The Development of Airborne Pulse Doppler Radar

The Development ofAirborne Pulse DopplerRadarLEROY C. PERKINSBoeing

HARRY B. SMITH

DAVID H. MOONEYWestinghouse

BACKGROUND .

Ground clutter has been a serious limitation to bothground and airborne radars for years. Moving targetindication (MTI) using delay line cancelers, when appliedto the airborne case, has not been very successful,because of the spectral spread caused by aircraft motion.As the aircraft flies faster, or looks at larger angles offthe velocity vector, the problem becomes overwhelmingbecause the clutter spread approaches the pulse repetitionfrequency (prf) in width, so little or no clutter-free space

remains for detection. Consequently, airborne radars werelimited to an uplook or co-altitude geometry, or flight atsuch high altitude that a target could be detected at rangesshorter than the altitude. This seriously limited theoperational usefulness of airborne radar, since the targetcould fly on the deck and be undetected. What wasneeded was a look-down capability. With theseconsiderations in mind, the development of pulse doppler(PD) filled a serious need.CW doppler radar [ 11 was developed near the end of

World War II. Its range was generally limited bytransmitter leak-through and near range mainbeam clutter.To solve this problem, pulsing the transmitter, whilegating off the receiver, was a potential solution. Theearliest record of a ground-based pulse doppler radar isdescribed by W. W. Hansen in Ridenour "Radar SystemEngineering," chapter 5-11, in 1947 [21. This radar useda high duty cycle, at a relatively low carrier frequency sothat both unambiguous range and dopper were available.

The first pulse doppler applied to the airborneproblem was the Boeing laboratory Bomarc seeker in theearly 1950s. This work, and the more generic work doneat Westinghouse thereafter for a number of airborneapplications are described. This brief history of threedecades is depicted in the flow diagram [3, 41 ofFigure 1.

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Author's present addresses: L.C. Perkins, 18843 First Place SW, Manuscript received March 8, 1984.Seattle, WA 98166; H.B. Smith & D.H. Mooney, Westinghouse, Box1693, Baltimore, MD 21203. This paper was prepared by the authors and formed the basis for their

talk at the Awards Luncheon at NAECON, May 23, 1984, Dayton, OH.

0018-9251/84/0500-0292 $1.00 (© 1984 IEEE

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-20, NO. 3 MAY 1984292

Transmitter Carrier

Forward-Hemisphere -Sidelobe Clutter

Clutter-

Free

Space I

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B. Pulse Doppler Echo SpectrumFig. 2. Comparison of doppler spectra for airbome cw and pulse doppler radars. a) cw doppler spectrum; b) pulse doppler echo spectrum

THE BOEING BOMARC RADAR .....

The U.S. Air Force IM-99 Bomarc project was begunin 1949 in response to a proposal submitted jointly byBoeing and the University of Michigan.

Each Bomarc missile had its own target seeker radarbecause its 400-mile range took it beyond accurateground radar control. It was known from the initialBoeing/Michigan studies that the airborne radar wouldhave to have some form of ground-clutter discriminationto be effective against incoming bombers at all altitudes.The first model of Bomarc (IM-99A) sidestepped theclutter problem by employing a high altitude attackgeometry which allowed the use of a conventional pulsedradar because targets at a range less than the Bomarc'saltitude would suffer no clutter interference.

Meanwhile, Cecil K. Stedman, head of Boeing'sPhysical Research Unit, addressed the full clutterproblem. He hired Raymond A. Glaser, who had beenworking on doppler radar at MIT's Radiation Laboratory,to head a group of mathematicians and radar engineers-including Leroy C. Perkins-to design an effective anti-clutter airborne target seeker. Glaser, from his MITexperience, believed that the transmitter-spillover noiseproblem of a CW doppler radar would prevent it fromever achieving the necessary 20-mile detection range on a

100-square foot target. Therefore, his group set aboutlooking at pulse doppler schemes such as those suggestedby W. W. Hansen and others at the MIT RadiationLaboratories [5].

Since the Air Force was not convinced that thepotentially simpler CW doppler system could not be madeto work, they also funded the Ryan Aircraft Company, ofSan Diego CA, to develop a CW seeker.

