# A Sub-6 GHz MIMO Antenna Array for 5G Wireless Terminals
## 3 Results and Discussion
Figure 11: (a) The 3D gain pattern of the proposed antenna array, (b) current distribution, (c) E field and (d) H field of the proposed array structure. The reflection coefficient for the proposed MIMO structure is presented in Figure 12a. For port-1, the antenna resonates with the central frequency of 5.57 GHz, gives a bandwidth from 5.59 to 5.54 GHz, and a magnitude of \(-25\) dB. Similarly, for port-2, the antenna resonates with the central frequency of 5.56 GHz, with a reflection coefficient magnitude of \(-26\) dB. The magnitude of the return loss remains below \(-10\) dB, within the resonant bandwidth (5.58 to 5.53 GHz). The isolation for the proposed MIMO antenna is presented and analyzed in Figure 12b for both the ports with respect to each other. The isolation is observed to be greater than 40 dB within the operating bandwidth, which clearly indicates that the isolation among the arrays employed is quite minimum. The gain patterns are analyzed and presented in Figure 13a in the 0- and 90-degree planes for the port-1. Initially, in the 90-degree plane, the antenna array main lobe direction is located at 2.0 degrees, while a very good side lobe level of \(-17.1\) dB is achieved with a 3-dB beamwidth of 82.1 degrees. The radiation pattern is quite directive, with minimum back lobes and side lobes. The 0-degree plane analysis shows that the main lobe is directed towards the 0-degree angle and the side lobe level is \(-17.1\) dB. Furthermore, a 3-dB beamwidth is 22 degrees. In this particular plane, the radiated beam is also seen to be highly directive with a low level of back lobes. Similarly, the radiation pattern analysis in the case of port-2 is presented in Figure 13b for the two main planes: E and H. The main lobe direction for the 0-degree plane is along the 355-degree angle, and the side lobe level is \(-3.1\) dB, while the angular width is 83 degrees in this particular plane. Likewise, the direction of the main lobe is along 1.0-degree angle in the 90-degree plane, with an angular width of 22.4 degree. The side lobe level is \(-15.1\) degrees in this plane. Further in-depth analysis of the radiation feature of the proposed MIMO configuration (antenna array employing a corporate feeding technique) is presented in Figure 14. The port-1 or antenna-1 has a narrow and directive beam with a peak gain of 12.6 dB. Figure 6:0 MIMO: (**a**) reflection coefficient; (**b**) isolation. The radiation efficiency and the total efficiency is 98.2% and 85.1%, respectively. Furthermore, for port-2 the radiation beam is shifted by a 90-degree angle, which shows  
Figure 6:1 MIMO 3D radiation pattern: (**a**) port-1; (**b**) port-2. Figure 6:2 MIMO polar radiation pattern: (**a**) port-1; (**b**) port-2. that pattern diversity) is achieved with the proposed MIMO structure. The peak gain of 12.6 dB is achieved with radiation and total efficiency of 97.8 and 79.6%, respectively. The Envelope Correlation Coefficient (ECC) is another parameter that describes the level of correlation among multiple antennas which come into close proximity of each other. For the proposed MIMO configuration of two port antenna array, the ECC value is below 0.005 for the entire operating bandwidth, which satisfies the standard criteria of a value of <0.5, and depicts that isolation among the antenna arrays is minimum as shown in Figure 15a. Another performance metric of MIMO is Diversity Gain (DG)--meeting or coming close to the standard value of 10 dB shows that reduction in the transmitted power will have no major effect on the quality of transmission or MIMO performance. As seen in Figure 15b, the DG value is close to 10 for the entire operating bandwidth, which satisfies the standard criteria. All the results discussed above show that MIMO-based corporate feed arrays are very suitable for future 5G Sub-6 GHz communication.