146 IRE TRANSACTIONS ON MILITARY ELECTRONICS April

2 7rh APPENDIX,7 .=_ (2 7)

X cos The predetectioni filterinig used oni the mi-ost recenitIn practice, onie WOuIld miiake onie stationl co0mmon11011 to experiments provides the theoretical limit in signial-to-

lnolse ratios. [Ihis is atcc(iii)lishedl by means of a Sinmo-the two base Ilines. tIn this case, the errors in the two initer- . -feromneters are Ino loinger independ(lenlt anid it canl be

(lelav linles to provide filterinig that is conltiIIuous in fre-shown that optinmumn arran,gemenit is to place the stationsin'anequilateral triangle. 'The errors are stIl given. by quenicv (rather thani at discrete frequelecies as in a

(26)and (27). Doppler filter bank). Thle phase recovery imiethods are(26) and (27). similar in priniciple to those described, but the processinigThe important result iS that the accuracy of angular baditsm tbehoansftmsasga.Tss

. ~bai-idwidtlis i-nust be thousaiids of tiinles clS great. Testsvelocity measurements depenIds only UpOnl the elevationl have just been completed in processing the receiver dataangle of the target, not upon whether its direction is in real time in the CG 24 computer at Millstonie. Thefavorably situated with respect to one or the other of the data so far indicate complete success in this method ofbase lines. At 50 elevation, the accuracv of the azimuthal

' . # ~~~~~~processing.rate would be 1.0 microradian per second anid the meas-urement of elevation rate would be 3 microradianis per ACKNOWLEDGMENTsecond.secotd.ha bencopuedtht,usnga ai f rf Ihe authors appreciate the help received froim- G. i\'.Ithabei ciipuedtht,usii apar f iierer

Hvde aiid E. N. Dupoiit in cojistructiiig the equipmeiitom1leters having 25-kmii base lines, a two-seconid obser- a .. . 1~~~~ used inlthis experiment, anld the assistaince aind eiicour-vation of a satellite of low orbital eccentricity, passinig utowithin 1000 km permits measurements of theposition ageimient of P. B. Sebrinig in the preparation of thisto withill t000 kin pernmits nlleasurenielits Of the position

of any point otn the orbit to within 10 km accuracy aind article.the orbital period to wAppreciation1 is expressed to the (Columibia Uniiversity

the arbitaciesriof th posithional measuemd s uhevaesedw Electroniics Research Laboratory anid to the Rome Air

those of the Millstone radar, 0.15 accuracye in elevation Development Center for makig available, on loan, theand azimuth, 5 km in range. In fact, it appears that the Simoramic Analyzerradar positional measurements conistitute the prinicipal 1ederal Scientific Co., New York, N. Y., Rept. T-1j100; Octo-aiccuracy limit to the orbital measurements. ber 15, 1958.

New Techniques in Three-Dimensional Radar*MURRAY SIMPSONt, MEMBER, IRE

Summary-The definition and basic equations defining the per- I. INTRODTCTIONformance of three-dimensional radar systems are given. In particularthe parameters defining data rate for different classes of three- 7 N recent years there has been a substantial amountdimensional radar are analyzed. Three-dimensional radars are 0 of initerest in the developmi-Xen-t of three-dimensionialdivided into three classes as follows: single beam-rapid scan sys- radar systems. The need for these systemiis has beenitems; multiple beam-scanning systems; and multiple beam-non- made more apparent by the rapid increase in speed alndscanning systems. Each of these types is defined and compared interms of important characteristics. It is shown that new developments other peroranee characteristicso air nstarets,ain electronic scanning and multiple beam antennas have made such as high-speed aircraft missiles, and satellites, asfeasible many of these new three-dimensional radar systems. A num- well as the continluing nleed inl mlilitary areas for obtain1-ber of the more important antennas and their method of utilization ing better search and trcack data on convenltional artil-in the three-dimensional radar equipment are described. Examples lerv; aIld mortar projectiles. Recent advances in the artare given of two types of three-dimensional radar that are typical of .two classes of this equipment. Finally, some of the more important of rai scnigadmlil ba nens swlapplications for modern three-dimensional radar equipment are as better techniques in radar-data handling anld process-noted. ing have made the new three-dimenlsionlal radar systems

feasible.* RecivedbythPGML, jauary24,161.X three-dimenlsional radar is defined aS a system

t Mnxson Electronics Corp., NTew York, N. S. which Canl provide conltinluous inftormationl of three inl-

