**1. Introduction**

Metamaterial is a specific type of artificial materials that is constructed with amount of sub-wavelength structure units and is able to realize the complex systems in a compact and planar configuration [1]. In the early stage, Metasurfaces with metal patterned surfaces have been used to achieve the desired phase-shift distribution for antenna design and EM wave manipulation in the microwave domain [2]. Among aperture antennas, lens has long been used in antenna design and lens antennas usually are electrically larger with volume constraints and the complex feeding structure. The conventional lens can be structured using dielectric lens and transmit-receive arrays. Metalens antennas provide much more flexibility of planar design and fabrication than the dielectric lenses, since it can realize spherical phase in the plane and replace the complex feeding structure with the waveguide or the novel coupler structure. Furthermore, the metalens also controls the amplitude and polarization direction of the incident electromagnetic wave, which is the most privilege advantage and the popular usage for most metalens applications [3]. Researchers have designed the high quality metasurface lens and beamforming on the grapheme terahertz metalens. Some traditional optical devices could be replaced by metasurface such as lens, gratings and prism [4]. The transformation optics has been employed to compress the sphere into a cylinder and the flat lens with a beam-steering by using cylindrical dielectric slabs. Such designs have

been widely applied in 5G NR and radar systems [5]. If the unit cell of metalens is dynamically adjusted, the focus of metalens could be managed accordingly and the system could scan the beam in the space, which is the highly desired feature in the area of microwave band for 5G MIMO applications, terahertz communications and imaging, and modern optical imaging and sensing system, such as 3D microscope and LiDAR [6, 7].
