The intent of this paper is to provide an overview of basic concepts, types, techniques, and experimental studies of the current state-of-the-art Frequency Selective Surfaces (FSSs). FSS is a periodic surface with identical two-dimensional arrays of elements arranged on a dielectric substrate. An incoming plane wave will either be transmitted (passband) or reflected back (stopband), completely or partially, depending on the nature of array element. This occurs when the frequency of electromagnetic (EM) wave matches with the resonant frequency of the FSS elements. Therefore, an FSS is capable of passing or blocking the EM waves of certain range of frequencies in the free space; consequently, identified as spatial filters. Nowadays, FSSs have been studied comprehensively and huge growth is perceived in the field of its designing and implementation for different practical applications at frequency ranges of microwave to optical. In this review article, we illustrate the recent researches on different categories of FSSs based on structure design, array element used, and applications. We also focus on theoretical breakthroughs with fabrication techniques, experimental verifications of design examples as well as prospects and challenges, especially in the microwave regime. We emphasize their significant performance parameters, particularly focusing on how advancement in this field could facilitate innovation in advanced electromagnetics.

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A novel approach is used to miniaturise the array size and broaden the bandwidth (BW) of a multilayer antenna‐filter antenna‐ based frequency selective surface (FSS). Although such FSSs have broadly been investigated for higher frequency selectivity and less thickness, they still own high periodicity and lower BW. The proposed fractal FSS with centre square slots consists of three metallic layers, separated by two dielectric substrates and periodicity of the unit cell is sub‐wavelength order (0.2λₒ). Central square slots are added in the external Minkowski fractal patches to increase the capacitive effect whereas fractal slots are etched on the ground placed in the middle for enhanced coupling. It is demonstrated through simulations that proposed design can effectively minimise the element size and enhance the BW. Owing to minuscule array size and symmetric fractal geometry, the presented structure is insensitive to higher incidence angles (up to 30°) for both polarisations. A prototype of the proposed FSS is also fabricated and tested in a microwave anechoic chamber. An equivalent circuit model, full wave simulation and measurement results agree well and demonstrate stable response with 3 dB fractional BW approaching 87.4 and 92%, respectively, at a normal angle of incidence.

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In this letter, a novel periodic crest‐trough (CT) shaped groove structure is proposed to excite and propagate spoof surface plasmon polaritons (SSPPs) at microwave frequency. Such a groove shape solves the problem of high transmission losses found in traditional microstrip transmission lines and presents tighter field confinement. Lower dispersion band is achieved by proposed CT‐SSPPs as compared to traditional structures, with 28% reduced asymptotic frequency than rectangular groove. Influence of some geometrical parameters is also explored. Further, planar low‐pass plasmonic filters with low reflection and high efficiency are investigated with compact transition circuitry for smooth and fast conversion between SSPPs and guided waves. To validate the proposed performance, two plasmonic filter structures are fabricated and measured. Full agreement is observed between the simulated and measured results for which reflection coefficient is lower than −10 dB in passband up to 3.07 and 2.52 GHz, respectively for both filters. The rejection level is higher than −15 dB in the whole stopband.

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