【正文】 (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 include air below the substrate as well as above! ? If ground plane is present, port should terminate at ground plane ? Port Width: ? Should contain 35g or 35s of the side grounds, whichever is larger ? Total about 10g or 10s ? Port outline must intersect side grounds, or they will ?float? and bee additional signal conductors along with the center strip. Larger of approx. 10g or 10s s h Larger of 4h or 4g g 273 CPW Wave Ports: Starting Remendations Wave Port Size The standard remendation 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 Location 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 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 any dimension, to avoid permitting a rectangular waveguide modal excitation 3 (2g + w) w h 4h minimum g Ungrounded CPW (Port height centered on trace) Grounded CPW (Port height begins at lower ground) 3 (2g + w) w h 4h minimum g 274 HFSS Ports: Sizing Handbook V。 Inductance。 Thickness/Type。 Layer。 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. ? R