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The length of trace for SOLT cal pad

Question asked by johnnyc on Mar 24, 2016
Latest reply on Mar 30, 2016 by Dr_joel
Dear experts,

I am learning to design a SOLT cal pad by myself. I would like to know how to determine the length of trace for the open ,short and load cal pad (Enclosed picture) . I have read the "In-Fixture Measurements Using Vector Network Analyzers". It mentioned that"the short (or open) defines a calibration plane to be in the center of the fixture. This means the thru will have a length of zero. we do not have to worry about characterizing the loss of the thru or its phase shift.".  Does this mean the calibration plane will be in the center of my cal pad PCB. If I solely want to make my cal plane at the probe tip, is it still need to design a trace? or just a very short trace is enough? If there is a principle, how to design the length of trace?  
Thank you for your help!