Synthesis Design of Wideband Absorber Based on 3-D Frequency Selective Structures

In this paper, a wideband 3-D absorber based on 3-D frequency selective structures (FSSs) is presented. It is composed of stacked printed circuit boards with non-uniform slot lines on one side and shunt microstrip lines on the other side as well as resistors. In order to provide a synthesis method for it, the equivalent circuit model is introduced, which can also be used to design high-order and wideband absorbers. The closed-form equations are derived, and all the circuit parameters can be solved through the synthesis procedure. Then, an absorber is designed and simulated. The simulated results exhibit a wide absorption bandwidth of 1.9-8.23 GHz, that is 125% in fractional bandwidth, with absorptivity more than 90%. Moreover, the absorber can achieve angular stability even under incident angle of 50°.