1961 Simpson: New Techniques in Three-Dimensional Radar 147

dependenit spiatial coordiniates, such as azimuth, eleva- seeing a target on aniy onie radar look. This derives fromtioin anid ranige, anid in this manniier identify the positioni the fact that noise is a statistical paranmeter. Tied inof the target in space. This is contrasted to a conveni- very closely with the probability of intercept is the false-tional two-dimenisional radar which provides continuous alarnm rate. TIhis is defined as the time initerval before ainiformationi oni onily two of these coordinates. The im- noise pulse will exceed the signial plus noise for a particu-portant term in this definitioni of the three-dimensionial lar threshold setting of the radar receiver. Fig. 1 showsradar is the word "continiuous." This implies that the the relationiship betweeni the silngle-pulse probability ofspatial iniforrmiationi onl all targets within the volume detection anid the signlal-to-nioise ratio for lnonifluctuatinigcovered by the radar be provided in a timie initerval targets anid for fluctuatinig targets for various false-which falls within the desired or required svstemii-data alarm rates.2rate. Thus, a convenitionial pencil beaml-tracking radarwould inot fall withini the definitioni of a three-dimenasionalradar by virtue of the fact that the time initerval re- oP4 10lo-5i8 10 10- 10 10lre- 9 1- I~~0-,.2 4 0 - 1quired to cover a reasonable space volutm e, such as a Y9-8 IIZ -- -hemiiisphere or a substanitial portioni thereof, would be -9 - Targetfar in excess of the mlaxinmunm time permiiitted to obtain 95 _ - -- -- -sufficienit information on high-speed target coordinates z 90 FlucuatIgITagetin order to imnake use of this data for trackinig purposes. , 8-This timiie initerval, known as the data rate of a system, : 60is an extremely important parameter which forms a o 4 - - . _ - - _basic part of the specificationi for any three-dimenisional , 20 _radar anid frequently governis the specific design of this _ -t

0equipmient. 1The other imiiportant paramiieters are those which are 0 2 4 6 8 10 12 14 10 18 20 22 24 26 28 30 22 24 36 38well known lo the radar designier, such as radar range, S/NIND.B

tranisml-itter pyower, beamwidth, accuracy anald resolutioni, Fig. 1-Sinigle-pulse probability of initercept vs SNR for variousinitegrationi timne, requiremenits for imoving target indica- false-alarm rates.tion and/or tlarget velocity data. -

Il. RADAR PARAMETERS The data rate of the radar system is given byIn order to determine better the basis for designi of a 0 X PRF

three-dimiensionial radar, it is desirable to review some D VAz+T- (3)of the basic equations governinig radar performance. Thebasic radar equation1 is where

PtG2j_X2 0 = anitennia solid anigle,-r PRF=4radar pulse-repetition frequenicy,(4r)IRI V= total solid-angle scani volume,

where N=niumber of pulses per look.Pr = power of radar receiver, The paramiieter 6 cani be comiiposed of a single antenniiaPt = radar transmitter power, beam or the conmposite of a niumber of multiple antennaG =radar antenna gain, beams. TIhe necessary anitennia beamwidth 0 is deter-cr=target cross sectioni, iminled by the required anigular accuracy anid resolutionR =wavelength, for the radar system, as well as by the range perform-R= target range. ance as giveni by (1) and (2). In (3), it can be seeni thatFor a specific radar systeml havinlg a pulse width T and for a given anigular accuracy, the data rate cani be in-

