微波无源电路仿真技术(04)

电子科技大学贾宝富博士微波无源电路仿真技术边界与端口设置HFSS中的边界条件PerfectEPerfectHFiniteConductivityImpedanceLayeredImpedanceRadiationSymmetryMaster&SlaveLumpedRLCScreenImpedancePML(PerfectMatchedLayer)边界条件定义的覆盖如果边界被多次定义，则后定义的边界条件覆盖前面定义的边界条件几种例外情况：端口不被覆盖如果用PerfectH覆盖PerfectE边界条件，则覆盖区域的边界条件实际为Natural，即自然边界条件PerfectEandPerfectH/NaturalPerfectE是理想电导体*E-场垂直于边界表面；可以表示金属表面、地平面、理想腔体表面等；无限大地平面选项：用于模拟I无限大地平面；PerfectH是理想磁导体H-场垂直于边界表面，,E-场平行于边界表面；现实世界不存在这种边界，但对模拟模型边界非常有用；Natural是指理想磁边界施加到其它边界(如.PerfectE)‘删除’理想电边界，但允许存在切向电场。其作用为在理想导电平面开了一个‘孔’。Boundary/Excitations-OverviewPerfectE应用实例不考虑损耗的金属平面地平面腔体表面微带线导带PerfectH应用实例对Outer定义PerfectH相当于理想开路在内部定义，用PerfectH覆盖PerfectE，用以在地平面上开孔=首先定义PerfectE将其中的局部定义为PerfectHPerfectH定义的区域实际为自然边界条件，相当于在零厚度的金属平面上开孔趋肤深度趋肤深度1=f趋肤深度f=1GHz铜的趋肤深度=2.088μm钛的趋肤深度=10.97μm趋肤深度正比于1/√f趋肤深度正比于to√fd=趋肤深度直流区域:d趋肤深度交流区域:d3×趋肤深度dFiniteConductivity参数:电导率和磁导率FiniteConductivityisalossyelectricalconductorE-fieldforcedperpendicular,aswithPerfectEHowever,surfaceimpedancetakesintoaccountresistiveandreactivesurfacelossesUserinputsconductivity(insiemens/meter)andrelativepermeability(unitless)Usedfornon-idealconductoranalysis*FiniteConductivityBoundarygattenuatinlarperpendicuE,Impedance参数:电阻和电抗ohms/squareImpedance边界使用户定义的表面阻抗；用于表示薄膜电阻（thinfilmresistors）用于表示电抗性负载（reactiveloads）电抗不随频率变化，所以他不能表示一个频段内的“电容”或“电感”。由需要的薄膜电阻值、宽度和长度计算设定的薄膜阻抗。Length(电流方向)Width=numberof‘squares’Impedancepersquare=DesiredLumpedImpedancenumberofsquaresEXAMPLE:ResistorinWilkensonPowerDividerResistoris3.5milslong(indirectionofflow)and4milswide.Desiredlumpedvalueis35ohms.squareNRRNlumpedsheet/40875.35875.045.3LayeredImpedance参数::SurfaceRoughness,LayerThickness/Typeandmaterial用于模拟由多个薄层构成的阻抗表面。它的作用与阻抗边界相同。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。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.Radiation,cont.Radiationboundaryabsorptionprofilevs.incidenceangleisshownatleftNotethatabsorptionfallsoffsignificantlyasincidenceexceeds40degreesfromnormalAnyincidentenergynotabsorbedisreflectedbackintothemodel,alteringtheresultingfieldsolution!Implication:Forsteered-beamarrays,thestandardradiationboundarymaybeinsufficientforproperanalysis.Solution:UseaPerfectlyMatchedLayer(PML)constructioninstead.IncorporationofPMLsiscoveredintheAdvancedHFSStrainingcourse.Detailsavailableuponrequest.-100-80-60-40-20020ReflectionCoefficient(dB)0102030405060theta(deg)ReflectionCoefficient(dB)708090ReflectionofRadiationBoundaryindB,vs.AngleofIncidencerelativetoboundarynormal(i.e.fornormalincidence,=0)ETMθRadiationSymmetryParameters:Type(PerfectEorPerfectH)SymmetryboundariespermitmodelingofonlyafractionoftheentirestructureunderanalysisTwoSymmetryOptions:PerfectE:E-fieldsareperpendiculartothesymmetrysurfacePerfectH:E-fieldsaretangentialtothesymmetrysurfaceSymmetryboundariesalsohavefurtherimplicationstotheBoundaryManagerandFieldsPostProcessingExistenceofaSymmetryBoundarywillprompt‘PortImpedanceMultiplier’verificationExistenceofasymmetryboundaryallowsfornear-andfar-fieldcalculationofthe‘entire’structureConductiveedges,4sidesThisrectangularwaveguidecontainsasymmetricpropagatingmode,whichcouldbemodeledusinghalfthevolumevertically....PerfectESymmetry(top)...orhorizontally.PerfectHSymmetry(leftside)Symmetry,cont.Geometricsymmetrydoesnotnecessarilyimplyfieldsymmetryforhigher-ordermodesSymmetryboundariescanactasmodefiltersAsshownatleft,thenexthigherpropagatingwaveguidemodeisnotsymmetricabouttheverticalcenterplaneofthewaveguideThereforeonesymmetrycaseisvalid,whiletheotherisnot!Implication:Usecautionwhenusingsymmetrytoassurethatrealbehaviorinthedeviceisnotfilteredoutbyyourboundaryconditions!!PerfectESymmetry(top)PerfectHSymmetry(rightside)TE20ModeinWR90ProperlyrepresentedwithPerfectESymmetryModecannotoccurproperlywithPerfectHSymmetryImpedanceMultiplierSymmetryLumpedRLCLumpedRLC参数:Resistance,Inductance和Capacitance；输入的是并联电阻、电容或电感的实际值。这个边界条件支持快速（Fast）扫频。Master/SlaveParameters:Coordinatesystem,master/slavepairing,andphasingMasterandSlaveboundariesareusedtomodelaunitcellofarepeatingstructureAlsoreferredtoaslinkedboundariesMasterandSlaveboundariesarealwayspaired:onemastertooneslaveThefieldsontheslavesurfaceareconstrainedtobeidenticaltothoseonthemastersurface,withaphaseshift.Constraints:ThemasterandslavesurfacesmustbeofidenticalshapesandsizesAcoordinatesystemmustbeidentifiedonthemasterandslaveboundarytoide