Boeing's breakthrough came in late summer of 1951in an all night brainstorming session between Glaser andPerkins. Mulling over the problems with the aid ofblackboard sketches, the solution was revealed when theyvaried the parameters on a spectral diagram ofhypothetical doppler target and clutter echoes.

The explanation starts with Figure 2a which shows:CW doppler transmitter carrier (amplitude not to scale);the echo from an incoming target as seen from a missileplatform in level flight; the antenna main-beam groundclutter with the beam at a depressed angle; and theantenna side-lobe clutter from the ground both ahead ofand behind the missile.

For pulsed operation we have the central portion ofthe spectrum of a pulsed transmitter and adjacent linesspaced at the repetition frequency, Fr; the envelope of thearray is a sin X/X characteristic. The received signalspectrum in Figure 2b is a similar array except that each"line" is a replica of the doppler-shifted target andclutter signals of Fig. 2a. It is clear that if the prf is toolow, the target at one line will be overlapped by theclutter from the next higher line.

If the carrier frequency is 101' Hz (X-band) andBomarc's horizontal speed is 2600 ft/sec the sidelobeclutter will spread 50 KHz. If the target is closing at a

ground speed of 1000 ft/sec its echo will have a

maximum additive doppler shift of about 70 KHz.Therefore, to create the clutter-free doppler space for thetarget as in Fig. 2b, the prf must be a minimum of 50KHz plus 70 KHz or 120 KHz!

Glaser and Perkins spent the rest of the nightassessing the implications of this radical departure of prffrom the usual one or two KHz. Items considered werethe following: Range determination becomes ambiguous


A. CW Doppler Spectrum

g i

I1

---

.Main-Beam Clutter

293

beyond about 0.8 mile. This was not a problem, since theBomarc needs only line-of-sight rate to steer a collisioncourse. If the prf is fixed at one particular value, aclosing target echo will be eclipsed periodically by thetransmitter pulse with probable loss of target resulting.Eclipsing can be avoided by increasing the prf graduallyand when it gets too high (say 250 KHz) cut it in halfand start over.

No adequate source of high-power, coherenttransmitter pulses was known. The solution was to havethe Varian klystron people put a control grid in one oftheir high-power oscillator tubes; then injection-lock thephase of each succeeding rf pulse to the stable localoscillator (STALO).

TR tube recovery time was too long to have fullreceiver sensitivity immediately following the transmitterpulse. Recovery time can be shortened by pulsing the TRkeep-alive electrode.

By late fall of 1952 a demonstration breadboard of thehigh-repetition-rate radar had been completed andinstalled in a rooftop "penthouse" overlooking BoeingField where real moving targets were to be seen. A C-47transport airplane was tracked from takeoff out to a rangeof about 6 miles.

Following the penthouse testing, the breadboard setwas moved into a Curtis C-46 Commando to measureground clutter from the air. Later the set was againmoved into a trailer and hauled to Fort Lawtonoverlooking Puget Sound where successful chaff andECM tests were made using a special ECM B-29 fromWright Patterson Air Force Base.

In the summer of 1953 the Air Force was convincedthat pulse doppler was a viable mechanization for theBomarc B target seeker, and terminated the Ryan CWbackup development work.

Boeing gave a bidders' briefing and requestedproposals for the development of a Bomarc B prototyperadar; RCA's Los Angeles Radar Division was thesuccessful bidder. It turned out to be a toughassignment-four and a half years later RCA was stillhaving trouble meeting the stringent requirements.

In the meantime Westinghouse had developed aprototype of such promise that, by the fall of 1958, theAir Force, with Boeing's concurrence, selectedWestinghouse to produce the target seeker, DPN-53, forthe Bomarc B missile. 301 seekers were delivered.

MEANWHILE AT WESTINGHOUSE .

The effort [6, 7] at Westinghouse differedsignificantly; the Boeing effort was directed to the singleapplication of the Bomarc target seeker, while theWestinghouse effort was devoted to a wide variety ofapplications. In addition, there were a number offundamentally different mechanization approaches.