a total loss L in the RF tranismissioni linie, as well as a creased either by reducing the scan volumle or, preferably,receiver nioise figure NF, the receiver signial-to-nioise by increasing the number of simiultaneous beamiis in theratio is giveni by radar system. The latter approach is most commiiiionily

used in three-dimensional radar.sS PG2X2j

v __ /1. )\ ' ' ~~~~III. 'hYPEs O)F TuRE1i-DMI1~NSLONALJ RADAR(47r)3R4LNP(KT)t ---) We w\ill no0w tconsider- the various gen1erall clalsses of

three-dlimlensionalI radalr syrstems which canble dividedTIhe p)robab<ility of in1tercept, mlore (0on1o18lVt1 kiitoxvii inlto thr-ee caItegories ats fl()lows:a1s thet blip) (scan ratito, is (lefilue(l als the pErol)ablilitvt of

l. N. Ridenlour, "Rtadatr Sy,stemis, ' M .Il.Tl. Rtad. Lab. Ser., 2 \V- Hall, "Predictionl of pullse radear performanic e, " l'itoc. lRE,M'cGraw-Hill Book Co., Inc., NVew York, N. Y., vol. 1. vol. 44, pp. 224-231; Februiary, 1956.

148 IRE TRANSACTIONS ON MILITARY ELECTRONICS April

Class 1: Single beam-rapid scan systenms. A typical techn-ique that is enmployed for beam selec-Class 2: Multiple beami-scanning systems. tion for systems of this type is shown in Fig. 3. A set ofClass 3: Multiple beam-nonscanning svstemiis. three adjacent beamns are indlicated, namely, N, N-i,

A Class 1 system is similar to a conventional radar and N+1. These beams are generallv designed to over-

lap at the 3-db point. The circuit is designed so that anwith the exception that the antenna beam can bescanned very rapidly over the required volume. This attenuated output (approximately 10 db) for each of

had niot been possible until the advent of electronicallv the three beams is given by A N, A (N -1), and A (N-l).In the svstem described, it is possible to provide iinfor-

scainned anteinnas, which made it possible to move the m o t p cbeam rapidly in either one plane or two planes without the b am,eknosithe pekregion, and midway be

. . ~~~~~thebeanm, kniown as the peak regioii, aind midway be-any miiechanical motion of the basic antenna structure.

* r * *11 *1 * 1 *1 1-f ~tween two adjacenlt beams, knlownl as the JUnlCtiOnl re-Sectioni IV of this paper will describe in more detail dif- i

ferent types of anitennia systemis which satisfy this re-giotl. In other words, tnumbceas naivpossfble target pOSi-

> ~~~tlOllS exist as there are i-luiiibers of beaiiis. FLi rther cir-Thuereme lit. cuit refinemiieint can provide additioinal possible targetTrhe ima'or Iilllitatioii ill the Class 1 ,three-diiiiejiloiilal ..radar derives f l positions. Thus, a target would be registered at the peak

ratdar derives froln limitation oii data rate, as giveiin poiit tbaiN' h otu fteA hnie(3). It can be seen that this system is most readlyv ap- Iexceeded the output of the N-+1 and N-i chaniiiels.plied to shorter-range applications where the PRF can If the outputs are received N and N- 1 channels, butbe made high and also where the number of pulses re- h r

do IlOt satisfv the requireiments for registratioii inl thequired to be integrated is small. Otherwise, the data

rate td o fr d eypeak of either of these two beamiis, they are automllati-rate tends to suffer and the systerni can iio longer be. . . -., callv assigiied to the 'uiictloii regloii. In1 this malllner, it

considered a true three-dimensioinal radar. As indicatedaabove, the electroinic scan can exist in onie plane, suchas in the height-finider application iin which the beamii is Beam n

scanned electroniically in elevationi, while the azimiiuth i Beam 2scani is obtained bv niormiial mnechanical rotationi of the . ,-anitenniia. Alterniatively, the svstemii caii be designied so /' ' / ea Ithat the beami- is scainned electronically in both azimiuth ,aind elevationi by mieanis of one of several types of two- w Rangedimensioinal electroniic-scani anitennas (lescribed in Sec- Range

