Design Pyramidal horn antenna Using HFSS

Specs:
freq= 2.8Ghz
wave guide dimension
a=86mm
b=43mm
power = 15 dbm
plz help me design it plzz
I hav tried it like a 100 times but something always goes wrong like directivity, gain or freq. I m in real trouble my FYP submission is due next month and i m stuck with this. Please if someone has the design or someone is an expert in hfss please help Sir.
Thanks You

Here is a hfss model which you might find useful for your specifications : WR340-2.8G.hfss.zip

The photo below is a summary of the design parameters.

Sir thnx for ur time n reply
i have already made the design with these specs.
And it produces all the right results untill i insert the probe.
the gain then drops from 12.7 to -4.
i can send u the file if u like.
thanx in advance

I have attached my design file. And to move the probe along easily parameters are
UD for x-axis
PS for z-axis
Plz Plz Plz help i need it..

I have attached my design file. And to move the probe along easily parameters are
UD for x-axis
PS for z-axis
Plz Plz Plz help i need it..