example waveguide feko

I've spent some time searching the web for an answer to this question and this forum seems like the best place to ask. I'm trying to feed a waveguide using Feko 5.0, but I can't seem to get any decent matching. My S11 measurement is always around .98 or higher. I've tried a lot of different combinations with no luck. Even the example model for the waveguide fed horn antenna, when you calculate the S-Parameters has an extremely high reflection. Any help would be greatly appreciated if anyone has any ideas.