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ADVANCED TECHNOLOGYMMW SEEKER TESTBED

A MULTI-TECHNOLOGY DEMONSTRATION SENSOR

Gary A. KillenSenior Professional Staff Member

Martin Marietta CorporationElectronic Systems

P.0.Box 555837,MP 200Orlando, Florida 32855-5837

Telephone: (407) 56-3278TeleFax: (407) 356-0933

PROCOGUE

The Advanced Technology Millimeter Wave Seeker Testbed(ATMMWST) may be characterized by thesedescriptors

1) High range resolution (HRR)via synthetic, coherent

2) Complete polarization scattering matrix in a circular

3) Dual-plane sum-anddifferencemonopulse with

processing

basis

complex angle processing.

This seeker technology is coupled with statistical patternrecognitionalgorithmsfor target/clutter discriminationandtracking algorithms for guidance signal generation. Thealgorithmsare embedded in the signal processing software/hardware system. The ATMMWST system consists of aseeker, a signal processor, an instrumentation system anddata recording system, and an independent line-of-sightreference system(E0SRS).The systemisused n both towerand captive flight programs to collect target signatures andto demonstrate various aspects of the mission scenario.

The ATMMWST system, with application to a variety ofmissions from several platforms, can demonstrate he severalmillimeter wave (MMW)technologiesbeingapplied o thesemissions. The hardware and software implementation

approach, primarily software-driven, allows a flexibleadaptation to the variety of potential missions anddemonstrations. Furthermore, the ATMMWST subsystemcharacteristics and radar system characteristics arecompatible with the various missions.

To authenticate the signal processing methodology for theradar targets, first radar/site characterizations and phe-

arrays should be measured and processedcorrectly.omenolot! urrently, the ATMMWST has been involved intower evaluations with characterization and phenomenol-ogy arrays. The tower evaluations are for collecting datarelated to target discrimination, tracking, and imaging ineither one, two, and three dimensions simultaneously. Thesearrays, along with the signal processing, verify the signaland data processing techniques and confirm the HRR proc-

essing coupled with polarization and monopulse process-ing. The arrays are a small ensemble of point scattererswhose different arrangements demonstrate HRR process-ing, angle-error generation from the HRR profiles, the con-

COPYRIGHP1988MARTIN MARIETTA CORPORATION, ALL RIGHTS RESERVED

ventional and complex-indicated-angle monopulse signals,and anglescanning monopulse processing. The arrayssupport demonstrating and illustrating, ina simple manner,the combinationsof range resolution, angle resolution, andpolarization resolution. After demonstrating the basics ofcoherent/polarization/monopulse processing,representative radar targets have been measured at severalranges toindicate theeffectsof target-induced noise, systemthermal noise, as well as other application factors.

INTRODUCTION

There are a number of applications where (MMW) radarsoperating at short-to-moderate ranges are quite attractive.The four mapr application areas' are: 1)surveillance andtarget acquisition radars, 2) tracking and fire control radars,3) seekers and terminal guidance radars, and 4)instrumentation and measurement radar systems.

Future radar systems have a need to field an all-weather,low-visibility, compact seeker/sensor with high systemeffectiveness in difficult, complex clutter scenes. Theserequire that more informationbe extracted about the targetand clutter scene. Thereareseveral possibleradar techniquesthat maybeusedfor target selectioninthecompetingclutterenvironment.This eeker technology embodies the followingtechniques2: 1) HRR, ) HRR with monopulse, 3) cross-

section fluctuations, 4) inverse synthetic aperture arrayIISAR), and 5 )polarization. Additionally, the radar systemshouldbe capable of interfacing with several airframes andtheir avionics.

The problem is to satisfy the requirements of future radarsystem applications in a reasonable time frame, at asatisfactory cost when in production, and adaptability to thevariety of applications. In past MMW programs, emphasishas been on functional performance without regard for size,cost, and mission flexibility. The thrust of the ATMMWSTproject is to develop a baseline design of system elements,including hardware, software, and processing algorithmsthat can be efficiently converted to a number of eventualradar system applications. This has been accomplished bydeveloping a welldocumented and characterized baseline

system design that is small, modular, and softwarereprogrammable.

