A Synthesis Approach for Enhancing the Aperture Efficiency of Wideband Reflectarray Antennas

This letter presents a novel synthesis approach, which can improve the aperture efficiency of wideband reflectarray antennas. It comprises two key components: unit cell structure optimization and array distribution calculation. In the unit design, this method employs intelligent optimization algorithms and utilizes multiparameter joint optimization to enhance the consistency of the reflection phase in the ultrawideband. The planar folded dipole unit is employed, offering ultrawideband capabilities while maintaining a low profile. For wideband phase calculation, it comprehensively considers the varying contributions of reflection phases at different frequency points, resulting in the more rational allocation of weighting values. A prototype of the broadband reflectarray is fabricated and measured to validate the proposed method. The reflectarray achieves a gain greater than 18.1 dBi and an aperture efficiency exceeding 36.2<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> over the frequency range of 4 GHz to 10 GHz. The maximum gain and aperture efficiency reach 25.0 dBi and 51.3<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula>, respectively. The design approach proposed in this letter addresses the limiting factors of reflectarray bandwidth from two dimensions: unit cell structure and array phase distribution, which provides a new perspective for designing reflectarray antennas with high aperture efficiency in ultrawideband.