When using a PNA what does the unwrapped phase measurement number mean, I am measured from 1000 to 2000 degrees and the inserted DUT has at least 11,000 degrees of delay?#
the normal phase measurement in a VNA always gives a number in between +/- 180 degrees. The unwrapped phase measurement simply linearly transforms the normal phase response to a linearly increasing phase trace by adding 360 degrees to the phase every time there is a wrap. So it is just another way to look at the same traditional phase response. the benefit of the unwrapped phase format is that is easier for the user to do post processing on. For example if you wanted to do your own Group Delay calculation (which is defined by:
it is a lot easier to operate on the unwrapped phase data then on the wrapped phase. So the unwrapped phase does not represent the delay in your DUT, but the derivative of the unwrapped phase does.
If you have a linear device that has 11,000 degrees at 11 GHz (say a cable) but you don't measure it starting at low frequencies, the unwrapped phase will not know how to extend the start frequency phase back to DC. So if you measure it from 9-11 GHz, you will see 2000 degrees of phase shift, but we don't know about the 9000 degrees from DC to 9 GHz. In fact, we can't know without measuring because it could be a filter structure that has some odd phase shift at low frequency and we can't presume to know what it is without measuring it.
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