微波无源电路仿真技术(04)

1、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nPerfect EnPerfect HnFinite ConductivitynImpedancenLayered ImpedancenRadiationnSymmetrynMaster & SlavenLumped RLCnScreen ImpedancenPML (Perfect Matched Layer)边界条件定义的覆盖n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n几种例外情况：q端口不被覆盖q如果用Perfect H 覆盖Perfect E边界条件，则覆盖区域的边界条件实际为Natu

2、ral，即自然边界条件Perfect E and Perfect H/NaturalnPerfect E 是理想电导体*qE-场垂直于边界表面；q可以表示金属表面、地平面、理想腔体表面等；q无限大地平面选项：用于模拟I无限大地平面；nPerfect H 是理想磁导体qH-场垂直于边界表面， , E-场平行于边界表面；q现实世界不存在这种边界，但对模拟模型边界非常有用；nNatural 是指理想磁边界施加到其它边界 (如. Perfect E) q删除理想电边界，但允许存在切向电场。q其作用为在理想导电平面开了一个 孔 。Boundary/Excitations - OverviewPerfec

3、t E 应用实例n不考虑损耗的金属平面地平面腔体表面微带线导带Perfect H应用实例n对Outer定义Perfect H相当于理想开路n在内部定义，用Perfect H覆盖Perfect E， 用以在地平面上开孔=首先定义Perfect E将其中的局部定义为Perfect HPerfectH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n趋肤深度1=f趋肤深度nf= 1 GHzn铜的趋肤深度=2.088 mn钛的趋肤深度=10.97 mn趋肤深度正比于1 /fn趋肤深度正比于to fd=趋肤深度直流区域:d 3趋肤深度dFinite Conductivityq参数:

4、电导率和磁导率nFinite Conductivity is a lossy electrical conductorqE-field forced perpendicular, as with Perfect EqHowever, surface impedance takes into account resistive and reactive surface lossesnUser inputs conductivity (in siemens/meter) and relative permeability (unitless)nUsed for non-ideal conducto

5、r analysis*Finite Conductivity BoundarygattenuatinlarperpendicuE,Impedanceq参数: 电阻和电抗 ohms/square nImpedance 边界使用户定义的表面阻抗；q用于表示薄膜电阻（thin film resistors）q用于表示电抗性负载（reactive loads）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”。n由需要的薄膜电阻值、宽度和长度计算设定的薄膜阻抗。qLength (电流方向) Width = number of squaresqImpedance per square = D

6、esired Lumped Impedance number of squaresEXAMPLE: Resistor in Wilkenson Power DividerResistor is 3.5 mils long (in direction of flow) and4 mils wide. Desired lumped value is 35 ohms.squareNRRNlumpedsheet/40875.35875. 045 . 3Layered Impedancen参数: : Surface Roughness, LayernThickness/Type and material

7、n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。RadiationqParameters: NoneqA Radiation boundary is an absorbing boundary condition, used to mimic continued propagation beyond the boundary planeAbsorption is achieved via a second-order impedance calculationqBoundary should be cons

8、tructed correctly for proper absorptionDistance: For strong radiators (e.g. antennas) no closer than /4 to any structure. For weak radiators (e.g. a bent circuit trace) no closer than /10 to any structureOrientation: The radiation boundary absorbs best when incident energy flow is normal to its surf

9、aceShape: The boundary must be concave to all incident fields from within the modeled spaceNote boundary does not follow break at tail end of horn. Doing so would result in a convex surface to interior radiation.Boundary is /4 away from horn aperture in all directions.Radiation, cont.nRadiation boun

10、dary absorption profile vs. incidence angle is shown at leftqNote that absorption falls off significantly as incidence exceeds 40 degrees from normalqAny incident energy not absorbed is reflected back into the model, altering the resulting field solution!nImplication: For steered-beam arrays, the st

11、andard radiation boundary may be insufficient for proper analysis.nSolution: Use a Perfectly Matched Layer (PML) construction instead.qIncorporation of PMLs is covered in the Advanced HFSS training course. Details available upon request.-100-100-80-80-60-60-40-40-20-200 02020Reflection Coefficient (

