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Clarifying procedure in Appendix B, 5989-4840 "Specifying Calibration Standards and Kits for Keysight Vector Network Analyzers"

Question asked by wb0gaz. on Aug 23, 2020
Latest reply on Sep 15, 2020 by uWHarry

I need to create a (standards) definition for a coaxial open cal kit standard for which the definitions do not exist. I propose to do this by measuring my new (un-characterized) open device (DUT) S parameters after calibrating the analyzer using an existing (characterized) open-short-load cal kit with the same connector/gender as my unknown (to clarify, the existing kit's open is a different device than the open for which I seek to generate standard definition.) I expect there will be a loss of accuracy due to transferring standards from the existing cal kit to the new device; this is OK.

 

The description copied below from Appendix B of publication 5989-4840 "Specifying Calibration Standards and Kits for Keysight Vector Network Analyzers" (without formula graphics --- the formulas are shown in publication PDF page 38) seems to suggest that delay (only) can be specified where frequency is low enough that the reactance from fringing capacitance can be neglected (assumed zero). I do not wish the DUT standard definition to be limited to such low frequencies (so I do want C0..C3 and Delay.)

 

The problem I am having is this - the existing coaxial open cal kit standard definitions I've encountered to this point (as in looked at the parameters in the 8753 firmware or specified in a document) specify BOTH a delay (formula 2B.9) and C0..C3 (formula 2B.8). Should the delay be calculated at some sufficiently-low frequency (where C1..C3 are negligible) after C0..C3 are generated in the first place, or am I failing to understand the process (or not posing this question clearly or correctly?)

 

Thank you for any advice or references

 

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The open’s fringing capacitance may be determined using three dimension microwave
structure simulators. However, the mechanical structure of the open assembly can be
quite complex and can cause simulation problems. It may be more realistic to measure
the open’s response using TRL or offset short calibration techniques where opens are
not employed as calibration standards. The measured results are then curve fitted to a
third order polynomial capacitance model. (2B.8)
At low frequencies where the capacitance is reasonably linear, it may be modeled as an
extra delay term. (2B-9)

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