Advancement of Metamaterial-Based Antennas

In recent years, metamaterials have been widely applied in the microwave and optical fields due to their unusual electromagnetic properties. Different from conventional materials in nature, metamaterials can exhibit tailored permittivity, permeability, and refractive index. Thus, they are usually utilized to improve radiation performance, including size reduction, bandwidth extension, gain increase, and exploration of new functionalities. This paper briefly presents and summarizes a number of metamaterials and antennas from the perspective of working principles and innovative properties. The metamaterials are discussed and divided into five categories: composite right/left-handed transmission line (CRLH-TL) based resonators & leaky-wave antennas, meta-resonator based antennas, small antennas with metamaterial loading, hybrid metamaterial antennas, and array applications with metamaterial elements. In addition, challenges in metamaterial-based antennas are highlighted and discussed. Numerous antenna examples are provided.