**From:** Degerstrom, Michael J. (*degerstrom.michael@mayo.edu*)

**Date:** Thu Dec 21 2000 - 06:37:01 PST

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Hi Bob,

I think what the original poster implied was that the

s-parameters are taken on a uniform transmission line

structure. Although I am not certain of this. If this

is the case then one can theoretically mathematically convert the

measured s-parameters to RLCG vs. frequency. But in practice,

I have been only able to do this for very good quality

structures with very good launch structures and very

good high frequency microwave probes. I have had much

better luck in converting s-parameters from simulation to

RLCG vs frequency.

Mike

_______________________________________________________________

Mike Degerstrom Email: degerstrom.michael@mayo.edu

Mayo Clinic

200 1st Street SW

Gugg. Bldg. RM 1042A Phone: (507) 284-3292

Rochester, MN 55905 FAX: (507) 284-9171

WWW: http://www.mayo.edu/sppdg/sppdg_home_page.html

_______________________________________________________________

*> -----Original Message-----
*

*> From: Bob Lewandowski [mailto:Bob.Lewandowski@Vixel.com]
*

*> Sent: Thursday, December 14, 2000 5:44 PM
*

*> To: Djohan Adrianus
*

*> Cc: 'si-list@silab.eng.sun.com'
*

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

*>
*

*>
*

*> 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
*

*> data.
*

*>
*

*> ---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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