A low cross-polarization circularly polarized spacecraft TC&R antenna

A spacecraft TC&R antenna provides telemetry, command, and ranging operation throughout all mission phases after launch vehicle separation. An ideal TC&R antenna should provide an omnidirectional pattern. In practice, an omnidirectional pattern is approximated by a cardioid pattern. Such cardioid patterns can be generated by a slotted-ring antenna, or a conical spiral antenna. There are two disadvantages associated with the slotted-ring, or the conical spiral antenna. These two disadvantages can be overcome by using a multiple-element TC&R antenna system. Such a system uses at least two identical antenna elements to provide the required coverage. The most commonly used antenna component is the open-end waveguide antenna with a septum polarizer. These antenna components were derived from the INTELSAT-V Hemi/Zone antenna feed array elements by chopping off the flare section in order to broaden the beam. A detailed configuration of the antenna is illustrated. However, the axial ratio performance for such an antenna in the diagonal planes (45/spl deg/ and 135/spl deg/ cuts) is generally poor. This paper presents a technique which utilizes a simple mechanism to improve the axial ratio performance (at 4 and 6 GHz) for such an antenna in the diagonal planes to a value better than 5 dB at /spl plusmn/70/spl deg/ from the antenna boresight.<
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