tioln IV. n 2 1

A Class 2, three-dimensional radar makes use of a Receiverimultiplicity of simultaneous beams in onie planie, theenitire group of which is scanned in thie orthogonial plane.A block diagramii of a systemii of tlis tNp)e is shoWIx iIIFig. 2. The necessary (lata rate inI a Class 2, three- 2 selector

dimienisionial radlar is obtainiedtby setting the value of 0ini (3) equal to the total soli(d anigle of n beallls in theantenniia, as slowln in Fig. 2. 'T'llUS, all other coniditiolns |cvbeing equal, the (lata rate of the svstemii is equal to ntimes that of a Class 1 svsteimi while, at the saime timiie,the accuracy anid resolutioni is giveni by 0/n, or the beamii- Duplexer Transmitters

width of atn individual beani in the systemn. It cani beseen from Fig. 2 that separate receiver chaninels are pro- Fig. 2--Typical imutiltiple-beamii radar systemii.vided for each of the beams of the antenina. Thus, it isnot only necessary to provide parallel beams in theantenna, but also a set of n chainnels in the receiving sys- lN (N +)tem. The number of transmitters emploved in this VPEAK- JNCTN PEAK JNCTN PEAK vJNCTN1 PEAK JNCTN PEAK

system may range anywhere from one to n, dependingonl the required performnace and legree of allowable \2) | N1) N (N+ 2)complexity.

It is interestinlg to nlote inl F ig. 2 thllat al requiremlenlt AI Nl ) ANA1 i>/ N+l)->! texists for a beaml selector. This is tIne to thle fatct thatl A(N-2) -\ -\/\/ s o\ / \AN2it is nlecessalry to tleternliiiie inl which} o)f the n beamls ande / As\/,/( \/,receivers the target or targ-ets are beinlg receivedl. This /'/^ ''\/\'\/,tdiffers from a Class 1 radar inl which this inlformationl is / ' Iobtained primarily by the scanlninlg informlationl whichl ''\ 'Acontinuously provides an indication of the beam pOSitiOnll' 'in1 space. F~ig. 3-Target locationl inl multltiple-beaml radlar.

1961 Simpson: New Techniques in Three-Dimensional Radar 149

is possible to idenitlfy instantaneously the positioIn of IV. ANTENNA SYSTEMS FORtargets withini the multiple-beam-l complex oni a pulse-by- THREE-DIMENSIONAL RADARpulse basis, without the necessitv for beam scannllilng. It has been indicated that the feasibility of three-

it should be inoted that the svstemii requires gaini sta- dimensional radar has been determined to a large extentbilltv in the parallel receiver channiiels in order to prevenit by the developmiienit of electronically scanniied anid Illul-errors In beam selectioni. The receivers uised in a systemss.. ~~tiple-beaml anltennalcs. Tahis h1as beenl mlad:e possible byof this typeac-re nioriiiallvr logarithm-i1c in order to provitle t a.. ~~~~thea;bility to iiiove az raldar beamll orders of iiia-gilitudethe niecessarv dyniamic range. In addition, tlhev Imiust beI ' .. > . lllore rapidlv thani couldl be accomiiplished by the miie-closelv illbatche(I to al toleranlce of alpproximlatelv t db in1 .ior ra.pately1 cha niicallv rotatinig ou nits that are used with co nive ni-order to niiiiiiilze positionacl errors.. .tionial radar anteninas. The technlique that is emliplovedAlthough the niormiial Class 2 radar system provides

