【正文】 adiation 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。 Sparameters for interactions between propagating and nonpropagating modes may not converge well ? What if I don?t know how many modes exist? ? Build a simple model of a transmission line only, or run your model in “Ports Only” mode, and check! ? You can alter the mode count before running the full solution. ? Degenerate mode ordering is controlled with calibration lines (see next slide) Circular waveguide, showing two orthogonal TE11 modes and TM01 mode (radial with Zponent). Neglecting the TM01 mode from your solution would cause incorrect results. 249 HFSS Ports: Degenerate Modes ? Degenerate modes have identical impedance, propagation constants ? Port solver will arbitrarily pick one of them to be ?mode(n)? and the other to be ?mode(n+1)? ? Thus, modetomode Sparameters may be referenced incorrectly ? To enforce numbering, use a polarize the first mode to the line ? OR, introduce a dielectric change to slightly perturb the mode solution and separate the degenerate modes ? Example: A dielectric bar only slightly higher in permittivity than the surrounding medium will concentrate the Efields between parallel wires, forcing the differential mode to be dominant ? If dielectric change is very small (approx. or less), impedance impact of perturbation is negligible For 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 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. 250 HFSS Ports: Impedance Definitions ? HFSS provides port characteristic impedances calculated using the powercurrent definition (Zpi) ? Incident power is known excitation quantity ? Port solver integrates Hfield around port boundary to calculate current flow ? For many transmission line types, the powervoltage or voltagecurrent definition is preferred ? Slot line, CPW: Zpv preferred ? TEM lines: Zvi preferred ? HFSS can provide these characteristic impedance values, as long as an impedance line is identified ? The impedance line defines the line along which the Efield is integrated to obtain a voltage For a Coax, the impedance line extends radially from the center to outer conductor (or vice versa). Integrating the Efield along the radius of the coaxial dielectric provides the voltage differ