Fluid Antennas: Reshaping Intrinsic Properties for Flexible Radiation Characteristics in Intelligent Wireless Networks

Fluid antennas present a relatively new idea for harnessing the fading and interference issues in multiple user wireless systems, such as 6G. Here, we systematically compare their unique radiation beam forming mechanism to the existing multiple-antenna systems in a wireless system. Subse-quently, a unified mathematical model for fluid antennas is deduced based on the eigenmode theory. As mathematically derived from the mul-timode resonant theory, the spectral expansion model of antennas that occupy variable spaces and have changeable feeding schemes can be generalized as “fluid antennas.” Non-liquid and liquid fluid antenna examples are presented, simulated, and discussed. The symmetry or modal parity of eigenmodes is explored as an additional degree of freedom to design fluid antennas for future wireless systems. As conceptually deduced and illustrated, the multidimensional and continuously adaptive ability of eigenmodes can be considered the most fundamental intrinsic characteristic of fluid antenna systems. It opens an uncharted area in the development of intelligent antennas (IAs), which brings more flexibility to on-demand antenna beam/null manipulating techniques for future wireless applications.