# How can I derive modeled phase (at connector) from cal kit definitions?

Question asked by cmains on Aug 30, 2016
Latest reply on Sep 8, 2016 by drkirkby

With Keysight 85052D cal kit definitions in hand, how can i mathematically determine the modeled phase of a coaxial open and/or short at the connector, rather than at the end of the offset?

I have Keysight measurement data for my 85052D which gives nominal values for modeled phase, so i know what sort of results I should be getting. However my calculations are a little bit off and I don't know why.

I've attached an excel spreadsheet with my calculations. I'll give a breakdown here of my steps:

Where f is frequency in Hertz, C is capacitance, PI is 3.14...;

Capacitance coefficients are computed like so: C = C0+C1*f+C2*f^2+C3*f^3

Phase from capacitance is computed like so: ATAN(C / ( -1 / ( 50*2*PI*f ) ) ) * 2

Phase from delay is computed like so: -(delay)( 360 * f ) * 2, Where delay is 29.243ps

Total phase that should be measure at the connector end is the sum of phase from capacitance and phase from delay.

...Except that its not... my results using these calculations do not precisely match the nominal values found on the cal cert. My only guess is that the offset loss coefficient should be involved somehow. If that's the case, then how do I determine a phase component from the offset loss coefficient?