# A 28 GHz 5G Phased Array Antenna with Air-Hole Slots for Beam Width Enhancement
## 3 Design of the Eight-Element Array on a Mobile Handset  
To verify the performance of a 5G phased array antenna on a typical mobile platform, the number of dipole elements is increased up to eight on a ground having the size of a typical mobile handset, as shown in Figure 8. The \(1\times 8\) phased array antenna is located at the top side of the ground with the total dimensions of 130 mm \(\times\) 42 mm \(\times\) 0.127 mm. The detailed antenna parameters and the substrate material are identical to those of the two-element array case.  
Figure 6: Introduction of the air-hole superposed with the slot in the ground: (**a**) top view of the simulation environment for surface current intensity around the slot (**b**) comparison of surface current intensity from the supposed two cases.  
Figure 7: Comparison of HPBW at 28 GHz in the YZ plane for the supposed three cases.  
As shown in Figure 9, the proposed antenna exhibits a \(-10\) dB reflection coefficient bandwidth of \(5.1\) GHz while having the worst-case isolation level of \(22\) dB within that frequency bandwidth range. Figure 10a,b illustrate the radiation pattern of the proposed array antenna at \(28\) GHz with a \(0\) degree phase difference between ports in the azimuth (XY plane) and elevation (YZ plane) planes, respectively. As shown in the figure, the peak gain in the azimuth plane is \(11.15\) dBi toward \(+y\) direction with a side lobe level (SLL) of \(13\) dB. On the other hand, the proposed antenna exhibits a very wide HPBW of \(221\) degree in the elevation plane with a peak gain of \(11.15\) dBi. Regarding such results, the air holes superposed with the slots in the ground can provide a wide HPBW to the array antenna in the elevation plane regardless of the number of elements. Figure 11 shows the beam-scanning performance of the proposed array antenna in the azimuth plane. As shown in the figure, the proposed antenna has a probable scan angle of \(\pm 45\) degree (i.e., a total of \(90\) degree resulting from the symmetric structure) while maintaining the worst-case peak gain and SLL of \(10\) dBi and \(12\) dB, respectively.  
Figure 8: Top view of the proposed \(1\times 8\) phased array antenna on a mobile handset ground.  
Figure 9: Reflection coefficient of the proposed antenna and isolation between the elements.  
In summary, the proposed antenna exhibits adequate performances of reflection coefficient bandwidth, isolation level, peak gain, scan angle, and SLL [13] while having very wide HPBW, up to 221 degree in the elevation plane. Therefore, the proposed antenna can provide coverage of more than half of a hemisphere as a sub-array element, since it covers 90 degree in the azimuth plane with beam scanning and 221 degree HPBW in the elevation plane. If four proposed \(1\times 8\) phased array antennas are mounted on four corners of the mobile handset device, they can thoroughly cover the whole isotropic sphere without having a shaded area, as shown in Figure 1. Such characteristics can be a very crucial advantage when developing an array antenna system for 5G mobile handset applications.