Phase center about microstrip antenna

Hey there,I want to know something about the phase center about microstrip antenna, such as how to calculate it , what of microstrip antenna can influnence it and how to consider it when you design microstrip antennas.

Thanks a lot!

the phase center is the radiated source of the antenna ,

many reason to affect it , like the structure of antenna itself ,

or the environment also can affect it..

to caculate the phase center is't easy , and it need NEC tools to

try many times ...