A Brief Review and Comparison Between Transmitarray Antennas, Reflectarray Antennas and Reconfigurable Intelligent Surfaces

In this paper, we review the conceptual architectures of two popular types of array antennas: transmitting array antenna and reflecting array antenna, as well as the latest technology in wireless communications: reconfigurable intelligent reflecting surface (RIS or IRS). In antenna engineering, the transmitting array antenna is called as the transmitarray antenna (TMA), whereas the reflecting array antenna is the reflectarray antenna (RTA). These have received much investigation in recent years. However, along with the depth of research, the similarity of structural natures and application fields, these have brought out confusion to researchers. In order to avoid confusion and misunderstandings between these new technologies, we have reviewed a large amount of literature and compared characteristics and similarities of the three, so that we can have a clearer understanding, and thus clarify misconceptions of them. Through a comparison, we summarize their similarities and differences in hardware structure, feed structure, radiation direction, and electromagnetic field confinement, etc. We explain the three from the above aspects to provide researchers with as much clarity as possible in understanding and their potential applications.