# Slotted Circular-Patch MIMO Antenna for 5G Applications at Sub-6 GHz
## 3 A 2-Port MIMO System Using Two Flipped Parallel 1 \(\times\) 2 Arrays Antenna
### Measurement Results Discussion of Two 1 \(\times\) 2 Arrays MIMO  
#### 3.3.1 Reflection, Transmission Coefficients, Radiation Pattern, and Gain Results  
Figure 14a illustrates the simulated and measured reflection coefficients (S11 and S22) of the proposed MIMO of two 1 \(\times\) 2 antenna arrays design. The measurement shows that the reflection coefficient S11 remains below \(-\)10 dB across a band of (2.27:4.94 GHz) and (5.53:7.84 GHz), where the minimum simulated S22 is \(-\)44 dB, and the measured S11  
Figure 13: The MIMO of two 1 \(\times\) 2 arrays: (**a**) the simulated top side, (**b**) back side, (**c**) fabricated prototype top side, (**d**) back side, and (**e**) radiation efficiency.  
appears very similar to the measured S22. In contrast, it shows that the simulated S11 for the antenna is below \(-\)10 dB from 2.1 GHz to 2.7 GHz and 3.05 GHz to 6.23 GHz, but achieves a lower minimum measured S11 of \(-\)31 dB, where the simulated S11 appears very similar to simulated S22. This indicates that the fabricated antenna effectively covers all required frequency bands while maintaining good matching and high performance compared to the designed antenna. Figure 14b illustrates the measured and the simulated S12 and S21. The measured data show that the S12 is \(<\)\(-\)20 dB over the band of (3:7 GHz), where the measured S12 appears very similar to the measured S21. In contrast, it shows that the simulated S12 for the antenna is below \(-\)20 dB from 3 GHz to 6.8 GHz, where the simulated S11 appears very similar to the simulated S21. This indicates that the fabricated antenna has high performance.  
Figure 15 shows a radiation pattern of both simulated and measured electric fields at the sub-6 GHz band. Figure 15a,b present a radiation pattern of both simulated and measured electric fields at frequencies of 3.5 and 5.8 GHz, respectively. At 3.5 GHz, the main lobe magnitude is 4.83 dBi. The high front-to-back ratio (the difference in gain between the main lobe and side lobes) indicates excellent directivity. The main lobe is centered around 183\({}^{\circ}\), which is almost perfectly aligned along the broadside. The 3 dB beamwidth is 94.1\({}^{\circ}\), which is relatively wide. At 5.8 GHz, the radiation pattern shows a main lobe with a peak gain of 8.33 dBi directed at 167\({}^{\circ}\), indicating slightly off-broadside radiation. The main lobe is quite strong, demonstrating good directivity. The angular width of 50.4\({}^{\circ}\) suggests a moderate beam spread that balances coverage and directivity.  
Figure 16 illustrates the changes in gain across the frequency band. The simulated gain starts from 3.2 dBi at 2 GHz and increases gradually, reaching 8.9 dBi at 6.8 GHz as a peak gain. At frequencies of 3.5 GHz and 5.8 GHz, the circular-shaped antenna exhibits gain of 5 dBi and 8.5 dBi, respectively. The measured gain starts from 1.7 dBi at 2 GHz and increases gradually, reaching 8.3 dBi at 6 GHz as a peak gain. At frequencies of 3.5 GHz and 5.8 GHz, the circular-shaped antenna exhibits gain of 4.45 dBi, and 8.3 dBi, respectively.  
Figure 14: A comparison of: (**a**) the measured and simulated S11, S22, and (**b**) the S12 and S21, of the MIMO of two 1 \(\times\) 2 arrays design.