Polarization–Insensitive Angularly Stable Compact Triple Band Stop Frequency Selective Surface for Shielding Electromagnetic Radiations

. A compact single-layer, polarization-insensitive, and angularly stable frequency selective surface (FSS) based multi-stop band filter is reported for shielding three useful frequency bands covering 1.82–2.86 GHz Industrial, scientific, and medical (ISM), 3.52–4.06 GHz Worldwide Interoperability for Microwave Access (WiMAX), and 7.42–8.72 GHz (satellite downlink), centered at 2.4 GHz, 3.6 GHz, and 8.1 GHz, respectively. The proposed unit cell (15 mm × 15 mm) contains four equal-sized square-headed dumbbell (SHD) shaped resonators surrounded by two square ring resonators. The outer and inner square rings offer the first and second stop bands, while the SHD resonators provide the third stop band. A highly polarization-insensitive response is realized owing to the four-fold symmetry in the proposed structure. The unique arrangements of the SHD resonators help to realize higher angular stability under transverse electric (TE), transverse magnetic (TM), and diagonally polarized incident electromagnetic (EM) waves for incidence angles up to 80°, 80°, and 70°, respectively. A detailed analysis in terms of equivalent circuit and parametric variation is carried out to illustrate the higher to lower frequency band ratio. A prototype is fabricated and tested through a proper measurement setup to validate its performance, and it shows good agreement with the simulated results. The proposed FSS unit cell offers better angular stability under diagonally polarised incident waves, attenuation level, minimum higher to lower frequency band ratio, good fractional bandwidth, and compactness. So the designed multi-stopband FSS can be considered a potential candidate for shielding EM radiation across the useful bands.