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Fitting problem of measured short standard

Question asked by lzw on Jan 3, 2007
Latest reply on Jan 4, 2007 by lzw
Hello everyone,

I have a little trouble with the user calkit parameter extracting using ADS test bench. The calikit is built on PCB and designed to use it both for the old VNAs and new PNAs.

The open, short, and load standard built on the same PCB. For open and load, it is quite easy to fit up the measured S-parameters. But for the Short standard, I run into trouble.

I have measured a Short Standard designed on PCB with a SMA connector soldered on the PCB. Without to remove the SMA board connector's influence. The ADS test bench gives a good fitting and reasonable offest  parameters. When I add a Coaxial part to simulate the SMA PCB copnnector,  the ADS test bench can not fit the measured S-parameters. No matter which optimization method used, the fitted curve always moves away the measured one. Even I tried to used data model for the SMA connector part, does not help either.

The SMA connector is a standard board mounted connector (50 ohm and 7.05 mm long with PTFE as the dielectric filling). I don't understand why this short stub can be a big problem in fitting?

Any tips?