Ultra-wideband circularly polarized cavity-backed crossed-dipole antenna.

This letter demonstrates an ultra-wideband circularly polarized cavity-backed crossed-dipole antenna. It consists of a modified crossed-dipole and a modified cavity. Each arm of the modified crossed-dipole is mainly made up by the combination of a triangle and a fan-shaped sector, and the arms within the same layer of substrate are connected by a vacant-quarter ring. The modified cavity is composed of a rectangular cavity, four coupled rotated vertical metallic plates, and four sequentially rotated metallic steps. Through combining the modified crossed-dipole and modified cavity together, ultra-wideband characteristics in terms of - 10-dB impedance bandwidth (IBW) and 3-dB axial-ratio bandwidth (ARBW) can be realized. The IBW and ARBW are correspondingly calculated to be 128.9% and 121.2%. The prototype of the proposed antenna was fabricated and measured. The proposed antenna has a compact size of 0.74 λ × 0.74 λ × 0.17 λ (λ is the wavelength at the lowest frequency of operation band). The measured IBW and ARBW are 125.2% (1.67-7.26 GHz) and 120.1% (1.79-7.17 GHz), respectively, which are in good agreement with the simulated ones. The proposed antenna has stable radiation patterns in the operation band and exhibits a right-hand circular polarization with a peak gain of 12.2 dBic at 6.7 GHz.