Achieving High-Capacity OAM Communication With Fluid-Antenna-Based Continuous-Aperture Arrays

The emerging technology of fluid antennas (FAs) offers significant opportunities for enhancing the performance of wireless communication. Hybrid antenna designs that incorporate reconfigurable antennas offer exceptional flexibility, thereby enhancing adaptability to diverse communication requirements. With their inherent reconfigurability and adaptability, hybrid antennas incorporating FAs represent a promising solution for realizing continuous-aperture array (CAPA). A CAPA is capable of flexibly and efficiently exciting surface currents, thereby generating the desired electromagnetic waves. Vortex electromagnetic waves with different orbital angular momentum (OAM) modes are spatially orthogonal, providing a novel spatial multiplexing dimension for wireless communication. To meet the demand of high-capacity communication, from the perspective of electromagnetic information theory (EIT), we investigate an OAM orthogonal transmission system based on CAPA and explore the performance limits of the system. We propose an innovative hybrid antenna that integrates FAs with fixed-position antennas (FPAs) to realize CAPA, and design the surface currents of the CAPA using Fourier basis functions. Furthermore, we explore the electromagnetic channel model and derive the upper bound of the spectrum efficiency for CAPA-based OAM orthogonal transmission. This paper establishes a theoretical foundation for applying EIT to the orthogonal transmission of vortex electromagnetic waves, offering a novel solution for achieving efficient and high-capacity communication based on CAPA integrated with FAs.