12、dB)Reflection Coefficient (dB)0 0101020203030404050506060theta (deg)theta (deg)Reflection Coefficient (dB)707080809090Reflection of Radiation Boundary in dB, vs. Angle of Incidence relative to boundary normal (i.e. for normal incidence, = 0)ETMRadiationSymmetryqParameters: Type (Perfect E or Perfect

13、 H)nSymmetry boundaries permit modeling of only a fraction of the entire structure under analysisnTwo Symmetry Options:qPerfect E : E-fields are perpendicular to the symmetry surfaceqPerfect H : E-fields are tangential to the symmetry surfacenSymmetry boundaries also have further implications to the

14、 Boundary Manager and Fields Post ProcessingqExistence of a Symmetry Boundary will prompt Port Impedance Multiplier verificationqExistence of a symmetry boundary allows for near- and far-field calculation of the entire structureConductive edges, 4 sidesThis rectangular waveguide contains a symmetric

15、 propagating mode, which could be modeled using half the volume vertically.Perfect E Symmetry (top).or horizontally.Perfect H Symmetry(left side)Symmetry, cont.nGeometric symmetry does not necessarily imply field symmetry for higher-order modesnSymmetry boundaries can act as mode filtersqAs shown at

16、 left, the next higher propagating waveguide mode is not symmetric about the vertical center plane of the waveguideqTherefore one symmetry case is valid, while the other is not!nImplication: Use caution when using symmetry to assure that real behavior in the device is not filtered out by your bounda

17、ry conditions!Perfect E Symmetry (top)Perfect H Symmetry(right side)TE20 Mode in WR90Properly represented with Perfect E SymmetryMode can not occur properly with Perfect H SymmetryImpedance MultiplierSymmetryLumped RLCLumped RLCn参数: Resistance, Inductance 和 Capacitance；n输入的是并联电阻、电容或电感的实际值。n这个边界条件支持快

18、速（Fast）扫频。Master/SlaveqParameters: Coordinate system, master/slave pairing, and phasingnMaster and Slave boundaries are used to model a unit cell of a repeating structureqAlso referred to as linked boundariesqMaster and Slave boundaries are always paired: one master to one slaveqThe fields on the sl

19、ave surface are constrained to be identical to those on the master surface, with a phase shift.nConstraints:qThe master and slave surfaces must be of identical shapes and sizesqA coordinate system must be identified on the master and slave boundary to identify point-to-point correspondenceUnit Cell

20、Model of End-Fire Waveguide ArrayWG Port(bottom)Ground PlanePerfectly Matched Layer(top)Slave BoundaryMaster BoundaryOriginV-axisU-axisScreen ImpedanceScreen ImpedanceScreen ImpedancePerfect Matched Layer（PML）nParameters: Resistance, Uniform Thickness, Frequencies and Minimum Radiation Distance.n理想匹

21、配层(PML) boundary is fictitious material that fully absorb the electromagnetic fields impinging upon them. There are two types of PML applications:qPML Objects Accept Free Radiation if the PMLs terminate in free space.qPML Objects Continue Guided Waves if the PMLs terminate in a transmission line.nGu

22、idelines for assigning PML boundaries qHFSS treats PMLs uniformly with regard to thickness. If the PMLs in your design vary in thickness, create a separate PML group for each thickness.nYou should manually create a PML whenqThe base object is curved.qThe material of the corresponding base object tou

23、ching the PML is not homogenous.HFSS中的缺省边界条件n与背景的交接面自动定义为Outer，即Perfect En良导体的表面自动定义为Perfect E或Finite Conductivityn不同介质之间的交接面自动定义为自然边界条件Natural默认边界条件HFSS中的激励源HFSS中的端口n端口（ Ports ）q端口是一种特殊类型的边界条件。它允许能量通过端口进入或流出仿真模型。端口定义在一个2维平面上。解算器首先计算该平面的本征模式。平面的背面等效为一个界面相同的半无限长的波导。n激励类型q波端口-外部n端口背后是外表面或良导体。n波端口支持多模（

