Flexible Dual-Band Ultrathin Frequency Selective Surface With Polarization Independence, Angular Stability, and Bending Insensitivity

This paper introduces a novel ultrathin frequency selective surface (FSS) based on interconnected logarithmic spiral geometries. The structure is fabricated on a flexible polyimide substrate with a thickness of 0.05 mm, a relative permittivity of 4.3, and a low-loss tangent of 0.004. The unit cell design follows a pursuit curve forming a logarithmic spiral, with four spirals symmetrically connected at the center. Our proposed FSS exhibits stopband resonances at 3.5 GHz and 9.2 GHz, with bandwidths of 680 MHz and 1.8 GHz, respectively. Owing to the ultrathin substrate, the overall thickness is just 0.05 mm (0.0005λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub>, where λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength at the lower resonance). Simulated results show excellent agreement with experimental measurements, confirming the accuracy of the design. Moreover, the FSS demonstrates polarization independence, angular stability up to 45° for both vertical and horizontal polarizations, and maintains performance under bending, highlighting its mechanical and electromagnetic robustness.