In April 1953 Harry Smith persuaded top Defensemanagement in Baltimore (Nick Petrou and Sy Herwald)

to start a Westinghouse generic R&D pulse doppler radarprogram with in-house funding. Also, in mid-1953,Westinghouse received a contract to study the Hawkmissile system for the Army. As the study progressed itwas concluded that pulse doppler ws an attractive choicefor the seeker radar. Since an experimental demonstrationseemed highly desirable for both programs, a laboratoryeffort was started in September 1953 with David Mooneyas the principal investigator. A partial radar wasassembled and was demonstrated to the Army evaluationteam in early 1954. The demonstration hardwareconsisted of a fully coherent grid-pulsed, 1-watt-peakpower, 1/12 duty-cycle klystron amplifier fed by a cavitystabilized microwave klystron oscillator; a 30-MHz i-freceiver; a single narrow band doppler filter, or velocitygate; receiver range gating and range tracking provisions;and a conical-scan angle track arrangement. Thedemonstration consisted of manually acquiring the signalfrom an unaugmented moving automobile at about onemile range, and tracking it in range, velocity and angle.While the performance was impressive, the Armyconcluded that a less risky approach was to go with aCW doppler semi-active seeker.

The in-house program was continued, withconcentration on airborne intercept and AEWapplications. Airborne intercept (AI) radar was a majorWestinghouse product line and a pulsed doppler (PD)version would provide a good base for development.Mooney and Smith were to be part of all Westinghousepulse doppler developments with over 25 pulse dopplerpatents jointly and individually.

The next model [Fig. 3], was configured to fit in thecabin of the DC-3 company aircraft and was instrumentedwith a magnetic tape recorder and scope camera forrecording clutter.

It had improvements in a number of different ways: Ithad a klystron transmitter of 100 watts average, and aduplexer to permit use of a single search-track antenna.Fig. 4 shows a typical block diagram of such a radar.

The development of the higher power transmitter wasa formidable task, and nearly stopped the program.Klystron amplifiers of that era had to be cathode gatedwith a pulse on the order of 20 kilovolts (at one ampere),with a pulse repetition rate of over 100 KHz. In addition,the jitter requirement on the pulsing was on the order of afew nano-seconds. Very low ripple voltages had to bemaintained to prevent putting sidebands on clutter.

Eventually, the transmitter was developed, and thesystem was flown over a four month period during 1955,and the nature of airborne clutter was verified andanalyzed [8-12].

Of all the problems encountered, the one requiring themost work was to get a receiver subsystem that was freeof spurious signals, or "birdies", caused by harmonics ofthe prf, or high order mixer products. The necessity toperform range gating and "main bang" blanking early inthe receiver before single sidebanding, makes birdiefreedom very difficult. This appeared to be impractical

1984 PIONEER AWARD294

Fig. 3. First pulse doppler Al radar (1956)

Platform AntennaMotion Position

Fig. 4. Block diagram of early Westinghouse pulse doppler radar.

IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. AES-20, NO. 3 MAY 1984 295

with a continuously variable prf, such as required in theBoeing approach. Our solution was to use discrete fixedprfs, all of which were harmonically related to the i-fcenter frequency. Even with this, several receiver localoscillators must vary in frequency in order to positionmain beam clutter into a notch filter, or to position atarget in a narrow band-pass filter. Great care in theselection of frequencies, and in choosing filtercharacteristics were an essential part of achieving birdie-free operation.

While the elimination of birdies, and the achievementof a high-prf transmitter were the major difficulties withthe early pulse doppler radars, there were a number oflesser problems:

One was getting a suitable duplexer which wouldprotect the receiver, but be fully recovered in amicrosecond or so, since weak targets from long rangecan appear just after a transmit pulse. In the first high-prftransmitter, the duplexer consisted of a ferrite circulatorand a ferrite switch to gate off the receiver duringtransmission. The switch provided enough isolation, buthad dredful drift problems, even at room temperature. Atesting program for a suitable TR gas tube turned up onebrand of one type which worked well enough at the highprf and low peak power to be useful. In the meanwhile,the Westinghouse tube laboratory worked on a gas tubeespecially aimed at the problem. Suitable tubes wereeventually developed, and all subsequent Westinghouseradars have used such tubes.

Another difficult problem was getting a flight worthySTALO [131, that would not spread main beam clutterdue to vibration-induced sidebands and pick-up. The earlystalos were cavity stabilized klystron oscillators, withspecial shock and vibration isolation, and were adequatefor the fixed tuned klystron amplifiers. Much later, whensuitable components became available, stalos becamefrequency synthesizers, that were channel tunable to becompatible with wide band TWT's.

