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Switch Error Terms

Question asked by j_williston on Oct 26, 2013
Latest reply on Nov 1, 2013 by j_williston
I am attempting to understand the math behind the 8-term error model in respect to the removal of the switch terms.  I have compared the description of these equations in Ken Wong’s app note and also the book on Microwave Component Measurements and they are both the same.  They describe the measurement as a2m/b2m using source 1 for the forward direction and a1m/b1m using source 2 for the reverse direction.  These I believe are the actual receivers in the PNA and would be representative of the reflection measurement of the switch from inside the PNA.   
The 6 thru terms that are displayed using ECal with the unknown thru shows the 4 required terms describing the DUT and then a2/a1 and a1/a2, which I believe are for switch removal.  If so this is different from what is written and seems to make the measurement through the external cables.  Can you explain why this seems to be different from what is written?  Is there further calculations to implement this to hardware?  

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