Cavity-backed, micro-strip dipole antenna array

An antenna system particularly adapted for mounting flush with the skin surface of a reentrant air/space vehicle, to generate selectable sum and difference, circularly polarized radiation patterns from an aperture substantially flush with said skin surface comprising:

• a conductive cavity of substantially square cross-section in a plane parallel to said skin surface and of uniform depth internal to said vehicle, said cavity providing an aperture substantially at said flush mounting at said skin surface;
• first means within said cavity comprising a pair of dielectric boards each in a plane normal to said cavity cross-sectional plane, said boards each fitting between opposite corners of said cavity and intersecting orthogonally substantially at the center of said cavity;
• second means comprising a plurality of printed circuit dipoles, located two to the broad surface of each of said boards, one on either side of said board intersection;
• third means comprising a printed circuit feed trace on the opposite side of said dielectric board from each said dipoles, said traces each feeding a corresponding dipole through said board dielectric;
• fourth means comprising an external connection for each of said feeds to facilitate independent excitation control for each of said dipoles;
• and fifth means comprising a first four-port hybrid connected from two orthogonally adjacent dipole feeds of said third means to provide a first combined signal, a second four-port hybrid connected from the two remaining dipole feeds of said third means to produce a second combined signal, and a four-port comparator hybrid connected discretely at two of its ports to said first and second combined signals, said comparator hybrid also having .SIGMA. and .DELTA. ports such that selective excitation of one of said .SIGMA. and .DELTA. ports produces a corresponding antenna pattern.