If I do the following on my HP 8720D VNA (50 MHz to 20 GHz)
1) Press PRESET
2) Connect the two test cables together
3) Measure S12 or S21 without calibrating
I see this (sorry about my poor Excel skills!)
One can expect ripples in S21 plot, as I've not calibrated the
instrument with a calibration kit, but is the fact the uncorrected S21
falls off so much at low frequencies to be expected?
I've been trying to make some measurement of fringing capacitance of
an open connector after doing a calibration kit. I see to have issues
with this at low frequencies. I don't know if this is because the
reactance of such a small capacitance is too large to measure, or if
there's some fault in the VNA.
Dave
