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LRL cal on 8720ES

Question asked by jf991 on Jul 8, 2010
This is an older NWA which I am renting, and I have made my own set of cal devices in the substrate and thickness I am using.  I am using an Anritsu UTF to transition down to my boards.  I use a THRU (1000 mils long), two lines which are longer and satisfy the 20 to 160 degree requirement, and I am using a piece of copper to short the UTF jaws for my REFLECT.
This results in a cal that gives me the proper phase and amplitude for my THRU (re-checking), and the return loss amplitude looks okay also.  But I am getting the 180 degree phase errors at some frequencies when I view S11 or S22.

I assume this is because I have not properly defined the delay for my REFLECT short.  But I have tried zero delay, and delay of half my THRU, both plus and minus, and I am still getting the 180 degree phase errors, although at different freqs.  I cannot find any guidance or examples of definitions for a full set of cal devices for this type of cal in the literature.

Is there anyone out there who knows the secret formula for defining the delay for a REFLECT short delay when doing a cal like this?

I have defined my 1 inch THRU as zero delay, and my lines as the delta delay from the THRU.  I have selected the center of the THRU as my ref plane.  My t-line delay is 142 psec per inch, so I have tried defining the SHORT delay as -71 psec, which makes the most sense to me, since I am placing the short right at the jaws of the UTF.  Or do I need the enter the actual delays of the lines, rather than deltas?