Periodic antennas

I am simulating far field pattern of periodic gold discs over glass substrate. For that, I am simulating a unit cell for scattered field with plane wave as background. ( I am working with COMSOL 4.3a) My major problem is how to place the far field boundary for this case. Do I need to include those boundaries which include floquet periodic conditions. Do I need to include PMC wherever I have floquet boundary conditions?

Thanks in advance

Adarsha