Plural frequency patch antenna assembly

A microstrip patch antenna assembly (20, 52, 106) is formed of a patch radiator (24, 58) and a feed structure (26, 64) of microstrip feed elements (48, 50, 66, 68) disposed on opposite sides of a ground-plane element (22, 54) and spaced apart therefrom by layers (28, 30, 72, 74) of dielectric material. A single slot (108) or a pair of orthogonally positioned slots (44, 46, 82, 84) within the ground-plane element couples linearly or circularly polarized microwave power from the feed structure to the patch radiator. Additional radiators (60, 62) may be stacked above the foregoing radiator, the radiators being separated by further layers (76, 78) of dielectric material. A plurality of square-shaped radiators (58, 60, 62) may be employed for multiple-frequency operation in which case the radiator size and the thickness of dielectric material between the radiator and the ground-plane element establish a resonant frequency. A single radiator (24) of rectangular shape may be employed for radiation at dual frequencies wherein short and long edges of the radiator are each equal to one-half of the respective wavelengths in the dielectric material. An array (124) of the antenna assemblies can be constructed in monolithic form for development of a steerable beam of electromagnetic radiation.