in electronic scanining is actuallv based on the earlvantenna beamiis whichi are spaced approximately 1 beam- priticiples used lIn directive aniteiiiia arravzs.width apart, in order to provide solid coverage over thewi I .As seeni in Fig. 4(a), a pair of radiatiiig sources fedanlgle 0, there have beenl svstemiis designied which comii- f9~~~~~froiii a COIiiliioii traiiti-iiutter caii be nialde directive at thebline Class 1 and(I (lass 2 operationis bymviieanis of sepa- anigle 0, providing the phase of onie elemenit with respectrafting the beams b1 a numiiber of Hidividual beam-* s * t r ~~~to the other iS set at 0=27rd/X Slll0?where d is thewidths and scanning electronically in the plane of the*' ~ ~ rn * -~Spacinlg betweeii elellleiits aild X iS the waveletigth. Trhisbeamlis, as wA,ell as in the orthogonal plaine. Iihis type of t thcani readilv be extenided to n radiating elemenits of adeslgll iS dlesirableA whiere tlle reqtiii-ed 1i1dlvldual beaill- .>.. >design is .eira)ewheeterquiednd u lnear array. For the series-fed array in Fig. 4(b) thewidth iS extremely smiiall and it is simply not feasible toprovide a total jiLimber of separate beams spaced one phase at each element is given bYbeamwidth apart to cover the required anigle 0.A Class 3, three-dimensionial radar is conmposed of 2 =n-i

simultaneous beams which clo nlot require any scanlninlg X x=1 x=l

TABLE I

Data IRate Volume of Antenna Receiver TransmitterCoverage Complexity Complexity Power CapabilityClass I low niediumii medium low low to high*Class 2 miiediuim high meditum nmediuim nmediumClass 3 high low high high high

* Dependinig onl specific con-figuration:; i.., wvhether a sinigle tranismiiitter is used for- entire system-1, or individual amiiplifiers for each elementof antenna.

over the requiredl coverage voluniie. Fig. 2 caii be used toillustrate a Class 3 radar, with the uniderstanding that \the n beanms exist simiultaneously over the required cov- Verage volumiie, genierally in two dimensionis.-This type ofantenna coverage can be provided by several types of TRANSMITTanitennas described in Section IV. Although Class 3radar provides nmaximiiumi data rate, since for this svstem 9 d-0= V in (3), it also inivolves the greatest system coml- (a)plexity, since it obviously requires a very large niumberof beams anid receiver chainnels anid, possibly, tranis-mitter chaninels for a reasoinable accuracy requiremenit.Class 3 radars have found particular applicationi for re- mquiremients where the total radar coverage volume V islimited so that the resultanit number of beamns is 1nottoo unlreasonlable. This systemn is also oftenl used inl COm1-binlationl wit:h CIlass 2 radar. 1In this case, a two-dimenl-sionlal clu1ster of beamls is scanned through the totalcoverage volumle V. The value of 6 inl (3) is thenl deter- TRNMTE {i~ 2~mined by the total solid-anlgle coverage of the two-dimnelsional beam cluster. kd d d3 ;--- dAA comparisonl of the importanlt characteristics for the mh)

threlbe clseJ ftre-iesoa.adri ie Fig. 4-(a) Two-element series-fed array.Table I. ~~~~~~~~~~~~~~~~~~~~(h)n-element .series-fed arrasy.

150 IRE TRANSACTIONS ON MILITARY ELECTRONICS April

For equLal spacing between elenmenits, this reduces to arrays that are used in this system are kn-owni as serpenl-2ird tinie arrays, due to the fact that the tranismnissioni lines

¢):1 = 02 =. = fM. = sin 0. (5) wind arouild betweeni i-adiating elements in order to

X produce a high L, X ratio, thus providing the desiredphase sensitivity for relatively- smialll-frequency chanige.For relatively loiig arrays (in1 waveleiigths), the beaiii- I

* 1 * *1 l \ ! 1- 1 I' ~~~~Ihe set of n aIrra-ys nialke up the coiiiplete anltennla. TIhewidth is approximately equal to Vid radianis, dependinig'.. . phase shIf~ters 01 to 0, are coiiiiected at the iilput of eachon the amplitude distributioni. In order to avoid gratinlg to.. . . arrsl- ~~~aiid provide beaiii scaliiiiiig ilthe orthogonallobes in spurious directions, it is necessary to maintaini array , I

spacing between elements approximately X/2 or less. plane to that produced by the frequency change. Theft o 1 t- . , . D~~Ihase-shifttig elenmeiits that are eiiiployed iii this systeniIt can be seen from the above discussion01 that in order p