:

i8

One principal application for the ATMMWST radar system

b

35 8~CH2685-6/89/0000-0035 $01 OO 1989 IEEE

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is with precision-guided delivery systems with the radarunit providing the "brilliant guidance'". Brilliant systemsare those having the capability of acquiring and identifyinga valid target without a man-in-the-loop process. In theATMMWST system, the decision-makingprocess is softwarebased and embedded in the digital signal processor.Autonomous target detection, classification, identification,and tracking of targets is accomplished in preselected regions

with appropriate nformation from the radar platform. Suchsystems then serve to increase the system effectiveness andsurvivability of aircraft and pilots. To perform these fourmajor functions, radar signaturesof both targetsandclutterare required before processing algorithms can be designedand implemented. These radar signature databasesmust becalibrated, intrinsic radareffectsmustbe emoved/modified,and provisionsmade to allow futureexploitationof emergingtechnologies such as MMW imaging.

ATMMWST FUNCTIONAL DESCRIPTION

The ATMMWST system consists of five major units: 1) heradar seeker; 2) the test instrumentation system; 3) the TVsystem, which provides an independent line-of-sightreference system; 4) the digital signal processor unit; and 5 )

the general electronics unit. The radar system and the lens/camera unit are illustrated in Figures 1 and 2, respectively.The transmitter/receiver, Figure 3, is the more commonmoving target indicator (MTI)designzconcept with frequencyagility incorporated in the frequency agile exciter. The radarwaveform, Figure 4, has been designed to accommodateboth stationary target and moving target concepts beingpursued to classify and identify targets in their clutterbackground through high range resolution, cross-sectionfluctuations, synthetic aperture radar (SAR), and ISARtechnologies. The 6-inch diameter antenna utilizes spatial-combining of linear polarizationwhich provides alternatingtransmit circular polarizations, dual-circular polarizationson receive, with sum-and-difference monopulse ports.

Radar signal processing is accomplished in the digital,

software-based signal processor. (Data processingalgorithmsare discussed in the Radar Signal Processing section.)

Figure 1. Radar System

36

Figure 2. Lens/ camera uni t

Basically, motion compensation has been incorporated to

remove the range cell shift and quadratic distortion due toradar platform motion. Discrete Fourier Transform (DFT)processing focuses the data in the measured range cell at allfine range cells and Doppler cells simultaneously or,alternately, provides coherent integration or waveformambiguity function.

This system configuration provides: 1)HRR via synthetic,coherent processing; 2) complete polarization scatteringmatrix in a circular basis for radar targets;3) and dual-planesum-and-difference monopulse with complex indicatedangle processin . Processing only the sum channel datasupports signapprocessing techniques of Doppler-beamsharpening (DBS, a S A R echnique), ISAR, and high rangeresolution. When coupled with monopulse signals, theadvantages of complex angle processing are available, and

generation of angle- error signals with glint reductionthrough frequency agility is provided.

The primary radar parameters and their values are providedinTable1.Of these parameters, he interrelationshipamongthe range resolution (pulse width), range sampling rate, andfrequencysteprequires hat even-indexed range cell samplesbe scrolled after being transformed from frequency space torange space. The even-indexed cells have the sampling pointlocated at the zero frequency line with lesser range objectsaliased into the last cells of the frequency/range transform(Figure 5).

RADAR DATA PROCESS N G ~

Thecoherentdata processing sequencesarebetter llustrated

in a set of figures. Digital processing to generate the HRRprofile, cross-section fluctuation profile, and HRR withmonopulse profile is illustrated in Figure 6. Similarly, theDBS and HRR with monopulse profiles are illustrated inFigure7.Calibration and data adjustmentsare discussed inthe Radar Calibration and Representative Data section.

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Figure 4. Radar waveform

-745

Figure 5. Relating range sampling, range response, andunambigious range extent

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Table1.ATMMWSTradar parameters

Parameter

CENTER FREQUENCYTRANSMllTERPeak PowerPolarization IsolationP u b WdthPRFNumber of Frequencies

ANTENNAGainBeamwidth (one way)

PolarizationpdatizationIsolation

RECEIVERChannelsNoise FigureBandwidthGain control ExtentRange SamplingRateDetectionOuanlizatiigital codeSIGNAL PROCESSORcoilerent BandwithChannel PRF-ng Types

RANGE RE SO LW NPulseHRR plocessing

RANGE AM IG WYPRF

RANGE RATEDopplerAmbiguity1 dB Disbllion Limit

Freqwney W n g

E~kzrDepph

Frequency *P

Measurement

35 G M

10 watls20 dB64ns4okHz647.95 MM

29 dBi

>25 dBSum and Difference>25 dB

4,2 simultaneous8.5 dB (SSB)15 MM76dB@ 0.5 dB inc15.91 MM

8 bib, natural

503Zlar

Coherentiaa

509 MHz2.5 ldizI-D DFTwith monopulseWR

9.4 in

0.29 m

3.75 km18.8 m

0.56 R/s19.1 ws

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RADAR CALIBRATION AND REPRESENTATIVE

DATA

Typically, the MMW radar functions as either aninstrumentation measurement radar, a prototypedemonstration radar system, or simultaneously satisfies

both functions.Formeasurements where theradar isutilized

to collect detailed target and clutter signaturecharacteristics,

the radar is generally consideredan nstrumentation radar

without the additional system complexities.

