sufficient to determine 0 and 4 to acceptable accura-y(v, 0; 4) f(6; 4)) cies.

y(v, Au; 4o) f(6o; 4o) Logarithmic Receiver

The normalized angle offset pattern f(6; 4))/f(6o; 4)) The dynamic range characteristics of AGC-type re-can be determined empirically by placing a target at ceivers limit their use for multiple-target applications.numerous offset values 6 and 4) in the radar beam and For example, an AGC receiver may not "see" weak tar-measuring v and y (v, 6; 4)). The measurement of vJ and gets when the AGC is determined by strong signals.Table I provides y(v, Go; 4)o). Making the division This difficulty can be eliminated by adding three loga-y(v, 6; 4>))y(v, Go; 4)o) in the computer permits compila- rithmic receivers to the radar for multiple-target data

362 IRE TRANSACTIONS ON MILITARY ELECTRONICS October

From (1), (12) and (13)

dZ IO mIls f(6; E)= /EG (16)O I t' Er/Gr

0-O mIls_ -- ,_- Dividing (16) by

4 ~~~~~~~~~~FIRSTREGION OF f(o;4))0

-/ & UNCERTAINTY IN A00; ") =

| | --iUNCERTAINTY AFTER yields

I ONE IT-ERATIONIAZIMUTHI OFFSET IN MILS

t ) EoGof(G; 4)) E0/G0tl0-DETERMINED FROM MEASUREMENT (17)ON UNKNOWN TARGET ff(0o; 4)o) Er Grl/'o

=10 mils The normalized angle offset pattern f(0; 4))f(So; 4)o) is_ 2 / /// obtained as previously outlined. The measurement of

Omils Eo and Table V provides P(E) =Eel/Got7o. The meas-urement of Er and Table VI provides P(Er) =Er/GrIGoThus, Table VII,

P(E0) _f(6; 4))4 CI FIRST REGION OF UNCERTAINTY IN - -vs V0,4CT) j /////< / ELEVATION OFFSET P(Er) f(00; (o)

REGION OF UNCERTAINTY AFTERONE ITERATION can be compiled and stored in the computer. In a similar

ELEVATION OFFSET IN MtLS manner one can obtain Table VIII, P=EOIGOo vsFig. 4-The normalized azimuth and elevation offset Es; and Table IX,

signals are not independent.P(E¢) _g();6)

= vs4 and 0,handling. Notation similar to that previously used is P(Er) g(0o; 60)employed for developing the mathematical rationale.The input-output relations are the same as (3) and (4). where G is a function of Ef only and g(4; 6)==i,.In this case however, Go is a function of Eo only and Gris a function of Er only. Multiple- Target DeterminationThe normalized angle offset pattern f'(; 4))/f(6o; O) As before, use can be made of the tabular informationcan be determined as follows,

stored in the computer to determine the beam positionLet the input signals be represented as the product of all observed targets in a cloud. For each target, meas-of (P), the total field voltage present at the antenna urements are made of Eo, Eo and Er. Then P(Eo) andhorns and a parameter (-q or s). Thus, P(Er) are obtained from Tables V and VI, respectively.

e6 =7P (12) A division P(Eo)/P(Er) and Table VII provides theer =p (13) values of 0. Similarly, P(Eo) and P(Er) from Tables

VIII and VI, respectively, provide values of 4) via Tablewhere -i and 41 are both functions of 0 and 4) alone. IX. More exact values of 0 and 4) can be found by itera-

Eqs. (3) and (4) can be restated as tion, as before.

F0

GP (14) CALIBRATION PROCEDURES

Er Receiver CalibrationP = - (15) This procedure provides the means for determiningGr4 receiver gain characteristics, either as a function of

The next step is to establish Table V, P = E AGot7ovs AGC (for AGC receivers) or as a function of input signalF0 and Table VI, P=Er/Gri/' vs Er. This is accom- strength (for logarithmic receivers). It is accomplishedplished by placing a target at a fixed arbitrary beam by coupling pulsed RF energy from the radar transmit-position 6o, t'o and varying P in known increments over ter (or a signal generator) through a calibrated antenu-the entire operating range. It is not necessary that the ator to a radiator (i.e., a simulated target) which isabsolute value of P be known. Any quantity propor- situated on a boresight tower. A pointing angle is se-tional to P is sufficient, as the proportionality factor is lected for the radar antenna such as to assure the pres-cancelled in taking ratios. ence of a strong signal in the angle offset channels. Once

