Hi, KBmani:
I assume you know how to simulate a probe-fed antenna on IE3D. Assume you have a probe fed antenna with a diode. What you should do is the following.
1. Build 2-ports to represent the probe-feed and the diode.
2. Simulate it.
3. On current distribution or radiation, you should specify the excitaiton for the 1st port or the one representing the probe-feed. For the 2nd port, you should specify no excitation, and an impedance to represent the on or off state. Then, your result is the case for your structure with the diode on or off.
Bset regards,