# Compact Quad-Port MIMO Antenna with Ultra-Wideband and High Isolation
## 4 Result and Discussion
### Far-Field Characteristics  
As shown in Figures 11 and 12, the radiation pattern in E-plane (XOZ), H-plane (XOY), and 3D radiation pattern at four frequency points (3 GHz, 6.16 GHz, 10.6 GHz, 14.92 GHz) are selected to study the far-field radiation characteristics of proposed MIMO antenna.  
Figure 11: Simulated radiation pattern of proposed MIMO antenna in: (**a**) E-plane (without strips); (**b**) H-plane (without strips); (**c**) E-plane (with strips); (**d**) H-plane (with strips).  
The first consideration is whether the introduction of the strip to reduce the coupling will affect the far-field characteristics of the antenna, so the simulation radiation patterns of the antenna in two main planes at the four frequency points without and with introducing strips are viewed, respectively, as shown in Figure 11. The radiation patterns in E-plane and H-plane are shown in Figure 11,b, when the metal strips are not introduced, and in Figure 11,d when strips are introduced. It can be observed that the introduction of the strip has almost no effect on the radiation properties of the proposed MIMO antenna.  
The radiation pattern of the proposed MIMO antenna at the four frequency points is shown in Figure 12, including the measured and simulated results in the E and H planes. From Figure 12, it can be seen that when the antenna works at 3 GHz, the antenna radiates omnidirectionally in the E plane, and shows slight directional radiation characteristics along \(0^{\circ}\) and \(180^{\circ}\) in the H plane. Figure 12 shows that the MIMO antenna shows similar radiation characteristics at 6.16 GHz of 3 GHz. The radiation patterns in Figure 12,d are  
Figure 12: Simulated and measured radiation patterns of the proposed MIMO antenna in two main planes at: (**a**) 3 GHz; (**b**) 6.16 GHz; (**c**) 10.6 GHz; (**d**) 14.92 GHz.  
slightly distorted, but also have basically omnidirectional radiation characteristics. At 10.6 GHz, the radiation pattern in the E-plane is collapsed at 90\({}^{\circ}\) in Figure 12c. When the antenna operates at 14.92 GHz, the E-plane in Figure 12d collapses near 210\({}^{\circ}\) and 330\({}^{\circ}\), and the H-plane also decreases sharply near 94\({}^{\circ}\) and 288\({}^{\circ}\), mainly because the parameters at high frequencies are more sensitive to size and more susceptible to influence.  
By comparing the measurement results and simulation results of the radiation patterns of the proposed MIMO antenna in two main planes in Figure 12, it can be seen that the overall trend of both is basically the same, and the reason for many burrs in the measured results may be due to manual testing and mechanical jitter. Comparing and analyzing the measurement and simulation results, the radiation pattern of the proposed MIMO antenna is similar to a circle in the E plane, which can radiate omnidirectionally, and has a slight directional capability in the H plane, which is more obvious at low frequencies and gradually weakened at high frequencies.  
Figure 13 gives a 3D radiation pattern for these four frequency points, which allows one to visualize the radiation properties of the antenna. Figure 14 shows the gain and radiation efficiency of the MIMO antenna for the two cases with and without the addition of the metal strip. It can be seen that the values of the gain and efficiency of the MIMO antennas are almost unaffected by the introduction of the strip to increase the isolation, and the trends of the variations almost coincide. The gain and radiation efficiency of the proposed MIMO antennas are favorable for the whole operating band. The gain steadily increases to a maximum of 7.81 dB and the radiative efficiency is always stable between 90% and 98%.  
Figure 13: Three-dimensional radiation patterns of proposed MIMO antenna at: (**a**) 3 GHz; (**b**) 6.16 GHz; (**c**) 10.6 GHz; (**d**) 14.92 GHz.