A rather mundane problem was developing a suitabler-f target simulator for system sensitivity minimumdetectable signal checking. Our initial simulator was ahom fed crystal detector, which was modulated by anaudio amplifier for doppler simulation. While it worked,it was unsatisfactory as a calibrated MDS test. A motordriven belt was trid next, with little reflectors attached tothe belt, but the reflectors flew off at high speed (the first"flyoff"). Finally, we found that a serrodyne providedthe solution by giving a known amplitude at a set-frequency, and compatible with multiple prfs.

System timing stability was a problem with thevacuum tube technology of the time and was solved bydc on critical heaters and care in wiring, grounding andshielding. All pulses were generated from a common highfrequency crystal oscillator, and used start and stoptriggers.

The doppler filter bank required some kind ofcommutating switch, to sequentially test the output with athreshold. The best device we could find at that time was

Fig. 5. First U.S. Air Force X-Band Al radar (1957)

a mechanically rotating switch which used a stream ofmercury as the contactor. It worked, but as the mercurygot dirty, the switch got very noisy. Later versions solvedthe problem with semiconductor switches.

The detection threshold in those days was a fixedlevel, and the noise level was set manually. The lack ofconstant false alarm rate (CFAR) technology forced oneto set the threshold higher than desired, so the earlysystems generally had sensitivities [14] less thantheoretical. Later radars used a cell-averaging CFARwhich solved the problem.


Fig. 6. U.S. Air Force C-Band long-range Al pulse doppler radar, AN/APG-55 (1959)

U.S. AIR FORCE INVOLVEMENT .....

As a result of these developments, the Air Forcedecided to fund Westinghouse to build advanced modelsof Al radars, which would demonstrate full functionalcapability. A breadboard X-band model [Fig. 5] similarto the previous flyable model, and a C-band model [Fig.6] with extended range performance and pre-prototypepackaging were contracted in July 1956 (AF33(616)3700). The Westinghouse Al radar had a numberof significant differences from the Boeing Bomarcapproach:

I ) It used a dual mode transmitter, with a high duty cycle (0.46) forsearch, and a lower duty cycle (0.1) for track, to optimize detectionrange, while measuring true range in track.

2) The transmitter was a klystron amplifier rather than an injectionlocked klystron oscillator.

3) It measured true range by comparing ambiguous range fromseveral fixed prf's. [15]

4) The multiple prfs distributed '-eclipsing' (due to the necessaryreceiver blanking) during ''search".

5) These multiple prf's were fixed, as a necessary step in avoidingspurious signals due to harmonics and PRF lines from clutter.

6) All prfs and i-f local oscillators were derived from a singlesource, to eliminate spurious signals.

7) It used a bank of narrow band doppler filters to speed up thesearch mode.

8) Mainbeam clutter acquisition and clutter track was provided towork with clutter reject filters and controlled frequency oscillators to-notch out" main beam clutter.

9) It was provided range-vs-azimuth,a nd doppler-vs-azimuthdisplays as well as a "pause-to-measure-range" to get range for thesearch display.

There were several state-of-the-art limitations. At thetime wide-band TWT power amplifiers, suitabletransistors or integrated circuits were not available. Dueto hardware size, only one or two receiver channelsseemed feasible for all but ground application. Rapidrecovery TR gas tubes were yet to be developed. Despitethese limitations, working radars were realized.

The X-band radar was accepted by the Air Force inOctober 1957, after demonstration of aircraft acquisitionand tracking from the rooftop lab, and flight tested in theDC-3 in 1958. Meanwhile, the high power C-band APG-55 was built, and was flight tested in a B-66 in 1959.

EARLY NAVY INVOLVEMENT .....

