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VNA Passivity Issues And Other Artifacts from Outer Space

Question asked by VNA123 on Sep 25, 2015
Latest reply on Oct 15, 2015 by VNA123
For a long time we used a N5245A VNA with a U3045A M12 12 Port Extension (Mechanical Switches).
NOW. I'm using a N5225A VNA with a U3045A M12 12 Port Extension (Same One Mentioned Above). I'm having two major issues.

1) Passivity Issues. I'm using a Two-Port 26.5GHz ECAL. When error correction is on I get passivity failure at 10MHz-50MHz on Single Ended THRU S-Parameters for short DUTs such as a 2xTHRU measurement (Maybe 4-5 Inches of Nelco 4000 SI Material). It's about 0.02-0.03dB at and near 10MHz on the THRU parameters. Also if I leave my Cables Open (No DUT) my corrected response is about 0.04dB 10Mhz-50Mhz for Single Ended Reflection Measurements. What could be causing this? This is a new issue I've seen with 1kIFBW  -15dBm and also 1kIFBW 0dBm.
I've only seen this issue with the new N5225A setup.

2) On S44 and ONLY S44, during a 16port Sweep what appears to be a glitch at 10-50MHz. What happens is S21,S65,S87,S14_13,S16_15 all start (for a ~3m Lossy DUT) at -0.3dB while S43 starts at -1.5dB, or -.8dB or -1.2dB or -.9dB or sometimes it is fine... it's random. Then around 50MHz it returns to normal, almost like there's a intermittent open and the capacitance is allowing 50MHz and above to pass unaffected. But it's ONLY on S44. Strangest thing. It happens at 1kIFBW linear sweeps @ -15dBmand also segmented sweeps where low freq (10-500MHz) is 70Hz or less and the rest of the spectrum is 7kHz at 0dBm Power level. If I leave the VNA in multiport mode and use a 4 port cal with the same ECAL unit there aren't any issues at all.
AND this happens whether I use the N5245A or the N5225A VNA. ALWAYS S44 working on a 16port Cal. A Keysight tech came here last week doing some onsite repairs and I showed him the problem. I told him the same info and he thinks there's something wrong with the 12Port Extension which makes sense. I'm just wondering  Weirdest thing ever. But this is a serious issue that I can use all the help I can get on.

Also, I check and we have never sent the Extension out for Cal.

Thanks,
KTB  

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