# Design Procedure of a Frequency Reconfigurable Metasurface Antenna at mmWave Band
## 1 Introduction  
The under-utilized mmWaves spectrum gave researchers an opportunity to investigate and exploit this band with the aim to curb issues on bandwidth and channel capacity associated with 5G and 6G technologies [1]. Consequently, new wireless communication technologies are emerging, including mmWaves utilization and further exploration of sub-mmWaves, as the need for higher data rates grows [2; 3; 4; 5]. However, high frequencies introduce high path loss, which results in the need for improved hardware designs and performance such as antenna gain requirements [2]. One enabling technology is massive multiple-input multiple-output (mMIMO), which is developed to increase the throughput and spectral efficiency by deploying thousands of antennas at a base station [6; 7]. In particular, mMIMO aims to have more antenna elements at the access points than the number of active user equipment in any cell at any point in time. This induces more orthogonal channels and consequently achieves high spectral efficiency. Despite these benefits of mMIMO, implementing large scale antenna arrays in practice has proven to be a challenge [8]. Among these challenges are high fabrication cost, increased power consumption,and constrained physical size [9, 10]. With significantly improved cost and manufacturing efficiency, metasurface antennas are emerging as an alternative to conventional electronic scanned antennas [8, 11, 12, 13, 14].  
Metasurfaces are the 2D counterparts of metamaterials, which consist of sub-wavelength metallic or dielectric particles that are used to control or modify various parameters, such as amplitude, phase, and polarization [15, 16, 17]. In recent years, scientists have been interested in the use of artificial materials, which are envisaged to generate significant benefits and introduces various applications. Metamaterials are among these artificial materials, as they are composed of closely spaced sub-wavelength meta-atoms which resonantly couple to both the electric or magnetic components of the incident electromagnetic fields, thereby exhibiting properties that are not found in nature [18, 19, 20]. By modifying their permittivity and permeability values, metamaterials can control the propagation of a wave, but they still rely on the propagation phenomena to manipulate electromagnetic (EM) waves [21]. In addition, their 3D nature makes them challenging to fabricate and also results in relatively bulky structures as they manipulate a wave over an extremely thin layer [19, 22]. Moreover, the planar structure of metasurfaces facilitates the easy fabrication and highly cost-effective fabrication process when compared to the creation of complex 3D metamaterials. Some of the shortfalls brought on by metamaterials can be addressed by the metasurface, which are less bulky. As compared to metamaterials, metasurfaces are considered to be 2D structures instead of 3D structures. As a result, these metasurface structures are used for a variety of applications, including controllable \"smart\" surfaces, miniaturized cavity resonators, novel wave-guiding structures, compact and wide-angle absorbers and impedance-matching surfaces.