# Mechanically Reconfigurable, Beam-Scanning Reflectarray and Transmitarray Antennas: A Review
## 3 Array Movement
### Translatable or Rotatable TA or RA Antennas  
Two-dimensional beam steering capability can be achieved by only moving or rotating one lens antenna. Figure 6 shows the working principle of the antenna system and the lens mechanical steering setup. Lens in-plane translation with respect to the feed antenna provides beam steering in the elevation plane, while rotation of the lens antenna provides full azimuth coverage. This concept has been reported and implemented for wide angle (0-50\({}^{\circ}\)) elevation scanning of high-gain beams with full 360\({}^{\circ}\) azimuth sweep with a simple mechanical setup at Ka-band [29].  
A mechanically reconfigurable reflector was reported in [30] based on a resonant textured ground plane, also known as a high-impedance surface. The tunable reflector consisted of a pair of printed circuit boards. When the two boards were placed against one another, the reflector functions as an array of tiny resonant cavities. By moving or rotating the upper array board, each individual tiny resonator was tuned to have a different reflected phase response. This resulted in a different phase gradient for the mechanically reconfigurable reflector by which the main beam was scanned. The presented structure was demonstrated to steer a reflected beam by \(\pm\)38\({}^{\circ}\) at 3.1 GHz with a physical motion of only \(\lambda/100\), where \(\lambda\) is the free-space wavelength. A beam-steerable RA antenna designed at millimeter wave frequency band is presented in [31]. This RA aperture employs circular rings as its constituting phase shifters. The main beam of the proposed array can be steered  
Figure 5: Different configurations of the Risley-prism-based beam-steerable antenna system reported in the literature. **(a)** A system employing a feed horn, a collimating lens and two flat prisms (used in [20]). **(b)** The system in part **(a)** in which the collimating lens are integrated with the first prism (used in [20; 21; 22; 26]). **(c)** The system in part **(a)** in which the horn antenna is replaced with a planar antenna or antenna array placed in close proximity to the two flat prisms (used in [23; 24]). In such a system, a collimating lens is not needed.  
Figure 6: Schematic view of the lens mounting structure.  
by tilting the entire RA panel at different angles from \(+30^{\circ}\) to \(-30^{\circ}\). The required tilt angles could be obtained by using a single stepper motor, which offers a much less complex implementation as well as lower power consumption compared to the arrays which require motors for each individual element of the apertures.  
The mechanical tuning approach can also be applied to RAs for achieving polarization reconfiguration. Reference [32] reported a wideband and polarization-reconfigurable RA antenna for 5G millimeter wave wireless communications. The proposed 2 bit unit cell consists of a U-shaped dielectric stub with a cuboid-shaped air void and a ground plane. By simply rotating the reflective panel mechanically, the proposed RA antenna can switch between linear polarization (LP), left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) modes. This mechanical RA antenna has demonstrated a 3 dB gain bandwidth of 37.5%, 34.4% and 37.5% for RHCP, LHCP and LP modes, respectively.