Need help with Pyramidal Horn Antenna Design

i've simulated a pyramidal horn antenna using dimensions from balanis' design procedure through the antenna designer kit. now when i try to excite the antenna with a simulated sma connector, i'm getting completely wrong return loss results ... what am i doing wrong?

It would be worth stating in the title what software you are using, since nobody has a clue unless they download the rar file.

OK, so after looking I can see it's HFSS. I would suggest two things.

1) When posting an example, don't have a load of frequency points so it takes ages for someone to run.
2) It would be worth uniting the coax_pin and feed_pin. They seem to be joined, but not united, which might, with numerical errors means HFSS is not considering them joined. Just one thought - others might have other ideas.