# MM-Wave Phased Array Quasi-Yagi Antenna for the Upcoming 5G Cellular Communications
## 3 The Phased Array 5G Smartphone Antenna  
Transparent and top views of a linear phased array design with the Quasi-Yagi antenna elements are shown in Figure 8. It has a low profile of W\({}_{\text{a}}\)\(\times\) L\({}_{\text{a}}\) = 9 \(\times\) 40 mm\({}^{2}\). The antenna elements are arranged with a distance of d = 5 mm. As it can be observed, it is composed of eight 26 GHz Quasi-Yagi antenna elements and could be used on the top/bottom portions of the smartphone PCB to form two  
Figure 6: Comparison of the antenna performance with/without directors: (**a**) radiation pattern and (**b**) gain. Figure 7: (**a**) Transmitted signal in free space and received pulses for (**b**) side by side and (**c**) face to face. sets of linear phased arrays [24; 25]. Figure 9 shows a phased array system architecture with a feeding network that could be used for the linear phased array Quasi-Yagi antenna and can be demonstrated using phase shifters for beam switching. Various techniques of feeding network design such as parallel and series can be employed for this purpose. In array designing, the spacing between the adjacent elements must be determined carefully due to its impact on the fundamental characteristics of the array [26]. The properties of the Quasi-Yagi array with various distances of the adjacent radiation elements have been studied in Figure 10. Its various configurations are illustrated in Figure 10a. Mutual coupling characteristics of the middle element of the array (\(\mathbb{S}_{21}\)) for various distances are plotted in Figure 10b. As seen, for different values of \(d\) (3.5 to 6.5 mm), the mutual coupling function varies from \(-8\) to \(-20\) dB. Figure 10c illustrates the 3D radiation beams of the Quasi-Yagi antenna array with directivity values for different values of \(d\) at 0\({}^{\circ}\) angle. As seen, by increasing the distance between the elements, the antenna radiation characteristics can be improved. However, on the other hand, the scanning angle of the array will be limited significantly. So, a trade-off between wide scanning and high radiation characteristics is needed. Figure 11 illustrates the proposed mm-Wave phased array 5G smartphone antenna. The antenna has an overall dimension of W\({}_{\text{sub}}\)\(\times\) L\({}_{\text{sub}}\) = 60 \(\times\) 120 \(\times\) 0.8 mm\({}^{3}\) and has been constructed on the Arlon Ad 350 dielectric. The designed linear array is placed on the top side of the PCB to provide beam-steering function at different scanning angles. In order to acquire a wide-scanning function (0 to \(\pm\)75 degree), the antenna elements are placed with a bit less than \(\lambda\)/2 (d = 5 mm) distance. Another set of the design could be deployed at the bottom side of the smartphone PCB. The S parameter results of the Quasi-Yagi 5G antenna array are shown in Figure 12: Good impedance-matching and same bandwidth of the single element (25 to 27 GHz) have been achieved for the proposed structure. In addition, a low mutual coupling function between the adjacent antenna elements has been achieved. Figure 8: (**a**) 3D transparent and (**b**) top views of the linear phased array antenna. Figure 9: Phased array system architecture. Figure 11: The mm-Wave smartphone antenna, (**a**) transparent, (**b**) top, and (**c**) bottom views. Figure 10: (**a**) Configurations, (**b**) S\({}_{21}\), and (**c**) radiation beams of the linear array for different vales of \(d\). The simulated surface current densities at 26 GHz for the phased array 5G smartphone antenna has been illustrated in Figure 13. It can be seen that the current flows are distributed around the radiation arms of the Quasi-Yagi antenna elements on the top side of the smartphone PCB. Each single-element Quasi-Yagi radiator has a high current density and appears very active at the resonance frequency (26 GHz) [27].