Circularly Polarized Waveguide Aperture Array Antenna With a Wide Axial Ratio Bandwidth

Abstract

In this letter, we design a circularly polarized (CP) waveguide aperture antenna with a wide axial ratio bandwidth. 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> in different rotating waveguides. Finally, a CP electric field is formed on the antenna’s surface. The phase difference and amplitude difference of orthogonal electric field are approximately 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> 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 show good agreement with the simulation. Measured impedance bandwidth of 37.9% (27.5–40.4 GHz), axial ratio bandwidth of 41.2% (27–41 GHz), and a gain of 15.7 dBi at center frequency have been obtained.