Dual-Band Second-Order Frequency Selective Surface With Sharp Roll-Off Using Aperture-Coupled Techniques

This research article presents the design and development of a dual-band, second-order bandpass frequency selective surface (FSS) characterized by sharp roll-off behaviour. The investigation begins by analyzing the dual-mode response using a circular patch resonator embedded with a diagonal triangular slot. To minimize cross-polarized reflections produced by these modes, four identical resonators are configured with a 90° rotational orientation. Thereafter, a FSS is developed to achieve dual-band bandpass performance using a multilayer aperture-coupled (AC) design. The designed FSS achieves good flexibility in realizing dual-band filtering characteristics when compared to conventional AC FSS. The effectiveness of the proposed design is confirmed through validation of electric and magnetic coupling within the patch resonators. Moreover, a lumped-element equivalent circuit model is developed, and performance is carried out using the even and odd mode analysis. The designed prototype of FSS undergo measurement verification, exhibiting polarization-insensitive performance and angular robustness over incident angles ranging from 0° to 40°. The structure consistently maintains stable resonant frequencies across both transmission bands, featuring pronounced transition with sharp roll-off characteristics.