Sparse Port Selection under Mutual Coupling in Fluid Antenna Arrays

2026-08-16

AI Summary

This study addresses beam distortion and port selection failures caused by mutual coupling in densely packed fluid antenna arrays. We propose a mutual coupling-aware design paradigm that models the array as a coupled multi-port network, explicitly incorporating inactive ports. By jointly optimizing active port selection and source voltages, this approach actively exploits mutual coupling effects rather than merely compensating for them passively. Compared to traditional uncoupled models and fixed arrays, the proposed method significantly enhances average main-lobe signal-to-noise ratio and reduces peak sidelobe levels within a limited aperture. These improvements effectively overcome performance bottlenecks inherent in dense configurations, enabling precise beamforming through the constructive utilization of electromagnetic interactions in compact fluid antenna systems.

Abstract

Fluid antenna systems obtain spatial degrees of freedom by reconfiguring antenna positions within a confined region, a principle that extends to beamforming: shaped beams can be synthesized using far fewer radio-frequency feeds than candidate antenna positions. When the candidates are densely arranged, however, electromagnetic mutual coupling changes the relationship among terminal voltages, induced currents, and radiated fields, so an uncoupled model no longer describes the hardware and may activate an unsuitable set of ports, distorting the synthesized pattern. This paper develops a mutual-coupling-aware framework that converts the desired beam amplitude into a finite-aperture-compatible complex target and models the complete antenna lattice as a coupled multiport network, selecting the active ports and their source voltages through the coupled voltage-to-field response. Inactive candidate ports remain part of the network and carry induced currents, and every compared design is evaluated through the same electromagnetic model under the same source-voltage budget. Numerical results show that the mutual-coupling-aware design improves both the average mainlobe signal-to-noise ratio (SNR) and the peak sidelobe level (PSLL) over coupling-unaware selection and a fixed array, demonstrating that mutual coupling should be exploited in the design itself rather than compensated only in the final evaluation.

Problem

• Fluid Antenna Arrays
• Mutual Coupling
• Sparse Port Selection
• Beamforming

Innovation

• Fluid Antenna Arrays
• Mutual Coupling
• Sparse Port Selection
• Coupled Multiport Network
• Beamforming