Ultra-Broadband Dual Mode Horn Antenna with Low Sidelobe Level and Axisymmetric Pattern at K-Band

In this paper, a method of broadening the bandwidth of dual-mode horns by loading multi-ladders is proposed. Based on this method, dual-mode horns are designed in this paper. The horn antenna works at 17-25 GHz and the relative bandwidth is 38%. The sidelobe level is less than -24 dB in the whole working frequency band, and the axisymmetric far-field pattern is obtained. The cross-polarization is consistently maintained below -20 dB, The antenna's gain is from 17 dB to 22 dB. The axial ratio is lower than 1.5 dB. At the same time, through theoretical and numerical calculation, the reason for the low sidelobe and axisymmetric pattern of the circular dual-mode horn is given, that is, when the TE11 mode and TM11 mode in the dual-mode horn are mixed according to a certain power ratio and phase difference, it can be considered that the electric field amplitude of the horn aperture presents Taylor distribution in the radial direction and uniform distribution in the circumferential direction. According to the relationship between the aperture electric field and the pattern, the pattern shows the performance of low sidelobe and axial symmetric.