Help!!! Leaky wave antenna-Simulation in HFSS9.1

The leaky-wave antenna I have to design consists of an open wave-guide. Do I use the PerfectH boundary condition for the aperture of the wave-guide in this version of HFSS? Please help, my results are disappointing!

Without seeing the geometry, it's hard to answer your question.

I've studied leaky wave modes in striplines and microstrips in HFSS 9.1. For these cases I had to use PML's to get the leaky mode. All other boundaries either reflected the leaky mode making it impossible to isolate the physics or did not allow the leaky mode to exist.