# Recent Developments and State of the Art in Flexible and Conformal Reconfigurable Antennas
## 3 Pattern-Reconfigurable Antennas
### Mechanically Pattern-Reconfigurable Antennas  
Mechanically pattern reconfigurable antennas are presented in response to disadvantages of using electrical switches, which were discussed in previous section. A pattern reconfigurable origami quasi-Yagi helical antenna using a copper film on DNA shaped PET substrate is presented in [91]. The pattern is reconfigured between four states at 2.2 GHz by changing the role of the DNA reflector and the DNA based director. In this antenna, three origami DNA geometries are used. Besides the reflector and the director, the antenna has a DNA shaped driven element. In States 1 and 2 of the antenna, the beam is directed to 30\({}^{\circ}\) and -30\({}^{\circ}\) where a parasitic director is designed by folded origami DNA and parasitic reflector is made of unfolded origami DNA for State 1 and vice versa for State 2. In State 3, the beam is directed to 0\({}^{\circ}\) and in State 4 it is directed at -50\({}^{\circ}\) and 50\({}^{\circ}\), where both the parasitic elements are folded in State 3 and unfolded in State 4. A thermally reconfigurable antenna based on origami reflectors with ability to switch the beam direction and beamwidth is presented in [92]. The proposed antenna comprises of a single monopole antenna and four origami reflectors made of copper-clad FR4 substrate. Smart shape memory polymer hinges are used to stimulate the reflectors. The beam of antenna is switched between omnidirectional pattern in State 1 (all reflectors are folded), directional pattern in the 45\({}^{\circ}\), 135\({}^{\circ}\), 225\({}^{\circ}\), and 315\({}^{\circ}\) in State 2 (by unfolding various reflector pairs) and directional beam in 0\({}^{\circ}\), 90\({}^{\circ}\), 180\({}^{\circ}\), and 270\({}^{\circ}\) in State 3 (by unfolding each origami reflector). In addition, the 3 dB beamwidth is changed from 52\({}^{\circ}\) (State 2) to 140\({}^{\circ}\) (State 3). The antenna's half-power beamwidth (HPBW) is changed from a 360\({}^{\circ}\) to 40\({}^{\circ}\) in a bi-directional pattern with a loop antenna array based on magic cube origami in [95]. The antenna is an array which consists of three single cubes with a single loop antenna, in serious form. The array can be folded and unfolded due to the nature of structure. The single antenna on a single cube was designed at 1.39 GHz with 4.03 dBi gain and 360 degrees HPBW. The series of two and three loops by using two and three cubes is increased to 5.2 dBi (HPBW = 60) and 5.53 dBi (HPBW = 40), respectively. Figure 5 shows the fabricated antenna for three states. In another quasi-Yagi monopole antenna based on origami magic spiral cubes, the pattern is reconfigured between omnidirectional radiations and three other broadside patterns at 1.9 GHz [93]. The antenna consists of a stacked L-shaped driven monopole, an L-shaped reflector on the first origami magic cube, and two L-shaped directors on the Cube 2 and 3 3, all are fabricated on paper. In the first state, the monopole antenna has omnidirectional pattern with 1.9 dBi peak gain, which is increased to 5.7 dBi by adding L-shaped reflector. By adding first and second directors to this antenna the gain is increased to 6.8 dBi and 7.3 dBi, respectively. One of the challenges in origami-based pattern reconfigurable antennas is to maintain the shape after being folded or unfolded. In Reference [98], a suitable Kresling conical is presented for a spiral antenna. This antenna shape can be kept by its internal tension after unfolding. The pattern of this antenna is reconfigured between omnidirectional (folded) for planar spiral and unidirectional for conical spiral shape (unfolded) with circular polarization at 2.5 GHz to 3.2 GHz. This challenge is also addressed in [94]. A pattern-reconfigurable axial-mode helix antenna by controlling the height of helix is presented. The height is controlled by applying a direct current to the SMA spring, which is an actuator.