Hi there,
You have to supply some more details:
- Antenna type and gain
- size of the surface
- position of the antenna on the surface
For example if you are talking about a sattelite dish (high directivity) that is pointing to the sky you won't have a problem.
On the other an antenna that has low directivity would interact much more with it's surrounding.
Heylal
RF-Link
http://www.rflinkcalc.com