# Mechanically Reconfigurable, Beam-Scanning Reflectarray and Transmitarray Antennas: A Review
## 6 Comparison and Discussion  
In this section, we perform a comparison of the different approaches discussed to achieve mechanical reconfigurability. Table 4 compares the scanning capabilities, cost and complexity and power consumption of the three major approaches discussed herein. These parameters are rated good, fair and poor with green, yellow and red colors, respectively. By scanning capabilities, we refer to the scanning resolution, range and loss of each approach. As observed, the element movement approach offers better scanning capabilities as it permits adjustments at the element scale. This requires dedicating a micromotor to each element, rendering the array and the controller unit more complex and increasing power consumption. Moreover, the scanning capabilities of such arrays depend on the adopted micromotors features. Specifically, the adjustment speed and the size of the micromotors limit the scanning agility and the integration capability of the array, respectively. The impact of micromotor size on integration explains why most of the reported RAs using integrated actuators were designed at relatively low frequencies, i.e., C-band and S-band [4,9]. Nevertheless, the favorable scanning capabilities of this approach still render it appealing to many applications such as microwave radar and communication systems [77]. Furthermore, the recent advancement of miniaturized actuators and MEMS, which appear in a myriad of forms and sizes, introduces opportunities for designing reconfigurable RAs at higher frequencies with agile scanning capabilities. It is also possible to sacrifice part of the scanning capabilities of the arrays by using subarray movement and, in turn, reducing complexity and power consumption. By allocating a micromotor to a group of adjacent elements (one micromotor per subarray), one may obtain a simpler reconfigurable RA by giving up the full phase compensation of each element. This can also relax the size constraint of the actuators.  
The array movement approach offers simple reconfigurability by using only a few actuators, which creates relatively low cost and less complex beam-steerable systems. These  
\begin{table}
\begin{tabular}{c|c c c c} \hline \hline \multirow{2}{*}{**Method**} & **Scanning** & **Frequency** & **Cost and** & **Power** \\  & **Capabilities** & **Bandwidth** & **Complexity** & **Consumption** \\ \hline Element & & & & \\ Movement & & & & \\ \hline Array & & & & \\ Movement & & & & \\ \hline Feed Movement & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparative analysis of reconfigurable approaches discussed in this paper.  
Figure 10: (a) Working principle of the hybrid beam scanning antenna. (b) Fabricated prototype. (Reprinted with permission from [76]).  
features render this approach suitable for large arrays with many elements. Some of the TAs using array movement, e.g., Risley-prism-based beam-steerable antennas, often have limited frequency bandwidth that can be addressed by using true-time delays [61]. The feed movement is the simplest approach for mechanical reconfigurability as it requires adjusting light feed antennas as opposed to moving the large array apertures. Similar to array movement approaches, the RAs and TAs using feed movement often have limited bandwidth and efficiency. Therefore, the feed and array movements are appealing solutions for applications that require moderate speed, limited and affordable beam-steering over a narrow bandwidth.