## 2 Design of the Six-Element MIMO Antenna Structure
The S parameters are calculated by considering excited at (**a**) Port 1, (**b**) Port 2, (**c**) Port 3, (**d**) Port 4, (**e**) Port 5, and (**f**) Port 6. Dotted line is put for the reference to identify the reflectance \(<\)\(-10\) dB. The split ring resonator shape provides advantages over a normalized patch structure in terms of compact size, metamaterial effect, broadband response, and flexibility of operation. The results shown in Figures 3 and 4 show an improvement in bandwidth as compared to the normal patch structure design. The detailed bandwidth variations for different frequency slots can be observed in Tables 3 and 4. It is also possible to tune these operating bands by changing the radius of the split ring resonator. Radiation losses may be \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Design**} & \multicolumn{2}{c}{**Minimum**} & \multirow{2}{*}{**Peak Gain**} & \multirow{2}{*}{\(f_{min}\) (GHz)**} & \multirow{2}{*}{\(f_{max}\) (GHz)} & \multirow{2}{*}{\(\dfrac{\text{Bandwidth}}{\text{(GHz)}}\)} \\  & **Return Loss** & & & & \\  & **(dB)** & & & & \\ \hline \multirow{2}{*}{Design 1} & \(-24.82\) & \(13.12\) & \(4.39\) & \(10.2\) & \(5.81\) \\  & \(-15.62\) & \(7.35\) & \(11.82\) & \(16.77\) & \(4.35\) \\  & \(-19.24\) & \(12.07\) & \(20.04\) & \(25\) & \(4.96\) \\ \hline \multirow{2}{*}{Design 2} & \(-21.17\) & \(11.77\) & \(4.75\) & \(8.88\) & \(4.13\) \\  & \(-18.22\) & \(5.81\) & \(12.4\) & \(16.37\) & \(3.97\) \\  & \(-26.50\) & \(16.47\) & \(18.68\) & \(24.58\) & \(5.9\) \\ \hline \multirow{2}{*}{Design 3} & \(-51.90\) & \(10.59\) & \(6.15\) & \(9.72\) & \(3.57\) \\  & \(-20.59\) & \(19.33\) & \(14.21\) & \(15.47\) & \(1.26\) \\  & \(-20.17\) & \(11.59\) & \(16.87\) & \(20.80\) & \(3.93\) \\ \hline \multirow{2}{*}{Design 4} & \(-22.29\) & \(22.91\) & \(4.32\) & \(9.09\) & \(4.77\) \\  & \(-27.25\) & \(6.08\) & \(12.33\) & \(13.12\) & \(0.79\) \\  & \(-15.45\) & \(13.90\) & \(14.62\) & \(18.46\) & \(3.84\) \\ \hline \multirow{2}{*}{Design 5} & \(-19.03\) & \(13.71\) & \(4.20\) & \(10.30\) & \(6.1\) \\  & \(-14.62\) & \(5.30\) & \(12.07\) & \(13.74\) & \(1.67\) \\ \cline{1-1}  & \(-17.23\) & \(19.53\) & \(14.37\) & \(17.69\) & \(3.32\) \\ \cline{1-1}  & \(-27.40\) & \(15.80\) & \(19.05\) & \(25\) & \(5.95\) \\ \hline \end{tabular}
\end{table} 
Table 4: Measurement-based derived results and comparative analysis for the different antenna designs. Figure 4: Measured values of reflectance coefficients for the different proposed MIMO antenna designs: (**a**) Design 1, (**b**) Design 2, (**c**) Design 3, (**d**) Design 4, and (**e**) Design 5. The results are presented in terms of the return loss parameters, such as S\({}_{11}\), S\({}_{22}\), S\({}_{33}\), S\({}_{44}\), S\({}_{55}\), and S\({}_{66}\). A dotted line is put for the reference to identify the reflectance \(<\)\(-10\) dB. minimized and overall efficiency increased by using split ring resonators instead of circular patches. Due to this, SRRs may be used in places such as radar systems and wireless power transmission where low-loss or high-efficiency performance is necessary. Additionally, the gain over the frequency range of 1-25 GHz is presented as the second antenna parameter for identifying the antenna's efficient operation. Gain values for each suggested antenna design have been computed and shown in Figure 5. Gain variations from \(-\)15 dBi to +30 dBi are visible. Out of all the results of the gain with the specified antenna radiation spectrum, we need to think about the effective gain values of each antenna structure. In the specific radiation bands shown in Table 3, the gain profile is considered for the observations. We have identified the peak gain values for the specific antenna and specific radiation bands. These results of gain are shown in Table 3. The derived values of gain from a fabricated prototype are presented in Figure 6 for the entire frequency spectrum.