[SI-LIST] : Moment Method/Ensemble/Touchstone/Errors

C Deibele (deibele@fnal.gov)
Mon, 20 Sep 1999 10:41:16 -0500

Hi,

I have been trying to design an equalizer (2GHz-4GHz) using stripline
structures. For this particular application, only the phase needed
adjusting and so I designed a phase shifter using Schiffman phase
shifters. The final equalizer was to be manufactured using
stripline. We use arlon 2.33 (+/- 0.02) dielectric boards....low
loss (loss tangent...0.002)

A Schiffmann phase shifter is simply a coupled line with one
end shorted together. An estimate of the design was performed
using Hewlett Pacard's touchstone program using ideal coupled line
structures. I then proceeded to make a layout of the structure
using the circuit models that touchstone has.

The problem I have is this: I used Ansoft's ensemble 6.0 moment
method program. The program that we bought was the 2.5D emulator
for infinitely thin circuit lines. I then refined my touchstone
results to get to what I thought would be a more accurate model.
I played with the mesh sizes so I found a stable regime in my
solutions.

When I had my boards manufactured, the results of Ensemble were
horrid--the de-embedded phase was off by circa 40%, while the
touchstone results were accurate to 2-3%.

Does anyone know why?? I can imagine that line thickness might play a
role in the solution, but has anyone else encountered such a result?

I am trying to equalize around 40 degrees of phase error in this band
and am using 8 Schiffman's...

Kindest of regards,

Craig

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