In 1957 the Navy began to cosponsor the PD effort.This resulted in a long range track-while-scan pulsedoppler radar, the APQ-81 [Fig. 7] which was started inMay 1957 (NOas 51-7500). The APQ-81 was intended to


Fig. 7. U.S. Navy track-while-scan pulse doppler radar, AN/APQ-81 (1960)

be used on the AWS-404 or ''missileer" airbornemultishot fleet defense system; that system wasdiscontinued but the radar development continued.Rooftop simultaneous tracking of multiple airborne targetswas achieved and later demonstrated in flight test,including range measurement within the search dwelltime. A key to the TWS operation was the programmingof the prf discretely and continuously over several valuesduring a dwell time of the antenna beam. The -81 useddigital processing of data to establish track files; it used amedium duty cycle (.08) and multiple range gatedchannels which increase the information rate and providedtime gating for additional clutter rejection. Thesetechniques along with an extremely low side lobe antennaprovided the technology needed for AWACS, and theiruse became more attractive with the advent of digitalrealization of the fast Fourier transform. Such digitaltechniques were reduced to practice on the FutureWeapon Control System (FWCS) a Navy developmentcontract that followed the APQ-81.

WESTINGHOUSE BOMARC SEEKER, DPN-53 .....

The credibility of pulse doppler radar as a solution tothe clutter problem was enhanced also by the productionand fielding of the AN/DPN-53 pulse doppler targetseeker. This equipment was developed and produced inthe late 1950s by Westinghouse for the USAF IM99BBOMARC under contract to Boeing (a precursor of thearrangement that would emerge 16 years later for theAWACS and 23 years later on the B-i).

In March 1956 Westinghouse decided to spin off adevelopment of a pulse doppler target seeker that wouldcompete for the production buy of the Bomarc, sinceBoeing had contracted with RCA for the developmentmodel. The Westinghouse model [Fig. 81 was based on a

simplified version of the Al radar, and had the followingcharacteristics:

I) It used a fully coherent klystron amplifier transmitter, with a gridfor pulsing.

2) It used multiple, fixed prf's to distribute eclipsing during search.3) During track it switched prf when eclipsing occurred.4) It used a STALO that could tolerate severe missile vibration.

As a result of evaluation by Boeing, theWestinghouse version was selected for production.

Over the life of the program, over 300 DPN-53'swere produced and deployed, constituting the firstoperational pulse doppler radar; BOMARC missiles weresuccessfully fired against drones at all altitudes.

LATER NAVY INVOLVEMENT: AWG 10, 11,12 .....

During the period 1959-65 Westinghouse proposed asystem for the Navy F4 that consisted of hardware andtechniques that had evolved from the U.S. AF and Navydevelopments and the DPN-53 seeker. The result was theAWG-10 fire control system using the APG-59 pulsedoppler radar [Fig. 9] which was also procured by theUnited Kingdom (AWG-1 1 & 12). In this same timeperiod, Ferranti Limited (of the United Kingdom)assigned a score of people to work at Westinghouse-aspart of a royalty agreement-a linkage which provedparticularly beneficial on the British AWG-1 1 and 12.Over 1000 AWG 10, 11 and 12 systems were deliveredstarting in 1963. This was one of the first all-solid-statedesigns with built-in test and fault isolation. Anotherunique feature was the ability to switch from PD to pulseoperation (the latter using CHIRP techniques). Thedisplay accommodated both modes, i.e., velocity vs.azimuth and range vs. azimuth.


Fig. 8. Westinghoulse BOMARC seeker pulse doppler radar, AN/DPN-53 (1959).

Fig. 9. U.S. Navy AWG-10 fire control pulse doppler radar, AN/APG-59 (1963).

In order to provide operation in the sidelobe clutterregion a low sidelobe antenna along with a change fromanalog to digital computation and built-in testing wasproposed to improve the AWG-10 (called the DAWG-10). While this antenna was never incorporated intoproduction radars, the antenna work set in motion the lowsidelobe technology required for AWACS.

AWACS RADAR.....

The E3A, or AWACS radar [Fig. 10] evolvedbetween 1962 and the mid 1970s and represents a verydemanding long-range surveillance application of pulsedoppler. Over 50 have been delivered since 1976.

The AWACS technology was founded on the APQ-81and made more feasible by the use of digital techniquesand dramatic antenna sidelobe reductions. The resultingconfiguration was demonstrated.in the Air Force OverlandRadar Technology Program (ORT) which started in 1965and ended in 1967. This program evaluated overlandradar performance of radar brassboards provided byHughes, Raytheon and Westinghouse, with AIL as thetest monitor and evaluator.