24、例如，耦合线）和端口偏移；n计算通常的S-Parameters；n端口阻抗与频率有关，但在任何一个频率端口都是匹配的。q集中端口 内部n建议端口处于几何模型内部；Recommended only for surfaces internal to geometric modeln集中端口仅支持单模 (TEM) 并且端口不能偏移；n端口阻抗Zo可以归一化到一个常数值。HFSS中的端口（续）n模式、反射和传播q一个特定信号的可以激励起3维场；q包含由高频结构不连续性产生的高次模反射q如果这些高次模被反射到激励端口或其它端口，与这些模式相关的S参数需要计算。q如果这些高次模在到达任何端口前由于衰减或不

25、传输的凋落模衰落了，端口不计算这些模式的S参数。n波端口需要一段一定长度均匀横截面波导。端口延伸和高次模问题高次模传输问题波端口中的简并模nDegenerate modes have identical impedance, propagation constantsnPort solver will arbitrarily pick one of them to be mode(n) and the other to be mode(n+1)qThus, mode-to-mode S-parameters may be referenced incorrectly nTo enforce n

26、umbering, use a polarize the first mode to the linenOR, introduce a dielectric change to slightly perturb the mode solution and separate the degenerate modesqExample: A dielectric bar only slightly higher in permittivity than the surrounding medium will concentrate the E-fields between parallel wire

27、s, forcing the differential mode to be dominantqIf dielectric change is very small (approx. 0.001 or less), impedance impact of perturbation is negligibleFor parallel lines, a virtual object between them aids mode ordering. Note virtual object need not extend entire length of line to help at port.In

28、 circular or square waveguide, use the calibration line to force (polarize) the mode numbering of the two degenerate TE11 modes. This is also useful because without a polarization orientation, the two modes may be rotated to an arbitrary angle inside circular WG.端口阻抗定义nHFSS provides port characteris

29、tic impedances calculated using the power-current definition (Zpi)qIncident power is known excitation quantityqPort solver integrates H-field around port boundary to calculate current flownFor many transmission line types, the power-voltage or voltage-current definition is preferredqSlot line, CPW:

30、Zpv preferredqTEM lines: Zvi preferrednHFSS can provide these characteristic impedance values, as long as an impedance line is identifiedqThe impedance line defines the line along which the E-field is integrated to obtain a voltageFor a Coax, the impedance line extends radially from the center to ou

31、ter conductor (or vice versa). Integrating the E-field along the radius of the coaxial dielectric provides the voltage difference. In many instances, the impedance and calibration lines are the same!X-波段波导中的传输模式阻抗线和极化线nImpedance line and polarization line are optional in port setup.nThey are located

32、 in the port and have a starting point and an end point.Port = cross section of waveguideI and/or P LineIntegration Line （积分线）集中端口（Lumped Port）qParameters: Mode Count, Calibration, Impedance, PolarizationnA port is an aperture through which guided electromagnetic field energy is injected into a 3D H

33、FSS model. nLumped Ports: Approximated field excitation is placed on the gap source port surfaceCharacteristic impedance is provided by the user during setup入射波（Incident Wave）入射波（Incident Wave）qParameters: Poynting Vector, E-field Magnitude and VectornUsed for radar cross section (RCS) scattering pr

34、oblems.nDefined by Poynting Vector (direction of propagation) and E-field magnitude and orientationqPoynting and E-field vectors must be orthogonal.qMultiple plane waves can be created for the same project.nIf no ports are present in the model, S-parameter output is not providedqAnalysis data obtain

35、ed by post-processing on the Fields using the Field Calculator, or by generating RCS PatternsIn the above example, a plane incident wave is directed at a solid made from dielectrics, to view the resultant scattering fields.电压源和电流源Example Voltage Drop (between trace and ground)Example Current Source

