[SI-LIST] HFSS S-parameters... issues?
- From: George Peterson <george_peterson@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 10 Nov 2011 13:31:02 -0500
Good Day All,
Is anybody else noticing unexpected behavior of S-parameters (Touchstone
models) generated from transmission line structures in HFSS v13.0.2?
I'm performing a linear port analysis in HSpice and when I use Touchstone
models generated from transmission lines in HFSS I get wacky results;
specifically, S11 magnitudes vary dramatically\unrealistically and expected
resonances change frequencies or are missing altogether.
When I take that same structure in HFSS and export a W-element model, the
HSpice results are as expected; for a 1 inch line, S11 peak ripples occur
at about -20 dB and, using lossless calculations as a rough guide, minima
match well at multiples of 1/2 lamdba (wavelength). I've also compared to
models generated in Polar and all transmission lines models exhibit roughly
the same S11 behavior... except Touchstone from HFSS.
Within HFSS, adjusting the size of the surrounding airbox, changing the
boundary conditions, adjusting the size of the waveports, and changing the
technique for modeling dielectrics all effect the outcome that I'm seeing
but I have yet to see a lot of rhyme and reason.
Can I get a sanity check please?
*Best Regards*,
George Peterson
Signal Integrity Engineer
Jabil Design Services
St. Petersburg, FL
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