## 1 Introduction
Transmitarrays (TAs) are primarily composed of several discrete unitary elements, and special feed sources (horn antenna, microstrip patch antennas, or other UWB antennas) are used to illuminate EM waves. They also used multilayer frequency selective surfaces, meta-materials, and metasurfaces [27; 28; 29]. There are various dynamic technologies exploited to enable the reconfigurable characteristics of TAs. Reconfigurable features perform electronic beam forming or beam steering, frequency tuning, and the control of polarization by solid-state electronics devices such as using PIN diodes [30; 31; 32], varactors [33], MEMS (micro-electromechanical systems) switches [34], tunable dielectric substance liquid crystals [35; 36], microfluidic systems [37], and graphene [38]. All these components have dynamic performance with respect to their advantages and disadvantages; PIN diodes and varactors are commonly used in solid-state devices available for lower radio frequencies up to 40 GHz [39; 40]. In recent years, substantial advancements have been made in the development and implementation of reconfigurable technology for antennas and other solid-state devices. Versatile communication systems and radars have upsurged the demand for reconfigurable devices and components. MEMS switches are reliable in operation but not an economical solution as compared to the diodes. However, these face challenges of wear and tear of the mechanical part. Therefore, liquid crystal and graphene are exotic solutions for high frequencies, particularly for terahertz (THz) frequencies. There are many applications of liquid crystal- and graphene-based transmitarrays reported in the literature [41; 42; 43]. They are feasible for phase integration, their small size and low biasing complexity at lower to higher frequencies. Due to their advantage of being able to vary the transmission phase change freely, most of the beam forming/beam steering reconfigurable transmitarrays are designed by the former method. However, there is a disadvantage of the overall radio performance of the transmitarray antenna that may deteriorate due to its complexity of implementation or the additional loss of active elements. The latter method structurally changes the wavefront shape of the source antenna electrically or mechanically and has the advantage of structurally fixing the TA. However, there is a disadvantage of a large motor for arrays as mentioned in [44; 45; 46; 47; 48]. Significant research has been conducted in recent years [49; 50; 51; 52; 53]. A transmitarray antenna has been implemented with a source antenna (horn, microstrip patch antenna) and a planar array. The working principle of a transmitarray antenna uses a high transmittance and a transmission phase change characteristic of more than 360 degrees to control the wavefront of the source antenna. This type of transmitarray antenna is a high gain antenna and is beam forming, beam steering, and multi-beam [54; 55; 56]. It is designed as a beam control system such as PIN diodes, varactors, MEMS systems, and microfluids. These reconfigurable devices can be used in many applications. In order to perform beam forming/beam steering in the desired direction, it can be roughly divided into two methods. The total wavefront of the transmitarray antenna can be calculated as the sum of the wavefront of the source antenna and the wavefront of the plane wave passing through the transmitarray. This point is used to implement beam steering by a transmitarray with variable transmission phase change or when the wavefront shape of the source antenna is applied. This paper is written in the following structure. Section 2 describes the beam forming/beam steering principle and characteristic analysis of a transmission antenna using a TA, and its relation to the aperture efficiency, which is an important performance indicator of the transmitarray antenna.