CST - TIME DOMAIN PULSE ANALYSIS IN ANTENNA APERTURE

How can I perform time domain pulse analysis on the antenna aperture using CST Studio Suite  ? I need to do the  surface equivalence method and have to apply a pulse to my antenna, I have my new pulse equation which I want to apply on the aperture of the antenna to check the time average Poynting power, How can I use CST for this time domain analysis of pulse?