Re: [SI-LIST] : s parameters to rlgc matrix

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From: Bob Lewandowski ([email protected])
Date: Thu Dec 14 2000 - 15:43:54 PST

I don't think there is any direct way to go from S-parameters to a model. Some
sort of circuit topology is needed.

If the circuit is a lumped structure with parasitics, some topology is defined
in schematic form, and model element values assigned. Then it is possible to
take an rf circuit simulator, (Agilent ADS, Ansoft, Eagleware, Aplac, etc.) and
match the calculated S-parameters of the model to the measured data. The
circuit model element values are adjusted by the software to minimize the
calculated-to-measured errors. This process assumes you have a good starting
value for each circuit element. You just can't put down a bunch of Rs, Ls, and
Cs and let the software go nuts. Garbage-in-garbage-out applies here big time.
If the network is resonably simple, inspection of the S11, and S22 plots in
Smith chart form will yield a circuit model and element values for input and
ouput circuits to an experienced eye.

If the circuit is a distributed structure then the problem is more difficult
because the order of the model has to be estimated (number of RLGC sections).
This will effect results big time. But the procedure is basically the same.
Assign starting values, and let the software optimize to match the model to the

---Bob Lewandowski
    Vixel Corp.

"Djohan, Adrianus" wrote:

> Hi,
> I'm wondering if anyone has success with finding an equivalent RLGC element
> for a set of s parameters. For example: Given a set of S parameter as a
> function of frequency (2 by 2 by f) as typically one would get from a
> network analyzer. What would be the method to compute an equivalent RLGC
> element for each frequency, assuming that the RLGC element is 1/nth of the s
> parameters?
> THanks,
> Adrianus
> Adrianus Djohan
> Hardware Engineer
> Tenor Networks, Inc.
> 100 Nagog Park
> Acton, MA 01720
> Phone: (978) 206-5175
> (978) 264-4900 Ext. 175
> Fax: (978) 264-0671

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