# Mechanically Reconfigurable, Beam-Scanning Reflectarray and Transmitarray Antennas: A Review
## 3 Array Movement
### Tiltable Ground Plane RA Antennas  
Instead of tilting the whole RA, the work in [33] only tilts its ground plane for simplification. An X-band beam-steerable nonuniform RA antenna was reported, which achieved beam steering by using small movements of a large ground plane. The proposed RA exhibited a maximum \(\pm 7.5^{\circ}\) beam scanning from the antenna broadside with only \(\pm 0.05\lambda\) ground tilting. This work also shows improved performance in terms of the half-power beamwidth (HPBW) and side lobe level, which were \(9^{\circ}\) and 20 dB, respectively. A new reconfigurable RA concept was studied in [34]. It involved only four mechanical actuators to change the orientation of an RF flexible ground plane to control the reflected phase. The ground plane was a flexible membrane that was deformable by actuators. Four actuators were distributed regularly along the membrane to control its vertical displacement. The magnitude of deformation was studied and the RF accuracy of the global system was optimized. The maximum slope of the membrane in this work was shown to be only 4.43%. This deformation slope is much lower than the required threshold of 15%, which is the acceptable stress in existing materials. A canonical 1D array providing three different shaped beams was designed and full-wave simulations were used to validate this preliminary design. Reference [35] reported the design of a reconfigurable high impedance surface (HIS) integrated with four commercial piezoelectric actuators. Piezoelectric actuators can convert an electrical signal into a precisely controlled physical displacement [36], which was translated to dynamic control of the reflection phase. The simulated and experimental results demonstrated a continuously tunable phase shift over \(200^{\circ}\) at about 60 GHz.  
Another new approach using the concept of piezoelectric actuators to perform mechanical beam steering of a RA was presented in [37]. The proposed technique exploited collective control over macro-scale movements of a ground plane to achieve 2D beam steering. By tilting the ground plane underneath the entire aperture, the phase shift gradient created over the RA was modified. Changing the direction and slope of this phase shift gradient allowed for achieving 2D beam steering using only one control parameter (i.e., tilt vector of the ground plane). Experiments demonstrated that \(0.05\lambda_{0}\) mechanical movements of the ground plane can steer the radiated beam direction in the \(\pm 10^{\circ}\) range. They further demonstrated that this beam scanning range could be significantly enhanced to \(\pm 30^{\circ}\) when the ground plane was segmented. The illustrations of the proposed mechanical reconfigurable RAs are shown in Figure 7[37]. Figure 7a shows the configuration of the proposed beam-steerable RA that moves a large ground plane. Figure 7b illustrates an implementation form of Figure 7a, where four piezoelectric actuators are employed to control the height or the tilt angle of the ground plane. Figure 7c shows a conceptual configuration of the RA with a segmented ground plane, which allows for a wider beam scanning range. The performance metrics of this RA are summarized in Table 2 and compared with other representative mechanical beam-steerable antennas that employ array movement methods.