I'm attempting to measure the impedance of an embedded antenna in a device enclosure. Frequency of operation is 2.45GHz and I have calibrated the reference plane as far as I can go. I have a 12.4mm feed line going into the enclosure that is attached to a cable at the referenceplane and planned on using the port extension feature to take this extra length into account.
When performing the auto-extension method, leaving the feed open & then shorting it , I receive values of 168mm/560ps and 171.5mm/572ps. (I'm using an E5071C)
However the physical length of both cables i'm using is 12.4mm/413.6ps. (measures with a ruler, edge of SMA connector to end of the feed line).
Is anyone able to explain the discrepency or give some insight as to what I am doing incorrectly? Thanks.