Scalable Pixel-based Reconfigurable Beamforming Networks for Designing Fluid Antenna Systems

Abstract: A novel scalable pixel-based reconfigurable beamforming network (PRBFN) that can be used to form a Fluid Antenna System (FAS), referred to as a PRBFN-FAS, is introduced. The concept of FAS has emerged as an attractive new technology for use in sixth-generation (6G) wireless systems, but most implementations of FAS rely on mechanically reconfigurable antennas which are hindered by inertia, and are therefore too slow to be useful. Using the insight that changing an antenna's physical position is equivalent to switching the excitation current vector of a multi-port antenna, a novel beamformer is proposed with a scalable methodology for incorporating into FAS to form a PRBFN-FAS. Key novelties in creating the PRBFN include selecting the required current vectors and concatenating beamforming networks together to form the desired PRBFN. Two PRBFN-FAS design examples are demonstrated with FAS equivalent physical movements of 0.5 and 1.5 wavelengths. Measurements demonstrate that the PRBFN-FAS provides good matching and Bessel correlation across the desired bandwidth, satisfying FAS requirements. System-level experiments confirm the viability of PRBFN-FAS in practical communication scenarios.