to obtain electronic scanning of the antenna beam, it is are ferrite devices whose phase is a function of the mag-

simply necessary to vary electronically the phase at netic field applied to the ferrites.4 Thus, ii the systemeachradiating element. This can be done in various showni in Fig. 5, beami scanniniig in the horizontal plane iseach radiating element. This cati be doine in various debytefrqe-csaiiigtaimterwhl

ways. Perhiaps the most straightforward technilque for provi-* 1 1 * * 1 1 1 r 1 ~~~~illdepenldeilt beaiil scann1iig iS provided in the verticalvarying the phase is simply to change the frequency of

the transmitter, since the phase at any point in anRE plane by the change in magnietic field determiined by thethe traiismitter, since the phase at ainy poiiit in ain RFttransmission line is proportionial to frequenicy3 This will antenna-beam computer. The position of the beam

* >~~~~I must, therefore, be deteriiiiined bv naotinlg the specificproduce a phase variation at each elemenit giveii by t t b

Af(L/X), where Af is the proportional frequency change transitter frequency and the ferrite-field current. Lim-1 T * 1 t1 r . * 1- 1 1- l~tations of this type of svstenm are causecl by the neces-and L is the length of transmission line between radiat- i

* £ ~~~~~~~~~~~~~sitvrto provide verv accurate calibration of the ferriteing elements. An array of this type is known as a fre-quency-scanned linear array, in wvhich the rate of scan phase as a function of currenit (a quantity which is gen-

* ~~~~~~~~~~~erallyhighly sensitive to temperature) as well as theis determined by the rate of frequency change, which e hcan be m ah adnecessity to make use of a relatively broad-frequency

cally-tunabe tansmitting tubes. band in the transmitter, thus occupying a substantiallyThelystunabem trnsh inFg.5tmakes. use of this princi- larger spectrum than would be required for the normalThe system shown in Fig. 5 makes use of this princi- rdrplewdh

ple in combination with a set of orthogonal phase shift- alserwidth.ers(1)-q?~,to rodce tw-diensona phs-re An alternative system iS shown in Fig. 6. In this case,ers q5j-q5, to produce a two-dimensional phase-fre--

quency, electronically-scanned radar system. The linear

Ferrite AntetnnaMagnetic Beam mn Ferrite 0 Field Control Computer

Field Conirol Computer Phase Shifters

c; 1{? L SU L l I em ; K t ' ' ' ' ' ' ''~~~~~neemens ad m

:> _> t

14 Two-dimension-dmensona

, antenna array havingIReceiver | n serpentine arrays Rc Ive

, 1 and m elements in e and m

each array.

Fig. 5-Phase-frequencyr electronically-scanlned radar systeml Fig. 6-Phase-phase electronlically7-scannled radar systeml.

3H. Shnitkinl "Survrey of electronlically scannledl an1tennat:s,' 4 H. Shnitkinl, "Survey of electronlically scannled antennas,"Mic?rowave J., vol. 3, pp. 67-72; l)ecemhber, 1960. Microw0zave J., vol. 4, pp. 57-64; Janulary, 1961.

1961 Simpson: New Techniques in Three-Dimensional Radar 151

the systenm is a three-dimienisionial phase-phase electroni- lens the capability of focusinig inito a parallel wave frontcally-scanned radar. Inl this system, phase shifters are an inlcidenlt radial wave provided by a radiatinig elemenitemliployed in each elemient, thus nmakinig a total of mn- at the opposite enld of aniy diamiieter through the lenis. Asphase shifters for the total antenna. The tranismiiitter shown in Fig. 7, it is therefore possible to inistall a largecan operate at fixed frequency, thus remiioving onie of the niumiiber of feeds arounid the circumlference of the lelns,limitationis of the phase-frequenicy systemii of Fig. 5. TIhe each of which prodtuces anl indepeindenit anitenniia beamii.prinicipal disadvantage of the phase-phase system-i, how- Inidividual receivers may be connected to each of theever, is the very large nunmber of phase shifters re- feeds which are, in turni, coupled to a sinigle tranismlitter,quired. Various modificationis in the phase-phase sys- or, as showni in Fig. 7, individual tranismitters illay betem have been developed. Amonig these are the use of used to provide a total power output equal to n1'. Theamlplifier tubes between the phase shifters anid the system can be designied as a Class 2 radar by