## 2 Antenna Design  
The flow chart depicted in Figure 1 shows an approach used to arrive at the optimum values of the MIMO antenna array for upper mid-band range. This includes the operating frequency selection of the chosen antenna structure, which is another process during the analysis of the given problem. The steps that follow target designing a more optimized antenna which satisfies the given objectives and, thirdly, checking on the fabricated improved version in order to compare its performance and efficiency with the simulated model. The methodology starts with the analysis of the dependency of the MIMO antenna pair performance on the design parameters of the element antennas and the operating frequency. It then determines the best MIMO antenna pair, which is then employed to provide optimization to a MIMO ten-element setup. As a result, the array is designed, simulated, and fabricated with the intention of testing it. Data acquisition and design validation were performed on CST MWS 2021. The systematic nature of how this is done also guarantees coverage of all the aspects of choosing antenna parameters and checking the final design on a test bed.  
The layout of the approximate Pi-shaped MIMO antenna is shown in Figure 2, and the fabricated prototype in Figure 3 is also illustrated. The overall dimension of the antenna measures 125 mm \(\times\) 70 mm, and the fabrication material used is Rogers RT/5880, which has a dielectric constant of 2.2 and loss tangent of 0.0009, with a thickness of 0.51 mm (semi-flexible). Each of the antenna elements was connected to a 50 \(\Omega\) feed line while having the N-S arrangement; the distance between two adjacent elements was about \(\frac{1}{2}\lambda\) at 5.8 GHz. The values of the parameters depicted in Figure 2 are presented in the Table 1.  
The proposed multi-port Pi-shaped MIMO antenna has been carefully designed to maintain reliable performance despite environmental interference and manufacturing variations. Factors like signal degradation due to surrounding obstacles, multi-path fading, and electromagnetic interference (EMI) from nearby devices can impact antenna efficiency and isolation. To address these challenges, the design has been optimized for stable impedance matching and high isolation across ports, reducing its vulnerability to external noise. Additionally, slight differences in manufacturing--such as variations in substrate thickness,etching precision, or connector placement--can affect the antenna's performance. By incorporating robust parameter optimization, the design ensures minimal performance deviation, even under practical fabrication conditions. These considerations make the proposed Pi-shaped MIMO antenna a dependable and adaptable solution for next-generation wireless communication systems.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Variable** & **Dimension (mm)** & **Variable** & **Dimension (mm)** & **Variable** & **Dimension (mm)** \\ \hline sl & 125 & sw & 70 & spacing & 25 \\ \hline pl & 7.5 & fl & 13 & fs & 2.63 \\ \hline gcw & 6 & gcw1 & 1 & gcs & 2.085 \\ \hline gcl & 4.9 & gcl1 & 20 & arm & 8 \\ \hline gap & 1.5 & gap1 & 14.915 & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Ten-element Pi-shaped MIMO antenna array parameters.  
Figure 1: The flow chart of a proposed Pi-shaped ten-element MIMO antenna array.  
Figure 3: The fabricated prototype. (**a**) Front view. (**b**) Rear view. (**c**) Measurement setup.  
Figure 2: The detailed dimensions of the proposed multi-port MIMO antenna array. (**a**) 10-port Pi-shaped MIMO structure. (**b**) Radiator (Patch) dimensions of single antenna. (**c**) Ground slots parameters.