An Overview of Fluid Antenna Systems: Fundamentals, Performance Analysis and Challenges

The upcoming sixth-generation (6G) is envisioned to transform wireless communications through groundbreaking performance targets that far exceed previous generations. Among the emerging technologies, the fluid antenna system (FAS) has gained significant attention as a flexible and reconfigurable antenna architecture. FAS can dynamically alter the position and shape of the radiating elements to exploit additional spatial degrees of freedom. In this paper, a comprehensive overview of FAS is first provided, including its fundamental principles and implementation methods. Then, the impact of key system parameters— such as the number of ports, the physical size of FAS, and the channel environment—on the performance of FAS is thoroughly investigated. Finally, open research challenges and future directions are highlighted for integrating FAS with other advanced 6G technologies. Ultimately, this paper aims to serve as a foundational reference for researchers seeking to unlock the full potential of fluid antennas in 6G wireless systems.