# Review of Recent Phased Arrays for Millimeter-Wave Wireless Communication
## 2 Millimeter-Wave Antenna Array for 5G Communication
### Millimeter-Wave Antenna Arrays for 5G Mobile Terminals
#### 2.1.3 Single-Layer Phased-Array Antennas for 5G Mobile Terminals  
A novel design of a Vivaldi phased antenna array is presented in [48] for 5G mobile terminals. A low-cost N9000 PTFE substrate was used for the proposed phased-array antenna. The proposed array antenna comprises eight antipodal Vivaldi antenna elements. A 50-\(\Omega\) microstrip feed line feeds the tapered arms on the upper side of the antenna and is used at the upper end of mobile PCB, as shown in Figure 9b. The simulated S-parameters of the eight Vivaldi elements with discrete ports are shown in Figure 9c. The antenna has an operating bandwidth of more than 1 GHz at a 28-GHz center frequency. The surface-current distribution of the proposed 5G array antenna at an operating frequency of 28 GHz is shown in Figure 9b. The proposed phased-array antenna has enough beam-scanning range in the \(\varphi\) direction ranging from 0\({}^{\circ}\) to 70\({}^{\circ}\), as shown in Figure 9d,e. Figure 8: (**a**) Geometry of the mobile terminal with array position in lateral and corner edges. (**b**) Prototype photograph of the multi-polarized quasi-Yagi-Uda antenna arrays for lateral and corner edges. (Redrawn from [47])  
A phased-array antenna with switchable three-dimensional (3D) scanning for 5G mobile terminals was proposed in [49]. Three similar subarrays of patch antennas arranged along the edge of the mobile terminal were proposed. Each subarray consists of eight microstrip patch antenna elements (MPAs) and has a beam-scanning capability of \(\pm 90^{\circ}\) in the \(\theta\) plane. The antenna was designed on the Nelco N9000 substrate having a thickness of 0.787 mm with a dielectric constant of 2.2 and tangent loss of 0.0009. Figure 10c illustrates an architecture to implement feeding using low-loss phase shifters with a  
Figure 9: (**a**) Geometry of the Vivaldi phased-array antenna. (**b**) Surface-current distribution of proposed phased-array antenna at 28 GHz. (**c**) Simulated S-parameters of the proposed Vivaldi antenna array elements. (**d**) Radiation patterns of the antenna at different scanning angles. (**e**) Realized gain patterns of the antenna at different scanning angles. (Redrawn from [48]). 4.5-dB insertion loss for beam-steering, and a microwave SP3T switch to switch between the subarrays. The proposed design has a 1-GHz 10-dB impedance bandwidth in the frequency range from 21 to 22 GHz, as shown in Figure 10b. The proposed phased-array design has a good beam-scanning range of \(-90^{\circ}\) to \(+90^{\circ}\) with a gain of more than 12.5 dBi, as shown in Figure 10d,e. Figure 10: (**a**) Proposed view of 5G phased-array antenna with full ground plane. (**b**) S-parameters of proposed phased-array antenna with eight elements. (**c**) Proposed phased-array architecture. (**d**) 3D radiation patterns of each subarray at different scan angles. (**e**) 2D realized gain patterns at different scan angles. (Redrawn from [49])  
The 3D beam coverage was achieved and proposed by [PERSON] et al. in [50]. Three planar phased subarray configurations, as shown in Figure 11b, were used to change/switch the beam pattern to their distinct regions using chassis surface-wave excitation. The 3D spherical coverage is achieved by merging the beam patterns of subarrays. The proposed antenna has a 2-GHz 10-dB impedance bandwidth at 28 GHz, as shown in Figure 11b. A Nelco N9000 PCB substrate was used to design the antenna with a dielectric constant of 2.2 and a loss tangent of 0.0009. The substrate dimensions are 65 mm \(\times\) 130 mm, with a thickness of 0.764 mm. A subarray comprises eight slot elements, each with a dimension of 4.85 mm \(\times\) 0.5 mm. The consecutive slot-element distance from center-to-center is 5.35 mm. The whole phased-array switches the main beam between subarrays in the \(\varphi\) direction, and scans the beam in the \(\theta\) direction with variable phase shifts, as shown in Figure 11c,d. All the elements between subarrays A, B and B, C have a mutual coupling lower than \(-\)12.3 dB and \(-\)9.4 dB, respectively.