Analysis and Design of Ultrathin Filtering Energy-Selective Surfaces With Ultrawideband and High Shielding Effectiveness

In this work, ultrathin filtering energy-selective surfaces (ESSs) for achieving a sharp bandpass function and an ultrawideband high shielding effectiveness (SE) are proposed and demonstrated. Based on the coupled resonator filter topology, the proof-of-concept first- and second-order filtering ESS cells with a sub wavelength element size and a total thickness of less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.03\lambda _{0}$ </tex-math></inline-formula> are designed and analyzed, operating at a center frequency of 3.5 GHz. By embedding pairs of oppositely oriented PIN diodes into the slots of the capacitive patches, both filtering ESSs exhibit a bandpass function with a broad upper stopband and a reflective response with a high SE under the illumination by low-power and high-power electromagnetic (HPEM) waves, respectively. Moreover, by extracting the power dependency of the conductive resistance of the embedded PIN diodes, the nonlinear working mechanism of the filtering ESSs is analyzed, indicating that higher SE and sharper band selectivity can be simultaneously achieved by increasing the order of the ESS structure. For experimental verification, four prototypes are fabricated and characterized in waveguide simulators, showing a good agreement between the measured and simulated results. The first- and second-order filtering ESS prototypes accomplish an ultrawideband electromagnetic protection with an SE of greater than 30 and 35 dB over the bandwidth ranging from 2.5 to 6 GHz at an incident power of 40 dBm, respectively, with a peak in-band SE of 33.8 and 39.2 dB. The proposed filtering ESSs can be useful protective radomes for wireless receivers.