【正文】 less) ? Used for nonideal conductor analysis* Finite Conductivity Boundary gattenuatinlarperpendicuE ,?215 HFSS Boundary Descriptions: Impedance ? Parameters: Resistance and Reactance, ohms/square (??/ ) ? Impedance boundary is a direct, userdefined surface impedance ? Use to represent thin film resistors ? Use to represent reactive loads ? Reactance will NOT vary with frequency, so does not represent a lumped ?capacitor? or ?inductor? over a frequency band. ? Calculate required impedance from desired lumped value, width, and length ? Length (in direction of current flow) ? Width = number of ?squares? ? Impedance per square = Desired Lumped Impedance ? number of squares EXAMPLE: Resistor in Wilkenson Power Divider Resistor is mils long (in direction of flow) and 4 mils wide. Desired lumped value is 35 ohms. squar eNRRNlu m p eds h eet /40875.35 ??????216 HFSS Boundary Descriptions: Layered Impedance ? Parameters: Surface Roughness。 Back side covered with Solid Cap 248 HFSS Ports: Mode Count ? Ports should solve for all propagating modes ? Ignoring a mode which does propagate will result in incorrect Sparameters, by neglecting modetomode conversion which could occur at discontinuities ? However, requesting too many modes in the full solution also negatively impacts analysis ? Modes in cutoff are more difficult to calculate。 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 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 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 w h 6h to 10h 10w, w ? h or 5w (3h to 4h), w h Note: Port sizing guidelines are not inviolable rules true in all cases. 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 portsonly model and test. 270 HFSS Ports: Sizing Handbook II ? Stripline 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 ? Boundary Note: Can also make side walls of port Perfect H boundaries w h 8w, w ? h or 5w (3h to 4h), w h 271 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 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 bee signal conductors relative to outline ?ground? g Approx 7g minimum h Larger of 4h or 4g 272 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 includ