A flyoff with Hughes between July 1970 and the fallof 1972 resulted in a full scale development contract fromBoeing to Westinghouse; production shipmentscommenced in 1976. This equipment is also being usedby NATO (with a "maritime" pulse mode added).

The AWACS radar scans 360 degrees continuously inazimuth with electronic scan in elevation to obtain heightinformation. It employs a medium duty cycle and adigital signal processor and computer for radar control.To enhance performance in the sidelobe clutter area, timegating is utilized. The processing provides the equivalentof n independently time-gated receivers that reduceaverage sidelobe clutter by n.

OTHER DEVELOPMENTS .....In October 1962 the IRE David Samoff medal was

awarded to Smith for contributions to pulse doppler radar.In the early 1960s some of the Missileer concepts,

particularly the track-while-scan and missile multishot,were incorporated into the U.S. Navy version of the''TFX" or F-111 aircraft. The radar/missile controlsystem for,such a system eventually was used in the F-14in the form of the AWG-9 and Phoenix missile system


DDP

CABINET EQUIPMENT Starboard Side

ANTENNA

Fig. 10. U.S. Air Force AWACS long range surveillance pulse doppler radar (Transmitter not shown), (1975).

produced by Hughes. (The AWG- 10 preceded the AWG-9 but was assigned nomenclature later).

By the latter part of the 1960s, analog to digitalconverters had achieved sufficient dynamic range andspeed to permit quantizing the received radar signal intoin-phase and quadrature channels; this digital formatcould be rapidly processed to perform filter bank andclutter elimination functions by a digital Fast Fouriertransform. These techniques were used on aWestinghouse candidate for the F-15 which lost a flyoffto a Hughes model in 1970. This outcome was reversedon the next two flyoffs (for the AWACS and F-16). Inthe later 1970s Hughes also designed and later producedthe radar for the F- 18 (no flyoff).

During this period the U.S. AF sponsored work [16,17] on "medium prf"; the use of a prf lower than thatrequired to yield a clutter free area was made possible bythe development of lower sidelobe antennas and thefeasibility of using digital processing. A motivation forthe lower prf was to obtain better tail chase capability by

working in the sidelobe clutter area. Actually thesebenefits derive from the time gating reduction of cluttersuch as used inthe AWACS radar. The time gatedapproach usually results in a lower duty cycle, hence theterm "medium duty cycle" would be more descriptivebut "medium prf" has become the term in common use.The velocity ambiguities of discrete clutter spikes broughton by the "'medium" prf were made more tolerble by useof a clutter "guard channel". The F-15 fly-off testedthese concepts which were incorporated as a mode of theAPG-63 produced by Hughes for the F- 15. A singlesignal/guard channel arrangement was devised for theWestinghouse WX radar described next. This was used inthe F-16 fly-off and is used in the APG-66 productionradars [18] produced by Westinghouse for the F-16.

In the early 1970s control of false alarms was carriedto extreme in a Westinghouse tail waming radar that wonanother U.S. AF flyoff (with AIL) in 1976. The ALQ-153 has virtually no false alarms (1 or less per day) andover 200 have been delivered for the B-52 fleet.


Fig. 11. U.S. Air Force pulse doppler radar for the F-16, AN/APG-66 (1976).

THE WX FAMILY .

In 1972 Westinghouse initiated the development of amodular radar family based on a -design-to-cost"concept. The family was designated the ''WX" andranged from a WX-50 to a WX-1000 with the WX-200pursued as a center line model to demonstrate the concept(the number represented the recurring price averaged over1000 units). A close derivative of this, the WX-160, wasthe basis of the Westinghouse entry into the F16 radarcompetition and it won the flyoff conducted by GeneralDynamics in 1975. This radar [Fig. 11] is now designatedthe APG-66 and about 1500 have been produced. Besidesthe multiple application provided by modularity therewere two other main thrusts of the WX radars: the use ofmodern digital technology to reduce recurring cost (by afactor of about 3) and to improve the reliability (by afactor of about 10) while providing equal or better radarperformance. This was conclusively demonstrated by theAPG-66 which was produced below its original design-to-cost target (equivalent to $160,000 in 1974 dollars). Animproved version of the radar, the APG-68, has added aprogrammable signal processor for more flexibility (suchas track-while-scan, etc.) and a dual mode transmitter(similar in concept to that used in the 1950 models),except for a TWT, and this version is just startingproduction.

