Capacitance from S parameters

If you can determine an RC time constant, and if you find out effective neighboring resistance, then apply the standard formula to calculate C value.

If you obtained s-parameters, you have to know how to extract Impedance.Since the impedance is known, the capacitance/inductance is also known..

The above responses have not asked a simple question: the capacitance of what? Please provide a circuit model.

Im trying to design a SOI MUMPS RF varactor for Ka-band applications