Design of <i>N</i> th-Order Frequency-Selective Polarization Rotation Reflective Surface Based on Transversal Coupling Topology

This article presents the principle, design, and implementation of the Nth-order polarization rotation reflective surface (PRRS) with high-frequency selectivity based on the transversal coupling topology. The transversal coupling topology allows all the radiative resonators of PRRS to couple to the free space simultaneously. All the resonators are simultaneously excited by the linearly polarized (LP) incidence and reradiate the LP reflection wave with 90° polarization rotation. As a result, the overall frequency response of the PRRS is the superposition of the counterparts of all the resonators. For an Nth-order PRRS, up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N} - 1$ </tex-math></inline-formula> cross-polarization reflection zeros can be achieved using N resonances in the transversal coupling topology. These N resonances can be realized by either single-mode or multimode resonators. Two second-order PRRS designs have been presented to verify the operating principle of PRRS and show the advantages of this design method. Then, the design guideline of the transversal PRRS has been drawn. Furthermore, the three X-band transversal PRRS prototypes exhibiting the third-order, fourth-order, and fifth-order quasi-elliptic bandpass frequency response have been presented. The cross-polarization reflection zeros can be found at both the lower and upper stopband of PRRS, leading to the high roll-off frequency response. To minimize the size of the PRRS unit cell, the dual-mode and triple-mode rectangular ring resonators have been utilized in the three PRRS designs. Good agreement between the simulation and measurement has been obtained by these PRRS prototypes, validating this proposed PRRS design method based on the transversal coupling topology.