36、(along trace or across gap)qParameters: Direction and MagnitudenA voltage drop would be used to excite a voltage between two metal structures (e.g. a trace and a ground)nA current source would be used to excite a current along a trace, or across a gap (e.g. across a slot antenna)nBoth are ideal sour

37、ce excitations, without impedance definitionsqNo S-Parameter OutputnUser applies condition to a 2D or 3D object created in the geometryqVector identifying the direction of the voltage drop or the direction of the current flow is also required本征模的边界与源qAn Eigenmode solution is a direct solution of the

38、 resonant modes of a closed structureqAs a result, some of the sources and boundaries discussed so far are not available for an Eigenmode project. These are:nAll Excitation Sources:qWave Ports and Lumped PortsqVoltage Drop and Current SourcesqMagnetic BiasqIncident WavesnThe only unavailable boundar

39、y type is:qRadiation BoundaryA Perfectly Matched Layer construction is possible as a replacement磁偏置qParameters: Magnitude and Direction or Externally ProvidednThe magnetic bias source is used only to provide internal biasing H-field values for models containing nonreciprocal (ferrite) materials.qBia

40、s may be uniform field (enter parameters directly in HFSS).Parameters are direction and magnitude of the fieldq.or bias may be non-uniform (imported from external Magnetostatic solution package)Ansofts 3D EM Field Simulator provides this analysis and outputnApply source to selected 3D solid object (

41、e.g. ferrite puck)波端口与集中参数端口的选择n什么时候你选择 Lumped Port 而不是 Wave Port呢?q当模型中导线之间的间隙太小时；q当使用Wave port很难确定一个端口的参考定位时；q当你希望使用电压降，而不是S参数作为输出时。Lumped Ports (blue)端口尺寸qA port is an aperture through which a guided-wave mode of some kind propagatesnFor transmission line structures entirely enclosed in metal, po

42、rt size is merely the waveguide interior carrying the guided fieldsqRectangular, Circular, Elliptical, Ridged, Double-Ridged WaveguideqCoaxial cable, coaxial waveguide, squareax, Enclosed microstrip or suspended striplinenFor unbalanced or non-enclosed lines, however, field propagation in the air ar

43、ound the structure must also be includedqParallel Wires or StripsqStripline, Microstrip, Suspended StriplineqSlotline, Coplanar Waveguide, etc.A Coaxial Port AssignmentA Microstrip Port Assignment (includes air above substrate)微带线qMicrostrip Port Sizing GuidelinesnAssume width of microstrip trace is

44、 wnAssume height of substrate dielectric is hqPort Height GuidelinesnBetween 6h and 10hqTend towards upper limit as dielectric constant drops and more fields exist in air rather than substrateqBottom edge of port coplanar with the upper face of ground planeq(If real structure is enclosed lower than

45、this guideline, model the real structure!)qPort Width Guidelinesn10w, for microstrip profiles with w hn5w, or on the order of 3h to 4h, for microstrip profiles with w hwh6h to 10h10w, w hor5w (3h to 4h), w hNote: Port sizing guidelines are not inviolable rules true in all cases. For example, if meet

46、ing the height and width requirements outlined result in a rectangular aperture bigger than /2 on one dimension, the substrate and trace may be ignored in favor of a waveguide mode. When in doubt, build a simple ports-only model and test.带状线qStripline Port Sizing GuidelinesnAssume width of stripline

47、 trace is wnAssume height of substrate dielectric is hqPort Height GuidelinesnExtend from upper to lower groundplane, hqPort Width Guidelinesn8w, for microstrip profiles with w hn5w, or on the order of 3h to 4h, for microstrip profiles with w hqBoundary Note: Can also make side walls of port Perfect

48、 H boundarieswh8w, w hor5w (3h to 4h), w h槽线qSlotline Port GuidelinesnAssume slot width is gnAssume dielectric height is hqPort Height:nShould be at least 4h, or 4g (larger)nRemember to include air below the substrate as well as above!qIf ground plane is present, port should terminate at ground planeqPort Width:nShould contain at least 3g to either side of slot, or 7g total minimumnPort boundary must intersect both side ground planes,