Novel Multimode A-T/A/R-A Type Absorptive Surface With Polarization-Independent Controlled Characteristic

In this article, a novel nine-mode absorption-transmission/absorption/reflection-absorption (A-T/A/R-A) active frequency-selective rasorber (AFSR) is proposed. It consists of a lossy array-I and a lossless array-II (and array-III) that could control the energy loss intensity and transmission state of electromagnetic (EM) wave, respectively. The lossy layer-I is constructed with an active-hybrid resonator, which realizes multiple current paths to contribute to in-band switchable lossy/lossless states while providing a stable out-of-band absorptive performance. Meanwhile, the lossless structure, composed of a double-layer active frequency-selective surface (AFSS) with symmetric and noncoupling characteristics, is employed for an ultrathin and switchable bandpass filter. Furthermore, attributed to the elaborately designed polarization-isolation bias system for both the lossy and lossless layers, all polarization-insensitive and polarization-independent functions could be realized in modes 1–3 and 4–9, respectively. As a result, this AFSR can independently provide ultrawideband (UWB-A), A-T-A (AFSR-T), and A-R-A (AFSR-R) modes, for both TE and TM incidences. In UWB-A mode, it achieves a −10-dB absorptive band from 2.6 to 9.7 GHz. When the operating mode switches, in AFSR-T and AFSR-R modes, the transmission or reflection band can be generated at the same frequency of 7.4 GHz with low energy losses of less than 0.1 dB. Finally, a prototype is manufactured, and the measured results are in good agreement with the CST simulation and circuit calculation results.