Hi I have an Agilent 8510C with a HP 8340A 26.5GHz Sweeper and a HP 8515A testset. I also tried as I have spares sweeper, display, IF detector and different cables. So I narowed down the problem to the test set. I did the test set performance tests and I got what you see on the images which is different of what they supposed to be (last picture). I got the same problem in S11 or S22. So I was wondering if only by calibrating the test set will remove all those ripples, my guess is that there is a fault in one of the common parts (to both couplers) inside the 8515A and a calibration will not fix this.
Performace verification shows this in the test set samplers tests: