Extremely Wideband Metamaterial Absorber Using Spatial Lossy Transmission Lines and Resistively Loaded High Impedance Surface

In this article, the design, principle, and characterization of a 3-D metamaterial absorber (MA) have been presented, which consists of the spatial lossy transmission lines (SLTLs) and the resistively loaded high impedance surface (HIS). The proposed MA possesses a fractional bandwidth of 193% with absorption rate of above 90% in the frequency range from 2 to 110 GHz under TM polarization while maintaining large oblique incident angle stability of over 50 ^{\circ} . For demonstration, a prototype is fabricated, whose measurement results are in good agreement with the simulation results. Losses from the periodically patterned SLTLs and resistively loaded HIS are introduced by resistive graphene films using screen-printing technology, resulting in avoiding conventional soldering of numerous lumped resistors. An equivalent circuit model and a surface loss distribution are given to better illustrate the physical mechanism. Our findings establish general and systematic strategies for guiding the design of extremely wideband MA with large incident angle and pave the way for enhancing the microwave performance in applications of electromagnetic compatibility, imaging, radar detection, and stealth.