## 3 Beam Steering/Beam Forming Using Reconfigurable Components
### Microfluids  
In the modern era, adaptability and versatility are fascinating characteristics of advanced communication systems. Microfluids have exotic parameters, flexible flow properties, and acquiescent elastic limits, and are mechanically flexible compared to copper or other metallic materials. These feathers are also helpful for innovative fabrication technologies such as 3D antennas, spraying antennas, and fluid conductive antennas. Compared to traditional high speed switching methods, beam steering reconfigurable antennas function with the reconfigurability of microfluid liquids related to electronic pumping and electro-mechanically controlled capillaries. Several articles for reconfigurable microfluid transmitarray beam steering are demonstrated in the preceding literature [105; 106; 107; 108]. Additionally, a circularly polarized microfluid-based transmitarray antenna unit cell is reported in [108]. The reconfigurable unit cell was manufactured with two split rings slots produced so that microfluid can pass through this channel, as shown in Figure 10. Microfluid passes through these split slot channels to obtain control on the phase shift beam steering. Microfluid circulates through the symmetric circular rings of elements and rotates through the circular slots causing liquid displacement to be controlled and the phase shift to double the rotation angle. The circulation of microfluid passing through the circular rings delivers continuous 0-360 degrees of phase shift. A microfluid transmitarray prototype is manufactured at glass substrate, and a slot channel is etched by Polydimethyl-siloxane (PDMS) at 8.8 GHz frequency. The expected insertion loss includes 2-3 dB, reaching up to 1 dB liquid rotation. The proposed element insertion losses become remarkably high \(-10\) dB with testing of waveguide characteristic setup. On the contrary, it takes time to reconfigure itself in the active mode, which reduces its effectiveness for applications. Each unit cell acquires many slot tubes to circulate microfluid inside the elements to gain reconfigurable characteristics. This feature will lead to an increase in the unit cell sizes to utilize the slot tubes.  
Moreover, a plasma reconfigurable transmitarray/reflectarray antenna is introduced in [109]. The radiating incident waves with a source feed antenna are placed in different directions. A 13 \(\times\) 13 elements array composed of 169 elements with reconfigurable plasma as a transmitarray/reflectarray antenna is demonstrated. The reflectarray antenna mode is exhibited due to the plasma ground plane acting as a perfect conductor and collision frequency of atoms 1 THz. Contrarily, when the plasma ground plane is not ionized, it behaves as a dielectric material to perform the transmitarray antenna mode. The phase shift of the array is controlled by argon gas density injected into symmetrical unit cells. Each element consists of a two cylindrical tubes setup on the top and bottom and a ground plate filled with argon (\(\rm{Arg}_{g}\)) gas. DC-bias voltage is applied to the end of the cylinder. The frequency of plasma argon gas (\(\rm{Arg}_{g}\)) is varied, leading to variation in the reflection coefficient from 0-305 degrees corresponding to the maximum reflection coefficient that reaches up to \(-8\) dB. The continuous transmiss  
Figure 10: (**a**) Top view of unit cell; (**b**) nested ring split ring prototype (reprinted with permission of [109]. Copyright 2015 [PERSON], et al.).  
executes from 0-345 degrees. Moreover, the remaining phase control compensates due to plasma frequency variation. Plasma transmitarray/reflectarray is accomplished with a 2D beam scanning ability of \(\pm\)30 degrees for the H-plane and E-Plane at 19.75 GHz and 19.39 GHz, respectively.