more than one antenna in cst (mesh problem)

Hi, i have a problem with cst 2011.
I'm trying to simulate two simple patch antennas in open space (@ 2.45 GHz).
The antennas are placed in a room (air) and the distance of the one from the other is about 2 meters.
Now, i need to increase the mesh around the antennas but decrease it in the rest of the free space but i don't know how can i do this.
Can you help me ?
Thank you!

I think you can chose your object and then use
Local mesh properties and Maximum mesh step width to do this.

Thank You!

You can use simple equations, instead of EM simulation:
Path loss - Wikipedia, the free encyclopedia
Path Loss in free space attenuation calculator