# 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
#### 2.1.1 Multilayer Phased-Array Antennas for 5G Mobile Terminals  
In [10], [PERSON] et al. presented the basic design concept of mm-wave 5G antennas for cellular phones at 28 GHz. In that study, the design of 1 \(\times\) 16 mesh-grid antenna-element phased arrays at the top and bottom positions of cellular phones has been realized using two sets of PCBs, as shown in Figure 5d. The mesh grid antenna elements are arranged in slanted angles of approximately 50\({}^{\circ}\) at each corner of the PCB. The proposed mesh-grid mm-wave antenna array configuration exhibits a fan-beam radiation characteristic, as shown in Figure 5e. The proposed array antenna was measured in the anechoic chamber at Samsung Electronics headquarters located in Suwon, South Korea. The measurement results show a 130\({}^{\circ}\) and 12\({}^{\circ}\) 3-dB beamwidth in the elevation and azimuth planes, respectively. The proposed array antenna exhibits a 10-dB impedance bandwidth of 1 GHz at a 27.9-GHz center frequency. The antenna array inside the cellular device has a measured peak gain of more than 10.5 dBi. The radiation pattern mismatch between the free-space and integrated scenarios is because of diffraction and refraction between the chassis and antenna elements of cellular phones. Figure 5f illustrates the radiation patterns of a mm-wave antenna array in specific beam directions for both free-space and integrated scenarios. The measurement shows an angular scanning range of \(\pm\)70\({}^{\circ}\). The proposed antenna array configuration on the top and bottom of the cellular device achieved an almost spherical radiation coverage, as shown in Figure 5e.  
Figure 5: _Cont._  
In [42], a planar quad-mode wideband phased array for a 5G mobile terminal device was reported. A phased-array design consists of eight antenna elements with eight MMPX (Micro-Miniature Connector) connectors. The proposed phased array is a multilayer design comprising two Taconic RF-30 substrate layers with thickness 0.762 mm, having a dielectric constant of 3 and loss tangent of 0.0014, vias, and microvias. Both layers were glued with FR4 glue having a thickness of 0.2 mm, and a dielectric constant of 4.3 and tangent loss of 0.025. The design overview of the proposed antenna is shown in Figure 6a. A coaxial-to-differential stripline transition feeding is proposed. The antenna is fed by a differential stripline feed. The top and bottom dipole antennas were connected to differential stripline through vias, as shown in Figure 6a. The proposed array antenna generates four distinctive modes when excited, as illustrated in Figure 6b, with an endfire radiation pattern in all modes. The measured reflection coefficients of the proposed eight-element phased-array antenna are presented in Figure 6d. The main beam-scanning range is from \(-90^{\circ}\) to \(+90^{\circ}\). Figure 6g illustrates the scanning results of the proposed beam-steering phased-array antenna at 25, 27, 29, and 31 GHz. The final prototype of the phased-array antenna with connectors is shown in Figure 6i.  
Figure 5: (**a**) Comparative illustration of the standard cellular antenna and mm-wave 5G antenna. (**b**) Proposed antenna. (**c**) Prototype photograph of the standalone mm-wave antenna array with coaxial connectors. (**d**) Photograph of mm-wave 5G cellular antenna array integrated inside a Samsung handset and zoomed-in views of 5G mm-wave antenna array. (**e**) mm-wave antenna array configuration for 5G cellular mobile terminals. (**f**) Measured and normalized radiation patterns for different beam directions (Figure 5f redrawn from [10]).  
Figure 6: _Cont._