Advanced Liquid Crystal Materials at Microwave and Millimeter‐Wave Frequencies: Design, Properties, and Applications

Abstract The rapid advancement of modern communication and sensing systems demands cost‐effective phased arrays that incorporate a large number of phase‐shifting cells to enable complex beamforming tasks. Liquid crystals (LCs) have garnered increasing interest for microwave (MW) and millimeter‐wave (mmWave) reconfigurable arrays due to their distinctive characteristics, including continuous tunability, low dielectric loss, and compatibility with low‐cost fabrication processes. Enhancing the performance of LC‐based radio‐frequency (RF) systems requires a multidisciplinary approach that integrates both advanced device design and optimization of materials properties. This review presents a comprehensive overview of recent developments in advanced LC materials operating at MW and mmWave frequencies. The fundamental design principles and innovative electromagnetic (EM) material characterizations of tunable LCs are firstly discussed. A series of novel nematic liquid crystals (NLCs) with judiciously designed molecular structure, as well as multicomponent‐doped LC materials, including polymer‐modified LCs, nanoparticle‐doped LCs, and dual‐frequency LCs (DFLCs), are systematically introduced, which are very important for the development of advanced RF devices with enhanced performance. The review concludes by providing insights into the emerging applications, current challenges, and future opportunities of advanced tunable LCs. This review can not only deepen the understanding of the fundamental properties of LCs in the MW and mmWave bands but also highlight their evolving role in diverse fields, including materials science, electromagnetics, device engineering, and beyond.