1962 Korff et al.: Multiple-Target Data Handling with a Monopulse Radar 363

chosen, however, the pointing angle is not varied during ured output voltage does not have a linear relationshipthe calibration. With the attenuator set to zero, the with respect to the input signal; therefore, it is "re-energy from the RF radiator is adjusted such that both flected" back to the antenna by proper processing withoffset channels and the reference channel are saturated. the receiver gain calibration data. The radar constantThen, with the radar transmitter (or signal generator) C of (18) is determined by measurements on a balloon-power output held constant, attenuation is added in borne metallic sphere of known cross section prior todiscrete steps from zero to that value at which no dis- the mission.cernible voltage change is observed at the output of An accurate determination of target cross section de-any channel. The output of each channel is measured pends upon knowledge of target beam position. For afor each setting of the attenuator. For the AGC-type constant value of transmitter output power and targetreceiver the AGC voltage must also be measured. This cross section, the antenna input signal varies in accord-data is used to establish Tables I and III. It is not neces- ance with the angular separation between the targetsary to record the attenuator setting for the AGC re- and the radar beam axis. This functional relationshipceiver because the receiver gains are treated as func- has been termed the antenna reference pattern. Fig. 5tions of AGC rather than input signal. For the logarith- shows the azimuth axis reference pattern for anmic receiver however, the attenuator settings and out- AN/FPS-16 radar. A similar pattern exists along theput voltages are used to construct Tables V, VI and elevation axis. A target whose cross section is to be meas-VIII. This is permissible because the measured quan- ured may appear anywhere in the beam. Therefore,tities P in these tables are used only in the form of ratios. allowance must be made for the attenuation resultingThus, the absolute value of P is of no interest and can from the reference pattern shape.be represented by a value of attenuation.

Offset Pattern Calibration - mi ii'Nl~ Of mils

The offset pattern calibration requires measurements 2 Non a boresight tower using implementation as described 4 - -sabove for the receiver calibration. Alternately, a bal-loon-borne metallic sphere can be used but this entails --6additional considerations which will not be described. Z .-The pattern calibration is usually done prior to a mis- 8sion in conjunction with the receiver gain calibration tominimize the effects of gain drift. It is accomplished by 10 - __ _ -perturbing the radar about the boresight tower radiator 642 2

line of sight. The azimuth and elevation perturbations MILLIRADIANS OFF AXIS-AZIMUTHare programmed to generate a square grid (say 289 Fig. 5-Two-way reference channel patternpoints) covering the beam pattern. Thus, the boresight for AN/FPS-16 radar.tower radiator sequentially presents a simulated targetsignal at each grid point. At each point digital records For the AGC-type receiver, the output that variesare made of offset angles, measured receiver output volt- with input signal strength is the AGC voltage. There-ages and AGC, if this type receiver is being used. This fore, when the receiver gain calibration previously de-data is combined with the results of the receiver gain scribed is being performed, a record of the attenuatorcalibration to obtain Tables II, IV, VII and IX as pre- is required if cross-section measurements are toviously defined.setn be made. This enables a table of AGC volts vs attenu-

CROSS-SECTION MEASUREMENT ator setting k to be stored in the computer.For the logarithmic receiver the required table al-

Target cross section is computed by use of the radar ready was determined for the angle pattern measure-equation ment. This is Er vs attenuator setting k, which is de-

CPa_ fined earlier as Table VI (k being equivalent to P if atS = (18) least one real cross-section value is known from the bal-

loon calibration).where The data accumulated during the calibration of the

offset pattern is sufficient to determine the referenceS is the total input power of the target return, atr.A ahvleo n h esrdotu

ff ls the arget cros sectlon,(AGC voltage for an AGC-type receiver, Er for a log-Pisthetranmited pwer type receiver) iS used with the appropriate table toCi acostat f heradr ysem determine the corresponding value of attenuator set-

R is the range to the target.ting k. The reference pattern iS provided by a plot of kAs mentioned previously, the reference channel meas- vs 0, k.

