## 3 Experimental Results
### MIMO Parameters  
MMO parameters are important to discuss while designing an MIMO antenna system. These MIMO parameters include Envelope Correlation co-efficient (ECC) and Mean Effective Gain (MEG). ECC is the measure of how well the antennas are isolated. Ranging from 0 to 1, an ECC of less than 0.5 shows that antennas are well-isolated. Figure 11 shows the ECC of the proposed MIMO system. The ECC obtained has been calculated using far-field results from the MIMO system. The equations used for calculating ECC and MEG have been derived from [13; 14; 15]. From the figure, it can clearly be seen that the ECC of the proposed MIMO system is less than <0.01 throughout the band of interest.  
Figure 10: Radiation Patterns (**a**) 2D antenna 1 and antenna 2 Phi90 (**b**) 2D antenna 3 and antenna 4 Phi90 (**c**) 2D antenna 1 and antenna 2 Theta 90 (**d**) 2D antenna 3 and antenna 4 Theta90 (**e**) 2D antenna 1 and antenna 2 Phi0 (**f**) 2D antenna 3 and antenna 4 Phi0 (**g**) 3D antenna 1 (**h**) 3D antenna 2 (i) 3D antenna 3 (j) 3D antenna 4.  
The mean effective gain (MEG) is an ability of an antenna in a multipath environment to receive electromagnetic power. The MEG of the proposed MIMO antenna is given in Table 1. Through Table 1, the MEG of the proposed antenna system satisfies the MIMO performance, exhibiting good channel characteristics.  
Table 2 shows a comparison of the proposed MIMO antenna with the proposed MIMO antenna system. The authors in [16; 17; 18] also present folk-shape structures, however, none of them resonate at the mmwave region and cover UWB characteristics from 3 to 12 GHz. Additionally, one study [16] shows some notching features. From the comparison table, it can be seen that our proposed MIMO system is compact in size compared to those in the published literature, and offers good performance MIMO characteristics.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Frequency (GHz)** & **MEG1** & **MEG2** & **MEG3** & **MEG4** \\ \hline
28 & \(-3.50\) & \(-3.21\) & \(-3.26\) & \(-3.10\) \\
29 & \(-2.99\) & \(-3.06\) & \(-3.61\) & \(-3.11\) \\ \hline \end{tabular}
\end{table}
Table 1: Mean Effective Gain of the proposed Antenna at 28 and 29 GHz Frequency.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Refs.** & **Ant.** & **Elements** & **Single Element (mm\({}^{2}\))** & **Array (mm\({}^{2}\))** & **Bandwidth** & **Isolation (dB)** & **Efficiency (\%)** & **ECC** \\ \hline
[7] & 4 & \(12\times 10\) & \(30\times 30\) & 27–30 & 28 & 84 & \textless{}0.1 \\ \hline
[8] & 4 & \(12\times 10\) & \(30\times 30\) & 26–30 & 24 & 82 & \textless{}0.2 \\ \hline
[9] & 4 & \(20\times 20\) & \(80\times 80\) & 23–40 & 26 & 85 & \textless{}0.01 \\ \hline
[12] & 4 & \(15\times 10\) & \(20\times 20\) & 27.5–28.5/37.5–38.5 & 24 & 80 & \textless{}0.1 \\ \hline
[16] & 1 & \(12\times 18\) & N/A & 3–12 & N/A & N/A & N/A \\ \hline
[17] & 1 & \(42\times 24\) & N/A & 3–12 & N/A & N/A & N/A \\ \hline
[18] & 2 & N/A & \(35\times 52\) & 3.28–12 & 20 & N/A & N/A \\ \hline Proposed & 4 & \(10\times 12\) & \(24\times 24\) & 24–39 & 26 & 92 & \textless{}0.05 \\ \hline \end{tabular}
\end{table}
Table 2: Proposed Four-Element MIMO Antenna comparison with published literature.  
Figure 11: ECC derived.