## 3 Results and Discussion
### Experimental Results  
A Vector Network Analyzer (VNA) with a frequency range of up to 67 GHz was employed to evaluate the scattering parameters of the fabricated structure. The antennas being tested were attached to the VNA via end-launch RF connectors, as shown in Figure 10. The depicted measurement setup serves multiple purposes: (a) gauging the reflection coefficients of individual ports, (b) assessing the mutual coupling coefficients among the ports, (c) presenting a sample result from the measurement of S\({}_{11}\), and (d) a comparison between the simulation and experimental results. The measured and simulated results demonstrate good alignment in all of the measured frequency band. However, minor discrepancies between the simulated and measured results can be accredited to  
Figure 6: (a) Top, (b) bottom view of four-port MIMO antenna; and (c) simulated s-parameters versus frequency. aspects such as impedance mismatch, the influence of the SMA connector, environmental sceneries, and/or modeling assumptions that may affect the experimental setup parameters. Nonetheless, the measured bandwidths do not significantly deviate from the simulated values, confirming the consistent performance of the realized antenna prototype across the entire measured frequency band. Table 2 provides a comparative analysis of the proposed MIMO antenna design alongside the latest reported works. The results validate that the proposed design achieves highly competitive performance across key metrics, particularly in bandwidth, gain, and isolation. The comparison highlights the superiority of the proposed MIMO antenna over existing designs, showcasing improved bandwidth efficiency, gain, and isolation characteristics. By contextualizing the proposed design within recent advancements, this assessment underscores its effectiveness for advancing MIMO technology in next-generation 5G communication systems. Figure 7: (**a**) Top, (**b**) bottom views of MTM unit cell and its computed (**c**) \(\epsilon_{\text{r}}\), (**d**) \(\mu_{\text{r}}\), and (**e**) n parameters. Figure 8: Computed frequency dependence of **(a)** ECC and **(b)** DG of four-port MIMO antenna. Figure 9: Radiation patterns of the 4-port MIMO antenna at 28.8 GHz: **(a)** E-plane and **(b)** H-plane. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Reference No.**} & **Frequency** & \multirow{2}{*}{**No. of Ports**} & **Dimensions** & **Bandwidth** & \multirow{2}{*}{**Gain (dBi)**} & **Isolation** \\  & **(GHz)** & & **(mm2)** & & **(GHz)** & **(dB)** \\ \hline
[21] & 28 & 2 & \(20\times 27\) & 3.6 & 11.9 & 37 \\ \hline
[23] & 28/39/48.7 & 2 & \(10\times 16\) &
\begin{tabular}{c} 1.8 (28 GHz) \\ 6.2 (39 GHz) \\ 3.8 (48.7 GHz) \\ \end{tabular} & 9.8 (28 GHz) & \\ \hline
[33] & 28 & 4 & \(30\times 35\) & 4.1 & 8.3 & 22 \\ \hline
[34] & 28 & 4 & \(32\times 8\) & 2.6 & 7.5 & 25 \\ \hline
[35] & 28/38 & 2 & \(55\times 110\) &
\begin{tabular}{c} 1.07 (28 GHz) \\ 1.43 (38 GHz) \\ \end{tabular} & 7 (28 GHz) & 27 \\ \hline
[36] & 28/38 & 2 & \(7.5\times 8.8\) &
\begin{tabular}{c} 1.23 (28 GHz) \\ 1.06 (28 GHz) \\ \end{tabular} & 6.60 (28 GHz) & 20 \\ \hline This work & 28.8 & 4 & \(68\times 80\) & 1.0 & 13 & 41 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparing attained results of this work with those of recent designs in terms of many assessment metrics. Figure 10: Measurement setup of **(a)** evaluating the reflection coefficients of individual ports, **(b,c)** assessing mutual coupling coefficients among the ports, and **(d)** displaying a sample result from the measurement of S\({}_{11}\). The proposed design showed high performance regarding its gain and isolation. The latter is owed to the precisely designed MTM, which played a crucial role in achieving high isolation and low mutual coupling, as clearly demonstrated by the experimental measurements. Additionally, the proposed design, with its achieved results, is well suited for low-power devices, including those powered by batteries [37].