Meniscus-lens-corrected corrugated horn: a compact feed for a Cassegrain antenna

The physical size of a corrugated conical horn feed having narrow beamwidth can be reduced considerably by correcting the spherical phase front in the aperture using a meniscus lens. Measured and calculated radiation characteristics of such lens-corrected scalar horns are presented. It is shown that the horns can provide efficient aperture illuminations when used as feeds for conventional Cassegrain antennas, for example radiotelescopes. Further, it is shown that the high crosspolarisation, which is normally present in lens horn designs, can be reduced to that of the horn itself by corrugating the lens surfaces with holes. Improved design formulas for such holes are given.