simulatedxjizz.com

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comConformalAntennaArrayDesignonaMissilePlatformKyleLabowski,ChristopherPenney,andJamesF.
Stack,Jr.
RemcomInc.
ApplicationsrangingfromcommunicationstoRADARandevenmedicaldevicesdependonantennaarrays.
Handcalculationssuccessfullyfacilitatetheconstructionofstand-alonearrays;however,whathappenswhenthemountingplatformbecomesapartoftheradiatingsystemBasicanalytictechniquescannoteasilyaccountforobstructionscreatedbyaircraftengines,re-radiationfromwings,irregulargroundplanesofcarsorthecurvatureofamissile.
Antennasandantennaarraystargetedtowardsvehicularapplicationsoftenfurthercomplicatethedesignprocesswithadditionalrestrictions.
Aircraftinparticularrequireconsiderationofaerodynamiceffectsandtheimpactonradarscatteringcausedbytheintegrationofexternalsystems.
Asaresult,designerstendtoincorporateconformalantennaelementsthatcannotberealizedthroughbasicantennatheory.
Theseapplicationsrequire3Dsimulationstoensurethatthefinaldesignmeetsallrequirementsbeforephysicalprototypingormanufacturingcanbegin.
Thisapplicationnotedemonstratestheprocessofaddinganelectricallysteerable,conformalantennaarraytothebodyofahighspeedmissile.
Aspecifiedsurfaceareaonagenericmissilebodyandasetofdesigngoalshasbeenprovidedtoillustratethechallengesofdesigningthearray;however,thisexampledoesnotrepresentanyactualmissileorantennasysteminproduction.
ProjectGoalsThedesigngoalsoftheconformalmissilearrayincludeanoperatingfrequencyof2.
4GHzwithamainbeamgaingreaterthan10dBiandsidelobelevelsatleast20dBdownfromthepeakgain.
Thearraymustscanfrombroadsideofthemissileuptoa45degreeforwardtilttowardthenoseoftheprojectile.
Themissileis2.
3mlongand24cmindiameter.
Thearraywillbelocatedonthecylindricalbodyofthevehicle,cannotinterferewiththecontrolsurfacesandmustfitwithina1mby10cmfootprint.
Forthisapplicationnote,Remcom'sXFdtd3DEMSimulationsoftware(XF7)willbeusedtogeneratethesimulatedresults.
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comArrayElementDesignThefirststepoftheprocessistochooseanddesignasinglearrayelement.
Theaerodynamicsofthemissilewillbeextremelysensitivetoanyperturbationtothesurface,soaplanarconformalantennaisrequired.
Acircularpatchantennaischosenforthisexample.
Severalbooks,Balanis1forexample,providedetaileddesignprocessesforthepatch.
Followingtheanalyticdesign,abrieftuningprocessensues.
Aparametricinvestigationofthefeedlocationproducesanantennawithanexcellentreturnlossof-20dBandapeakgainof7.
5dBiat2.
4GHz.
Havingachievedacceptableperformancewiththeflatpatch,thenextlevelofcomplicationisintroduced.
XF7'sCADmodelingtoolsbendthepatch,substrateandgroundplanetomatchthecurvatureofthemissilebody.
XACTAccurateCellTechnology,XF7'sconformalmeshingtool,allowsthesoftwaretopreciselycapturetheeffectsofthisbendduringsimulation.
Thebendcausestheoperatingfrequencytoshiftslightlyhigherthandesiredtoabout2.
45GHz;however,aquickparametersweepfindsanincreasedpatchdiameterthatreturnstheoperatingfrequencytothedesiredpoint.
Table1demonstratestheevolutionofthepatchparametersfromtheinitialanalyticdesigntothecurvedimplementation.
ArrayDesignForthenextstep,ascriptfromRemcom'sXTendScriptLibrarysynthesizesanarraydesignbasedonthespecifiedperformancecriteria.
ThescriptemploysaFouriertransformtechniquetodeterminetheappropriateamplitudeandphasingofeacharrayelementandappliesamodifiedTaylordistributiontotheamplitudestobettercontrolthesidelobes.
AsshowninFigure1,theinputstothetoolarethecenterfrequencyof2.
4GHz,thehorizontalbeamwidthof65degrees,theverticalbeamwidthof12degrees,andthedesiredsidelobesuppressionof20dBdownfromthepeak.
Amaximumelectricaldowntiltof45degreesisalsoentered.
Thescript-basedGUIrecommendstheminimumnumberofelementsrequiredineachdimensiontomeetthespecificationsandprovidesanestimateddirectivityoftheproposedarray.
Table1AntennaFeedOffsetPatchDiameterPatchAntenna(Initial)4.
982mm44mmPatchAntenna(Final)7.
5mm44.
5mmBentPatchAntenna7.
5mm45.
25mmREMCOMINC.
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comThescriptsuggestsa2x11elementarray;however,thelimitedspaceonthemissilebodyonlyaccommodatesasinglecolumnofantennaelements.
Theuseroptsforaninitialdesignusinga1x12arrayofthecircularpatchelements,andthescriptpreparestheprojectusingthecalculatedspacing,phasesandamplitudes.
Themodifiedprojectusesparameterizedspacingandamplitudestoexpeditepossiblefutureparametricinvestigationsoroptimization.
Theelementphasingisdefinedasafunctionofelectricaldowntilttoprovideeffortlesscontroloverbeamsteering.
Aswithanysimpleanalyticprocess,theFouriertransformtechniqueincludescertainassumptions.
