2009-PIER-A HETERODYNE SIX-PORT FMCW RADAR SENSOR

ProgressInElectromagneticsResearch,PIER93,307–322,2009

AHETERODYNESIX-PORTFMCWRADARSENSORARCHITECTUREBASEDONBEATSIGNALPHASESLOPETECHNIQUES

B.Boukari,E.Moldovan,andS.A?es

´CentreEnergie

Mat´eriauxetT´el´ecommunications

InstitutNationaldelaRechercheScienti?que

800delaGaucheti`ere,Montr´eal,QCH4N1K6,Canada

K.WuandR.G.Bosisio

Poly-GramesResearchCenter´D´epartementdeG´enieElectrique´EcolePolytechniquedeMontr´eal

Montr´eal,QCH3T1J4,Canada

S.O.Tatu

´CentreEnergie

Mat´eriauxetT´el´ecommunications

InstitutNationaldelaRechercheScienti?que

800delaGaucheti`ere,Montr´eal,QCH4N1K6,Canada

Abstract—AHeterodynesix-portFMCWcollisionavoidanceradarsensorcon?gurationbasedonbeatsignalphaseslopetechniquesispresentedinthispaper.DigitalIFcircuitryhasbeenusedinordertoavoidproblemsrelatedtoDCo?setandamplitudeandphaseimbalance.Simulationsshowthatthevelocityandrangetothetargetisobtainedsimultaneously,withverygoodaccuracy.Resultsarecomparedtoothertechniquesandsystemarchitectures.

Correspondingauthor:B.Boukari(boukari@emt.inrs.ca).

308Boukarietal.

1.INTRODUCTION

Thepaperpresentsnewsix-portarchitectureusingfrequencymodulatedcontinuouswave(FMCW)technique,toobtainrangeandspeedinformationsimultaneously.Thisinformationisembeddedinthespectrumofthebeatsignal,whichisthemixingproductofreceivedsignalwithtransmittedone.Beatfrequencymeasurementisperformedconventionally,bymeansoffrequencycountingorFastFouriertransform(FFT)techniques.Foraccuratemeasurement,theseconventionaltechniquesrequirealongdataacquisitiontimewhichmustcoverseveralcyclesofthebeatsignal.Fordataacquisitiontimecoveringlessthanonecycleofthebeatsignalforbeatfrequencymeasuring,thephaseslopemethodcanbeuseful.ThismethodwasusedforrangeandspeedmeasurementinFMCWradarin[1,2]andforDopplerfrequencymeasurementin[3–6].Theimplementationofthephaseslopemethodrequiresaninterferometerwhichcanbeseeninmillimeter-wavedomainasanI/Q-mixer.Forcoste?ciencyandcompactnesssix-portinterferometersorsix-portI/Q-mixerhavebeenused[1–6]inthehomodynearchitectureinradarsensorreceivers.AlthoughhomodyneFM-CWradarisknownforitssimplicity,itincorporatesseveralproblems:DCo?set,amplitudeandphaseimbalance,FM-AMconversionnoise.DCo?setandamplitudeandphaseimbalancearecausedbythesix-portimbalanceandthenon-linearanalogdevices(diodes,transistors,etc)usedfortheI/Q-mixer.TheFM-AMconversionnoiseisproducedbyunwantedenvelopecomponentsresultingfromtransmissionlinee?ects,mixing,andfrequencyresponselimitationsoftheFMmodulator[7].InfactDCo?set,amplitudeandphaseimbalanceandFM-AMconversionnoisecauseunacceptablemeasuringerrors.ToovercometheproblemrelatedtotheDCo?set,amplitudeandphaseimbalance,six-portcalibrationisperformedconventionally,inthefrequencydomainwithnetworkanalyzerandimportantdataprocessingmeansarenecessaryin?naldeterminationofspeedandrange[4]and[5].Inordertoavoidthiscomplicatedcalibrationwithnetworkanalyzer,basebanddataprocessingtechniques,knownasbasebandanalyticalcalibrationwereproposedin[1]and[2].BothmethodsdonotreducetheFM-AMconversionnoise.

Inpresentpaper,aheterodynearchitectureusingadigitalIFI/Qmixerisproposedforthephaseslopemethodimplementation.TheheterodynearchitecturereducestheFM-AMconversionnoiseandlowfrequencynoiseasdemonstratedin[7]and[8],improvingtherebythereceiversensitivity.ThedigitalIFI/QmixeravoidDCo?setandamplitudeandphaseimbalance.

