Advancement of Metamaterial-Based Antennas

In recent years, metamaterials have been widely applied in the microwave and optical fields due to their unusual electromagnetic (EM) properties. Unlike conventional materials in nature, metamaterials can exhibit tailored permittivity, permeability, and refractive index. Therefore, EM metamaterials are usually utilized to manipulate the radiation and scattering characteristics, including but not limited to size reduction, bandwidth extension, gain increase, pattern modulation, scattering control, and exploration of new functionalities. This review briefly presents and summarizes a number of metamaterial-based antennas from the perspective of working principles and innovative properties. The metamaterials are discussed and divided into six categories: composite right/left-handed transmission line (CRLH-TL) based resonators & leaky-wave antennas, metamaterial-resonator-based antennas, small antennas with metamaterial loading, hybrid metamaterial antennas, reconfigurable intelligent surfaces (RIS) & low-cost metamaterial-based arrays, and multi-functional metamaterial-based antennas. In addition, challenges and future research trends in metamaterial-based antennas are highlighted and discussed. Numerous antenna examples are provided.