A Wideband Dual-Circularly Polarized Inverted Quad-Ridged Elliptical Waveguide Horn Antenna

This letter presents a balanced-feed circularly polarized inverted quad-ridged elliptical waveguide horn antenna with a low-axial ratio (AR) and elliptical radiation pattern. A wideband single-mode operation in dual polarizations is achieved based on initial analysis of the modes and field patterns within the inverted ridged elliptical waveguide, which is essential for achieving a broadband low AR. Furthermore, a slotted ridge is proposed to elegantly adjust the phase relationship between the two polarizations over the entire operating frequency range in response to the nonlinear variation in propagation phase velocity with frequency caused by elliptical nonrotational symmetric structures. The fabricated antenna exhibits a 66.7% relative bandwidth from 4 GHz to 8 GHz with an AR < 2.6 dB, reflection coefficient < -17 dB, and isolation > 35 dB for dual circular polarizations.