Introduction
Themillimeterwaveradarworksinthemillimeterwaveband.Usuallymillimeterwavereferstothe30-300GHzfrequencyband(wavelengthis1-10mm).Thewavelengthofmillimeterwaveisbetweencentimeterwaveandlightwave,somillimeterwavehastheadvantagesofmicrowaveguidanceandphotoelectricguidance.Comparedwiththecentimeterwaveguideseeker,themillimeterwaveguideseekerhasthecharacteristicsofsmallsize,lightweightandhighspatialresolution.Comparedwithinfrared,laser,TVandotheropticalseekers,themillimeterwaveguideseekerhasastrongabilitytopenetratefog,smoke,anddust,andhasthecharacteristicsofall-weather(exceptheavyrain)all-weather.Inaddition,theanti-interferenceandanti-stealthcapabilitiesofthemillimeterwaveguideseekerarealsosuperiortoothermicrowaveseekers.
Advantages
Theattenuationoflightwavepropagationintheatmosphereisserious,andtheprocessingprecisionofthedeviceisrequiredtobehigh.Comparedwithlightwaves,millimeterwavesuseatmosphericwindows(whenmillimeterwavesandsubmillimeterwavespropagateintheatmosphere,someoftheattenuationduetotheresonanceabsorptionofgasmoleculesisaminimumvalue).Andtheheatradiationsourcehaslittleinfluence.Forthisreason,theyareofgreatsignificanceincommunications,radar,guidance,remotesensingtechnology,radioastronomy,andspectroscopy.Usingthemillimeterwavefrequencyoftheatmosphericwindowcanrealizelarge-capacitysatellite-groundcommunicationorgroundrelaycommunication.Thenarrowbeamandlowsidelobeperformanceofthemillimeterwaveantennacanbeusedtorealizelow-elevationprecisiontrackingradarandimagingradar.Whenalong-rangemissileorspacecraftreturnstotheatmosphere,itisnecessarytousemillimeterwavesthatcansmoothlypenetratetheplasmatoachievecommunicationandguidance.Thehigh-resolutionmillimeterwaveradiometerissuitableforremotesensingofmeteorologicalparameters.Usingmillimeter-waveandsub-millimeter-waveradiotelescopestodetecttheradiationspectrumofspacecaninferthecompositionofinterstellarmatter.Themainadvantagesareasfollows:
(1)Smallantennaaperture,narrowbeam:hightrackingandguidanceaccuracy;easytotrackatlowelevationangles,resistinggroundmultipathandclutterinterference;Highlateralresolution;highangularresolutionforregionalimagingandtargetmonitoring;highanti-jammingperformancewithnarrowbeam;highantennagain;easytodetectsmalltargets,includingpowerlines,electricpoles,andprojectiles.
(2)Largebandwidth:withhighinformationrate,itiseasytousenarrowpulseorbroadbandFMsignaltoobtainthedetailedstructurecharacteristicsofthetarget;withwidespectrumspreadingability,reducemultipath,clutterandenhanceanti-interferenceAbility;Adjacentfrequencyradarormillimeterwaverecognizerwork,easytoovercomemutualinterference;highrangeresolution,easytoobtainaccuratetargettrackingandrecognitioncapabilities.
(3)HighDopplerfrequency:gooddetectionandrecognitioncapabilitiesforslowtargetsandvibratingtargets;easytousetargetDopplerfrequencycharacteristicsfortargetfeatureidentification;penetrationcharacteristicsfordryairpollution,Providegooddetectionabilityunderdust,smokeanddrysnowconditions.
(4)Goodanti-stealthperformance:Thecurrentabsorbingmaterialscoatedonstealthaircraftareaimedatcentimeterwaves.Accordingtoforeignresearch,thestealthtargetilluminatedbythemillimeterwaveradarcanformstrongelectromagneticscatteringinmanyparts,whichgreatlyreducesthestealthperformance.Therefore,themillimeterwaveradaralsohasthepotentialofanti-stealth.
Disadvantages
Themainlimitationsoftheapplicationofmillimeterwavesinradarare:theattenuationofhighhumidityenvironmentssuchasrain,fog,andwetsnow,aswellasthereducedimpactofhigh-powerdevicesandinsertionlossThedetectiondistanceofmillimeterwaveradar;thepenetrationabilityoftreesispoor,comparedwithmicrowave,thepenetrationofdensetreesislower;thecostofcomponentsishigh,theprocessingaccuracyisrelativelyhigh,andthedevelopmentofmonolithictransceiverintegratedcircuitsisrelativelyslow.
