ie3d教程CHAP12.docx
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ie3d教程CHAP12
Chapter12AccuracyandEfficiencyEnhancement
TheIE3Demploysanintegralequation,methodofmomentformulation.Integralequationformulationitselfisnotanapproximatemethod.However,theGalerkin’sprocedureandthefinitetruncationofthebasisfunctionsintroduceapproximation.Basically,weusefinitedimensionalfunctionstoapproximatetheinfinitedimensionalcurrentdistributiononacircuit.Becauseitisanumericalprocedure,manyfactorsinvolvedinthenumericalcalculationareaffectingtheaccuracyofasimulation.FollowingaresomeofthemajorfactorsmayaffectanIE3Dsimulation.
(1).MeshingFrequency(orFmax);
(2).MeshingCellSize(CellsperWaveguideWavelength,Ncell);
(3).De-embeddingSchemes;
(4).TheNumberofCellsinDe-embeddingRegion(De-embeddingCells);
(5).TheMeshingSchemes(WithorWithoutEdgeCells).
(6).ThenumberofimagesusedintheenclosedorperiodicGreen’sfunctions,whichwewilldiscussinthenextchapters.
Usually,morecellsinasimulationyieldhigheraccuracy.LargerMeshingFrequency(Fmax)orCellsperWavelength(Ncells)meansmorecellsandmeansmoreaccurateresult.However,wecannotjusttrytoincreasetheFmaxorNcellsindefinitelybecausewewillrunoutofmemoryverysoon.Ifweusethecellssmartenough,wecanachievehighaccuracywithsmallnumberofcells.
Inthischapter,wewillconcentrateonhowwecanimprovethesimulationaccuracybysmartlyconstructingastructure.
Section1.AddingEdgeVerticestoControlMeshing
WhenwediscussourfirstexampleinChapter3,wehavedemonstratedhowwecanuseAutomaticEdgeCells(AEC)toimprovesimulationaccuracy.Edgecellsarecertainlyverycriticalincapturingtheedgeeffectsofmicrostripstructures,anduseofedgecellscanimprovethesimulationaccuracysignificantlyespeciallyforstronglycoupledstructures.WecanclaimthatAECguaranteeshighaccuracyfornoviceusers.IntheIE3D11,wedefineAECbaseduponAECRatioortheratiobetweentheedgecellsizeandtheregularcellsize.Inthisway,itsignificantlyreducesthechanceforausertousetoosmallortoolargecellsaccidentallybecausetheedgecellwidthisautomaticallyscaledwiththemeshingfrequency.
IntheIE3D11,wealsoimplementedthemulti-layerAECandAECforthicknesstraces.Multi-layerAECallowsausertodefinemultipleedgecellsalongtheedgestofurtherimprovetheaccuracy.Itcanyieldextrememodelingaccuracyforhighaccuracyrequirementssuchasdesigning40-dBdirectionalcouplers.AECforthicknesstracesfurtherimprovetheaccuracyformodelingtraceswithtruethickness,whichnormallydonotneedAECunlessextremehighaccuracyisrequired.
AECiscertainlyverygoodforaccuracy.Forsmallandmediumsizeproblems,wenormallyshouldenableAEC.Itwillyieldhighaccuracywithoutextrageometrymodelingeffort.However,AECnormallyincreasestheproblemsize(numberofunknowns)significantly.Foralargestructure,enablingAECandwithoutenablingAECmaymakeabigdifferenceinthesimulationtime.Itwouldbeniceifwecangethighaccuracyresultswhilewemaynotneedtouseedgecellseverywhere.Forsomepartsofastructure,wemaygethighaccuracyresultswithoutedgecells.Normally,iftwoedgesarenotveryclose,edgecellsmaynotbeveryimportant.IfatraceisnotacriticalpathforatransmissionandtherelatedS(i,i),asasmallquantity,isnotaverycriticalparameter,wecanalsoomittheedgecellsonit.
ForexperienceduserswhoknowaboutwhereedgecellsmightormightnotbecriticalcandisableAECwhiletheycancreatetheedgecellsbyinsertingverticestocontrolthemeshing.Wewilldemonstratesomeexamplesonmanuallyinsertingverticestocontrolthemeshing.
Ourfirstexampleisthesuspendedstriplinestructurein.\ie3d\samples\one_cell.geo.Itisthesameoneasthe.\ie3d\samples\connect.geo.Wehaveusedthisexampletodemonstratetheimportanceofpolygonconnection.Wewillusethisexampletodemonstratehowwecaninsertverticestocontrolthemeshingprogramtocreateedgecells.
Step1RunMGRID.Openfile.\ie3d\samples\one_cell.geo.Saveitinto.\ie3d\practice\one_cell.geo.
Step2SelectProcess->DisplayMeshingcommand.TrytodoitwithAECdisabledandAECenabledwithAECRatio=0.05.ThemeshingresultsareshowninFigure12.1.
(a)AECdisabled(b)AECenabledwithAECRatio=0.05
Figure12.1Themeshedstructureofone_cell.geo.
(a)BeforeRectanglization(b)AfterRectanglization
Figure12.2ThestructurebeforeandafterRectanglization.
Step3Wearegoingtomodifythegeometrytoforceittobemeshedinto3-cellsinthetransversedirection.ThecommandweareusingistheEdit->AddEdgeVerticescommand.However,beforeweapplythiscommand,wewouldliketorectanglizethestructurefirstbecausetheEdit->AddEdgeVertice