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Why use phase matched cables?

Question asked by scottrf on Jul 8, 2010
Latest reply on Jul 10, 2010 by Dr_joel
What is the significance of phase matched cables between the network analyzer (8753) and the S-parameter test set? Doesn't calibration take care of things?

second related question:

If I'm making a two port measurement of a connectorized DUT, I usually put the approprite ACP7toWhatever adaptor on one test port (to mate with one connector on the DUT), and connect the other port to a cable which terminates with the mating Whatever connector. Calibrate and measure. I see that there are phase matched cables to extend the test ports, but why? Doesn't calibration remove the phase mismatch? In my setup the phase is mismatched by the length of the one connecting cable. If I used two phase matched cables instead of only using one cable, what would I see different? Are my S parameters wrong? I like to minimize the amount of cabling, and having none on one end seems to help with repeatability (having a solid connection setup).

A typical setup:

I cal at the DUT interface with a 3.5mm cal kit

Scott O