A Flexible Multifunctional Active Frequency Selective Surface with Angular and Polarization Stability for Curved Surface Conformal

This article demonstrates a miniaturized flexible multifunctional active frequency selective surface (MAFSS) with excellent angular stability and polarization insensitivity. The proposed structure consists of two metal layers printed on a thin, flexible substrate to achieve curved surface conformal capability. The PIN diodes are welded on two metal layers. By independently switching the bias voltage of PIN diodes, four working states and two functions, including electromagnetic (EM) switching and polarization selection, are realized. The unit cell takes itself as a bias feeder to excite the PIN diodes, avoiding the negative impact of the additional feeding network on the overall performance. A spiral wire-based miniaturization technique is utilized to achieve excellent angular stability in the planar and conformal states. On this base, a double-layer symmetrical structure based on the via-connected metal strips is designed to realize polarization insensitivity. The miniaturized unit size can reach $0.082\lambda _{0} \times 0.082\lambda _{0} \times 0.005\lambda _{0}$ at the center resonance frequency. The flexible MAFSS prototype is measured in planar and conformal states. The measured operating bandwidth with a transmission coefficient difference greater than 10 dB is 2.8 GHz (5.2–8 GHz). The measured and simulated results have good consistency, demonstrating the effectiveness of the proposed structure.