Fluid Antenna-Enhanced Flexible Beamforming

TL;DR

The paper addresses flexible beamforming for fluid antennas by transforming beam-pattern synthesis into a sparse-regression problem with port selection on a 2-D planar antenna. It introduces an FFT-based phase retrieval method to ensure physically consistent phase modeling and a modified Orthogonal Matching Pursuit approach to select active ports under spacing constraints. The combined framework improves beam-pattern reconstruction accuracy, concentrates energy in the main lobe, and suppresses structured side lobes, with additional gains when phase initialization is imperfect. The results suggest fluid antennas offer substantial benefits over fixed arrays for high-resolution, adaptive beamforming and may enhance physical-layer security through irregular radiation patterns.

Abstract

Fluid antenna systems encompass a broad class of reconfigurable antenna technologies that offer substantial spatial diversity for various optimization objectives and communication tasks. Their capability to enhance spatial resolution within a fixed physical aperture makes fluid antennas particularly attractive for next-generation wireless deployments. In this work, we focus on the beamforming problem using a two-dimensional planar fluid antenna array. Since both narrow-beam and broad-beam patterns are essential in practical communication networks, enabling flexible beamforming through fluid antennas becomes an important and interesting research direction. We establish a unified and flexible framework that connects arbitrary beam-pattern synthesis with fluid-antenna port selection. The resulting formulation transforms beam-pattern reconstruction into a sparse regression problem, which is addressed using a tailored compressive sensing algorithm designed to operate efficiently with the fast Fourier transform (FFT). Furthermore, to ensure physically consistent phase modeling in the desired beam, we introduce an iterative FFT-based phase retrieval method. Owing to its structure, the proposed phase-refinement procedure exhibits low computational complexity and rapid convergence, requiring only one FFT and one inverse FFT per iteration. Simulation results demonstrate the effectiveness of the proposed flexible beamforming framework. Compared with conventional fixed-array architectures, fluid antennas exhibit significantly improved beam-pattern reconstruction accuracy, highlighting their potential for high-resolution and adaptive beamforming in future wireless systems.

Figures (8)

• Figure 1: Illustrations of wide and narrow beams.
• Figure 2: Illustration of the 2-D planar fluid antenna array.
• Figure 3: Illustrations of beams near the zero elevation angle.
• Figure 4: Illustrations of phase domain $\angle\mathbf{G}$ with and without phase retrieval.
• Figure 5: Normalized beam heatmap for a fixed antenna array, showing structured and predictable side-lobe patterns.