【正文】 217 218 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 secondorder impedance calculation ? Boundary should be constructed correctly for proper absorption ? Distance: For strong radiators (. antennas) no closer than ?/4 to any structure. For weak radiators (. 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 surface ? 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. 219 HFSS Boundary Descriptions: 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: For steeredbeam 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. 1 0 0 8 0 6 0 4 0 2 0020Reflection Coefficient (dB)0 10 20 30 40 50 60t h e t a ( d e g )R e f l e c t i o n C o e f f i c i e n t ( d B )70 80 90Reflection of Radiation Boundary in dB, vs. Angle of Incidence relative to boundary normal (. for normal incidence, ? = 0) ETM θ 220 Radiation 221 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: ? Perfect E : Efields are perpendicular to the symmetry surface ? Perfect H : Efields 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? verification ? Existence of a symmetry boundary allows for near and farfield 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. Perfect H Symmetry (left side) 222 HFSS Boundary Descriptions: Symmetry, cont. ? Geometric symmetry does not necessarily imply field symmetry for higherorder 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 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 Properly represented with Perfect E Symmetry Mode can not occur properly with Perfect H Symmetry 223 Impedance Multiplier 224 Symmetry 225 Symmetry 226 Lumped RLC 227 HFSS Boundary Descriptions: Lumped RLC ? Parameters: Resistance。 Lumped Ports (blue) 267 HFSS Ports: Sizing ? A port is an aperture through which a guidedwave 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, Elliptical, Ridged, DoubleRidged Waveguide ? Coaxial cable, coaxial waveguide, squareax, Enclosed microstrip or suspended stripline ? For unbalanced or nonenclosed lines, however, field propagation in the air around the structure must also be included ? Parallel Wires or Strips ? Stripline, Microstrip, Suspended Stripline ? Slotline, Coplanar Waveguide, etc. A Coaxial Port Assignment A Microstrip Port Assignment (includes air above substrate) 268 HFSS Ports: Sizing, cont. ? The port solver only understands conductive boundaries on its borders ? Electric conductors may be finite or perfect (including Perfect E symmetry) ? 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 circuitry 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) 269 HFSS Ports: Sizing Handbook I ? Microstrip Port Sizing Guidelines ? Assume width of mi