The radar system has four major types of data: 1)HRR, 2)

polarization scattering matrix data, 3) ISAR data, and 4)

complex monopulse data. There are other pertinent factors

(e.g., gain control, noise level) hat mustbecalibrated as part

of an overall system calibration. These calibrationsestablish

and validate he correct processingof the dataand determine

the systematic (deterministic) distortions induced into the

data via the minor distortions of the radar system. The

minor distortions include power fluctuations of thebandwidth, phase distortion over the bandwidth, inphase

Profileof

Elavauon

Slgnala A d 1) Sad1

3DDisplayTemplaw

MS8A3k3E

?@re 6. Digital processing to generate 1-D range profiles and 3-D images (from echoes of a singleburst of n frequency steps)

P h u d@mentn

I J

L Compbx. nl lu nn t

Error sbpmleFmmNBurets..V roc l t ycm m t od

ErrorSlgml

T h e Hbtoq

nlbmant n. S h t -

Error Sbm l md D ~ Q C

(N h f l l r )

d P k .

Rdllr d sh l t Rmg.

w. h g .

Figure 7.Digital processing to generate2-D nd 3-D images from echoes of N bursts of n frequency steps

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and quadrature imbalance, relative phase in the sum anddifference channels5, and relative spatial orientation of thepolarizations. To fully characterize a coherent, polarimetric,monopulse radar system, a 14-element characterizationmeasurement sequence is utilized as shown in Table2. Noradar field measurement is without the competing nfluenceof noise and clutter; all measurements are made at a highsignal-to-interference ratio to minimize the bias andfluctuationof the measured parameter.

These empirical measurements, when accompanied bycorresponding system analysis, demonstrate the quality ofthe MMW radar system utilized in the measurements.Analysis of these radar/site characterization measurementscenariosindicates the various pertinent radar characteristicsusually desired or questioned. Experience indicates thatthese will support and enhance a quality signaturemeasurement effort. Most of the items are radar metricitems.

, The basic characteristics of the ATMMWST system are itscoherent HRR processing, dual-polarization processing,complex indicated angle and conventional angle monopulseprocessing, and imaging in two dimensions via ISAR

processing4.6. A 3-element array, with polarization selectivescatterers (i.e., trihederal, dihederal) and its responses areshown in Figures 8 and 9(a)-(e), respectively. Shown arefour and one-half scans across the array. The high rangeprofile is numbered 0 through 64 (1 ft ) and the 400 HRR

profile sequence is displayed. Amplitude is the magnitude

of the quanta values after DFT. This array is an exemplary

sample of range resolution, polarization resolution, angle-

scanning monopulse, and angle resolution. The complex

Table2.Radarkite characterization measurements

1) Radar ntrinsic Noise2)Cross Polarization and Channel Balance3) MeasurementStability

RepeatabiliiReproducibility

4) Dynamic Range5) Range Ambiguity

Coherent ProcessingEnvelope Processing

6) Range Cell Weighting7) lutter Levelat S ie8) Multipath/ Elevation Plane Weighting9) Radar Turntable Alignment

10)Azimuth Weighting11)PolarizationScatteringMatrib Distortion Factors12) Gain ControlTransfer Charaderistics13) PhenomenologyAmaging rrays

> Dlhdral

A - Trlhednl

A

\Figure 8. Range, angle, and polarization resolutionangle-scanning monopulse demonstration array

Figure 9. Angle-scanning monopulse/polarization/rangeresolution

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II I 1 T--- I

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Range Sample PolntTurntable Center

-Real term of deltdsum

Figure 10.Complex indicated angle processing phaseadjustment

Real term of deltahum

Figure11. Conventional monopulse processing

4c

20

0.-a

' " c

3sa!-20

-40I I I I I J

MS8A74-12

-4 0 4 88

Angle

Figurel2. Monopulse error signal dihedral response

indicated angle processing, phase adjustment (75 degrees),

and conventional monopulseprocessingareshowninFigures

10, 11, and 12, respectively. A polarization selective

phenomenology/ISAR array and its accompanying

responses are shown in Figures 13 and 14(a) and (b),

respectively.

