Finding Z21 using HFSS

I am trying to find the Z21 in HFSS for a modal of interdigital Capacitor which i have simulated. Can anyone tell me about Z21, Z12 parameter. Is it normalized to 50 ohm or not which HFSS is giving me? HFSS giving me img (Z21) = 63.154.
Please someone guide me. Thanks

If you know S-Parameters, you can transform them into Z-Parameters by using well known equations.

if i know Z parameter then how will i find the capacitance for interdigital capacitor in HFSS ?

C(Farad)=1/{2*PI*Imag[(z11*z22-z12*z21)/z21]}

Thank you so much. You did a great help for me.
Can i please get the reference for this formula of C(Farad) ? I will be grateful.

Dear Sir,

Can you please tell me the corresponding reference/link to this formula;

C(Farad)=1/{2*PI*Imag[(z11*z22-z12*z21)/z21]} ?

Please share it with me because i also have to mention the reference while explaining it. I will be grateful to you.
Thanks