Investigation of a 90-deg corrugated horn

The paper analyzes a 90-deg corrugated horn with a structure having a finite number of annular slots in the flange and excited by the TE(11) mode in a smooth-wall circular waveguide. It is assumed that the electric field is zero everywhere in the aperture plane except over the finite number of apertures comprising the feed waveguide and the short-circuited annular slots, implying that the complete structure is embedded in an infinite ground plane. The measured and computed E- and H-plane patterns of the feed with three annular slots is illustrated, and the correlation between the computed and measured results is found to be extremely good, except in the vicinity of the 90-deg angle in the E-plane. This discrepancy is shown to be a direct consequence of the finite size of the flange, and it is noted that the discrepancy can lead to large errors in the computed crosspolar performance of the feed at wide angles due to the noncircularity of the beam in the affected regions.