A Single-Layer Wideband CP Filtering Reflectarray With Wide Out-of-Band Rejection via Intrinsic Orthogonality of CMs

This article proposes a novel design method for a circularly polarized filtering reflectarray (CPFRA). The method first exploits the inherent orthogonality of characteristic modes (CMs) to convert circularly polarized (CP) reflection responses into the modal characteristic angle difference ($\Delta $CA) of the reflecting cell. The$\Delta $CA is then correlated with the modal resonance frequency difference ($\Delta f_{\mathrm {res}}$), which can be effectively tuned via characteristic mode analysis (CMA). With the aid of CMA, multiple appropriate$\Delta f_{\mathrm {res}}$are obtained to synthesize the desired CP filtering reflection response. For next-generation low-Earth orbit (LEO) satellite applications (e.g., Starlink), three design strategies for the wideband CPFRA with wide out-of-band rejection are further formulated using the proposed method and applied to a single-layer right-triangular patch reflectarray (RA) cell. By adjusting the locations of six grounded vias loaded near the three edges of the cell, multiple modal current path lengths are modified to obtain the target$\Delta f_{\mathrm {res}}$. Ultimately, the fabricated RA exhibits a 3-dB gain bandwidth of 28.86% and a 3-dB axial ratio (AR) bandwidth of 32% in the passband, along with 15-dB rejection bandwidths of 37.92% and 33.84% in the lower and upper stopbands, respectively. These results validate the effectiveness and feasibility of the proposed design method and strategies.