Multifunctional metasurfaces: From versatile electromagnetic control to array antenna applications

Metasurfaces, the two-dimensional counterparts of metamaterials, have emerged as a powerful platform for tailoring electromagnetic (EM) waves with unprecedented flexibility. By exploiting multiple input and/or output degrees of freedom, multifunctional metasurfaces can concurrently manipulate amplitude, phase, polarization, frequency, and scattering modes of EM waves across multiple channels, thus enabling versatile wavefront engineering and increasing functional integration within compact and low-loss platforms. Here, in this article, we provide an overview of multifunctional metasurfaces from both fundamental and application perspectives, paying special attention to array antenna designs in the microwave regime. We begin by revisiting the underlying physical principles and various modulation mechanisms, followed by design strategies for multifunctional metasurfaces. Building upon these foundations, we examine representative implementations that exploit versatile EM wavefront control covering both static and dynamic multifunctional metasurfaces. Particular emphasis is then placed on array antenna applications, where metasurface-enabled reflectarray antennas and transmitarray antennas have demonstrated significant advances in channel multiplication, broadened operational coverage, compact architectures, add-on functional integration, and dynamic beamforming. Finally, we discuss the emerging challenges and opportunities in this rapidly evolving field, highlighting directions toward the sixth generation wireless communications, new physics for dynamic reconfiguration, artificial-intelligence-driven design methodologies, and advanced manufacturing technologies. This review aims to provide both a systematic framework of the existing attempts and forward-looking insights to stimulate further innovations in multifunctional metasurfaces and their array antenna applications.