# 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  
The application of antenna technologies for mm-wave 5G cellular handsets is still not widespread with respect to antennas architectures. Considering the significance and role of cellular phones in the mobile network industry, mm-wave antennas for 5G cellular handsets are considered as the trend-shifting technology for 5G mobile networks. The use of a mm-wave transceiver within a mobile phone presents significant challenges that should be considered [7; 16]. The importance of these challenges is found because of the unique scenarios related to the use of mobile phones. Mobile phones are more compact in size relative to tablet PCs and wireless docking stations, and owing to the expanded use of smart phones, their usage scenarios are highly varied [7]. Secure and reliable communication link at Gbps speeds need to be guaranteed by the 5G transceivers within a mobile phone. Among the key factors considered in the establishment of mm-wave 5G networks, the antenna design requires the most extensive modifications. The antennas, which are technically described as omnidirectional antennas that transmit and receive RF signals equally in all horizontal directions in both geometrical planes, are the focus of resonant-type antennas implemented in user devices. The omnidirectional antennas inside mobile phones have gains that generally fall within the range of -8 to 0 dBi [28]. To compensate for the high signal attenuation at mm-wave frequencies with increased gain, the idea of antenna arrays for mobile phones was proposed.  
In the wireless communication industry, the design of antennas for mobile phones is considered by RF and antenna engineers to be an engineering art. This is because of the difference in the performance  
Figure 4: Beamforming antenna array scenario at BS and MS.  
of antennas when in an ideal situation in free space and when installed inside a handset. It is not possible for an antenna that is installed in a mobile phone to behave identical to one in free space without considering real-time scenarios. The induced electric and magnet field-coupling due to the antenna surface currents eventually affect the characteristic impedance matching and designed antenna efficiency in free space [16; 25; 40]. Moreover, the radiation performance of the antenna varies owing to the presence of other electronic components and the metallic casing [41]. Most of the space inside mobile phones is taken up by the large liquid-crystal display (LCD) and battery. The metallic brackets located behind the LCD effectively limit the design of current mobile phone antennas to the device edges [40]. Moreover, the use of certain metallic frames that are employed for different types of sensors, cameras, speakers, and microphone modules further reduce the available antenna space inside cellular phones [16]. Therefore, antenna arrays with single- and multilayer printed circuit board (PCB) technologies, polarization diversity, and a wide scanning range will be presented in this paper.