A Broadband Circularly Polarized Microstrip Antenna Based on Polarization Conversion

This paper proposes a broadband circularly polarized microstrip antenna based on linear-to-circular polarization conversion. The polarization converter consists of two layers of radiating structures, both made of metasurfaces with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$4 \times 4$</tex> rectangular patch arrays cut at a 45° angle, with slightly different sizes. By employing SIWprobe hybrid feeding, the antenna impedance matching is significantly improved, achieving bandwidth broadening. After simulation optimization, the final results show an impedance bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$38.1 \%(23.4-34.4 \text{GHz})$</tex> for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{S} 11&lt;- 10 dB$</tex>, an axial ratio bandwidth of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$29.3 \%(25.6-34.4 \text{GHz})$</tex> for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{AR}&lt;3 ~\text{dB}$</tex>, a gain greater than 8 dBic, and a maximum gain of 12 dBic. The polarization is left-hand circularly polarized. The antenna features a simple structure, small size, lightweight design, low cost, easy fabrication, and high integration feasibility.