# Compact Sub 6 GHz Dual Band Twelve-Element MIMO Antenna for 5G Metal-Rimmed Smartphone Applications
## 4 Experiment and Measurement Results
Moreover, the trends of the simulated and measured ECC variations are in favorable agreement. Although the twelve-antenna units have the same structures, the ECC values between the antenna pairs (i.e., Ant 1-Ant 2, Ant 2-Ant 3, and Ant 3-Ant 4) differ because of the different ground plane positions adjacent to the antennas. However, all ECCs are sufficiently low for practical applications. Therefore, the antennas can be considered to have favorable channel independence. MEG is a crucial parameter in diversity power analysis, representing the ratio of the average power absorbed by the antenna to the average incident power of the antenna system. This serves as an important metric in evaluating the efficiency and performance of the antenna system. In the lower frequency band, the MEGs range from \(-3.90\) to \(-5.57\) dBi, while in the higher frequency band, they range from \(-4.10\) to \(-4.92\) dBi, as shown in Figure 13. It is worth noting that the maximum difference in excited MEGs between Ant-3 and Ant-6 is only 1.10 dB, occurring at 3.48 GHz. This difference is considered small enough for practical applications. In addition, DG is a significant parameter in MIMO systems as it measures the reduction in transmitted power loss achieved through the implementation of diversity mechanisms. Figure 14 displays the DG curves of the proposed MIMO antenna. The antenna system exhibits a diversity gain greater than 7.66 dB at low frequencies and 9.43 dB at high frequencies. Figure 12: ECCs of the (**a**) simulated and (**b**) measured radiation patterns of the twelve-antenna system. Next, TARC is the square root of the incident power obtained from all excitations minus the radiant power, divided by the incident power. To maintain clarity and avoid a cluttered appearance, Figure 15 presents TARC data for only three specific values of \(\theta\): 0\({}^{\circ}\), 90\({}^{\circ}\), and 180\({}^{\circ}\). However, the average TARC, calculated by averaging over the range of \(\theta\) from 0\({}^{\circ}\) to 180\({}^{\circ}\) with a sampling spacing of 9\({}^{\circ}\), consistently remains below \(-\)7.5 dB within the desired frequency range. This value is smaller than the -6 dB threshold for the impedance band. Figure 14: DGs of the twelve-antenna system. Figure 6:0 TARCs for the proposed twelve-antenna system. Figure 16 presents the three-dimensional (3D) radiation patterns for each antenna at 3600 MHz and 4800 MHz. The far-field radiation patterns of the twelve-antenna units operating at 3600 MHz and 4800 MHz were found to be similar but not identical. The 3D radiation pattern provides a full range of radiation performance information, including the radiation characteristics of the antenna in the horizontal (H-plane) and vertical (E-plane) directions. The computed ECC values from the measured radiation patterns were all less than 0.38. This result is also consistent with the ECC values shown in Figure 6:1 It can also be observed that the two sets of six-antenna units each are configured in a slanting mirror image arrangement, which results in a slanting mirror image characteristic in their radiation patterns. Figure 17 presents the simulated and measured antenna efficiency of the system. The simulated and measured efficiencies for each frequency band are both greater than 36%, indicating good performance. The measured efficiency values of the high- and low-frequency bands are 36-62% and 46-63%, respectively. The simulation and measurement data have a slight discrepancy. This may be attributable to the transmission line and its length, which were not included in the simulation. Moreover, the soldering, FR4 substrate, and copper sheet used to fabricate the antennas may not have been accurately reproduced in the simulation.