## 4 Conclusions  
In this review and simulated study paper, we demonstrated how isolation is affected with and without the application of different DTs in UMAs. The mutual coupling can modify the impedance matching, reflection coefficients, and far-field radiation patterns of the AEs. Practically, the mutual coupling relies on the MIMO design as well as on the excitations of other nearby AEs. The antenna radiation pattern of a single UWB AE has an omnidirectional shape, and two-port UMAs tend to radiate in opposite directions (making the patterns orthogonal to each other) due to the mutual coupling, with/without CG. The isolation without CG is higher than with CG because, due to the lack of connection between the ground planes of both AEs, no current will flow to the other port. Similarly, the ECC of the antenna without CG is lower than that with CG. By maintaining a proper gap between AEs, an ECC of less than 0.02 is achieved. The MIMO antenna with CG causes changes in \begin{table}
\begin{tabular}{l l l l l} \hline \hline \multirow{2}{*}{**DT**} & \multirow{2}{*}{**Benefits**} & \multirow{2}{*}{**Limitation**} & \multicolumn{2}{c}{**Minimum Isolation within UWB**} \\ \cline{3-5}  & & & **CG (dB)** & **Without CG (dB)** \\ \hline Without DT & Does not affect & Low isolation in CG MIMO & & \\  & radiation pattern & antennas & & \\ \hline AEs arranged in & High isolation in MIMO & Unable to suppress coupling & & \\
90\({}^{\circ}\) direction & antennas with & effect in the lower frequency in & 13.6 & 19.5 \\  & separate grounds & CG scenario & & \\ \hline AEs arranged in 180\({}^{\circ}\) & Provides moderate & Does not improve the isolation & & \\ direction & isolation & and pattern diversity so much & 15.2 & 15.5 \\ \hline DS & Easy to design with good & High level of cross-polarized & & \\  & wideband impedance & and directional radiation & & \\  & matching & patterns are obtained; & 14.8 & — \\  & matching & sometimes additional space & & \\  & generates ohmic losses & & & \\ \hline NL & Wideband impedance & No significant improvement in & & \\  & matching and shapes of & isolation as compared to the & & \\  & radiation patterns & MIMO antenna with no DT & 8.9 & — \\  & are disturbed & and low isolation at the lower & & \\  & frequency band & & & \\ \hline DGS & It has a very low effect on & & & \\  & antenna impedance because & Slits/slots in the ground & & \\  & an extra current path is & surface are not preferable for & & \\  & introduced through the & housing and increasing & & \\  & addition of a coupling slot & fabrication complexity & & \\  & in the ground & & & \\ \hline Metamaterial & Easy layout and & It makes the system complex, & & \\  & moderate isolation & with short bandwidth and low & — & 14.7 \\ \hline PE & Controls the isolation and & There is no common ground & & \\  & easy to use and design & and shift in frequency due to & — & 16.1 \\  & parasitic elements. & & & \\ \hline CBF & The highest isolation & Highly distorted radiation & & \\  & is achieved & patterns & 27.5 & — \\ \hline SES & Does not distort & Almost no improvement in & & \\  & radiation patterns & isolation as compared to & — & 15.07 \\  & MIMO antenna without DT & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparative analysis of various DTs. the shape of the radiation pattern. The isolation is greater in 90\({}^{\circ}\) placed AEs as compared to 180\({}^{\circ}\) placed AEs. With CG structure, isolation is very low in 90\({}^{\circ}\) placed AEs and very high in 180\({}^{\circ}\) placed AEs at lower frequencies of the UWB. In DS, the radiation pattern becomes directional. With two-port UMA with CG, isolation is highly increased at the lower, middle, and higher frequency ranges. In NL, the shape of the radiation pattern is deformed and becomes directional. Also, impedance matching is disturbed at lower and higher frequency ranges, and poor isolation is obtained at lower frequencies.