mechaini-radiating elements, providing the ability to obtain ex- cally scainning the feed systemii in the orthogonal plane,tremely large total-power output from the system. or it can be designed as a Class 3,;,three-dimensionalOther systenms make use of heterodvninig techniques in radar by arranging separate feeds in two dimensionswhich the phase shift is provided at low frequency, around the circumference of the Luneberg lens.thereby eliminating the use of miicrowave phase-shifting Aniother multiple-beam system that has been de-elements, such as ferrites, which are subject to stringent veloped by the Sanders Corporation is shown in Fig. 8.calibration restrictions. Both of the above systems fall In this system the multiple beams exist in the RE-into the general category of Class 1, single beam-rapid CEIVE ON-LY imiode. A set of tapped delay lines followscan systems. individual IF amplifiers which, in turn, are connected toA number of differenit antennias have been developed each receiving element of the antenna array. Separate

for multiple beam, Class 2 and Class 3, three-dimen- beams are produced by properly coninecting the taps ofsional radar systems. Perhaps the oldest and most the individual delay lines corresponding to the desiredwidely used of these antennas is the so-called stacked- wave front of each beam. The signal is then brought to abeam antenna, in which several individual feed elements high level by providing an amplifier for each of theare installed in the vicinity of the focal point of a para- beams. The principal disadvantages of this type of sys-bolic reflector. Each of the feeds produces an independ- tem are the requirement for individual amplifiers atent beam whose position in space is a function of the each receiving element of the array, and the necessitydisplacement of the feed from the true focus. The num- for the maintenance of phase stability in each amplifier.ber of beams in this type of system is limited as a result The system must also make use of a separate transmit-of the rapizl deterioration of the beam shape as it is dis- ter which may or may not have multiple beams. The ad-placed from the focal point. vantage of this type of system is the relatively straight-An antennra system which has found wide use in three- forward means for obtaining a very large number of an-

dimensional radar is shown in Fig. 7. This makes use of tenna beams by the use of delay linles which can bethe well-knowni Luneberg lens. The Luneberg lens is a readily designled at IF frequenlcies.spherical antenna, composed of dielectric material, with An interesting new antenna system that has been de-a dielectric constant which is inversely proportional to veloped at Maxson by Dr. J. Blass is shown in Fig. 9.its position trom the center of the sphere. This gives the

Element 1 Ap Delay Line

Receler | Luneberg Lens Antenna I m

Transmitter Elmet2F Delay dLine--

Fl > | !Element 2 Amp Delay Line

Compuater L Oscillator

F7ig. 7-Multiple-beam fLueberg lenls radar system. Fig. 8-Delay linenEltiple-beae3 radar systeey.

152 IRE TRANSACTIONS ON MILITARY ELECTRONICS April

'I'his antenna, knowii as the series-fed, multi-directional (lass 2 or a Class 3, three-dimensional radar system.antennt, is composed of coompletely passive tranLsmis- 'Ihe princil)al advantage of this type of system is the usesion-line elements connlecte(l in maltrix form with direc- of completely passive elements which determine beamtional couplers at each of the jtinctionI points between (lirectioii and shape. Iltis, the major characteristics ofthe vertical-beaam lines and the horizontal-elemient linies. the radar beanlns will 1ot change as a resLIlt of electronicThe direction of each beamli is given to the first or(ler by elenient deterioration. In addition, in this system the(6) and is determinied by the geomletric position of eac(h ntnitlher of receivers re(liire(l is, tt n)iost, equlul to thebeamll line. number of beatmns, rather thalni the number of elemiienits

in the antennia. "I'he power-handling capacity of thesin 0 = [ sec 3 + tan - (6) system is leterminied by the power-handelinig capacity of

Xg 2d the transmiiissionl linie used anid by the lirectional

