Reconfigurable Frequency selective reflectors

Can you help me to design a Reconfigurable Frequency Selective Reflector in HFSS.It is fed by the monopole antenna and the FSR plates are made up of copper.FSR acts as a reflector when the switch is ON and it acts as a transparent when the switch is OFF.For this i want some formulas like how to calculate impedence for the FSR and what should be the distance between the reflectors etc can you plz help me?