Microwave antenna system having enhanced band width and reduced cross-polarization

Claim 1

A microwave antenna system for producing when energized by a source of microwave signals, first and second simultaneously propagating beams of microwave radiation, said first beam being of left-hand circularly polarized radiation, said second beam being of right-hand circularly polarized radiation, comprising in combination: a curvilinear microwave-reflective surface defining a focal region within which parallel beams of microwave electromagnetic radiation impinging on said surface are brought to focus; and disposed within said focal region, a microwave feed array, said feed array comprising a plurality of waveguide feed elements disposed mutually adjacent to one another and commonly aligned to propagate microwave energy toward, and receive microwave energy from said reflective surface, each of said waveguide feed elements comprising a circular waveguide terminating in a circular aperture facing toward said reflective surface; and disposed about each of said circular apertures, inductive tuning means to selectively reduce mutual coupling between said adjacent feed elements, and to minimize cross-polarization between adjacent feed elements, whereby adjacent feed elements can be energized with signals of alternate polarization sense while substantially avoiding cross-polarization; said inductive tuning means comprising an inductive stub of generally U-shape, including a first leg, a second leg spaced from said first leg and generally parallel thereto, and a root portion extending between and interconnecting said first and second legs, at least one of said legs being of trapezoidal shape, having a greater width near the portion thereof adjacent said root portion and a lesser width at a tip portion thereof.