Abstract: An orthogonally-polarized microstrip patch radiator feed structure comprising a cavity of circular cross section, a microstrip radiation emitter including a first ground plane at the bottom of the cavity, a first non-conductive substrate overlying the first ground plane, a circular conductive transmit patch on the first substrate, and a first input line on the first substrate extending radially to the transmit patch, and a microstrip radiation receiver, including a second non-conducting substrate overlying and spaced from said first substrate, a second ground plane on the inner surface of the second substrate in the form of a first array of spaced parallel conductive bars orthogonal to the radius of the first input line, a circular receive patch on the outer surface of said second substrate in the form of a second array of spaced parallel conductive bars aligned with the bars of the first array, and a second input line of the second substrate connected to the receive patch and extending radially in a directio