## 3 Results and Discussion  
The dimensions of the three antennas were optimized using parametric studies. Figure 5 illustrates the full-screen handset model flanked by the three antenna prototypes. The antennas are soldered to semi-rigid 0.047 coaxial cables from Woken Technology Inc., Taiwan, for measurement purposes. Figure 6 shows the reflection coefficients for the unit elements. Referring to Figures 2-4, the input ports were evaluated at \(F_{1}\), \(F_{13}\), and \(F_{21}\), respectively. With respect to a \(-10\) dB threshold, the simulated (and measured) impedance bandwidths were 26.5-32.0 GHz (25.7-28.0 GHz), 35.2-42.0 GHz (34.0-38.1 GHz), and 2.41-2.48 GHz (2.40-2.48 GHz) for each antenna. Slight frequency shifts were observed for the  
Figure 4: (**a**) The geometry and (**b**) surface current distributions for the 2.45 GHz loop antenna (all measurements are in mm). Figure 5: The prototype of the proposed antenna design and integration. These discrepancies were mainly attributed to the soldering process, since soldering a connector within parallel conductive plates adds to the manufacturing complexity. According to the 5G NR FR2 standard, the maximum input power for the antenna is 26 dBm. When this input power was transmitted by the antenna, less than 10% was reflected to the transceiver. This indicates that the proposed antenna is capable of transmitting and receiving signals in practical use. It should be noted that satisfying the bandwidth requirement for the WLAN antenna was challenging due to the presence of the parallel conductive plates, yet the proposed loop antenna achieved the desired bandwidth. Figure 7 provides mutual coupling between adjacent elements for the millimeter-wave arrays. The results for the 28 GHz array were measured between ports \(F_{1}\) and \(F_{2}\), whereas ports \(F_{13}\) and \(F_{14}\) were used for the 38 GHz array. The isolation was generally larger than 20 dB, which indicates that less than 1% of power was coupled to adjacent ports when one port was excited. This isolation is sufficient to guarantee the integrity of the signal. Although the measured mutual coupling was obviously larger than the simulated results on a logarithmic scale, the difference was insignificant when plotted on a linear scale. Note that there were other mutual coupling coefficients for the proposed arrays. Among all these mutual coupling coefficients, the worst-case scenario applies to adjacent elements. These other coefficients were lower than the results shown in Figure 7, which are intended to demonstrate the worst-case scenario for each array. Next, the isolation of the 28 GHz and 38 GHz bands was investigated. While there are three operating bands, the isolation of the two millimeter-wave bands is more important, since the frequency of the WLAN band is more than 10-times lower than the millimeter-wave bands. The first element of the 28 GHz band (\(F_{1}\)) and that of the 38 GHz band (\(F_{13}\)) were excited, and the results for their simulated and measured mutual coupling are shown in Figure 8. Due to the physical separation of the elements and the frequency separation, mutual coupling was generally below \(-40\) dB, indicating high isolation of the two bands. As a result, when the two modules are operated simultaneously, the interference will be insignificant. Figure 6: Reflection coefficients for the 28 GHz unit element, 38 GHz unit element, and 2.45 GHz loop antenna. Figure 9 illustrates the antenna efficiency and realized peak gain for each module. For the two arrays, only single ports (\(F_{1}\) and \(F_{13}\)) were excited individually. At 28 GHz, the simulated (measured) efficiency and peak gain were 96.4% (91.4%) and 6.3 dBi (6.6 dBi), respectively, whereas at 38 GHz the simulated (measured) efficiency and peak gain were 96.2% (69.5%) and 7.7 dBi (6.0 dBi), respectively. The simulated (measured) antenna  
Figure 8: Mutual coupling of the millimeter-wave elements. (**a**) 28 GHz and (**b**) 38 GHz bands. Figure 7: Mutual coupling between adjacent elements of the two antenna arrays.