364 IRE TRANSACTIONS ON MILITARY ELECTRONICS October

TEST PROGRAM

Tests

A series of offset pattern measurements on an AN/- *0 --FPS-16 radar were performed during a one-month pe- 1 - - - - -riod to test the basic premise. Other objectives of the ,2experimental program included determination of theeffects of variations in equipment parameters, insta- ' _ _ - _-bilities, atmospheric variations and cross-coupling deg- -radation. K _

Figs. 6 and 7 show results of the first group of meas- AZIMUTH OFFSET t Iurements, recorded and reduced by hand from digital ,4' - 6 MILS

~~~o. ~~~~~~- OMILEvoltmeter indications. This partial grid served as a 8-_S___ ___ qi ___check of the technique and to indicate behavior at the _ _ -large offset value of 14 mils (well beyond the nominal DATA TAINED TO A SI SAL-TO- AOE RAT OF 3|limits of the beam). Time limitations and the shape of IS __ __ __ _the reference pattern (high magnitude of signal attenu- 2.0 .1 4 2 OFST1ILation at remote points in the beam) influenced the deci- AZIMUTHOFFSETIN MLS

sion to stop at 14 mils. Fig. 6-AN/FPS-16 offset pattern calibration.For all succeeding measurements the antenna was

programmed over a raster of 289 points, one mil apartin both azimuth and elevation. All output voltage meas- -urements were recorded on digital tape. Relinearizing _of all data through the receiver calibration curve and _ _the normalization process were accomplished automati-cally by a digital computer, with the subsequent graph

Z.MUAlFF TIPTT - - - - -

of the offset pattern being generated by the associated LOS T FLATpunch card and plotter equipment. SANOT SAOFEFG.6 APFLY / *.SL-

Altogether, data for nine test runs was obtained and ;Xlreduced by the completely automatic system (angle - - 1 - 1 1perturbation, digital recording and processing). Operat- -' _ -ing frequencies were 5400, 5750 and 5900 Mc; SNR's - - - --.-were 4, 3, 38, 45, 28, 34 and 48 db; the tests were per- _formed at random intervals being on the 10th, 16th, -A -17th, 28th and 29th days of the month at different times -44 SAAA,1 .! 1! 0of the day; atmospheric conditions varied drastically MINS AZIMUTH OFFSET IN MILSfrom moderate clear weather to cold clear weather to Fig. 7-Logarithmic plot of Fig. 6.cold weather and snow covered ground. Fig. 8 shows theazimuth pattern resulting from one of the tests. Theazimuth patterns from all the tests were similar in form L__ Xexcept for variations in the average gradient between - AZIMUTH OFfSET PATthe values shown by the dotted lines of Fig. 8.

12 OF 55 MC AND-ASN RAI O1.2 1 1 q ~~~~~~~~~~~~~~DOTTEDLINES SHOW REGION IN WHICH ALL~~~~~~~~INDIVIDUAT PATT ERNS WERECONTATIAOFThe plots of the elevation offset pattern were similarto those of the azimuth error pattern. °,0 -- A6__

A nalysis \ / 7

First consider a single test pattern. __l

1) The offset pattern is fairly well defined and does ____ ___not differ greatly from a straight line relationship 7up to an offset value of fourteen mils which was zl- _ __\ '_ __ __ _the maximum offset at which measurements were [ < 7.made. The offset gradient iS approximately eight -± 8 6I0 2 4Lmils per unity ratio. The significance of a well- OZIBATE AFFET INSIdefined offset gradient for the AN/FPS-16 extend- Fig. 8-Results of nine additional offset patterning out to fourteen-mils offset is that the capability measurements on AN/FPS-16 radar.exists for determining cross sections and trajec-tories of targets even at angular separations well

1962 Korff et a!.: Multiple-Target Data Handling with a Monopulse Radar 365

outside the nominal limits of the radar beam CONCLUSIONS AND REMARKS(±10 mils). Prior to these test results it was With proper system design the angular offset patternsthought that offset measurements were limited to of a monopulse radar can be established and used tooffsets no greater than one half the nominal beam- determine the angular positions of all targets appearingwidth. in a radar beam. Preliminary experiments have been

2) The offset pattern definitely varies as a function hindered by test equipment problems but still showof elevation offset. This is apparent from the nor- that large angular separations between the beam axismalized offset curve in decibels where the magnifi- and target lines of sight can be measured with errors ofcation provided by taking the logarithm of a small less than 10 per cent of their value. Even higher accura-number (near zero) results in separation of the cies should be attainable and efforts to optimize thecurves in the vicinity of the notch. The individual technique for field applications are in progress.curves are clearly defined in this region, the degree The technique described in this paper has a numberof separation being far greater than that which of advantages over earlier methods for angle offset esti-could be caused by system drifts. At azimuth off- mationsets of approximately 1 mil the individual curvesbegin to cross each other and the ability to dis- 1) The angle offset pattern obtained through the usecriminate between them is lost. This affect is of this scheme is completely independent of theattributed to random drift in the signal generator signal-to-noise ratio of the target return. Trans-which was misbehaving all through the test period. mitter power variations, target scintillations and

