A Three-Dimensional Design of Ultra-Wideband Microwave Absorbers

A three-dimensional (3-D) structure is proposed in this article for ultra-wideband absorber design. The ultrawideband absorber is implemented by properly combining two subabsorbers. The first subabsorber operates in its fundamental mode ( f
₀
) and the third-order mode (3 f
₀
). Its lossy layer is designed with an infinite impedance at the second-order mode frequency (2 f
₀
). The second subabsorber is designed to operate in its fundamental mode frequency, which is corresponding to 2 f
₀
of the first subabsorber. A double-sided parallel-strip line (DSPSL) is employed to produce the required infinite impedance of the first absorber. A simple equivalent circuit model of the DSPSL is established to explain the operating principle. A conventional parallel LC circuit is also provided for comparison to show the advantages of the DSPSL. Single-polarized and dual-polarized ultra-wideband absorbers are designed by combining these two subabsorbers, and their simulated fractional bandwidths (FBWs) of 151.6% and 150.9% are achieved, respectively. A prototype of the dual-polarized ultra-wideband absorber is fabricated and measured to validate the design concept. Its measured absorption band from 1.50 to 12.31 GHz with an FBW of 156.6% is in a good agreement with the simulated one. The proposed absorber features a wide absorption band and few lumped elements, which makes it more useful in practical applications.