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Ripple in S11 with 87104/6D switches

Question asked by tork on Mar 22, 2011
Latest reply on Mar 22, 2011 by Dr_joel
I am calibrating a PNA-X using an ECal module.2 ports, S parameters, Fstart = 1GHz, Fstop = 40GHz, smoothing off. There are (1) 87104D RF switch and (1) 87106D RF switch between port 1 and the ECal module. There are also (2) 87106D RF switches and (1) 87104D RF switches between  port 2 and the ECal module. After I perform a calibration, I place a load between port 1 and 2. Without moving the switches, the load looks as expected. After I move a switch and return to the cal 'ed position, the S11 or S22 have ripple on the trace above 20GHz especially aroung 26GHz. The S12 and S21 seem unaffected. These are 40GHz terminated switches. Is smoothing the only way to eliminate this?