## 3 Beam Steering/Beam Forming Using Reconfigurable Components
### PIN Diodes
Furthermore, a novel architecture of a reconfigurable coupling slot transmitarray is mentioned in [83]: a prototype of a 1-bit electronically reconfigurable transmitarray for Ku-band. Two orthogonal H-shape slots were integrated on patches that act as transmitter and receiver, respectively. Electromagnetic energy was transmitted by coupling a transmit line in between slot patches. Diodes were mounted on the coupling line to realize the electronic phase control in an anti-parallel direction to produce 180\({}^{\circ}\) phase difference. The oblique incidence performance of the elements was maintained by sub-wavelength element spacing \(\lambda_{0}/3\). A 16 \(\times\) 16 element 12.5 GHz reconfigurable transmitarray was designed and tested. The maximum gain of 17.0 dBi corresponds to an aperture efficiency of 14.0%  
Figure 4: (**a**) Geometry of [PERSON] reconfigurable transmitarray with WIAM metasurface; (**b**) fabricated 1 \(\times\) 16 subarray prototype (reprinted with permission of [76]. Copyright 2021 [PERSON], [PERSON], et al.). Figure 5: Geometry of 3 \(\times\) 3 1 bit RTA element with biasing circuit; (**a–f**) exploded view, top view; (**g**) measures radiation pattern of E-plane and H-plane, respectively (reprinted with permission of [80]. Copyright 2021 [PERSON], [PERSON], et al.). presented in experimental results. The H-shape coupling slot transmitarray realizes a beam scanning angle within \(\pm\)50 degrees for E- and H-planes. The 3 dB gain bandwidth retains 9.6% in the measured results. This work is further improved in [84]: a 16 \(\times\) 16 elements reconfigurable transmitarray is proposed in this paper. The transmitter is designed as a C-shape feed probe placed beneath a rectangular patch to obtain the feathers of broad bandwidth and lower insertion loss. The receiver of the transmitarray is a U-shaped slot etched on a simple rectangular patch. To induce a reverse current path, two PIN diodes are symmetrically placed on the feed probe of the unit cell shown in Figure 6. The minimum measured insertion loss is realized at 0.47 dB for each phase state with 16% of 3 dB broad bandwidth achieved by stepped impedance matching performance. There are 256 elements in the feed shape probe transmitarray with 512 PIN diodes used in its manufacturing and testing. The maximum peak gain is 22.1 dBi at 12.5 GHz with an aperture efficiency of 21.2%. The 3 dB insertion bandwidth is realized at 12.3% with electronic beam scanning performance of \(\pm\)60 degrees for two-dimensional H- and E-planes, respectively. This novel reconfigurable transmitarray is a good solution for many applications in wireless communication systems. Another advanced technique structure of a transmitarray is reported in [85] with a polarization rotation unit cell. Two split circles are connected with two narrow strips with pin diodes mounted in between them. Polarization control structures sandwich the PIN diode loaded with a transmitter and receiver. The air gap is presented between the transmitter and receiver to mount diodes on patches easily, and bias circuits are etched on the polarization control structure. The phase difference 180\({}^{\circ}\) is achieved for two outgoing polarized waves for 0 and 180 degree phase states. The polarization control structure reduces the blocking effect of dc-bias lines and improves the aperture efficiency of the structure. A 16 \(\times\) 16 1-bit transmitarray is designed, fabricated, and tested in a test setup. Two-dimensional electronic beams scanning of \(\pm\)40 degrees is realized by the polarization rotation element. The maximum measure 3 dB and 1 dB insertion loss of 45% and 17%