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Affects of error in the load

Question asked by CHoggatt on Oct 24, 2007
I'm calibrating using SOLT and a Cascade ISS, and making on-wafer measurements with an Agilent 78753ES.  The 50 ohm load is spec'd to +/-0.3% (which translates to about +/- 0.150 Ohms),

Suppose the worst case happens, and the load for Port 1is actually 49.850 ohms and the load for Port2 is actually 50.150 ohms.  How will this error propagate to my measurements?  Will a 'true' 50 ohm resistor measure as 50.000 ohms?  What about a 1 port (port to ground) vs. a two port (Port1 to Port2) for the same resistor?

I ask this, 'cause I'm trying to measure devices in the tens of milli-ohms range for series resistance, and would like an idea of how much inherent calibration error is still there.