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pnax comb filter generator cal phase vs power measurement

Question asked by rok on Feb 24, 2015
Latest reply on Feb 25, 2015 by daras

I am using the Windows XP PNA-X with the comb filter generator Tier 1 cal for my downconverter DUT. I am taking phase vs power measurement. (from -60dBm to -30dBm). I used a regular E-Cal for the regular calibration. (with no power cal required)

The issue I am encountering is that I seem to get different phase values readings at a particular power level for different calibrations. For instance, at -60dBm, I get a phase reading of ~-108 degrees. I then replaced the test cable on that same PNA-X and recalibrated. Now I am getting a phase reading of -63degrees at -60dBm. So it is roughly off by 45 degrees. Is this the expected behavior, such that we should only be concerned about the differences between two phase points values (i.e. for AM/PM Conversion computation) rather than absolute phase value repeatability at a particular power level on any PNA-X utilizing the comb filter generator cal? I know for the group delay measurement that we should be able to measure absolute group delay, so I'm not sure if the same would apply for phase shift.