Patent ID: 7023394

Claim:
A cassegrain-type feed for an antenna, comprising: a) a waveguide section having an end-portion, the waveguide section having internal dimensions which support a propagation of a fundamental quasi-TE 11 mode in lower and upper frequency bands; b) a dielectric cone having a small-diameter end and a large-diameter end, the small-diameter end adjoining the waveguide end-portion; c) a subreflector adjoining the large-diameter end of the cone; d) a multi-stage step transformer attached to the small-diameter end of the cone for matching an impedance of the cone to the waveguide section; e) the feed being a dual-band feed covering the lower and upper frequency bands; and f) the waveguide end-portion being provided at an inner wall thereof with a wall-impedance changing means comprising grooves formed in the inner wall of the waveguide section, and operative for changing an impedance of the inner wall to couple the quasi-TM 11 mode in the upper frequency band, to thereby achieve a rotationally substantially symmetric illumination of the subreflector in the upper frequency band.