AnsweredAssumed Answered

SOLT raw data looks wrong

Question asked by cnice37 on Mar 4, 2016
Latest reply on Mar 4, 2016 by bar28
Having trouble with an E5071C VNA and associated SOLT calibration.

What I am seeing is odd I believe and has forced me to send a unit out for repair to no avail.

Performing a standard 2 port calibration, using the same standards on ports 1 & 2.  When measuring on port 2 with either the open or short, I see a drastic deviation from 0dB on the S22 plot; with the standard ripple in view and past 8GHz up to 20GHz showing <-20dB.  Port 1 shows a nearly flat line at 0dB as expected.

A load measured on port 2 will also show poor response higher in frequency, exceeding 10dB on the high end of the spectrum.  It is so bad, that the load looks worse RAW than the short/ open.

I understand the data being shown is raw, and the calibration appears to be correcting for it.  I have compared measuring a lossy cable between a rental (does not show this phenomenon) VNA and the "bad" VNA and the correlation is excellent.

My gut told me that port 2 would have a very poor match which would explain this "far out" impedance wrapping around the Smith Chart.  Measuring each port with a rental VNA did not show any appreciable difference in the match.

Any idea what is going on?  I was told the repair to the VNA was to swap out the NMD connector on port 2.  I don't think the repair facility was made aware of the problem and just sent back a unit that was in spec.

Thanks in advance