Design of an ultra‐broadband microwave metamaterial absorber based on multilayer structures

An ultra‐broadband double‐layer microwave metamaterial absorber (MMA) with reflectivity below −10 dB ranging from 1.4 to17.31GHz is presented in this article. The MMA has a fractional bandwidth of 170% and a total thickness of 20.8 mm. By analyzing the function of different layers, the MMA can be simplified to the combination of a dual‐band (DB) absorber and a single‐band (SB) absorber. Layer I consists of a square loop loaded with asymmetric resistors and achieves a DB absorption by exciting high‐order modes covering the low‐frequency and high‐frequency. Layer II is composed of double‐ring structures integrated with resistors and realizes an SB absorber in the middle frequency. To understand the physical mechanism in detail, the equivalent circuit model (ECM) is proposed and illustrates a good impedance match within the entire absorption bandwidth with free space. An in‐depth analysis has been carried out by illustrating several key dimensions. To verify our idea, a prototype has been designed, fabricated, and measured. Measurement results show an ultra‐broadband absorption with the reflectivity below −10 dB ranging from 1.7 to 17.27 GHz under the normal direction, which agrees well with simulation and ECM results.