Circularly polarized broadband antenna using waveguide and an L-shaped feed probe

This paper presents a circularly polarized broadband waveguide antenna using an L-shaped feed probe. Higher order mode (TM₁₁ mode) in the waveguide which prevents bandwidth enhancement is reduced by inserting the poles at the inside corners to expand bandwidth in axial ratio (AR). In this paper, the center frequency is changed close to the middle value of cutoff frequency between the dominant mode (TE₁₀/TE₀₁) and the second higher order mode (TE₂₀/TE₀₂) from the middle value between cutoff frequency of the dominant mode and the first higher order mode (TE₁₁/TM₁₁). In addition to this, the effect of additional poles is studied. Furthermore, the length of the waveguide aperture is adjusted to control the direction of the electric field near aperture. As the results, the AR bandwidth of the proposed antenna expanded to 54.4% (6.68-11.67 GHz) from 49.4%.