A Rasorber With Energy-Selective Passband and Ultrawideband Absorptive Out-of-Band

In this article, a rasorber with energy-selective passband and ultrawideband absorptive out-of-band is proposed, which combines the advantages of conventional frequency-selective absorber (FSA) and energy-selective surface (ESS). The proposed design consists of an upper lossy layer and a lower active layer. By analyzing the equivalent circuit model (ECM), the lossy layer could generate three transmission zeros, thereby achieving ultrawideband out-of-band absorption independent of the incident power. The active layer embedded with p-i-n diodes exhibits a nonlinear response to the incident intensity of spatial waves, which can be switched between bandpass and bandstop resonances under low and high incident intensities based on ECM. The steady-state and transient-state characteristics of the proposed power-dependent rasorber are analyzed as well. For demonstration, a prototype with 13
$\times$
13 unit cells is fabricated and measured in free space for a low-power experiment, while two prototypes with 4
$\times$
2 unit cells and 2
$\times$
1 unit cells are processed and measured in rectangular waveguides for a high-power experiment. Under low incident power level, a high-selectivity transparent window is successfully realized with simulated (measured) low insertion loss (IL) of 0.9 dB at 3.58 GHz (0.83 dB at 3.44 GHz) and an ultrawide absorption band range of 5.87–17.88 GHz (5.98–18 GHz). As the incident field is higher than 740 V/m, the transmitted power undergoes a rapid reduction in the passband. The maximum shielding effectiveness (SE) reaches 18 dB at 3.58 GHz and the SE is better than 10 dB in the range of 0.5–17.5 GHz. The excellent nonlinear transmission characteristic with ultrawideband out-of-band absorption makes the proposed rasorber have various application prospects in the high-power microwave (HPM) protection and stealth.