[SI-LIST] Re: why do I need mixed mode S parameters?
- From: dgun@xxxxxxxxxx
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 21 Sep 2004 13:30:43 -0800
Ken,
See my comments interspersed with yours below...
From: Ken Vaz <kenvaz@xxxxxxxxxxxxxxx>
> Vince,
>
> Regarding software which simulate mixed-mode s-parameters, Ansoft's HFSS
> can do this. One thing I have noticed about these simulations is that the
> single-ended as well as the differential s-parameter output files I can
> export from HFSS seem to be almost exactly the same, but when I view the
> plots in HFSS, the single-ended and mixed-mode s-parameters are,
> obviously, different. But using the Bockelman conversions on these
> s-parameters, in say MATLAB, I do end up getting the mixed-mode
> s-parameters that I see in the plots in HFSS. So I'm not sure how HFSS
> computes the mixed-mode s-parameters. I don't see why it should, but it
> seems like HFSS also uses the Bockelman conversions from single-ended to
> mixed-mode. If anyone knows if HFSS actually computes the mixed-mode
> s-parameters, please let me know. Also, Agilent's ADS computes mixed-mode
> s-parameters, but it does it too quick. I'm not sure of the accuracy of
> these simulations since it most likely doesn't solve for the fields
> first, as HFSS does.
ADS is not a physical simulator. It incorporates a physical simulator called
Momentum (which is not a full 3D simulator). Both can be much faster than
a full-wave 3D simulator. If you let me know whether you're referring to
the Momentum simulator or the schematic simulator, I might be able to
answer your question in a little more detail.
> About the VNAs, the four-port VNAs available today use the same
> architecture as two-port VNAs, with with a single synthesized sweeper. For
> true four-port analysis we would need a VNA with dual synthesized
> sweepers, especially if we need to synchronize the two input signals as in
> the case of differential signaling.
There are a few different architechtures for 4-port VNAs. It is usually a
compromise of economics vs. performance (with some measurement science
difficulties thrown in for good measure--especially when it comes to non-
linearities). Bockelman and Eisenstadt's "Pure-mode VNA" does not require
dual-synthesized sweepers, for example.
--
Daniel
--
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