# Fringing Capacitance Error Correction

Question asked by SOLT_guy on Jul 26, 2009
Latest reply on Aug 5, 2009 by daveb
I use SOLT calibration methods.

My network analyzer manual states that the open standard fringing capacitance equation is:

C = C0 + (C1 * F^1/Hz^1) + (C2 * F^2/Hz^2) + (C3 * F^3/Hz^3)

I am seeking to calibrate out the residual fringing capacitance from NA - the frequency range is 300K to 3GHz.

Application notes direct me to make a 1 Ghz admittance measurement and input that value into my open cal kit definition as the CO term.

The manual states that the C0 term is scaled by 10^-15 farads.

Is it correct to input the B term in femto*Farad units as the C0 term for my open cal kit definition?

I would like to know how the NA processes this data.   From a purely mathematical analysis of cubic polynomials, the C0 term is a horizontal line if all other terms are equal to zero.  If I input a positive non-zero value for C0 into my cal kit but my open standard's true admittance, "raw data", at 300Khz is zero,  what will I see on my Smith chart at 300Khz after calibration?  Similarly, at 3 Ghz, if my open standard's true admittance is minus 1.5  (the fringing capacitance has increased at 3 Ghz) times whatever was input as C0 into my open cal kit , what will I see on my Smith chart at 3Ghz after calibration?

When one has to calibrate a network analyzer above three GHz, all the other cubic polynomial coefficients become relevant, my manual states that:

C1 is scaled by 10^-27

C2 is scaled by 10^-36

C3 is scaled by 10^-45

Can you please elaborate upon how these scaling terms came to be and how one should interpret them with respect to inputting the correct values into my open cal kit definition?

Can you please send me mathcad file which has modelled the fringing capacitance of an open standard (I have found no application notes which have specified numerical examples)?