HFSS 边界与端口设置.ppt

1、边界与端口设置,电子科技大学 贾宝富,HFSS Boundary List,Perfect E and Perfect H/Natural Ideal Electrically or Magnetically Conducting Boundaries Natural denotes Perfect E cancellation behavior Finite Conductivity Lossy Electrically Conducting Boundary, with user-provided conductivity and permeability Impedance Used f

2、or simulating thin film resistor materials, with user-provided resistance and reactance in /Square Layered Impedance Radiation An absorbing boundary condition, used at the periphery of a project in which radiation is expected such as an antenna structure Symmetry A boundary which enables modeling of

3、 only a sub-section of a structure in which field symmetry behavior is assured. “Perfect E” and “Perfect H” subcategories Lumped RLC Master and Slave Linked boundary conditions for unit-cell studies of infinitely replicating geometry (e.g. a slow wave circuit Layer; Thickness/Type; Materials 用于定义多层均

4、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。,HFSS Boundary Descriptions: Radiation,Parameters: None A Radiation boundary is an absorbing boundary condition, used to mimic continued propagation beyond the boundary plane Absorption is achieved via a second-order impedance calculation Boundary should be const

5、ructed correctly for proper absorption Distance: 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 structure Orientation: The radiation boundary absorbs best when incident energy flow is normal to its sur

6、face Shape: The boundary must be concave to all incident fields from within the modeled space,Note 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.,HFSS Boundary Descriptions

7、: Radiation, cont.,Radiation boundary absorption profile vs. incidence angle is shown at left Note that absorption falls off significantly as incidence exceeds 40 degrees from normal Any incident energy not absorbed is reflected back into the model, altering the resulting field solution! Implication

8、: For steered-beam arrays, the standard radiation boundary may be insufficient for proper analysis. Solution: Use a Perfectly Matched Layer (PML) construction instead. Incorporation of PMLs is covered in the Advanced HFSS training course. Details available upon request.,Reflection of Radiation Bound

9、ary in dB, vs. Angle of Incidence relative to boundary normal (i.e. for normal incidence, = 0),ETM,HFSS Boundary Descriptions: Symmetry,Parameters: Type (Perfect E or Perfect H) Symmetry boundaries permit modeling of only a fraction of the entire structure under analysis Two Symmetry Options: Perfec

10、t E : E-fields are perpendicular to the symmetry surface Perfect H : E-fields are tangential to the symmetry surface Symmetry boundaries also have further implications to the Boundary Manager and Fields Post Processing Existence of a Symmetry Boundary will prompt Port Impedance Multiplier verificati

11、on Existence of a symmetry boundary allows for near- and far-field calculation of the entire structure,Conductive edges, 4 sides,This rectangular waveguide contains a symmetric propagating mode, which could be modeled using half the volume vertically.,Perfect E Symmetry (top),.or horizontally.,Perfe

12、ct H Symmetry(left side),HFSS Boundary Descriptions: Symmetry, cont.,Geometric symmetry does not necessarily imply field symmetry for higher-order modes Symmetry boundaries can act as mode filters As shown at left, the next higher propagating waveguide mode is not symmetric about the vertical center

13、 plane of the waveguide Therefore one symmetry case is valid, while the other is not! Implication: Use caution when using symmetry to assure that real behavior in the device is not filtered out by your boundary conditions!,Perfect E Symmetry (top),Perfect H Symmetry(right side),TE20 Mode in WR90,Pro

14、perly represented with Perfect E Symmetry,Mode can not occur properly with Perfect H Symmetry,HFSS Boundary Descriptions: Lumped RLC,Parameters: Resistance; Inductance; Capacitance,HFSS Boundary Descriptions: Master/Slave Boundaries,Parameters: Coordinate system, master/slave pairing, and phasing Ma

15、ster and Slave boundaries are used to model a unit cell of a repeating structure Also referred to as linked boundaries Master and Slave boundaries are always paired: one master to one slave The fields on the slave surface are constrained to be identical to those on the master surface, with a phase s