Thisapproachassumestheradiationemanatesfromauniformlyilluminatedaperturewhichfailstoaccountforthenon-uniformfieldproducedbytheactualantennaelements.
Italsoneglectsfringeeffectsfromthegroundplane,substrateandedgeoftheantenna.
Asaresult,weexpectthattheinitialarraydesignmayfailtomeetsomerequirements,andtheinitialflatdesignsimulationresultsinFigure2indeeddemonstrateaslightlyhighsidelobelevel.
Figure1:InputstothearraydesignertoolREMCOMINC.
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comXF7providesmultipleapproachestoaddressthisissue.
Aparametersweeporoptimizationcouldbeusedtorefinethearrayparametersinordertoimproveperformance;however,asimpleroptionistorepeatthearraydesignprocesswithstrictercriteria.
Thedesignerisrunagainwithatighterrestrictionof-34dBsidelobesuppression.
Followingthisprocess,theflatarraygreatlyexceedsthetargetperformancecriteriaasevidencedbycomparingtheblueandgreenplotsshownintherevisedradiationpatternofFigure3.
Havingverifiedthearrayperformancewiththesimpleplanarelement,theusernowappliesthearraydefinitiontothepreviouslytunedcurvedelements.
TheredplotinFigure3indicatesthatthecurvaturenegligiblyaffectsoverallarrayperformance,sonofurthertuningisrequiredatthisstage.
Thearrayisfoundtohaveapeakgainofnearly14dBiwithsidelobelevelsthatexceedtheoriginalspecifications.
Figure3:Optimizedsimulatedantennagainvs.
angleFigure2:Simulatedantennagainvs.
angleREMCOMINC.
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comFinalValidationTheuserintegratesthecurvedarraywiththemissilebodyinordertovalidatetheoveralldesign.
Asexpected,thepresenceofthemissilebodydoeschangetheperformanceofthearrayandthefinalshapeofthegainpattern;however,theresultingpatternstillmeetsthedesigncriteria.
Thefinalsystemexhibitsgreaterthan14dBigain.
Sidelobesuppressionexceeds32dBasseeninthemagentaplotofFigure3.
Altogether,thedesignrequiresnofurtheradjustments.
Figure4displaysmultipleviewsofthecompletedsystemincludingacloseupviewofthecompletedarrayonthemissilebodyandtwogainpatterns.
Fortheseplots,theelectricaldowntiltparameterhasbeensetthefull45degreeforwardtilt.
HardwareandSimulationTimesTheiterativenatureofthedesignprocessoftenthreatenstoconsumeanunacceptableamountoftime.
Thisapplicationnoterequirednumeroussimulationstoprogressfromtheanalyticallydesignedpatchthroughtheinitialarraydesigntothefinalintegratedsystem.
Inarealproductionenvironment,thenumberofsimulationscaneasilyincreasebyordersofmagnitude.
Antennadesignsareoftentreatedalmostasanafterthought,andantennasareexpectedtofitwithineverdecreasingvolumesinordertomakeroomforothersystemcomponents.
Theevolutionoftheoverallsystemgenerallytranslatestosignificantlymodifiedrequirementsfortheantennasubsystem.
TheentiredesignandworkflowofXF7helpsaddressthechallengesofworkingwithinaniterativeprocess;however,XStreamGPUAccelerationoffersthemosteasilymeasuredtimesavings.
XStreamtremendouslyimprovesEMsimulationperformancebyleveragingthepowerofCUDAcapableGPUsfromNVIDIA.
Forexample,thefully-integratedsysteminthisexamplerequiresapproximately1.
5GBofRAMforsimulation.
AneightcoreIntelcorei7CPUneedsoverthreehourstocompletethiswork.
However,thesamesimulationcanbecompletedinjustoversevenminutesusingmultipleGPUs.
SeeTable2formoredetailedtiminginformation.
Figure4:CompletedarrayonthemissilebodyandtwogainpatternsREMCOMINC.
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comSummaryThisapplicationnotefocusedonthedesignofaconformalarrayonthesurfaceofamissile.
Theinitialcircularpatchdesignchosenprovidedagoodstartforadevelopingthecurvedarrayduetotheminimalimpactthatbendinghadonthereturnlossandgainoftheantenna.
Thearraysynthesistoolrapidlyprovidedagooddesignwithonlyslightadjustmentneededtoreachtherequiredsidelobelevels.
Thefinaldesigneasilyintegratedintothefullmissileplatformandsimulatedwithgoodresults,completingthefinalstepintheprocess.
ItwasalsoshownthatbyleveragingXF7'sXStreamGPUAcceleration,acomplex3Dsimulationincludingmultiplearrayelementswithcurvedsurfacesthatcouldtakeseveralhourswascompletedwithinafewminutes.
Applyingthesetechniquestogethercanhelpincreaseproductivitywhileincreasingthefidelityofthedesign,allbeforephysicalprototypinghasbegun.
1Balanis,C.
A.
(2005).
AntennaTheory(3rded.
).
Hoboken:JohnWiley&Sons,Inc.
Table2HardwareRunTime(H:MM:SS)IntelCorei7CPU(2.
8GHz);8threads3:13:00NvidiaTeslaC2070GPU;1GPU0:29:40NvidiaTeslaC2070GPU;2GPUs0:14:10NvidiaTeslaC2070GPU;4GPUs0:08:50NvidiaTeslaC2070GPU;6GPUs0:07:20