An Active Wideband and Wide-Angle Electromagnetic Absorber at Microwave Frequencies

Two-dimensional (2-D) metamaterials (MTMs) can be used to create perfect electromagnetic absorbers. In this letter, a novel active MTM absorber with non-Foster loads is proposed. For obliquely incident plane waves with both transverse-electric (TE) and transverse-magnetic (TM) polarizations, its effective circuit model is analytically demonstrated, accounting the material losses. Based on the circuit model, a stability characterization is introduced to give the design principles for the non-Foster elements to achieve a wideband and wide-angle metamaterial absorber (MA). These active elements are achieved by a two-port non-Foster circuit based on the resonant tunneling diodes. For the purpose of verification, a sample active MA design is presented, exhibiting a high electromagnetic absorption rate for wideband and wide-angle incidence for both TE and TM polarizations at microwave frequencies, as compared to its passive counterpart.