Metamaterial Lenses and Their Applications at Microwave Frequencies

Metamaterials (MTMs) are artificial structures characterized by flexible and designable electromagnetic (EM) properties, including permittivity, permeability, and refractive index. Because of their subwavelength‐scale composing units, MTMs are able to manipulate the propagation of EM waves at extremely fine resolutions and offer solutions for new‐concept devices and components with novel functionalities and challenge‐breaking properties. From among the attractive applications of MTMs, this review article focuses on MTM lenses (also termed metalenses) developed in recent years for the purpose of microwave engineering, including beam forming, beam steering, and imaging. Bulk lenses made of 3D MTMs and planar lenses made of 2D transmission‐type metasurfaces are both involved and investigated. Different categories of metalenses, together with the theory, principles, methods, and advantages of their designs, are introduced and discussed. Potential and future applications of metalenses at microwave frequencies are also presented.