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Transform of Meas Refl Stds prior to calc Cal Constants

Question asked by daidnik on Jan 8, 2010
I have a situation where I must get a 2 port cal at the ends of semi-rigid test cables with the ends of the cables at ~74 Kelvin.

Unfortunately, use of the SOL reflection standards is not supported in this chilly environment.

Because of this and several other reasons, I would like to measure the reflection standards at 295K then apply a transform to the measured value(s) to compensate for the fact that the loss and the phase length of the cable(s) changed prior to measurement of the DUT.

Since the semi-rigid test cables that 'see' the temp gradient from 295K to 74K are fixed in position, the mismatches in the test system are fixed and constant; it's not like I'm trying to add in an adapter after calibration and trying to remove the effect of it, but rather that the reflection standards 'should' have been measured thru the test cables with a lower loss per unit length and a slightly shorter phase length.

Since my measurements are in the vicinity of 1 GHz, I don't think the phase shift amounts to much as a consequence of the cooling, but the loss of the stainless steel outer conductor semi-rigid does change significantly.

Without making my own reflection standards to go down to 74K, I am faced with making some modification to the measured SOL standards prior to the calculation of the error terms.

What's the best way to approach this using the PNA?  We have several species of the P3 processor instruments; I'm mostly working with a 3383A 3-port unit.