## 4 Dual-Band MIMO Antenna Designs
The inverted L-antenna is responsible for the higher band and by the interaction of the inverted L-antenna and interconnected GP, the lower frequency band is created. The SRR loading makes it easier to build a wide-band antenna mode that can span across lower WLAN, WiFi, and WiMAX application bands. In [56], a meander dipole, a concave parabolic reflector, and a parasitic strip are used to provide good impedance matching in the antenna. The parabolic reflector is used to reduce antenna size and also to improve the lower band directivity. The upper band is created using a metal strip. To accomplish the dual band antenna, in [57], the radiating patch has two asymmetric U-shaped slots printed on the substrate. Improved isolation is achieved by using a composite GP with four metallic strips. In [58], to produce a tiny dual-band WLAN MIMO antenna, lower and higher band dummy elements are employed. The desired frequency bands are achieved by adjusting the width of two branches and the angle between the branches. In [59], to produce a dual band, a rectangle split-ring-resonator (RSRR) slot is placed into the patch. Two arrays of 2 \(\times\) 1 antenna elements make up an optically transparent MIMO antenna in which a slotted circular ring monopole antenna with a partial GP is used to increase the operation bandwidth and dual band operation [60]. A 2 \(\times\) 2 MIMO antenna is presented in [61] using a semi-annular patch embedded with a zig-zag conducting strip. It is seen that the higher frequency band is controlled by the zig-zag structure while the lower band is unchanged. Further, the isolation is improved using a fork-shaped feedline. In [62], for a dual-band MIMO antenna, the mushroom type EBG is placed between two antenna elements, providing excellent isolation and reducing mutual coupling. In [63], four simple elliptical-shaped patches are arranged orthogonally around a plus-shaped partial GP. Two opposite slots are introduced into the patch elements to achieve dual band and the plus shape improves the isolation of the designed MIMO antenna. Two symmetrical monopole antenna elements make up the reported MIMO antenna in [64]. By modifying the current distribution on the GP, a DGS and grounded branches are loaded to minimize mutual coupling across the lower band. Between the two antenna elements, there is a T-shaped parasitic element which introduces an inverted path for mutual coupling cancellation, considerably improving the isolation at higher frequency band. As a result, this antenna is capable for 5G dual-band operation. In [65; 66], the slots are created on the GP to achieve dual-band MIMO antennas. In [67], for WiMAX/WLAN applications, a compact dual-band MIMO-stacked DRA is designed. The total height of the antenna is 7.0 mm, and the ground area is 50 \(\times\) 50 mm\({}^{2}\). The DGS approach is employed to create strong isolation between antenna ports. The various dual-band MIMO antenna designs and the different antenna parameters are compared in Figure 10.1 This comparison is presented in terms of antenna size, MIMO elements, and various techniques to achieve the dual-band operation and better isolation. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Ref. ** & **MIMO** & **Antenna Size** & **Antenna Frequency Band (GHz)** & **Technique to Daula-band** & **Isolation (dB)** & **Estimation (dBi)** & **Efficiency** & **ECC** & **CCL (bits/s/Hz)** \\ \hline
[42] & \(2\times 2\) & \(20\times 34\times 16\) & \begin{tabular}{c} 2.11-4.19/ \\ 4.98–6.81 \\ \end{tabular}  & \begin{tabular}{c} Embedding a pair \\ 4.98–6.81 \\ \end{tabular}  & \ \begin{tabular}{c} \(<\)–21 \\ \end{tabular}  & \begin{tabular}{c} \\ T-stub with \\ comb-shaped slots in the GP \\ \end{tabular}  & 2.75–4.19 & \(>\)70 & \(<\)0.004 & \(<\)0.32 \\ \hline
[48] & \(2\times 2\) & \(46\times 30\times 1.6\) & \begin{tabular}{c} 1.85–3.63/ \\ 5.07–7.96 \\ \end{tabular}  & \begin{tabular}{c} Swastika-shaped \\ slot in the \\ rectangular patch \\ \end{tabular}  & \begin{tabular}{c} \(<\)–17.21 \\ \end{tabular}  & \