16、hift. Constraints: The master and slave surfaces must be of identical shapes and sizes A coordinate system must be identified on the master and slave boundary to identify point-to-point correspondence,Unit Cell Model of End-Fire Waveguide Array,WG Port(bottom),Ground Plane,Perfectly Matched Layer (t

17、op),Slave Boundary,Master Boundary,Origin,V-axis,U-axis,HFSS Boundary Descriptions: PML,由物体表面创建PML层,HFSS Boundary Descriptions: PML,HFSS Boundary Descriptions: PML,由三维物体创建PML层,HFSS Boundary Descriptions: PML,HFSS Source List,Wave Port and Lumped Port Most Commonly Used Source. Its use results in S-p

18、arameter output from HFSS. Apply to Surface(s) of solids or to sheet objects Incident Wave Used for RCS or Propagation Studies (e.g. Frequency-Selective Surfaces) Results must be post-processed in Fields Module; no S-parameters can be provided Applies to entire volume of modeled space Voltage Drop o

19、r Current Source Ideal voltage or current excitations Apply to Surface(s) of solids or to sheet objects Magnetic Bias Internal H Field Bias for nonreciprocal (ferrite) material problems Applies to entire solid object representing ferrite material,HFSS Source Descriptions: Wave Port,HFSS Source Descr

20、iptions: Wave Port,EXAMPLE WAVE PORTS,EXAMPLE LUMPED PORTS,Parameters: Mode Count, Calibration, Impedance, Polarization A port is an aperture through which guided electromagnetic field energy is injected into a 3D HFSS model. Wave Ports: The aperture is solved using a 2D eigensolution which locates

21、all requested propagating modes Characteristic impedance is calculated from the 2D solution Impedance and Calibration Lines provide further control,Impedance and Polarization Lines,Impedance line and polarization line are optional in port setup. They are located in the port and have a starting point

22、 and an end point.,Port = cross section of waveguide,I and/or P Line,Impedance Line,Without impedance line, HFSS computes port impedance from power and current: Zpi With impedance line, a voltage can be defined: Edl . Two more port impedances result: Zpv and Zvi . These are not the same for non-TEM

23、transmission lines.,Polarization Line,Imposes polarization in case of ambiguity,e.g. in square or circular guides with degenerate modes.,Port = cross section of square waveguide,HFSS Source Descriptions: Lumped Port,Parameters: Mode Count, Calibration, Impedance, Polarization A port is an aperture t

24、hrough which guided electromagnetic field energy is injected into a 3D HFSS model. Lumped Ports: Approximated field excitation is placed on the gap source port surface Characteristic impedance is provided by the user during setup,HFSS Source Descriptions: Incident Wave,HFSS Source Descriptions: Inci

25、dent Wave,Parameters: Poynting Vector, E-field Magnitude and Vector Used for radar cross section (RCS) scattering problems. Defined by Poynting Vector (direction of propagation) and E-field magnitude and orientation Poynting and E-field vectors must be orthogonal. Multiple plane waves can be created

26、 for the same project. If no ports are present in the model, S-parameter output is not provided Analysis data obtained by post-processing on the Fields using the Field Calculator, or by generating RCS Patterns,In the above example, a plane incident wave is directed at a solid made from dielectrics,

27、to view the resultant scattering fields.,HFSS Source Descriptions: Voltage Drop and Current Source,Voltage Drop,Current Drop,HFSS Source Descriptions: Voltage Drop and Current Source,Example Voltage Drop (between trace and ground),Example Current Source (along trace or across gap),Parameters: Direct

28、ion and Magnitude A voltage drop would be used to excite a voltage between two metal structures (e.g. a trace and a ground) A current source would be used to excite a current along a trace, or across a gap (e.g. across a slot antenna) Both are ideal source excitations, without impedance definitions

29、No S-Parameter Output User applies condition to a 2D or 3D object created in the geometry Vector identifying the direction of the voltage drop or the direction of the current flow is also required,Sources/Boundaries and Eigenmode Solutions,An Eigenmode solution is a direct solution of the resonant m

30、odes of a closed structure As a result, some of the sources and boundaries discussed so far are not available for an Eigenmode project. These are: All Excitation Sources: Wave Ports and Lumped Ports Voltage Drop and Current Sources Magnetic Bias Incident Waves The only unavailable boundary type is:

31、Radiation Boundary A Perfectly Matched Layer construction is possible as a replacement,HFSS Source Descriptions: Magnetic Bias,Parameters: Magnitude and Direction or Externally Provided The magnetic bias source is used only to provide internal biasing H-field values for models containing nonreciproc

32、al (ferrite) materials. Bias may be uniform field (enter parameters directly in HFSS). Parameters are direction and magnitude of the field .or bias may be non-uniform (imported from external Magnetostatic solution package) Ansofts 3D EM Field Simulator provides this analysis and output Apply source

33、to selected 3D solid object (e.g. ferrite puck),HFSS Ports: A Detailed Look,The Port Solution provides the excitation for the 3D FEM Analysis. Therefore, knowing how to properly define and create a port is paramount to obtaining an accurate analysis. Incorrect Port Assignments can cause errors due t

34、o. .Excitation of the wrong mode structure .Bisection by conductive boundary .Unconsidered additional propagating modes .Improper Port Impedance .Improper Propagation Constants .Differing phase references at multiple ports .Insufficient spacing for attenuation of modes in cutoff .Inability to conver

35、ge scattering behavior because too many modes are requested Since Port Assignment is so important, the following slides will go into further detail regarding their creation.,HFSS Port Selection: Wave Port or Lumped Port?,什么时候你选择 Lumped Port 而不是 Wave Port呢? 当模型中导线之间的间隙太小时； 当使用Wave port很难确定一个端口的参考定位时；

36、 当你希望使用电压降，而不是S参数作为输出时。,Lumped Ports (blue),HFSS Ports: Sizing,A port is an aperture through which a guided-wave mode of some kind propagates For transmission line structures entirely enclosed in metal, port size is merely the waveguide interior carrying the guided fields Rectangular, Circular, Elli

37、ptical, Ridged, Double-Ridged Waveguide Coaxial cable, coaxial waveguide, squareax, Enclosed microstrip or suspended stripline For unbalanced or non-enclosed lines, however, field propagation in the air around the structure must also be included Parallel Wires or Strips Stripline, Microstrip, Suspen

38、ded Stripline Slotline, Coplanar Waveguide, etc.,A Coaxial Port Assignment,A Microstrip Port Assignment (includes air above substrate),HFSS Ports: Sizing, cont.,The port solver only understands conductive boundaries on its borders Electric conductors may be finite or perfect (including Perfect E sym

39、metry) Perfect H symmetry also understood Radiation boundaries around the periphery of the port do not alter the port edge termination! Result: Moving the port edges too close to the circuitry for open waveguide structures (microstrip, stripline, CPW, etc.) will allow coupling from the trace circuit

40、ry to the port walls! This causes an incorrect modal solution, which will suffer an immediate discontinuity as the energy is injected past the port into the model volume,Port too narrow (fields couple to side walls),Port too Short (fields couple to top wall),HFSS Ports: Sizing Handbook I,Microstrip

41、Port Sizing Guidelines Assume width of microstrip trace is w Assume height of substrate dielectric is h Port Height Guidelines Between 6h and 10h Tend towards upper limit as dielectric constant drops and more fields exist in air rather than substrate Bottom edge of port coplanar with the upper face

42、of ground plane (If real structure is enclosed lower than this guideline, model the real structure!) Port Width Guidelines 10w, for microstrip profiles with w h 5w, or on the order of 3h to 4h, for microstrip profiles with w h,Note: Port sizing guidelines are not inviolable rules true in all cases.