3) In the section on data operations it was stated changing range-to-target thus have no effect onthat an iterative process was required to deter- the offset angle measurements. This produces amine a target's exact position in the beam. How- pronounced saving in calibration time and com-ever, an iteration cannot be performed in the re- puter storage space required.gion where the individual curves cannot be dis- 2) The use of digital data processing exclusivelv andtinguished (although calibrations performed with the particular formulation of the scheme elim-a stable signal generator would in all likelihood mates a number of complications which charac-render them distinguishable). Therefore, in the terized earlier methods. For example, it is not re-region from 1 to 14 mils, the average value of the quired that the radar design include any of theazimuth offset, corresponding to the particular following:voltage ratio, must be assumed on the basis of the a) Special RF normalizing circuits,actual test data. From the spread of the curves b) Extremely accurate gain control (AGC),this assumed value will have a maximum error of c) Matched receiver gain characteristics,approximately +0.25 mil, or an rms error of 0.15 d) Linear receiver, "box-car" circuits or recordermil. characteristics.

Now consider a comparison of all rasters. 3) 'Fhe use of multiple-range gates in conjunctionFig. 8 shows that the average gradient varies between with the logarithmic receivers permits real-time

values of 7.5 to 9.8 mils per unity ratio of f(O; q5)/f(Oo; angle tracking of any reasonable number of targetsqo). If a normal distribution is assumed, ignoring cross- that appear in the radar beam. For example, itcoupling effects, this uncertainty in the offset gradient has been calculated that a computer equivalentresults in a standard deviation equal to to the IBM 709 would be able to provide real-time

output of target trajectories and radar cross sec-0.4 tions for as many as 30 different targets. Also, no8.7 limitation iS placed on the comparative sizes of the

targets which can simultaneously appear at anyThis result does not invalidate the system hypothesis point in the 80-100-db dynamic range achievable

as it is related to extreme variations of frequency and in logarithmic amplifiers.atmospheric conditions and the effects of ground re- 4) If real-time tracking of multiple targets is not re-turns and gain drifts in the measurement system. It quired, the scheme is also well adapted to post-appears almost certain that better controlled experi- flight operations on multiple targets using dataments with reduced gain drift would indicate that the from video recorders. The calibration procedureserror in the estimate of the angle offset, considering all are specifically designed to include the entire datavariations of operating parameters (frequency, at- chain simultaneously, eliminating any require-mospheric conditions, S/N, etc.), would be very much ment for independent measurement of the charac-less than that denoted by (19). teristics of video recorders or the post-flight data

Until more experimental data is obtained, the only processing equipment.conclusive statement regarding errors in the estimate 5) It also follows from items 3 and 4 above that theof angular offset is that denoted by (19). scheme is appropriate to the requirements of

366 IRE TRANSACTIONS ON MILITARY ELECTRONICS October

single-target tracking-angle error correction either ACKNOWLEDGMENTin real time or post flight. The authors wish to acknowledge the contributions of

A/I. L. Aitel and A. I. M\lintzer, Senior Systems EngineersIn summary, the application of the proposed tech- at RCA Laboratories, Moorestown, N. J. The former

nique should result in: significant improvement to the performed an earlier series of error pattern measure-already high performance of existing monopulse radars; ments on the AN/FPS-16 tracking radar and designedaccomplishment of in-flight error correction for applica- the test set (automatic angle perturbation programmer)tions such as range safety and down-range designation without which the experimental program described inand acquisition; and miss-distance measurements be- this paper could not have been conducted. The lattertween two airborne vehicles by a single radar. Consider- has been engaged in a similar program of error correc-able saving in equipment complexity can be obtained by tion for a five-horn monopulse system and has madeutilization of video recording techniques and post-flight advancements in the art of radar signal and datadata processing. processing.