z in of antenna in cst

i design a microstrip patch antenna how i can see in cst wether it is matched or not ?

Hi,
You can check by calculating port modes only to check the impedance. You can also check the return loss and if the value is at least below -10dB at your desired frequency, then the antenna is matched.

s11 is return loss?

i think, you don't know all parameter of microstrip antenna. you can read in7-ANTENNA FUNDAMENTALS .pdf
follow me, relation of all parameter as: S11, Z_anten, Z_feed. VSWR is parameter you need.