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Trying to understand corrected load match

Question asked by ehaskell on Dec 29, 2015
Latest reply on Jan 4, 2016 by Dr_joel
I am having a lot of trouble trying to understand how load match correction works.  In particular I am measuring directicity of directional couplers integrated into duplexers accurately.  I don't see how the VNA knows to apply a load correction.  Lets say I have a 2 port network and want to see the s11 response with port 2 terminated in as close to an ideal 50 Ohm load as I can.  I am comfortable with connecting UUT port 2 to a good load such an a cal kit load.  I have also read that with a 2 port analyzer and full 2 port calibration that the VNA can correct the port 2 load match to look like like a good load to the UUT port 2?  I can only assume this is happening via the magic of matrix math.  (The analyzer is not actively sourcing any signal for port 2 during a s11 measurement).  How can the VNA "know" if the UUT port 2 is terminated with the cal kit termination with no port 2 load match correction needed or with a cabled connection to the VNA port 2 that will require the load match correction to accurately measure the s11  for a low loss UUT? How does this extend to a multi-port analyzer?  

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