In this letter, we design a circularly polarized (CP) waveguide aperture antenna with a wide axial ratio bandwidth (ARBW). The unit is composed of three waveguides with different rotation angles and width. The reflected and transmitted orthogonal electric fields are superimposed on the asymmetric plane of the rotating structure in each layer, which not only reduces energy reflection but also promotes the decomposition of the electric field with the same amplitude and the phase difference 90° in different rotating waveguides. Finally, a circularly polarized electric field is formed on the antenna's surface. The phase difference and amplitude difference of orthogonal electric field a e approximately 90° and less than 1.2 dB, respectively. In addition, the different width of the waveguide plays a role in impedance matching. A 2 × 2 array is fabricated and measured to verify the validity of the design. The measured results shows good agreement with the simulation. Measured impedance bandwidth of 37.9% (27.5-40.4 GHz), axial ratio (AR) bandwidth of 41.2% (27-41 GHz), and a gain of 15.7 dBi at center frequency have been obtained.

A dual-band dual-linearly polarized waveguide slot array antenna is proposed in this paper. Two orthogonal slots share a short-circuit wall on broad side. The horizontal and vertical slots, which actualize dual-frequency bands and dual-linear polarization, generate vertically polarized electric fields in 9.39–9.78 GHz and horizontally polarized electric fields in 11.62–12.3 GHz, respectively. The equivalent permittivity of the waveguide is changed by two grooves at the bottom of the waveguide, which improves phase velocity. Two grooves can also reduce the distance between the elements while suppressing the side lobes. Compared to filling the medium in the waveguide, two grooves have less losses. Moreover, the antenna is simple with one input port. The array antenna also overcomes the problems of beam scanning compared with the traditional waveguide slot array antenna. A 1 × 8 antenna array is fabricated and measured to verify the design. The horizontal polarization is formed in 9.39–9.78 GHz, the vertical polarization is generated in 11.62–12.3 GHz, and the antenna gain can reach 15 dBi.

In this study, a novel broadband circularly polarised waveguide slot array antenna with a wide axial ratio bandwidth is designed. The circular polariser is excited by the waveguide radiation linear polarised antenna, whose end is bent by 90° and generates a circularly polarised electric field. The matching waveguide between the slot and the polariser improves impedance matching. Furthermore, the structure with the added waveguide changes waveguide impedance, which can be used to realise impedance matching, and reduces the spacing between the units. In this study, a 4 × 4 antenna array is fabricated. The measured results reveal that the array achieves −10 dB impedance bandwidth of 27% (11.15–14.63 GHz) and the 3 dB axial ratio bandwidth of 23% (11.48–14.52 GHz). An aperture efficiency higher than 71% is obtained, with the maximum gain of 22 dB. The antenna side lobes levels are less than −13 dB in the operating bandwidth.

A novel wide 3-dB axial ratio (AR) circularly polarized 2 × 2 array antenna is proposed in this paper. The spindle-shaped coupling cavity with tilted waveguide is capable of generating circular polarization waves from incident linear waves, which improves the AR bandwidth (ARBW) of the antenna. With this structure, a similar amplitude of the two orthogonal transmitted wave components and a stable phase difference of nearly 90° can be generated. The circularly polarized antenna proposed herein has been fabricated. According to the measurement results, the operating bandwidth from 5.32 to 6.13 GHz is <−10 dB. In addition, the measured ARBW, which is below 3 dB, can cover the range of 5.41–6.02 GHz. The maximum gain of the antenna can attain 15.65 dBi, and the efficiency is better than 80%.