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Measurements >> RF Measurements >> Propagation coefficient extraction
https://designers-guide.org/forum/YaBB.pl?num=1574274157

Message started by Horror Vacui on Nov 20^th, 2019, 10:22am

Title: Propagation coefficient extraction
Post by Horror Vacui on Nov 20^th, 2019, 10:22am

Hi everyone,

I have reached again my limits. I must make an error in interpreting the phase coefficient (the imaginary part of the propagation coefficient). I've got transmission lines, where the A value in the ABCD (or 1,1 index element in the chain matrix) supposed to be as in the attached formula.
Therefore I expect the angle of A to increase linearly with the frequency. Instead of that I see step-like function when I plot my measurement or simulation results. I've attached one - in the next post - based on simulated S-paramters, i.e. there should not be any effect of pads or noise. The only discrepancy should be the not exactly 50Ohm characteristic impedance, but for any practical considerations, it is 50Ohm. The permittivity is also not constant and a function of the frequency, but not in this way.

Am I wrong somewhere? Is the attached plot normal?

Title: Re: Propagation constant extraction
Post by Horror Vacui on Nov 20^th, 2019, 10:24am

And the angle vs freq plot