Separate receivers and tranismiiitters may be cojiinectedi couplers. 'Ihis system lend(is itself particularly well to

to each of thlebeam line outputs, thlusprovidingeither a al)plications where long arrays and large nutmnibers ofbeamis are (lesirecl.Another type of linear array, multidlirectional antenna

arralnged in a parallel-feed structure has been designie(d\ 8 }1 makiiig use of hybrid elemlenits in a corporate-feed net-

Radiating Work.Y~~r (4~~~~ Elementswok

\( r i (I, V. -XAMPIES OFI TIIREL)-DiM1ENS1oN.\[IRADAR SYSTIEMS

I Multidirectional antenna\having n beams and m TIwo typical exanmples of three-dimiienisionial radarradiating elements systems developed at Maxson are given below. The

\I I |......................firstsystem is a Class 1, three-dimensional radar similarin design to that shown in Fig. 5, namely, a phase-

Directional frequency electronic scan system. An artist's sketch ofCouplers the complete system is shown in Fig. 10.

\n 3 2 1

_ Beam Feeds

Computer Indicator

IFig. 9 --Series-fed muIltidirectionalia anteninia radair systeni.

Fig. 10 -Class 1, phase-frequency electronic-scan radar system. Iig. I 1---Air-height surveillance radar IIRAS-1.

1961 Simpson: New Techniques in Three-Dimensional Radar 153

The anteinna is seen to be a two-dimensional linear This system is presently undergoitng flight-test evalu-array in which electronic scanning in azimuth is ob- ation.tained by frequency change, while electronic scan in ele-vation is provided by change in the magnetic field offerrite phase-shifter elements. Transmitter, receiver, The principal approaches used in the design of three-computer and indicator equipment is contained in the dimensional radar systems have been described. Uni-van. The antenna forms part of one side of the van and fortunately, it has not been possible in this survey to gois permnanently fixed to the structure. into great detail regarding the design characteristics ofAn example of an important application of a Class 2, each type of system. It is hoped that the information

three-dimensional radar system is shown in Fig. 11. This presented above will provide a good indication of theis a photograph of the Maxson Air Height Surveillance different approaches that can be used for three-dimetn-Radar system, developed for the Federal Aviation sional radar systems. It is expected that, nmore and more,Agency, anid installed at their Bureau of Research and the modern radar equipments will fall inito one of theDevelopnmenit's facility in Atlantic City, N. J. This sys- above categories, and thus provide a substantial in-temn is basedi on a design shown in Fig. 9. The tower crease in performance over existinig coinventional two-shown in Fig. 11 is 168 feet high and contains a series- dimensional equipment.fed, multidirectional antenna providing 110 beams in Some of the nmore importalnt applicationi areas forthe elevation plane, 0.50 to 400. A large part of these three-dimensional radars are for use in air-traffic conl-beams are 3 mils wide at the 3-db point, and provide the trol, artillery and mortar location, nmissile-range instru-capability for resolving two aircraft in the same range mentation, ballistic-nmissile detection an-d tracking and/azimuth sector, located 1000 feet apart in altitude at satellite surveillance and tracking systems. Many ofa range of 50 nautical miles, as well as providing a the systems described above lend themselves particu-+500-foot altitude accuracy. larly to uses in which very large antenna systems areThe system shown is passive and obtains its radiation required. In such cases, it is ofteni impractical to con-

from a staridard FAA, ASR radar which provides azi- sider mechanical rotation in more thani a very limitedmuth and ranige informnation. The AHSR equipment sense for the aintennia. Therefore, it is imiperative thatprovides the third-altitude dimension. The electronics either electronic scan or multiple-beanm systems be pro-equipment, consisting of 110 receiver channels, beam vided. Substantial strides can be expected in the comingselector, height computer and three-dimensional indi- years in the further development and application ofcator, are located in the adjoiniig electronics building. three-dimensional radar systems.