# Slotted Circular-Patch MIMO Antenna for 5G Applications at Sub-6 GHz
## 4 A 2-Port MIMO System Using Two Opposite 1 \(\times\) 4 Antenna Arrays
### Design of (1 \(\times\) 4) Antenna Array Arrangement  
Maximizing antenna gain for improved coverage and connection performance in 5G applications, particularly in the sub-6 GHz range can achieve an increase in gain of approximately three times in dBi, when comparing a 1 \(\times\) 4 array antenna configuration to a single element or a 1 \(\times\) 2 array. The simulated top and back sides of the design are illustrated in Figure 18. The design's input impedance is around 50 ohms at 3.5 GHz and 5.8 GHz, as shown in Figure 18c. Table 6 lists the design dimensions.  
The simulated reflection coefficient (S11) of the suggested 1 \(\times\) 4 array of circular antennas is shown in Figure 19. The antenna resonates at dual bands: 2.68 GHz to 4.4 GHz and 4.85 GHz to 5.69 GHz. The minimal value measured reflection coefficient (S11) is \(-36\) dB. Figure 20 illustrates the changes in gain across the frequency band. The simulated gain starts from 6.1 dBi at 2 GHz and increases gradually, reaching 10.8 dBi at 6 GHz as a peak gain. During the frequency band from 3 GHz to 6 GHz, the gain grows from 8.5 to 10.7 dBi. At frequencies of 3.5 GHz and 5.8 GHz, the circular-shaped antenna exhibits gain of 9.2 and 10.6 dBi, respectively.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref. No.** & **Size** & **Bandwidth** & **Max Gain** & **Max Efficiency \%** & **ECC** \\ \hline
[27] & 85 \(\times\) 97.73 \(\times\) 1.6 & 3.43–3.9 & 6.56 & 70 & - \\ \hline
[36] & 160 \(\times\) 75 \(\times\) 7.5 & 3.4–3.6 & - & \textgreater{}55 & \textless{}0.1 \\ \hline
[37] & 150 \(\times\) 75 \(\times\) 7.8 & 3.3–3.6 & - & 60 & \textless{}0.31 \\ \hline
[38] & 150 \(\times\) 75 \(\times\) 7 & 3.1–6 & 5.8 & 65 & \textless{}0.02 \\ \hline
[39] & 95 \(\times\) 65 \(\times\) 0.2 & 3.05–3.07 & 2.2 & - & \textless{}0.1 \\ \hline Proposed MIMO of two 1 \(\times\) 2 arrays & 132 \(\times\) 66 \(\times\) 1.57 & 2.27–4.94 & 8.3 & 95 & \textless{}0.006 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of the proposed MIMO of two 1 \(\times\) 2 arrays with previous studies.  
Figure 19: The simulated S11 of the 1 \(\times\) 4 array.  
Figure 20: The simulated gain of the 1 \(\times\) 4 array.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Parameter** & **Substrate Width** & **Substrate Length** & **W\({}_{\mathbf{f}}\)** & **L\({}_{\mathbf{f}}\)** & **W\({}_{\mathbf{1}}\)** & **W\({}_{\mathbf{2}}\)** & **W\({}_{\mathbf{3}}\)** & **L\({}_{\mathbf{1}}\)** & **L\({}_{\mathbf{2}}\)** & **L\({}_{\mathbf{g}}\)** \\ \hline (mm) & 140 & 66 & 4.21 & 7.72 & 16 & 12 & 15 & 13 & 10 & 27.67 \\ \hline \end{tabular}
\end{table}
Table 6: Dimensions of the 1 \(\times\) 4 array.  
Figure 18: The 1 \(\times\) 4 array: (**a**) the simulated top side, (**b**) the back side, and (**c**) input impedance over frequency.  
Figure 20: The simulated gain of the 1 \(\times\) 4 array.  
The radiation pattern of the simulated antenna is established for the E-plane radiation pattern at 3.5 GHz and 5.8 GHz, as demonstrated in Figure 21. Figure 21a shows that, at a frequency of 3.5 GHz, the main lobe peaks at 9.25 dBi, demonstrating high directivity with a beam pointing at 196\({}^{\circ}\). The 3 dB beamwidth is 71.6\({}^{\circ}\), offering a balance between directionality and coverage. The lack of prominent side lobes indicates effective sidelobe suppression, reducing interference. Figure 21b shows that, at frequency 5.8 GHz, the main lobe reaches a peak gain of 10.4 dBi, showing strong directivity with the main beam centered at 30\({}^{\circ}\). The 3 dB beamwidth of 58.7\({}^{\circ}\) reflects a focused beam with good spatial resolution. The well-formed radiation pattern features minimal side lobes, resulting in low interference and high efficiency.