微波工程边界与端口设置1

2-1边界与端口设置电子科技大学贾宝富2-2Boundary/Excitations-OverviewWhyareTheyCritical?Formostpracticalproblems,thesolutiontoMaxwell’sequationsrequiresarigorousmatrixapproachsuchastheFiniteElementMethod(FEM)whichisusedbyAnsoftHFSS.ThewaveequationsolvedbyAnsoftHFSSisderivedfromthedifferentialformofMaxwell’sequations.Fortheseexpressionstobevalid,itisassumedthatthefieldvectorsare:single-valued,bounded,andhaveacontinuousdistribution(alongwiththeirderivatives)Alongboundariesofmediaoratsources,FieldvectorsarediscontinuousDerivativesofthefieldvectorshavenomeaningBoundaryConditionsdefinethefieldbehavioracrossdiscontinuousboundaries2-3Boundary/Excitations-Overview2-4Boundary/Excitations-Overview2-5HFSSBoundaryListPerfectEandPerfectH/NaturalIdealElectricallyorMagneticallyConductingBoundaries‘Natural’denotesPerfectE‘cancellation’behaviorFiniteConductivityLossyElectricallyConductingBoundary,withuser-providedconductivityandpermeabilityImpedanceUsedforsimulating‘thinfilmresistor’materials,withuser-providedresistanceandreactancein/SquareLayeredImpedanceScreenImpedanceRadiationAn‘absorbingboundarycondition,’usedattheperipheryofaprojectinwhichradiationisexpectedsuchasanantennastructureSymmetryAboundarywhichenablesmodelingofonlyasub-sectionofastructureinwhichfieldsymmetrybehaviorisassured.“PerfectE”and“PerfectH”subcategoriesLumpedRLCMasterandSlave‘Linked’boundaryconditionsforunit-cellstudiesofinfinitelyreplicatinggeometry(e.g.aslowwavecircuit&anantennaarray)PML(PerfectMatchLayer)2-6边界条件定义的覆盖2-7HFSSBoundaryDescriptions:PerfectEandPerfectH/NaturalParameters:NonePerfectEisaperfectelectricalconductor*ForcesE-fieldperpendiculartothesurfaceRepresentmetalsurfaces,groundplanes,idealcavitywalls,etc.PerfectHisaperfectmagneticconductorForcesH-fieldperpendiculartosurface,E-fieldtangentialDoesnotexistintherealworld,butrepresentsusefulboundaryconstraintformodelingNaturaldenoteseffectofPerfectHappliedontopofsomeother(e.g.PerfectE)boundary‘Deletes’thePerfectEcondition,permittingbutnotrequiringtangentialelectricalfields.Opensa‘hole’inthePerfectEplanePerfectEBoundary*PerfectHBoundary‘Natural’BoundarylarperpendicuEcontinuousEparallelE*NOTE:Whenyoudefineasolidobjectasa‘perf_conductor’intheMaterialSetup,aPerfectEboundaryconditionisappliedtoitsexteriorsurfaces!!2-8PerfectE应用实例2-9PerfectH应用实例2-10PerfectHfor2DAperture(I)MonopoleOveraGroundplanePerfectHSurfaceInteriortotheProblemSpaceBehavesLikeanInfinitelyThin2DAperturePerfectH2-11PerfectHfor2DAperture(II)SmallHoleCanbe“Cut”ininfinitelyThinSeptumBetweentheUpperandLowerGuideUsingaPerfectHSurfaceattheHolePerfectH2-12FiniteConductivity趋肤深度1=f2-13DCversusAC2-14HFSSBoundaryDescriptions:FiniteConductivityParameters:ConductivityandPermeabilityFiniteConductivityisalossyelectricalconductorE-fieldforcedperpendicular,aswithPerfectEHowever,surfaceimpedancetakesintoaccountresistiveandreactivesurfacelossesUserinputsconductivity(insiemens/meter)andrelativepermeability(unitless)Usedfornon-idealconductoranalysis*FiniteConductivityBoundarygattenuatinlarperpendicuE,2-15HFSSBoundaryDescriptions:ImpedanceParameters:ResistanceandReactance,ohms/square(/)Impedanceboundaryisadirect,user-definedsurfaceimpedanceUsetorepresentthinfilmresistorsUsetorepresentreactiveloadsReactancewillNOTvarywithfrequency,sodoesnotrepresentalumped‘capacitor’or‘inductor’overafrequencyband.Calculaterequiredimpedancefromdesiredlumpedvalue,width,andlengthLength(indirectionofcurrentflow)Width=numberof‘squares’Impedancepersquare=DesiredLumpedImpedancenumberofsquaresEXAMPLE:ResistorinWilkensonPowerDividerResistoris3.5milslong(indirectionofflow)and4milswide.Desiredlumpedvalueis35ohms.squareNRRNlumpedsheet/40875.35875.045.32-16HFSSBoundaryDescriptions:LayeredImpedanceParameters:SurfaceRoughness;Layer;Thickness/Type;Materials用于定义多层均匀材料组成的边界。如在某种涂敷吸波材料散射特性的计算中，可以使用这种边界。2-172-18HFSSBoundaryDescriptions:RadiationParameters:NoneARadiationboundaryisanabsorbingboundarycondition,usedtomimiccontinuedpropagationbeyondtheboundaryplaneAbsorptionisachievedviaasecond-orderimpedancecalculationBoundaryshouldbeconstructedcorrectlyforproperabsorptionDistance:Forstrongradiators(e.g.antennas)nocloserthan/4toanystructure.Forweakradiators(e.g.abentcircuittrace)nocloserthan/10toanystructureOrientation:TheradiationboundaryabsorbsbestwhenincidentenergyflowisnormaltoitssurfaceShape:TheboundarymustbeconcavetoallincidentfieldsfromwithinthemodeledspaceNoteboundarydoesnotfollow‘break’attailendofhorn.Doingsowouldresultinaconvexsurfacetointeriorradiation.Boundaryis/4awayfromhornapertureinalldirections.2-19HFSSBoundaryDescriptions:Radiation,cont.Radiationboundaryabsorptionprofilevs.incidenceangleisshownatleftNotethatabsorptionfallsoffsignificantlyasincidenceexceeds40degreesfromnormalAnyincidentenergynotabsorbedisreflectedbackintothemodel,alteringtheresultingfieldsolution!Implication:Forsteered-beamarrays,thestandardradiationboundarymaybeinsufficientforproperanalysis.Solution:UseaPerfectlyMatchedLayer(PML)constru