Developmentprofile
Thedevelopmentofmillimeterwaveradarstartedinthe1940s.Inthe1950s,millimeter-waveradars(workingwavelengthofabout8mm)forairporttrafficcontrolandmarinenavigationappeared,showingtheadvantagesofhighresolution,highaccuracy,andsmallantennaaperture.However,duetotechnicaldifficulties,thedevelopmentofmillimeterwaveradarwasoncerestricted.Thesetechnicaldifficultiesaremainly:astheoperatingfrequencyincreases,theoutputpowerandefficiencyofthepowersourcedecrease,andthereceivermixerandtransmissionlinelossesincrease.Sincethemid-1970s,millimeterwavetechnologyhasmadegreatprogress,andsomebetterpowersourceshavebeensuccessfullydeveloped:solid-statedevicessuchasavalanchetubes(seeavalanchediodes)andGunnoscillators(seeelectrontransferdevices);thermionicDevicessuchasmagnetrons,travelingwavetubes,klystrons,extendedinteractionoscillators,backwardwavetubeoscillatorsandgyrotrons.Pulseworkingsolid-statepowersourcesmostlyuseavalanchetubes,andtheirpeakpowercanreach5to15watts(95GHz).Themagnetroncanbeusedasahigh-powerpulsedpowersource,thepeakpowercanreach1to6kilowatts(95GHz)or1kilowatt(140GHz),andtheefficiencyisabout10%.Thegyrotronisanewtypeofmicrowaveandmillimeterwaveoscillatororamplifierthatcanprovidemegawatt-levelpeakpowerinthemillimeterwaveband.Intermsoflow-noisemixers,Schottkydiodes(seecrystaldiodes,Schottkyjunctions)mixershavebeenappliedinthemillimeterwaveband.Intherangeof100GHz,thenoisetemperatureoflow-noisemixerscanbeaslowas500K(Uncooled)or100K(cooled).Inaddition,technologiesinhigh-gainantennas,integratedcircuits,andfin-linewaveguideshavealsodeveloped.Sincethelate1970s,millimeter-waveradarhasbeenusedinmanyimportantcivilandmilitarysystems,suchasshort-rangehigh-resolutionairdefensesystems,missileguidancesystems,andtargetmeasurementsystems.
Applicablerequirements
Accordingtothecharacteristicsofmillimeterwaveradar,itcaneasilymeetthefollowingapplicationrequirements:
(1)High-precisionmulti-dimensionalsearchmeasurement:highprecisionMeasurementandpositioningofdistance,azimuth,frequencyandspatialposition;
(2)Theradarinstallationplatformhasstrictrequirementsforvolume,weight,vibrationandotherenvironments:themillimeterwaveradarantennaissmallinsize,lightinweight,andeasytomeetSpecialenvironmentalrequirementsfordifferentplatformssuchasportability,missile-borne,vehicle-mounted,air-borneandspace-borne;
(3)Targetfeatureextractionandclassificationrecognition:millimeter-waveradarhighresolution,wideworkingfrequencyband,largevalueDopplerfrequencyresponse,shortwavelength,easytoobtaintargetdetailedfeaturesandclearcontourimaging,etc.,suitableforimportanttacticalrequirementsfortargetclassificationandrecognition;
(4)Smalltargetandcloserangedetection:Thesizeoftheopticalzonecorrespondingtotheshortwavelengthofthemillimeterwaveissmall,anditismoresuitableforsmalltargetdetectionthanthemicrowaveradar.Exceptforlong-rangemillimeter-waveradarssuchasspecialspacetargetobservations,generalmillimeter-waveradarsaresuitableforshort-rangedetectionbelow30km;
(5)Strongresistancetoelectronicwarfareinterference:widebandsavailableformillimeter-wavewindows,Easytocarryoutbroadbandspreadspectrumandfrequencyhoppingdesign.Atthesametime,thereconnaissanceandjammingequipmentformillimeter-waveradarsfacesinterferenceproblemssuchasbroadband,atmosphericattenuation,andnarrowbeams.Millimeter-waveradarshavebetteranti-interferencecapabilitiesthanmicrowaveradars.
Application
①Missileguidance:Oneofthemainusesofmillimeterwaveradaristheterminalguidanceoftacticalmissiles.Themillimeterwaveguideseekerhasthecharacteristicsofsmallsize,lowvoltageandfullsolidstate,whichcanmeettherequirementsofthebomb-borneenvironment.Whentheoperatingfrequencyisselectedat35GHzor94GHz,theantennaapertureisgenerally10-20cm.Inaddition,millimeter-waveradarsarealsousedinbeamguidancesystemstocontrolshort-rangemissiles.②Targetsurveillanceandinterception:Millimeterwaveradarissuitableforshort-range,high-resolutiontargetsurveillanceandtargetinterception,andisusedtomonitorlow-altitudeflyingtargets,groundtargetsandouterspacetargets.③Gunfirecontrolandtracking:Millimeterwaveradarcanbeusedforgunfirecontrolandtrackingoflow-altitudetargets.Ithasbeendevelopedintoa94GHzmonopulsetrackingradar.④Radarmeasurement:High-resolutionandhigh-precisionmillimeter-waveradarcanbeusedtomeasurethetargetandcluttercharacteristics.Thiskindofradargenerallyhasmultipleoperatingfrequencies,multiplereceivingandtransmittingpolarizationforms,andvariablesignalwaveforms.Theradarcross-sectionalareaofthetargetismeasuredusingthefrequencyratiomethod.Usingmillimeter-waveradartomeasurethescaled-downtargetmodel,thecross-sectionalareaoftheradartargetatalowerfrequencycanbeobtained.Inaddition,millimeter-waveradarsarealsousedinterraintracking,missilefuzes,andmarinenavigation.