Impedance Calculation in cst

how can i calculate the impedance at any point of the model using CST?
for example:
in case of designing FSS or metamaterials onto lossy substrate, i need to calculate the total impedance of the model, or calculate the impedance of the surface, so is it possible to calculate it and how?

Input impedance of what mode? A normally incident plane wave?
You can always calculate input impedance from (de-embedded) S11. I don't have CST, but I imagine this is pretty straight forward.

i dont know the modes but i simulate the FSS printed onto lossy substrate with PEC ground plane and want to calculate the total impedance. the incidence may be normal or oblique, but i want to know how?

Input impedance (or any other type of impedance representation, such as an impedance network) will depend on the properties of the observed mode(s). Figuring out which modes you're talking about is step number one.

Thanks for your replay,
it is known for the TL to extract their modes, but any other configuration of structures, i think it is not easy.
so how can i know the modes of any structure?

I am not sure about your problem but in CST you can use post processing tools to calculate impedance along a line for a particular material- Q value and losses can also be directly calculated. I have used these techniques for cavity simulations but not sure if this can help in your case