A rotating mode radial line slot antenna fed by a cavity resonator

The radial line slot antenna (RLSA) is high gain and high efficiency planar antenna proposed for DBS subscribers. It is a kind of slotted waveguide array with very small conductor loss and high predicted efficiency. An efficiency of 80-87% has been realized for RLSAs with the antenna diameters of 30-60 cm at 12 GHz. A key difficulty is the aperture efficiency reduction by the rotational asymmetry due to the spiral arrangement of the slots for the RLSA. In a small sized antenna, the antenna efficiency is reduced by the propagating mode distortion due to the large slot coupling. The rotational symmetry of the field in the oversized waveguide, such as radial line, should be carefully maintained. We propose an RLSA with a concentric arrangement to keep the rotational symmetry. The feed circuit for this RLSA consists of a cavity resonator excited by a feeding pin which radiates a rotating mode in the radial-line waveguide. The basic design of a concentric array type RLSA is presented and some experimental results are included.