A>

adar _____)Location

>

I

a. 3-D presentat ionAV . 2-D presentatil

Figurel4. Phenomenology array, trihedral response(Inverse Synthetic Aperture)

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TARGET DETECTION. CLASSIFICATION

IDENTIFICATION

Target acquistion, clhification, and identification arebecoming increasingly important in several applications.Radar targets must be located in adverse environments indifficult clutter situations. In most previous MMW radarapplications, the types of information extracted from the

backscattered signal are target presence and, if a target ispresent, target positional information. Target contrast withthe background provides insufficient signal information foracquisition, classification, and identification.

In most previous radar applications, properties of the targetmeasured have been its presence (i.e., detection)and relativespatial coordinates (range, range rate, angles). It ispossible,however, to extract more information about the target basedupon the variations in amplitude, more importantly phase,and polarization. Thisadditional information is utilized ina pattern recognition system. Generally pattern recognitionwith a radar sensor involves examining the structure of thebackscattered signal in more detail than required for targetdetection. For radar-based pattern recognition systems,several possible techniques maybeused singly or jointly for

target classification and identification problems.

The pattern recognition system, Figure 15, consists of threemajor components: 1) adar sensor,2)feature extractor, and3)classifier. The radar sensor interacts with its environment,which contains the target, andoutputs n observation vector(e.g., the HRR profile) periodically. The particular source

LIsM71.15

generating the observation vector is unknown; theprobabilistic decision (under some decision rule) is used tospecify the sourcetype.The feature extractor processes eachobservation vector to form a corresponding feature vector.Values of the feature vector components are used in adecision process (i.e., classifier) which results in specifyingthemost similar class to associate with theinput observationvector. Further processing of the feature vector will identifythe most probable target type within the target class. Thepattern recognition system performs the functions of targetdetection, recognition, and identification by providing anindication only when targets are assigned to the input data.The pattern recognition system design methodology andphilosophy have been particularly useful for MMW radarprograms. This methodology and philosophy are theoutgrowth of several separate measurement efforts andclassifierdevelopmentseffortsutilizing arious radar sensorconfigurationsand reflect the programmatic realities amongmeasurement effortsand pattern recognitionsystemdesign.

The pattern recognition methodology, Figure 16, for MMWradar-based systemshasbeen used successfully to developstatically based pattern classification systems. This

methodology is considered as three major units: 1)source

database, 2) observation vector generation and featureselection,and3)classifier designandperformance evaluation.Realizing patern recognition is an interactive process, Figure16 shows the nature of pattern recognition design efforts. Itdepicts the basic relationships and threeunitswith the majorpaths while the myraid of reciprocal relationships, dynamicrelationships, and judgements are not indicated.

Figure15 Pattern recognition system Figurel6. Automatic pattern recognition system

REFERENCES

1)Cume,N.C.andBrown, C. E.,Principlesand Applicationsof Millimeter-Wave Radar, Artech House House, Inc., 1987

4) Wehner,Donald R., HighResolution Radar Artech House,Inc., 1987

2) Skolnik,Merril I., Introduction to Radar Systems, 2 Ed.McGraw-Hill BookCo.,1980

3) Steere, R. E., 'Tomorrow's Weapons - Not Just Smart,They're Brilliant", Journalof Electronic Defense, September,1988

5 )Sherman, Samuel M., Monopulse Principles andTechniques Artech House, Inc., 1984

6) Mensa, Dean L., High Resolution Radar Imaging ArtechHouse, Inc., 1981

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A 150-MHZ COHERENT RADAR SYSTEM

R. K. Moore, G. Raju, W. Xin, C. Davis, K. R. D e m a r e s t and D. I. Rummer

Radar Systems and Remote Sens ing Labo rat or y

Unive rs i ty o f Kansas Center f o r Research , Inc .

2291 Irving H i l l Road

Lawrence, Kansas 66045-2969

ABSTRACT INTRODUCTION

A 150-MHz coherent radar has been developed

f o r s o u n d i n g t h e A n t a r c t i c i c e cap , bu t it

may have ot he r ap pli ca t io ns . The rad ar has

a peak p o w e r of 20 W , b u t h a s a c h i r p g a in

of 26 and coh ere nt proce ssi ng gai n from 256

t o 64 ,000, depending on co nt r o l se t t i ng s

a n d a p p l i c a t i o n . W e needed the low t i m e -

b an dw id th p r o d u c t f o r t h e c h i r p t o a l l o w

opera t ion f rom the sur fac e of the i ce w i t h

a minimum range of only 250 m.

