A Waveguide Antenna With Bidirectional Circular Polarizations of the Same Sense

Abstract

A square-aperture metallic waveguide antenna with bidirectional circularly polarized (Bi-CP) radiations of the same sense is proposed in this letter. Circular polarization was realized by two identical rectangular metal strips installed on one lateral side of the waveguide with a 45 $^{\circ}$ inclination angle. The two rectangular metal strips were vertically separated by a distance of a quarter guided wavelength and horizontally intersected with an angle of 90 $^{\circ}$ . They were excited with the same amplitude and phase by feeding the antenna in the middle of their diagonal line. A 90 $^{\circ}$ phase difference between the two rectangular metal strips was introduced by the spatial distance of a quarter guided wavelength, and thus circular polarizations of the same sense in the two opposite radiating directions were generated. A quarter-wavelength impedance transformer was designed to help with the antenna's matching characteristic. The measured impedance bandwidth for $\vert { S} _{11} \vert \le -10 ~$ dB was 710 MHz (1.92 $\,\sim\,$ 2.63 GHz), and the measured 3-dB axial-ratio bandwidth was 200 MHz (2.34 $\,\sim\,$ 2.54 GHz). The measured bidirectional 3-dB axial-ratio beamwidth at 2.44 GHz was 62 $^{\circ}$ , and the power variation was smaller than 3 dB within this angular range.