Design of ultra wide-bandwidth double-layer electromagnetic wave absorbers with square-loop frequency selective surfaces

摘要

A thin and ultra wide-bandwidth microwave absorber is demonstrated theoretically and experimentally through simple layering 2 square loop-frequency selective surfaces (SL-FSSs) with different geometries on a grounded dielectric substrate. The circuit parameters of the SL-FSS inductance (L) and capacitance (C) are retrieved using the equivalent circuit model and are utilized in the design of the wide bandwidth absorber. The L and C values increase with increases in the unit cell dimension, and thereby the absorption frequency band can be controlled by the SL-FSS geometries. The optimal control for the surface resistance of the SL-FSSs and the spacer (assumed by air) thickness of the double-layer absorber provide a 10 dB absorption bandwidth of 6.3-38.3 GHz with a total thickness of 6.4 mm. The free-space measurement with the test samples fabricated by the screen printing process provides a still wide bandwidth of 5.6-30.8 GHz with the same total thickness.