ProgressInElectromagneticsResearch,PIER93,2009309

2.THEHETERODYNERADARSENSOR

CONFIGURATION

FM-AMconversionnoiseisthelargestnoisecomponentinahomodyneradarreceiver[7].TheFM-AMconversionnoiseisproducedbyunwantedenvelopecomponentsresultingfromtransmissionlinee?ects,mixing,andfrequencyresponselimitationsoftheFMmodulator.GiventhattheFM-AMconversionnoiseanditsharmonicslieinthesamefrequencybandasthedetectedbeatsignal,thesensitivityoftheradarreceiverisdegraded.Inordertoimprovethesensitivityofthereceiver,thefrequencyrangeofthebeatsignalmustbeseparatedfromthatofFM-AMconversion.Thisisachievedbyaheterodynedown-conversion.Inaheterodynecon?gurationthebeatsignalisintheIFbandandtheFM-AMconversionnoise,remaininginbaseband,canbe?lteredbytheIFband-pass?lter.Theheterodynecon?gurationalonecannotsolvetheremainingproblems,namelyDCo?set,amplitudeandphaseimbalance.Theyareproducedononehandbytheimbalancestructureoftheanalogpassivemulti-ports(suchasbaluns,couplersandsix-ports),and,ontheotherhand,bythefactthattheanalognon-linearcomponentsusedformixers(diodes,transistors),whichgeneratetheDCcomponentbyrectifyingthemillimeter-wavesignals,arenotideallyidentical.InordertoovercometheproblemsrelatedtoDCo?setandamplitudeandphaseimbalance,theheterodynedown-conversionmustbeperformedinconjunctionwithdigitalIFcircuitry.TheDCo?setproblemissolvedinsuchawaythat,inplaceofanalogmixers,digitalmultipliersareused.Theygenerateonlythelowerandtheuppersidebands,DCandothermixingcomponentsarenotgenerated.Theamplitudeimbalanceresultsfromunequalpowersplittinginanalogcon?gurations.Indigitaldomain,inplaceofpowersplitting,dataareduplicated.ThesamedatagotobothIandQchannels.Inthismannertheproblemofamplitudeimbalanceissolved.

Figure1showsthesimpli?edoperatingprincipleoftheheterodyneFMCWradarwithavectorreceiverusingasix-portdouble-balancedmixer[9]andasinglesidebandmixerinthereceiver.Themillimeter-wavevoltagecontrolledoscillator(VCO)ismodulatedbyalinearlysweptfrequencysignalwhichgivesalinearfrequencymodulatedsignalatitsoutput.AportionofthegeneratedFMCWsignaliscoupledtothesix-portmixeratport5andservesasreferencesignal.ThemainpartofgeneratedFMCWsignalisampli?edandtransmittedtowardsthetarget.Thesignalre?ectedfromtargetisreceivedbyradarantennaandampli?edusingalownoiseampli?er(LNA).Theampli?edreceivingsignalis?rstdownconvertedbythe?rstmixer.Becauseofthefactthattheusedsix-portsarenotverywidebandinfrequency,

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Boukarietal.

Figure1.BlockdiagramoftheheterodyneFMCWradarsensorwith

asix-portdouble-balancedmixera?ve-portsinglesidebandmixer.theresultingIFfrequencycannotbehigh.Therefore,bothsidebandsignalsmoveclosertogetherinfrequency,forcingtheselectivityofthe?ltertobehighenough,inordertoseparatethetwosidebandsignals.Duetothefactthatitisimpossibletodesignabandpass?lterwithverysharpcut-o?satmillimeter-wavefrequencies,asinglesidebandmixerhasbeenused.Unlikeconventionalmixers,singlesidebandmixersachievesidebandrejectionthroughphasecancellation,not?ltering,sothefrequencyspacingbetween,thedesiredandundesiredsidebandscanbesmall.Thismeansthatdown-conversioncanbeaccomplishedwithout?ltering,andinfewerstages,savingthecostofextramixers,ampli?ers,localoscillators,and?lters.Theoutputsignalofthesinglesidebandmixerismixedbythesix-portdouble-balancedmixerwiththereferencesignaltogivetheIFsignal.TheIFsignalisampli?ed,A/Dconverted,andthendownconvertedtobasebandwithadigitalI/QmixerwhosesineandcosinefunctionarenumericallygeneratedandhavetheirfrequenciesequaltotheIFfrequency.TheoutputsoftheI/Qmixerareprocessedtoobtainrelativespeedandrangeoftarget.

ProgressInElectromagneticsResearch,PIER93,2009

311Figure2.Blockdiagramofthesix-portjunction.

Figure2showstheblock-diagramofthesix-portusedforthedouble-balancedmixer,apassivecircuitcomposedoftwo90?andtwo180?hybridcouplers.Therelationshipbetweenoutputandinputnormalizedwavesishighlighted.Itistobenotedthatvariousmillimeter-wavesix-portfront-endarchitectures,fabricationtechnologies,andmodulationschemeswereproposedinrecentyears[12,13].

3.RANGEANDSPEEDMEASUREMENT

InordertoimplementthephaseslopemethodforbeatfrequencymeasuringinFMCWradar,DCo?set,amplitudeandphaseimbalanceandFM-AMnoisemustbenegligible.Twosolutionsareo?eredtousforsolvingtheproblem.The?rstoneistousesimplehomodynearchitecture(hardware)andspendmuchtimeinsignalprocessing(software).Thesecondoneistouseacomplexheterodyneordoubleheterodynearchitectureandspendlittletimeinsignalprocessing.In[1]and[2]weproposedthe?rstkindofsolution,namelyasimplehomodynearchitecturewithacomplexsignalprocessingtoovercometheproblemsrelatedtoDCo?setandamplitudeimbalance.Inthepresentpaper,weproposethesecondkindofsolution,namely,