Double-Layer Circuit Analog Absorbers Based on Resistor-Loaded Square-Loop Arrays

Based on the equivalent circuit model, it is demonstrated that five resonances can occur within the absorption band of a circuit analog absorber containing two lossy layers. The lossy layers are composed of resistor-loaded square-loop and double-square-loop arrays. In the absence of a dielectric skin, an initial design with four resonances observed from its reflectivity exhibits a simulated bandwidth ratio (BWR) of 1:8.45 for at least 10 dB absorption. To facilitate physical implementation of the wideband absorber, a modified design is proposed to compensate the effect of parasitic parameters of actual resistors on reflectivity. It is shown through measurement that an operating BWR of 1:8.78 is achieved with the reflectivity smaller than -10 dB under normal incidence. The total thickness of the absorber prototype is only 0.096 λ at the lowest operating frequency. The agreement between simulation and measurement validates the proposed design.