A novel dual mode circular waveguide horn antenna

Horn antennas have been used in diverse applications in communication systems, electromagnetic sensing, radio frequency heating, and antenna measurement, as well as feeds in lens and reflector antennas [1]. The application of pure-mode horn antennas is limited to array elements because of their poor electrical characteristics. In symmetric reflectors, an optimum feed must provide symmetric field patterns for both the field amplitude and phase to optimize the gain performance [2]. The corrugated conical horn is an example of this optimum feed [3]. Another example is the multimode horn antenna. Potter [4] designed a dualmode horn antenna to provide low sidelobe levels and symmetric patterns. Koch designed a multimode coaxial feed to optimize the spillover and the aperture efficiency of reflector antennas [5]. The applications of multi-mode horns are not limited to feeds in symmetric reflectors as the higher order modes can be appropriately combined to illuminate an offset reflector antenna to cancel or decrease the crosspolarization level, as reported in [6–8].