Single-FSS-Layer Absorber With Improved Bandwidth–Thickness Tradeoff Adopting Impedance-Matching Superstrate

The bandwidth-thickness tradeoff is fundamental to the design of thin absorbers based on frequency-selective surfaces (FSSs). In this letter, we challenge the common belief that adding a dielectric superstrate will enlarge the bandwidth at the cost of increased thickness. It is first demonstrated using lumped circuit considerations so that a wider relative operating bandwidth can be achieved with a thinner absorber including an impedance-matching cover. By adopting this dielectric superstrate, we further show on the basis of full-wave simulation that the highest bandwidth ratio (BWR) at 10 dB absorption can be increased from 1:3.54 to 1:6.94, with the normalized thickness being reduced from 0.0920 to 0.0906 λ _L (including superstrate). Restricted by readily available materials, an experimentally validated design obtains a BWR of approximately 1:5.32 at 10 dB absorption for a figure of merit of 88.26%. This performance is superior to existing designs with more complicated FSS patterns.