Off-Grid Position Optimization under Mutual Coupling in Fluid Antenna Arrays

2026-08-16

AI Summary

This study addresses the challenge of coupled geometric optimization and voltage constraints arising from mutual coupling effects in fluid antenna arrays. To overcome this, we propose an electromagnetic-aware beamforming framework that integrates phase retrieval with electromagnetic-aware orthogonal matching pursuit for robust initialization. Furthermore, an alternating optimization strategy combined with a projected Adam algorithm is employed to achieve continuous off-grid position refinement under strict voltage constraints. Experimental results demonstrate that, compared to uniform arrays and discrete port selection schemes, the proposed framework significantly enhances the average main-lobe signal-to-noise ratio while effectively suppressing peak sidelobe levels. Consequently, this approach successfully overcomes performance bottlenecks imposed by mutual coupling, offering a superior solution for fluid antenna array optimization.

Abstract

Fluid antenna arrays exploit continuous antenna repositioning within a finite aperture to provide geometry diversity beyond grid-constrained port selection. Every displacement, however, changes both the radiation response and the multiport mutual-impedance network, coupling geometry optimization with the source-voltage constraint. This paper develops an electromagnetic-aware (EM-aware) beamforming framework for planar fluid antenna arrays. Phase retrieval converts an amplitude-only shaped-beam specification into an aperture-compatible complex target, and an EM-aware orthogonal matching pursuit (OMP) method selects grid-constrained initial antenna positions. Continuous refinement then alternates exact voltage-constrained current optimization with movement-constrained projected adaptive moment estimation (Adam) updates of all physical antenna positions. Across independently perturbed symmetric dual-beam targets, the proposed method consistently improves the average mainlobe signal-to-noise ratio (SNR) and reduces the peak sidelobe level (PSLL) over a uniform array and discrete port selection.

Problem

• Fluid Antenna Arrays
• Mutual Coupling
• Off-Grid Position Optimization
• EM-aware Beamforming

Innovation

• Fluid Antenna Arrays
• EM-aware Beamforming
• Phase Retrieval
• Mutual Coupling
• Off-Grid Optimization