Multi-layer frequency selective surface wideband filter with high selectivity operating in L, S, and C bands

This paper presents the design and analysis of a novel 2D multilayer frequency selective surface (FSS) passband filter conceived for broadband response with pronounced roll-off characteristics. Unlike conventional 2D structures, the proposed multi-layer architecture improves bandwidth and filter selectivity while preserving an easy manufacturing process. The design is carried out by adopting a layer-by-layer equivalent circuit extraction technique that allows accurate impedance tailoring in order to accomplish the desired behavior in the L, S and C bands. The complete structure is composed by 3 stacked FSS layers, opportunely separated by foam gaps, achieving a compact 67 mm overall thickness. The performance predicted by the analytical modelling was also confirmed through full-wave simulations and experimental measurements, highlighting an excellent agreement. The proposed filter achieves an extensive - 3 dB passband from 2.79 GHz to 6.65 GHz, reaching 90% of fractional bandwidth, with sharp roll-offs of 42 dB/GHz and 70 dB/GHz. Thus, the - 10 dB rejection bands cover the 1.2 -2.62 GHz and the 6.75 -7.9 GHz ranges, accomplishing a full operation coverage of L, S and C bands. Finally, the filter's lightweight and affordable design makes it particularly suitable for modern communication systems that require effective out-of-band attenuation with elevated selectivity and compact integration.