Abstract
The advent of 6G wireless networks necessitates a synergistic design approach for sensing, communication, and protection, highlighting the capability of systems to function in transition between wideband transmission, narrowband transmission, and wideband reflection. This study introduces a novel trifunctional active frequency selective surface (TA-FSS) for this scenario. Compared with the conventional structures that can only realize frequency tuning or mode switching, this design has the versatility to switch the bandwidth of the passband and operate in three distinct modes: wideband communication mode with a passband of 18.9% relative bandwidth, narrowband tunable sensing mode with a tunable passband of 3.4% relative bandwidth and 37.9% relative tuning range, and a wideband protection mode with a reflection band from 1 to 5 GHz. First, a novel approach is devised to facilitate the passband width modulation at a consistent frequency through the established equivalent circuit model and verified through a single-polarized TA-FSS prototype. Afterward, based on a quasi-symmetric design methodology, a dual-polarized TA-FSS is achieved with a periodicity of 0.09\lambda and thickness of 0.018\lambda. The dual-polarized TA-FSS is angular stable up to 45^\circ and polarization insensitive. A physical prototype of the envisioned FSS is constructed for experimental evaluation. The measured results are closely aligned with the theoretical predictions.