## 4 Conclusions  
In this paper, a high-performance graphene plasmonic two-port MIMO antenna has been introduced to be used in terahertz wireless communication applications. In the theory of characteristic mode analysis (CMA) with the help of a complementary Dumbbell-structure MTM unit cell, the mutual coupling between the antenna elements has been significantly reduced. The MTM structure acts as a band stop filter in the desired bandwidth. It is etched in the ground plane so as to reduce the mutual coupling from \(-25\) dB to \(-55\) dB in the presence of the MTM unit cell. The CMA has been used to study the behavior of the antenna modes of operations and clarify the mode responsible for the coupling between the elements and detect the optimum position of this mode which can be illuminated by the MTM structure without any distortion in the main antenna resonance mode (dominant mode). Furthermore, the MIMO antenna parameters such as ECC, DG coefficients, and CCL are investigated and presented to confirm the suitability of the proposed graphene MIMO antenna for different THz applications. The proposed MIMO antenna resonates at 3.5 THz with a return loss of \(-35\) dB and exhibits a wide impedance characteristic bandwidth covering 3.2 to 3.8 THz frequency spectrum in the THz regime (BW = 600 GHz). The designed MIMO antenna maintains maximum isolation of \(-55\) dB at the resonance frequency of 3.5 THz. The good MIMO performance is ensured by achieving the MIMO performance parameters (ECC = 0.000168, DG = 9.999, and CCL = 0.006) within acceptable limits. The proposed MIMO antenna design in the future can be used as a massive MIMO and used the reconfigurable intelligent surfaces to be suitable for the 6G communication technology The proposed MIMO antenna is suitable for high-speed short-distance indoor communication applications such as video-rate imaging, biomedical imaging, sensing, and security scanning in the terahertz frequency band. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref.** & \begin{tabular}{c} **Freq.** \\ **(THz)** \\ \end{tabular} & \begin{tabular}{c} **Antenna Size** \\ **(\(\mu\)m\({}^{2}\))** \\ \end{tabular} & \begin{tabular}{c} **Isolation Technique** \\ \end{tabular} & \begin{tabular}{c} **Mutual Coupling** \\ **(dB)** \\ \end{tabular} & \begin{tabular}{c} **Gain** \\ **(dB)** \\ \end{tabular} & \
\begin{tabular}{c} **ECC/DG (dB)** \\ \end{tabular} &
\begin{tabular}{c} **CCL** \\ \end{tabular} \\ \hline
[14] &
\begin{tabular}{c} (1–10) \\ (15–30) \\ \end{tabular} & \(620\times 800\) & Separated Distance & \(-20\): \(-45\) & \(7\) & \(0.01/10\) & \(0.5\) \\
[40] & \(0.472\) & \(600\times 300\) & Separated Distance & \(-52\) & \(4.27\) & \(0.0458/9.99\) & \(0.00018\) \\
[41] & \(1.82\) & \(60\times 40\) & Separated Distance & \(-25\) & \(4.45\) & \(0.0372/9.99\) & - \\
[42] & \(0.2\)-\(10\) & \(125\times 125\) & elliptical fractal slots & \(-20\) & \(8.2\) & \(0.0022/9.98\) & \(0.31\) \\
[43] & \(0.33\)–\(10\) & \(1000\times 1400\) & DGS & \(-25\) & \(19\) & \(0.0015/9.99\) & \(0.25\) \\
[44] & \(1.68\) and \(1.81\) & \(60\times 40\) & Slots & \(-40\) & - & \(0.177/9.99\) & - \\
[45] & \(2.3\), \(3.2\) and \(4.5\) & \(50\times 40\) & Decoupling structure & \(-17\), \(-30\) and \(-23\) & \(5\) & \(0.2/10\) & - \\
[46] & \(1.1\)–\(1.7\) & \(84\times 84\) & FSS & \(-25\) & \(15\) & \(0.01/.\) & - \\
[47] & \(1.1\) & \(380\times 380\) & MTM & \(-20\) & \(8.28\) & - & - \\
[48] & \(1.76\) & \(56\times 56\) & Slots & \(-50\) & \(4.02\) & \(0.0086/9.989\) & - \\ Proposed Work & \(3.5\) & \(130\times 85\) &
\begin{tabular}{c} MTM+CMA+ \\ Elements Arrangement \\ \end{tabular} & \(-55\) & \(7.23\) & \(0.000168/9.999\) & \(0.006\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of the proposed antenna performance with the state-of-the-art works.