## 3 Scope and Methodology  
Steering antenna systems have been classified in the literature based on various factors, including their size [47], the involvement of mechanical and non-mechanical movement [48], lens-based antennas supported by the European Space Agency [49], and other system properties [50]. Some previously reported articles focus solely on electronically steerable antennas, as seen in [44], while others discuss high-throughput SATCOM antennas, such as in [12]. Unlike earlier works on beam steering antennas, this article provides a comprehensive review of dual-band beam steering antennas that incorporate only passive metasurfaces. A passive metasurface-based antenna system can enable the design of high-gain, low-cost antennas with comparable G/T, thereby reducing overall antenna design complexity. The fundamental component in a passive metasurface-based beam steering system is the phase-gradient metasurface (PGM). This review also examines various unit cell topologies, which serve as the starting point for designing a dual-band PGM. The following key features are summarized in this article. * The review encapsulates passive beam steering techniques focusing on full-duplex systems incorporating passive metasurfaces. * Since the first step in designing a passive metasurface is finalizing the phase shifting cell, a subwavelength element that repeats periodically/aperiodically over the entire surface, careful design and selection are crucial and require deliberation. Therefore, the \begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Technique** & **Reconfigurable** & **Steering Mechanism** & \begin{tabular}{c} **Feed** \\ **Network** \\ **Complexity** \\ \end{tabular} & \begin{tabular}{c} **Metasurface** \\ **Type** \\ \end{tabular} & \(\eta_{ap}\)**(\%)** & **EIRP** & **G/T** \\ \hline Transmitarrays [32, 33, 34, 35, 36, 37] & No & \begin{tabular}{c} Mechanical \\ Translation/rotation \\ of feed or surface \\ \end{tabular} & Less & Passive & \begin{tabular}{c} 22.3– \\ 77.5 \\ \end{tabular} & \begin{tabular}{c} Medium to \\ High \\ \end{tabular} & \begin{tabular}{c} Medium \\ to High \\ \end{tabular} \\ \hline Reconfigurable Reflectarrays [38, 39, 40, 41] & Possible & \begin{tabular}{c} Electrical using PIN \\ or Varactor diodes, \\ and Motor in some \\ cases \\ \end{tabular} & More & Active & 7–69.41 & Low to High & \begin{tabular}{c} Low to \\ High \\ \end{tabular} \\ \hline \
\begin{tabular}{c} Phased Arrays [29, 42, 43] \\ \end{tabular} & Possible & Electrical & More & Active & High & High & High \\ \hline Near Field Meta-steering [31] & No &
\begin{tabular}{c} Mechanical rotation \\ of metasurface \\ \end{tabular} & Least & Passive & Medium & N/A & N/A \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Performance comparison of different beam steering techniques. Figure 3: Commercially available antennas for SOTM and COTM applications. (**a**) Electronically Steered Antenna by Kymeta [43, 44], (**b**) Mechanically Steered Antennas by Honeywell [45]. (**c**) Meta-surface Antenna by Waveup [46]. focus of this article is the design analysis of different dual-band phase transformation cell topologies available in the literature, with the pros and cons of each on the system-level parameters. This analysis aims to provide a valuable resource for designers beginning the development of dual-band PGMs used in various applications such as dual-band beam steering, dual-band phase correction, and dual-band lenses. Given the emphasis on designing and developing dual-band PGMs, we briefly discuss the steering mechanisms that incorporate dual-band PGMs to provide context. These steering mechanisms can be categorized into three main types: transmitarrays (TAs)-based beam steering, reflectarrays (RAs)-based beam steering, and near-field meta-steering (NFMS). A brief overview of these techniques is provided in the following subsequent section.