Cassegrain-type feed for an antenna

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 formed as an integral part of the cone at 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 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.

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 an outer flared surface, a small-diameter end and a large-diameter end, the small-diameter end adjoining the waveguide end-portion, the outer flared surface having a series of corrugations;
• 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 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.

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 dielectric 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 a dielectric sleeve received in the waveguide end-portion, 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.

A parabolic antenna arrangement, comprising:

• A) a parabolic reflector having a central portion, and
• B) a cassegrain-type feed passing through the central portion, the feed including:
• 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 dielectric 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 a dielectric sleeve received in the waveguide end-portion, 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.