# MM-Wave Phased Array Quasi-Yagi Antenna for the Upcoming 5G Cellular Communications
## 2 Quasi-Yagi Antenna  
In recent years, printed Quasi-Yagi antennas have been exhaustively analyzed and experimentally researched. According to the driven element form, the existing Quasi-Yagi antenna can be divided into a microstrip patch, double-sided dipole, or single-sided dipole form [19]. A schematic of the designed Quasi-Yagi antenna is displayed in Figure 1. The antenna was designed on a 0.8 mm Arlon Ad 350 (\(\varepsilon=3.5\) and \(\delta=0.003\)) dielectric to operate at 26 GHz. As shown in Figure 1, the antenna is fed by a coax-to-microstripline. The feeding point of the coaxial cable has been surrounded by a cylindrical metal vias. It is seen that the inner connector of the probe is connected to the feed line of the Yagi's arm while the outer connector has been connected to the ground plane. The final dimensions of the proposed Quasi-Yagi antenna and its linear array parameters are specified in Table 1. Figure 2 depicts the frequency response (S\({}_{11}\)) of the Quasi-Yagi  
Figure 1: Quasi-Yagi antenna schematic; (**a**) transparent view, (**b**) top, and (**c**) bottom layers. antenna. For comparison purposes, the antenna element was also designed using Ansoft high frequency structure simulator (HFSS) software [20], and its S\({}_{11}\) result has been added to Figure 2. As shown, more than 2 GHz bandwidth with good impedance-matching function in the frequency range of 25 to 27 GHz has been achieved. The operation frequency of the Quasi-Yagi antenna can be controlled by changing the size of the critical parameters. Based on the obtained results in Figure 3a,b, the resonance frequency of the antenna can be tuned by changing the values of W (width of antenna arm) and L\({}_{\text{g}}\) (length of the ground plane). Furthermore, as evident from Figure 3c, the length of the directors (W\({}_{1}\)) has a significant impact on the matching function of the designed Quasi-Yagi antenna. Figure 4a represents the simulated surface current densities of the Quasi-Yagi antenna at its resonance frequency (26 GHz): the current flows are opposite around the antenna driving arms and directors. The radiation pattern of the antenna at 26 GHz is displayed in Figure 4b: the Quasi-Yagi antenna exhibits an end-fire radiation pattern and provides 4.4 dB realized gain level at its frequency resonance. The realized gain is the power gain of the antenna including mismatch losses [21]. It should be noted that the directors of the antenna improve the radiation behavior and impedance-matching of the designed Quasi-Yagi antenna [22]. Figure 5 illustrates the Quasi-Yagi radiation and total efficiencies versus its impedance bandwidth. It can be observed that high-efficiency characteristics (radiation efficiency > 95% and total efficiency > 85%) have been achieved over the antenna operation bandwidth. Using the directors, the antenna can provide a well-defined and more directional end-fire radiation pattern. It can also improve the gain level of the antenna at the operation frequency. Figure 6 illustrates a comparison of the antenna radiation behavior with/without the directors. As seen in Figure 6a, the antenna with directors can provide a good radiation pattern with higher gain and efficiency properties at 26 GHz compared with the antenna without the directors. In addition, as illustrated in Figure 6b, using the directors, the realized gain function of the antenna over the operation band has been increased significantly.