Calculated and measured radiation characteristics of a Torus antenna above a conducting plane

Some properties of a torus receiving antenna at the primary focus of a radio telescope have been theoretically and experimentally investigated. The torus has a major radius of 10.2 cm, a minor radius of 1 cm, is mounted in front of a metallic plate 1 m in diameter, and is capacitatively coupled by a small plate to the coaxial feed line. The studied frequency range is between 460 and 538 MHz. The theoretical treatment uses Wu's (1962) integral equation for the antenna current and spherical harmonics expansions for the radiation field from King and Smith (1981). The agreement between measured and calculated field patterns is good to fair in the H-plane, but is poor in the E-plane. The return loss shows very narrow dips at 575, 1025, and 1460 MHz for the first three resonances.