The WX introduced the use of a mux bus (termed"digibus") concept to connect all modular units in adigital fashion and all units could be easily substitutedsince there are no adjustments-a far cry from the earlydays. In the early WX models it was decided toincorporate the ability of the processor (and the receiver)

to handle doppler beam sharpening and synthetic aperture(SAR) type processing so as to make the radar moreuseful for air to ground applications.

The modularity concept has proved itself in theadaptation of the APG-66/68 to other applicationsyielding a great deal of commonality of hardware and agreat reduction of non-recurring costs. For example, aderivative of the 66 is being produced for the U.S.Army's DIVAD system (a single radar serves twoantennas in a prf interlaced time shared manner toprovide simultaneous search and track by the twoantennas).

Using the APG-68 as a baseline, Westinghouse wasselected by Boeing and the U.S. AF in late 1981 toprovide the radar for the B 1-B, later designated the APQ-164.

Other pulse doppler radars have been built for specialapplications in smaller numbers.

SUMMARY .. . . .

It is interesting to look back over thirty years of pulsedoppler development. Current systems are modular,reliable with very predictable performance, and manymodes of operation that are largely controlled bysoftware. Most of the theory corresponds closely to thatwhich was known in the 1950s, and much of theperformance accomplishments are things that we strovefor in the early 1960s but could only accomplish to alimited degree. Working in the sidelobe clutter region hasimproved the usefulness and versatility of pulse dopplerand this was made possible by the achievement of ultra-


low sidelobe antennas and the extensive use of digitaltechniques. The latter not only contributed to flexibilityand reliability but provided performance that could nototherwise be achieved with a reasonable amount ofhardware. We progressed from keyed CW operation to atime gated operation with an intermediate duty cycle andhave ultimately arrived at radars that combine the ease ofuse associated with pulse radar but with clutter rejectionand the ability to perform special functions provided bythe doppler-such as beam sharpening, SAR, navigationand identification of airborne and ground-moving targets.This has been achieved in many incremental steps, bymany individuals and organizations, working within thepattern of a coherent radar approach.

ACKNOWLEDGMENTS .

The Boeing Pulse Doppler development teamachieved much in a short span of time. Among the groupled by Ray Glaser there were some outstanding talents:Robert B. Robinson worked out the automatic pulserepetition frequency control (APRFC) and other clevercircuitry; Raymond E. Pederson performed systemanalysis and invented a continuously variable, ultrasonic,mercury delay line used to test the APRFC; Kenneth J.Hammerle performed mathematical analyses; Pierre E.Dorratcague and Bruno Strauss designed the transmitter;Robert C. Lee designed the STALO; William B. Adamand Eli J. Titefsky devised the rf plumbing, antenna andTR tube arrangement; Harold L. Rehkopf, George F.Sullivan and Harlow J. Evenson conducted systemtesting.

Joe Korosei, Wright Field Air Force representative,was a valuable ally, not only in approving funds but ingiving access to U.S. Air Force (AFSD) resources suchas the B-29 ECM airplane.

One of the most significant contributors to theWestinghouse radars was William Skillman as a technicalarchitect and analyst on a number of programs, includingthe AWACS radar and the APQ-81.

Louis P. Goetz performed systems analysis during theearly phases. Walter Ewanus developed the rangingsystems, while William Quigley did the same for thedoppler tracker and later got the DPN-53 throughacceptance tests. Lewis Heyser tackled the earlytransmitter, as well as the challening AWACStransmitter. Tom Fell did much of the "birdie" huntingon early as well as later radars (81 and AWACS). BillDempsey was responsible for getting the APG-55 built.Herbert Grauling worked on the early STALO design andD. Cooke on the later ones. Bill List led the developmentwork on the DPN-53 while Ben Vester phased it intoproduction. The late Jim Finlayson was responsible forthe technical aspects of the AWG-10 design while EarlRix, Carl Shyman and Hank Lawton led the design andproduction.

