infinite wall with PML boundaries

Hi to everyone!

I have to simulate with hfss an infinite wall of a given material next to a radome structure (with an antenna inside) wich I already have designed. (the basic idea is to study the behaviour of an antenna inside a radome and with the radome structure fixed on a wall)

I tried to apply a PML boundaries to the face of the radome wich is in touch with the wall but i had a couple of problems:

-i have to give a finite depth to the PML block (i would like to be infinite).
-the 2 dimension of the PML block are exctly the same as the face of the radome. And I would like to be infinite or at least larger in high and length.

Am i doing something wrong?
Any suggestion?

Thanks for your help.