Design of Left-Hand Circular Polarization Ultra-Wideband (UWB) Horn Antenna

Horn antenna has the advantages of simple structure, large power capacity and high gain. The ridge structure is mainly used to expand the effective operated bandwidth of the horn antenna. Dual-ridged and quad-ridged horn antenna structures are proposed in many papers. In order to meet the actual needs, the circular polarization radiation can be realized by combining the ridge horn structure with the hybrid structure. This paper proposes a quad-ridge conical horn antenna structure. The horn structure mainly consists of four parts: the coaxial connectors, the back cavity, the horn flared section and the ridge structure. There are two coaxial feed structures: one for vertical polarization and the other for horizontal polarization. In order to ensure that high order modes are not introduced, the length of the horn should be longer than half the maximum operating wavelength. The quad-ridge section is used to match the characteristic impedance, allowing a smooth transition of the feed structure into the free space. The ridge structure realizes the UWB characteristics. The hybrid structure provides 90 degree transmission phase difference. Finally, the combined structure can achieve left-hand circular polarization radiation. The operation frequency band is 2-18GHz, the VSWR results are less than 1.5, the gain results are 14dB Typ., the axial ratio results are 3dB Max. and the radiation pattern results are stable during high frequency band.