## 2 Configuration and Design of the Proposed UWB-MIMO Antenna
### MTM Elements and Array Integrations  
Periodic structures are used to create metamaterials (MTM). They are used to obtain a broad bandwidth and greater directional gain while keeping a low-profile construction. In the direction of end-fire radiation, we suggest employing MTM in a planar structure.  
The suggested MTM unit cell is illustrated in Figure 10a. The primary model of the MTM unit cell is based on a Split-Ring Resonator (SRR) structure with two circular  
Figure 8: Distribution of the SCD after Ant 1 and Ant 2 were combined at: (**a**,**f**) 3.8 GHz, (**b**,**g**) 5.4 GHz, (**c**,**h**) 8 GHz, (**d**,**i**) 15 GHz), and (**e**,**j**) 28 GHz.  
rings [66]. The SRR is modelled as a magnetically resonator affected by a vertical magnetic field to create permeability [67]. Splits (gaps) are usually carved out of structures to produce capacitance and check the structure's resonant specification. The MTM structure is tuned to function in the necessary frequency spectrum by adding a Capacitive-Loaded Strip (CLS). It should be noted that a CLS functions in the same way as an electric dipole [68]. The proposed MTM shape is only present on one side of the substrate.  
Figure 10a,b displays the unit cell of MTM on a denim substrate with a \(\varepsilon_{r}=1.4\), tan \(\delta=0.02\), and h = 0.5 mm thickness. Perfect magnetic and electrical barriers surround the MTM structure (xz and yz planes, respectively). Parallel to the xy planes, two waveguide ports are attached to the two sides of the MTM cell. In the direction of the z-axis, an open border is assumed. Utilizing the simulated S\({}_{11}\) and S\({}_{21}\), the Nicolson-Ross-Weir (NRW) technique [69] was used to evaluate the electromagnetic properties of the proposed MTM unit cell in order to ascertain and then extract the \(\varepsilon_{r}\) and \(\mu_{r}\) as in (Figure 10c). Figure 10 summarizes the operational BW range of \(\varepsilon_{r}\) and \(\mu_{r}\). After that, ten units of the suggested MTM were added to the antenna to enhance its characteristics in terms of gain, directivity, radiation efficiency, and impedance matching by suppressing surface waves caused by the reduced tapering angle. Figure 11 indicates the reflection and transmission coefficient results for the single cell of MTM structure. Figure 12 shows how the MTM components were rotated in different orientations at every 90\({}^{\circ}\) increments.  
In order to improve the performance antenna while maintaining a compact printing area, the angle (\(\alpha\)) was lowered to generate greater focus towards the broadside direction. That will minimize the antenna's breadth after the ideal dimensions of the proposed MVA antenna were determined. Consequently, the decrement affected the surface waves increment, thus, the antenna's performance as well.  
Figure 9: The radiation patterns of MVA antenna considering both Ant 1 and Ant 2 at: (**a**) 3.8 GHz, (**b**) 5.4 GHz, (**c**) 10 GHz, (**d**) 12 GHz, (**e**) 20 GHz, and (**f**) 38 GHz before combination and loadings.  
Figure 11: MTM unit cell structure S-parameters.  
Figure 10: MTM unit cell structure: (**a**) 2D view, (**b**) 3D view and (**c**) effective permittivity (\(e\)) and permeability (\(u\)).