The radar w a s tes ted s u c c e s s f u l l y i n b o th

su rfa ce and ai rb or ne modes i n West Antarc-t i c a du ri ng December 1987. For t h e s u r f a c e

mode, we mounted t he r ad ar i n a plywood hu t

on runners , w i t h t h e separate t r a n s m i t t i n g

and rece i v in g 8-e lement -ar ray an tennas

suspended from a t r a n s v e r s e s t r u t mounted

on th e r o o f . A t r a c k e d v e h i c l e p u l l e d the

h u t across the sur fac e . The a i rb orn e t e s t

w a s i n a D e Havilland Twin O t t e r f l y in g a t

abo ut 500-m he ig ht . The 4-element ar ra ys

were suspended from th e wings, one on each

s i d e . For both t e s t s the bot tom of t h e i c ew a s c l e a r l y s e e n a t 1200-m depth, along

w i t h l a y e r s w i t h i n t h e ice.

The system uses 17-MHz bandwidth t o a c h i e v e

abou t 5-m re so lu t i on in ice o r a b o u t 9 m i n

a i r . A pair of SAW d i s p e r s i v e d e l a y l i n e s

p r o v i d e l i n e a r FM pulse expansion and com-p r e s s i o n . A m p l i f i c a t i o n i s provided a t t h e

150-MHZ ca r r ie r f requency , us ing a program-

mable STC. W e then beat t h e s i g n a l t o

baseband and d ig i t i z e the in -phase ( I ) and

q u a d r a t u r e (Q) components. Coherent in te -

gr at io n of the se components i s p r o v id e d i n

r e a l t i m e . Up t o 256 pulses may be added

c o h e r e n t l y i n a r e c i r c u l a t i n g spec ia l pro-

cessor ( 18 .7 5 MHz s a mp li ng r a t e ) . F or

f u r t h e r c o h e r e n t p ro c e s s i n g , s q ua re - la w

de tec t io n , and non-coheren t p roce ss ing , weu se a DSP co nt ro ll ed by a Compaq portable

microcom puter. Recording of the d a t a i s on

a Be rn ou ll i box. The system mounts i n as i ng le 36-inch-high s tand ard rack .

68CH266S-6/69/0000-0042 01 00 1g89 EEE

~ ~ ~~--v-

The University of Kansas Radar Systems and

Remote Sens ing Labo rato ry has been engaged

i n th e deve lopment and appl ica t io n of spe-

c i a l purpose rad ars fo r remote sens ing of

the env i ronment over the past s e v e r a l d e -

cades. The Coheren t An tar ct ic Radar Depth

Sounder has been under development for the

p a s t t h r e e y e a r s i n a p r o j e c t f u n d e d by the

Nat iona l Sc ience Founda t ion Antarc t ic Re -

search Program. A pro to type sys tem w a s

f i e l de d dur ing the 1986-87 season a t t h e

S o ut h P o l e s t a t i o n f o r t e s t i n g . An i m -

proved version w a s tes ted d u r i n g th e 1987-88 season, and us efu l mapping dat a were

o b t a i n e d . A s u b s t a n t i a l mapping e f f o r t h a s

j u s t been comple ted dur ing t he 1988-89

season .

DESCRIPTION OF RADAR SYSTEM

RF P o r t i o n

The radar system operates a t a c e n t e r f r e -

quen cy of 150 MHz, and th e ba s i c sys tem

design emphasizes th e n ee d f o r i n c r e a s e d

s i g n a l - t o -n o i s e r a t i o w i t h m o d e r at e l y l o w

RF tr an sm it te r p o w e r . This i s achieved by

c h i r p i n g t h e t r a n s m i t t e d p u l s e an d by f u l l y

c o h e r e n t i n t e g r a t i o n . The o v e r a l l s y st em

i s shown i n t he block diagram of Fig. 1 ,

and the RI? system i s d e p i c t e d i n Fig. 2.

The bas ic pu lse i s about 60 ns wide; it

modulates a s t a b l e ca r r i e r f requency of 150

MHz. The ca r r ie r s i g n a l i s obta ined by

m u l t i p l y i n g a s t a b l e c r y s t a l o s c i l l a t o r ,

which operates a t 9.375 MHz. The modul at ed

p u l s e i s expanded t o about 1 .6 usec i n a

SAW expander. The expanded pu ls e is ampli-

f i e d a n d g a t e d t o r e d u c e t h e r an g e s i d e -

l o b es a nd a m p l i f i ed f u r t h e r i n s e v e r a ls t a g e s t o a c h i e v e a peak RF power of 20

w a t t s . A pa i r of four -e lement d ipo le a r r ay

a n t e n n a s s e r v e as t h e t r a n s m i t t i n g a n d

r e c e i v i n g a n t e nn a s .

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