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Differential Measurement with multiport switches

Question asked by sn_lee on Jan 25, 2016
Latest reply on Feb 1, 2016 by Dr_joel

I am doing differential measurement with a 4-port N5224A.
I need to connect a SP10T multiport swithces to each of my test port.
One path of every switches is turned on, then I perform a full 4-port cal with N4692A.
When I perform a transmission measurement, the single ended transmission test data seems normal but the SDD12 is not, as attached.
I can't figure out what happen. So I removed all the switches from my test ports, do a full 4-port cal again with N4692A, and measure transmission, this time both single-ended and differential parameter (SDD12) are normal.
Seems like the switches affected my differential measurement, but I can't explain why.
Do you have any advice for me?

Thank you.