## 7 MIMO Characteristics for 6G Technology  
Although the 5G mobile communications standard is still in the growing stage of deployment, investigations are in pace for the next generation of wireless technology, 6G wireless systems. In order to overcome the operational difficulties experienced by fifth \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Ref.**} & **MIMO** & **Antenna Size** & **Frequency** & **3-dB AR Bandwidth (GHz)** & **CP Technique** & **Gain (dBi)** & **Isolation (dB)** & **ECC** & **CCL bits/s/Hz** \\ \hline \multirow{3}{*}{[71]} & \multirow{3}{*}{\(2\times 2\)} & \multirow{3}{*}{\(24\times 24\times 1.6\)} & & \multicolumn{3}{c}{Asymmetric \(Z\)-shaped patch \(with\) stub loaded \(with\) defected GP} & \multirow{3}{*}{0.28-2.76} & \multirow{3}{*}{\(<\)\(-\)16} & \multirow{3}{*}{\(<\)\(0.004\)} & \multirow{3}{*}{\(<\)\(0.32\)} \\  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \hline \multirow{3}{*}{[73]} & \multirow{3}{*}{\(2\times 2\)} & \multirow{3}{*}{\(56\times 32\times 3\)} & \multirow{3}{*}{5.10–5.85} & \multirow{3}{*}{5.10–5.85} & \multirow{3}{*}{\(5.10\)–\(5.85\)} & Truncated corner \(patch\) with defected \(periodic\) GP} & \multirow{3}{*}{5.8} & \multirow{3}{*}{\(\leq\)\(-20\)} & \multirow{3}{*}{-} & \multirow{3}{*}{-} \\  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \hline \multirow{3}{*}{[74]} & \multirow{3}{*}{\(2\times 2\)} & \multirow{3}{*}{\(95\times 49.7\times 1.6\)} & \multirow{3}{*}{3.15–3.93} & \multirow{3}{*}{3.3–3.8} & Cross ring slot with \(DRA\) truncation & \multirow{3}{*}{4.83} & \multirow{3}{*}{\(<\)\(-26\)} & \multirow{3}{*}{\(<\)\(0.03\)} & \multirow{3}{*}{\(<\)\(0.10\)} \\  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \hline \multirow{3}{*}{[75]} & \multirow{3}{*}{\(2\times 2\)} & \multirow{3}{*}{\(50\times 70\times 1.6\)} & \multirow{3}{*}{3.40–3.92} & \multirow{3}{*}{5.62–5.86} & Dual strips along with single slot in \(the\) GP} & \multirow{3}{*}{4.1} & \multirow{3}{*}{\(<\)\(-28\)} & \multirow{3}{*}{\(<\)\(0.15\)} & \multirow{3}{*}{\(<\)\(0.23\)} \\  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \hline \multirow{3}{*}{[77]} & \multirow{3}{*}{\(2\times 2\)} & \multirow{3}{*}{\(40\times 65\times 1.6\)} & \multirow{3}{*}{5.16–6.30} & \multirow{3}{*}{5.20–5.58} & \multirow{3}{*}{L-shaped DRA} & \multirow{3}{*}{4.011} & \multirow{3}{*}{22.284} & \multirow{3}{*}{\(<\)\(0.112\)} & \multirow{3}{*}{\(<\)\(0.338\)} \\  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \hline \multirow{3}{*}{[78]} & \multirow{3}{*}{\(2\times 2\)} & \multirow{3}{*}{\(22.5\times 50\times 1.6\)} & \multirow{3}{*}{3.50–4.95} & \multirow{3}{*}{3.58–4.40} & Rectangular DRA & \multirow{3}{*}{6.2} & \multirow{3}{*}{\(<\)\(-28\)} & \multirow{3}{*}{\(<\)\(0.04\)} & \multirow{3}{*}{-} \\  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \hline \multirow{3}{*}{[82]} & \multirow{3}{*}{\(4\times 4\)} & \multirow{3}{*}{\(70\times 68\times 1.6\)} & \multirow{3}{*}{4–13} & \multirow{3}{*}{4.2–8.5} & Cross-shaped structure on ground & \multirow{3}{*}{\(6.4\)} & \multirow{3}{*}{\(\leq\)\(-18\)} & \multirow{3}{*}{\(<\)\(0.25\)} & \multirow{3}{*}{-} \\  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \cline{1-1}  & & & & & & & & \\ \hline \multirow{3}{*}{[85]} & \multirow{3}{*}{\(2\times 2\)} & \multirow{3}{*}{-} & \multirow{3}{*}{4.75–5.9} & \multirow{3}{*}{5.1–5.8} & \multirow{3}{*}{Parasitic elements} & \multirow{3}{*}{7.5–8.2} & \multirow{3}{*}{\(<\)\(-22\)} & \multirow{3}{*}{-} & \multirow{3}{*}{-} \\ \cline{1-1}  & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of different circularly polarized MIMO antennas.