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s1p manipulation - I've confused myself

Question asked by rogerfreeman on Jul 7, 2012
Latest reply on Jul 8, 2012 by rogerfreeman

Short version: Please could someone explain how would I implement a phase offset to an existing s1p data file I have captured in order to effect a lambda/4 transformation for every data point?  Do I just add  "90" to the "degrees" column?

background: I've measured the input Z of a resonator - it's a fairly high impedance (not matched to the usual system Zo) and hence the reflection coefficient approaches unity at all frequencies. The Smith chart trace is in the "detuned open" position and, for the measurements I want to do, I need to transform it to the "detuned short" position.

Normally I would use the "phase offset" control on the VNA to rotate the position of the resonant point (X=0) so that it ends up positioned on the real axis, but now at the low impedance end. However, for various reasons I have had to record the s1p data without that transform being applied.

I'm left with an s1p data set of the form

# GHz MA
1.100000 1.000 -0.408 
1.200089 0.999 -0.406 
1.300179 0.998 -0.380 
2.249777 0.999 0.561 
2.49888 1.000 0.582 
2.50000 1.000 0.584 

and I want to transform it numerically (using Octave for example) to it's phase shifted equivalent.  I modelled a quarterwave line with zero loss in order to apply the impedance transform I wanted, but of course, that's only valid at one frequency - in my case, the resonant point of the resonator - so outlying points don't receive the correct phase shift.

Please can someone put me on the right track? I've confused myself.


Roger Freeman