Impedance of horn antenna?

Hi Fellows,

can somebody tell me how to calculate the input impedance of a Pyramidal horn antenna. how can the mismatch b/w the horn and coax cable is minimized. Secondly the horn I designed shows a big back lobe where as in the antenna thoery books there are no back lobes associated with horn antenna. If back lobes exists in horn how to minimize those backlobes( electroplating on the inside with a certain metal can help it or not ). provide me some useful links where i can get this required stuff or information. waiting an early reply.
regards

Hi there, I could almost take poison on the fact that every antenna type has a backlobe.
Else antenna engineers who design military radars would choose the horn antenna, since one of their biggest problem are how to minimize the side and backlobes.

Kindest regards,
StoppTidigare