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In this letter, a novel and effective design method for multilayer and multiresonant absorbers is proposed. The two-layer absorber is composed of two resistor-loaded square loop frequency selective surface (FSS) arrays printed on the Rogers 4003 dielectric substrate and a backed metal plane. Equivalent circuits for two-layer absorbers with resistive sheets and resonant FSSs are proposed, analyzed, and further improved to provide great insight into the existence of the four resonances and ultrawide bandwidth. In the equivalent circuit model, the substrate is transformed to a parallel admittance and a positive susceptance is introduced in the whole operation band, which contributes to an extra resonance. After the measurement of a fabricated sample, a fractional bandwidth of 171.2% is obtained for at least 10 dB reflection reduction, with a total thickness of only 0.087λL (wavelength at the lowest absorption frequency). The good agreement between the calculated, simulated, and measured results validates the designed absorber.
Yao et al. (2020) studied this question.