# Review of Recent Phased Arrays for Millimeter-Wave Wireless Communication
## 2 Millimeter-Wave Antenna Array for 5G Communication
### Millimeter-Wave Phased Arrays for 5G Access Terminals
#### 2.2.1 Millimeter-Wave PCB Phased Arrays  
In [9], [PERSON] et al. presented a comparative analysis of different antenna array architectures and beamforming techniques for outdoor mm-wave communication systems. Four different types of array architectures, i.e., an \(8\times 8\) rectangular element array, 64 circular element array, 61 hexagonal element array, and 16 cross-shaped element array architectures were analyzed, as depicted in Figure 15. The 2D radiation plots that were retrieved from 3D radiation patterns are illustrated in Figure 15. The analysis of different array architectures shows that the array architecture with circular elements has a larger coverage area with high gain and directivity compared to those of the other antenna array architectures. Figure 15: 2D radiation plots of (**a**) \(8\times 8\) rectangular element array, (**b**) 16 cross-shaped element array, (**c**) 64 circular element array, and (**d**) 61 hexagonal element array (Redrawn from [9]). In [13], a testbed with a bandwidth of 800 MHz at an operating frequency of 28 GHz, which was built to test the practicality of mm-wave cellular communications at Samsung Electronics, (Suwon) Korea, was presented. The BS antenna array consisted of (6 \(\times\) 8) 48 antenna elements that are grouped as subarrays in groups of three antenna elements to reduce the complexity of the system components. Each subarray provides a horizontal beam-scanning of 110\({}^{\circ}\) with the aid of a connected phase shifter, mixer, and an RF path. The MS antenna array was composed of two antenna subarrays, where each subarray provides horizontal beam-scanning of either 90\({}^{\circ}\) or 180\({}^{\circ}\), with four elements designed on one of the sides of the RF board. The design overview of the BS and MS antenna arrays are shown in Figure 16a,b, respectively. In [39], [PERSON] et al. proposed a novel array architecture for beamforming and multibeam massive MIMO systems using a metamaterial-based thin planar lens antenna. The proposed antenna comprises an EM lens combined with an antenna array. The EM lens together with an antenna array helps to increase the throughput and data rate of massive MIMO (m-MIMO). Both the lens and antenna elements were fabricated using PCB technology. Figure 17a,b respectively presents the side and top views of the proposed lens antenna. An array of a seven-element SIW-fed stacked patch antenna operating at 28 GHz is placed at the focal region behind the EM lens. Each subarray comprises four SIW-fed square patches as radiating patches. Each array element is connected to the input port using SIW-to-grounded-coplanar-waveguide (GCPW) transition feeding. The design overview of the seven-element SIW-fed stacked patch antenna array is given in Figure 17b. The proposed multilayer antenna array is fabricated on a Rogers RO4003C substrate having a dielectric constant of 3.55 and loss tangent of 0.0027. The thickness of the top and bottom layers is 0.508 mm and 0.813 mm, respectively. Figure 16: (**a**) Transceiver array antenna for BS. (**b**) Transceiver array antenna for MS. (**c**) Block diagram of testbed for mm-wave cellular communication with beamforming antenna array. (**d**) Testbed structure built at Samsung Electronics, Korea. (Redrawn from [13])  
Both layers are joined together with a bonding layer of Rogers RO4450B, which has a dielectric constant of 3.54, loss tangent of 0.004, and height of 0.202 mm. A photograph of the fabricated prototype of the proposed seven-element array loaded with an EM lens is shown in Figure 17c. The measured 10-dB impedance matching ranges from 25.8-28.9 GHz, as shown in Figure 17d. The angular beam-scanning range of the proposed phased array is from \(-27^{\circ}\) to \(+27^{\circ}\). Figure 17e shows the experimented radiation patterns of the proposed phased-array lens integrated antenna at 28 GHz. The measured peak gain of the lens-fed phased-array antenna is 24.2 dBi, with an efficiency of 24.5% at a frequency of 27.5 GHz.