ant ground plane

I am an newcommer to CTS MWS and this kind of microwave simulating stuff.

Now I am trying to design an differential antenna for an 2.4G RFID chip. In single-end antenna feed mode, I simplely connect the excitory port pin to ground and ant feed point, but for differential antenna, I connect the port directly to antenna's dual input. How should I do to cop with the large area copper foils as ground plane? just left them floating and unconnected?