Johnnie Pearson, Bill Jones and Bob Cowdery werekey contributors to the APQ-81 and AWACS whileWayne Fegely, Noel Longuemare, Jack McDonough,Keefer Stull, George Reeder, Wes Bruner, Erv Smith,Harry Brown, Bill Long and many others were involvedin the hardware that was developed in the late 1960s andearly 1970s; Wayne Weigle, Larry Schafer and JohnStuelpnagel mastered the software that made the digitalradars work. Freeman Fruge led the debugging andacceptance testing of almost all of the major PD radarsafter 1958. The late Dick Bauer led the tail warningeffort. Phil Hacker and Ed Mittleman developed theantennas required for the different models. John Stuntzplayed key management roles, especially in the AWACSand F-16 radar programs.

In the customer community, Hal Reese and TomJones at the U.S. AF Avionics Lab sponsored the earlywork; Herb Carlson, Jack Russell and later ChuckFrancis, did the same for the U.S. Navy. Hans Peotfostered the ORT and early AWACS work along withBill Canty of MITRE. Ron Longbrake, Mike Lowe andBill Judd provided direction to the F-15, F-16 and relatedefforts.


REFERENCES

[1] Barlow, E.J.Doppler Radar.Proceedings of IRE, April 1949, pp. 340-355.

[2] Ridenour, L.N.Radar System Engineering, (McGraw-Hill, 1947), Chapter5- 11, pp. 150- 157.

[3] Perkins, Leroy C.Boeing Pulse-Doppler RadarResearch and Development Board Symposium on the Low-Altitude Problem, Redstone Arsenal, Huntsville, AL, Jan.6-8, 1953, ASTIA AD No. 17855, Log No. 53-1139.

[4] Proceedings of Joint Services Symposium on Pulse DopplerRadar.February 15-16, 1956, Dept. of NAVORD 5355.

[5] Chance, Hulsizer, MacNichole, and WilliamsElectronic Time Measurements.McGraw-Hill, 1947, Chapter 2-8, pp. 18-19.

[6] Barton, D.K.CW and Doppler RadarsArtech House, 1973.

[7] Goetz, L.P. and Albright, J.D.Airborne Pulse Doppler Radar. Reprinted in D.K. Barton(ed.)Radars, Vol. 7, Artech House, 1979.

[8] Mooney, D.H. and Skillman, W.A.Pulse Doppler RadarRadar Handbook, (New York: McGraw-Hill, 1970), ed.M.I. Skolnik, chapter 19.

[9] Mooney, D.H. and Ralston, G.Performance in Clutter of Airborne Pulse MTI, CW Doppler,and Pulse Doppler Radar.

IRE International Convention Record, Vol. 9, pp. 52-62,1961.

[10] Farrell, J. and Taylor, R.Doppler Radar Clutter.IEEE Trans. Aerosp. Nav. Elec., Vol. ANE-1 1, pp. 162-172, Sept. 1964.

[11] Ringel, M.B.An Advanced Computer Calculation of Ground Clutter in anAirborne Pulse Doppler Radar. Reprinted in D.K. Barton(ed.), Radars, Vol. 7; House, 1979.

[12] Hovanessian, S.A.Radar Detection and Tracking Svstems.Artech House, 1979.

[13] Goetz, L.P. and Skillman, W.A.Master Oscillator Requirements for Coherent Radar Sets.NASA-SP-80, November 1964.

[14] Meltzer, S.A. and Thaler, S.Detection Range Predictions for Pulse Doppler Radar.Proc. IRE, pp. 1299- 1307, August 1961.

[15] Skillman, W.A. and Mooney, D.H.Multiple High PRF Ranging.Reprinted in D.K. Baron (ed.), Radars, Vol. 7; Dedham,Mass, Artech House, 1979.

[16] Arnoff, E. and Greenblatt, N.M."Medium PRF Radar Design and Performance.Reprinted in D.K. Barton (ed.), Radars, Vol. 7; ArtechHouse, 1979.

[17] Hovanessian, S.A.Medium PRF Radar Performance Analysis.IEEE Trans. Aerosp. Electron. Svst., Vol. AES-18, No. 3,May 1982, pp. 286, 296.

[18] Ringel, M.B., Mooney, D.H., and Long, W.H."F-16 Pulse Doppler Radar (AN/APG-66) Performance".IEEE Transactions Aerosp. Electron. Svst. (Jan. 1983), Vol.AES-19, pp. 147-158.


Documents

The Development of Airborne Pulse Doppler Radar