Design of Angular Stability Dual‐Stopband Frequency‐Selective Surface With Tightly Spaced Frequency Response Characteristics

ABSTRACT With the development of electronic communication and wireless communication devices, some traditional multi‐frequency system designs are no longer suitable for closely spaced applications, so there is an urgent need to propose some new closely spaced frequency‐selective surface (FSS) designs. In this study, a novel dual‐stopband FSS design with closely spaced frequency response characteristics is presented. The structure resonates at 6.75 and 8.72 GHz with a frequency ratio of 1.29, features a compact unit cell size of 8.0 × 8.0 mm, supports TE and TM incidence angles up to 80°, and maintains low insertion loss at the transmission poles to ensure precise signal transmission. In addition, a novel closely spaced design approach is presented to reduce interference between neighboring resonances and improve frequency stability. By studying the surface current distribution and the equivalent circuit model, the correlation between the geometrical element parameters and the resonance frequency is thoroughly analyzed, and the design is optimized accordingly. Finally, a prototype FSS was fabricated and its superior shielding performance was verified in a microwave darkroom. The proposed FSS achieves lower frequency ratios, smaller cell sizes, and significantly improved frequency stability compared to previous designs.