Design of modified dual mode horn antenna to improve E/H-plane radiation pattern symmetry

Dual mode horn antenna is widely used in reflector antenna systems to illuminate symmetric E/H-plane radiation patterns to a reflector surface. Symmetric E/H-plane radiation pattern can improve the total gain of the reflector antenna system and allows a design of a reflector to be symmetric [1]. Dual mode horn antenna was developed by Potter [2] and many designs have been proposed to have symmetric E/H-plane radiation pattern [3]-[7]. The mode at the aperture of the dual mode horn antenna is hybrid mode (HE₁₁ mode) which consists of approximately 85% of TE₁₁ mode and 15% of TM ₁₁ mode [8] and the antenna radiates gaussian-like beam pattern, and therefore the E/H-plane radiation patterns are symmetric ideally. However, if the aperture size of a dual mode horn antenna is increased to attain the desired gain or beamwidth for the reflector antenna system, ideal HE₁₁ mode is difficult to be attained at the aperture because undesired high order modes which lead asymmetric E/H-plane radiation patterns are generated. In this paper, modified dual mode horn antenna with rectangular aperture is proposed to improve the E/H-plane radiation pattern symmetry in oversized aperture horn. Simulation and experimental results show that the proposed dual mode horn antenna has the improved E/H-plane radiation pattern symmetry compared to a conventional circular dual mode horn antenna.