A Miniaturized Low-RCS Active Frequency Selective Surface With Passband Tunability and Out-of-Band Diffuse Scattering

In this letter, a novel active frequency-selective surface (AFSS) featuring a wide-range tunable passband and an ultrawide radar cross-section (RCS) reduction band based on diffuse scattering is proposed. The proposed AFSS consists of a top chessboard polarization conversion metasurface (CPCM) with chip resistors loaded, a bottom bandpass frequency-selective surface (FSS) with embedded varactors, and an intermediate dielectric substrate. The key innovation of this work lies in the integrated design of a tunable FSS and CPCM on a single substrate. Crucially, the CPCM not only realizes wideband RCS reduction but also serves as a DC biasing network, directly driving varactors through the metal vias connecting the two layers. The relationship between insertion loss (IL) and structural parameters is systematically analyzed based on the equivalent circuit method, and the menderline technique is accordingly applied to minimize IL. The simulation results show that the proposed AFSS can achieve a continuous tunable passband from 1.4 to 4 GHz with an IL of 0.6-4.67 dB. Meanwhile, a 10-dB RCS reduction band covering 7.8-18.4 GHz with a fractional bandwidth of 80.9% can be realized. To validate the design, a 16×16 prototype is fabricated and measured. The measured results align closely with the simulated ones. The proposed AFSS yields great potential in the radar stealth radome applications.