Yes, thanks for the suggestions. Primary pattens of the feed horn show 10-12dB edge taper at the half angle. Just what you expect. I haven't look at the intercardinal planes but that's a good idea. Did you determine how the "odd mode" was generated in your antenna? When you say "odd mode"...
I'm currently going through a similar problem with a center feed axial-symmetric antenna. The issue is that gain calculated using 3dB and 10dB beamwidth (AZ,EL cuts in E and H-planes) are 1.0 to 2.0 dB higher than boresight gain referenced using a std. gain horn. I've taken the antenna to a...
