# A 28 GHz 5G Phased Array Antenna with Air-Hole Slots for Beam Width Enhancement
## 4 Experimental Results  
To verify the beam-steering performance, the proposed antenna was fabricated as a \(1\times 8\) mobile handset array antenna, as shown in Figure 12a. Etching process was applied to print the metal patterns on both sides of the substrate while simple drilling was used to realize the air-hole slot. Two types of fixed microstrip feeding networks were implemented to represent the linear phase differences of 0 degree and 120 degree for a 0 and 45 degree scan, respectively, as shown in Figure 12b. The substrate material and detailed antenna parameters for the proposed array antenna are identical to those of the two-element array design.  
Figure 11: Radiation pattern of the proposed phased array antenna at 28 GHz in the XY plane (azimuth) when the phase difference between element ports is varied from 0 degree to 120 degree with a step of 60 degree.  
Figure 10: Radiation pattern of the proposed phased array antenna at 28 GHz when the phase difference between element ports is 0 degree (0 degree scan): (**a**) XY plane (**b**) YZ plane.  
For measuring the reflection coefficient and the radiation pattern, Agilent N5230A vector network analyzer with Agilent/HP 85056D calibration kit and millimeter-wave anechoic chamber equipped with MTG operating software were used, respectively.  
Figure 13 illustrates the measured reflection coefficients at the input port of the 1 8 array antenna with fixed microstrip feeding networks. The proposed array antenna has a 10-dB reflection coefficient bandwidth from 27.2 GHz to 29.2 GHz. As show in Figure 13, the measured results agree reasonably well with the simulated ones implemented with the fixed feeding network. A slight discrepancy between the simulated and measured results can be explained as an outcome of errors from measuring and manufacturing.  
Figure 14 shows the measured radiation patterns of the proposed array antenna at 28 GHz along with the simulated results. Since the available anechoic chamber was technically specified to provide accurate results only for a rotational range from \(-120\) to \(+120\) degree relative to the boresight, plots in Figure 14 are illustrated within that range. As shown in Figure 14a,b, the measured peak gain of the array antenna with a 0-degree scan is 10.33 dB in the XY plane with a HPBW of 219 degree in the YZ plane. As shown in Figure 14c, the measured peak gain of the array antenna with a 45 degree scan is 9.64 dBi in the XY plane with an SLL of 10.1 dB. As shown in the figures, the measured radiation patterns reasonably agree well with the simulated results, except for a small discrepancy in the gain value of approximately 0.8 dB, which can be interpreted as an experimental error, including loss from the feeding connector. In summary, the fabricated antenna shows very wide HPBW in the elevation plane, while maintaining adequate performance in the other criteria, and agreeing reasonably well with the simulated results.  
Figure 12: Fabricated \(1\times 8\) array antenna: (**a**) top view (**b**) bottom view  
Figure 13: Measured and simulated reflection coefficient of the proposed array antenna.