# Design of a 3-Bit Circularly Polarized Reconfigurable Reflectarray
## 1 Introduction  
With the rapid development of the wireless communication industry, there is an increasing demand for antennas with high gain and high directivity characteristics. These antennas are capable of providing directional radiation in specific areas, offering a strong anti-interference ability and good angular resolution, which can be widely used in radar systems, satellite communication, and deep space exploration. The two traditional types of high-gain and high-directional antennas are the parabolic antenna [1; 2; 3; 4; 5] and the phased array antenna [6; 7; 8; 9; 10; 11; 12]. The parabolic antenna consists of a metal reflecting surface and a feed antenna used to transmit the incident wave. It has the advantages of a high gain, simple structure, and broadband operation. However, due to the reflection of the metal surface, the antenna tends to be bulky and heavy, making it difficult to move flexibly in practical application. Moreover, the beam scanning of the parabolic antenna can only be achieved through mechanical rotation, resulting in limitations in beam switching speed and pointing accuracy. In contrast, the phased array antenna is composed of a large number of antenna units with a controllable feed phase. By adjusting the feed phase of each unit, beamforming can be controlled. It has flexible beam control, a fast scanning speed, the ability to adapt to a complex electromagnetic environment, and the ability to strike against multiple targets. However, the cost of the phased array antenna is higher, as each antenna unit requires an independent feed network, which greatly increases the complexity and cost of design and manufacture, particularly in the millimeter wave or higher-frequency bands. The reconfigurable reflectarray antenna is a new type of beam scanning array antenna that has been widely studied in recent years. It is achieved by incorporating reconfigurable technology into the traditional reflect array antenna. Through the use of reconfigurable components in the control unit, the reflective phase of each unit can be adjusted with a certaindegree of precision, and then the reflected beam of the array can be controlled. Compared with the parabolic antenna, the reconfigurable reflectarray antenna can be processed and designed by planar microstrip printing technology with lower profile and light structure. With the help of reconfigurable technology, the beam control can be realized more flexibly and quickly. In contrast to the phased array antennas, the reconfigurable reflectarray antenna does not require a complex feed network or subsequent transceiver system, which will simplify the design process and make it more convenient. Furthermore, the manufacturing costs and transmission loss caused by the feed network are significantly reduced. In addition to traditional applications, reconfigurable reflectarray can also be used in the next-generation wireless communication systems. It can be used to construct wireless relays [13; 14], actively modulate the wireless channel environment, enhance signal coverage strength, and improve the transmission rate of the communication system. Additionally, it can be used to construct new wireless communication transmitters [15; 16; 17; 18]. By controlling the array unit's reflective phase, amplitude, frequency, or polarization characteristics, the feed-incident carrier signal can be modulated directly, without the need for an analog-digital/analog-digital converter, a modulator, and other components, thus greatly reducing the hardware complexity, energy consumption, and manufacturing cost. The structure is simple and easy to deploy in practical applications. Therefore, the study of reconfigurable reflectarray antennas is of great significance and value for the future development of wireless communications and related fields.