43、For example, if meeting 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.,HFSS Ports: Sizing Handbook II,Stripline

44、Port Sizing Guidelines Assume width of stripline trace is w Assume height of substrate dielectric is h Port Height Guidelines Extend from upper to lower groundplane, h Port Width Guidelines 8w, for microstrip profiles with w h 5w, or on the order of 3h to 4h, for microstrip profiles with w h Boundar

45、y Note: Can also make side walls of port Perfect H boundaries,HFSS Ports: Sizing Handbook III,Slotline Port Guidelines Assume slot width is g Assume dielectric height is h Port Height: Should be at least 4h, or 4g (larger) Remember to include air below the substrate as well as above! If ground plane

46、 is present, port should terminate at ground plane Port Width: Should contain at least 3g to either side of slot, or 7g total minimum Port boundary must intersect both side ground planes, or they will float and become signal conductors relative to outline ground,g,Approx 7g minimum,h,Larger of 4h or

47、 4g,HFSS Ports: Sizing Handbook IV,CPW Port Guidelines Assume slot width is g Assume dielectric height is h Assume center strip width is s Port Height: Should be at least 4h, or 4g (larger) Remember to include air below the substrate as well as above! If ground plane is present, port should terminat

48、e at ground plane Port Width: Should contain 3-5g or 3-5s of the side grounds, whichever is larger Total about 10g or 10s Port outline must intersect side grounds, or they will float and become additional signal conductors along with the center strip.,Larger of approx. 10g or 10s,s,h,Larger of 4h or

49、 4g,g,CPW Wave Ports: Starting Recommendations,Wave Port Size The standard recommendation for most CPW wave ports is a rectangular aperture Port width should be no less than 3 x the overall CPW width, or 3 x (2g + w) Port height should be no less than 4 x the dielectric height, or 4h Wave Port Locat

50、ion The wave port should be centered horizontally on the CPW trace If the port is on GCPW, the port bottom edge should lie on the substrate bottom ground plane If the port is on ungrounded CPW, the port height should be roughly centered on the CPW metal layer Wave Port Restrictions As with all wave

51、ports, there must be only one surface normal exposed to the field volume Port should be on exterior model face, or capped by a perfect conductor block if internal The wave port outline must contact the side grounds (all CPWs) and bottom ground (GCPW) The wave port size should not exceed lambda/2 in

52、any dimension, to avoid permitting a rectangular waveguide modal excitation,Ungrounded CPW (Port height centered on trace),Grounded CPW (Port height begins at lower ground),HFSS Ports: Sizing Handbook V; Lumped Ports,Lumped ports behave differently from Wave Ports Any port edge not in contact with m

53、etal structure or another port assumed to be a Perfect H conductor Lumped Port Sizing (microstrip example): “Strip-like”: RECOMMENDED No larger than necessary to connect the trace width to the ground “Wave-like”: No larger than 4 times the strip width and 3 times the substrate height The Perfect H w

54、alls allow size to be smaller than a standard port would be However, in most cases the strip-like application should be as or more accurate Further details regarding Lumped Port sizing available as a separate presentation,Perfect H,Perfect H,Perfect E,Perfect E,Perfect H,Perfect H,Perfect E,Perfect

55、H,HFSS Port Selection Example: Parallel Traces,Spaced by 8 or more times Trace Width Inputs sufficiently isolated that no coupling behavior should occur Sufficient room for Wave port apertures around each trace Use Wave Ports as shown Spaced by 4 8 times Trace Width Inputs still fairly isolated, lit

56、tle to no coupling behavior should occur Insufficient room for Wave port apertures around each trace without clipping fringing fields Use Lumped Ports as shown Spaced by less than 4 times Trace Width Traces close enough to exhibit coupling Even and Odd modes possible; N modes total for N conductors

57、and one ground reference odd mode shown at right Lumped Ports from trace to ground neglect coupling behavior and are no longer appropriate Use multi-mode Wave Port Terminal line assignments can permit extraction of S-parameters referenced to each trace,HFSS Ports: Spacing from Discontinuities,Struct

58、ure interior to the modeled volume may create and reflect non-propagating modes These modes attenuate rapidly as they travel along the transmission line If the port is spaced too close to a discontinuity causing this effect, the improper solution will be obtained A port is a matched load as seen fro

59、m the model, but only for the modes it has been designed to handle Therefore, unsolved modes incident upon it are reflected back into the model, altering the field solution Remedy: Space your port far enough from discontinuities to prevent non-propagating mode incidence Spacing should be on order of port size, not wavelength dependent,Port Extension,HFSS Ports: Single-Direction Propagation,Wave ports must be defined so that only one face can radiate energy into the model Lumped Ports have no such rest