## 2 Configuration and Design of the Proposed UWB-MIMO Antenna
### Mava
\[y(x)=\pi\left(r_{2}^{2}-r_{2}^{2}\right) \tag{3}\]2 \(S_{11}\) results of both antennas. Ant 1 and Ant 2 modes of operation give vertical and horizontal polarizations, respectively. W\({}_{\text{f}}\) and W\({}_{\text{f1}}\) are taken into account to match the width of the feed lines. L\({}_{\text{f}}\) and L\({}_{\text{f1}}\) also have an impact on the matching. We included SMA connections in the simulations to account for the influence of the connectors (two different ports used here (only normal SMA which covers till 18 GHz is shown). After we measured the antenna and were sure that the results agreed, the ports changed to the new one taken from the following port. [60]). High isolation is expected because two radiation modes (Ant 1 and Ant 2) are both horizontally and vertically polarized. The simulated S\({}_{11}\) and S\({}_{21}\) results of the combined antennas are presented in \[y(x)=\pi\left(r_{2}^{2}-r_{2}^{2}\right) \tag{3}\]3 The high level of isolation is evident since the S\({}_{21}\) value is less than \(-18\) dB. In addition, a perfect impedance matching was also obtained when reflection coefficients \(\leq\)\(-10\) dB. The antenna demonstrates the matching at most of the band for both antennas' operational modes. \[y(x)=\pi\left(r_{2}^{2}-r_{2}^{2}\right) \tag{3}\]4 The antenna prototype after combination (**a**) front and (**b**) back views. \[y(x)=\pi\left(r_{2}^{2}-r_{2}^{2}\right) \tag{3}\]5 The antenna’s simulated reflection and transmission coefficients results. A staircase meander line near the Ant 1 parasitically loads the planned UWB-MIMO antenna. This meander line's staircase nature enhances the BW shifting it to the lower band like here, it yields a resonance at 3.8 GHz, which covers the lower 5G spectrum too. The reflection coefficient results with the staircase meander line are shown subsequently, together with its results for each step of antenna design and loading [61; 62; 63]. SCD of the two modes at operating BW is depicted in \[y(x)=\pi\left(r_{2}^{2}-r_{2}^{2}\right) \tag{3}\]6 The planned antenna's SCD at the lower and upper ends of the BW, as well as the poles in the operating BW for the two ports, were examined to assure dual-polarization functioning. Figure 8a-e is the SCD when port 1 is active and Figure 8f-j when port 2 is active. Figure 8 illustrates that while port 1 is active, the SCD travels along the y-axis, but when port 2 operates, SCD flows in the direction of the x-axis. The polarization diversity is one of the most important antenna diversity techniques that helps in improving the signal quality as well as enhancing the channel capacity and spectrum efficiency [64]. In general, Co-polarization is the desired polarization of the wave to be radiated by the antenna. On the contrary, cross-polarization (X-pol) is the orthogonal radiation of the desired polarization of wave (the polarization of above wave). For instance, if the desired polarization is horizontal, the X-pol is vertical. Figure 9 depicts the 2D radiation patterns of the proposed antenna for the antenna modes at working BW, lower end, and upper end of the working BW before they were combined and the loadings (meander line and MTM structure) were added. At the resonance frequencies, the simulated radiation pattern for Ant 1 (towards co-polarization) and Ant 2 (towards co-polarization) does not change much from the measured radiation pattern. It can be noticed that the ground and the patch are connected. It is to improve isolation, thus ensuring a common reference voltage level in the ground plane of the MIMO antenna. However, it is quite difficult to retain circular polarization behavior of the antenna elements in the ground radiating CP MIMO structures when the ground patches are connected together. This is due to the fact that the connecting strip is made up of conductor, and, therefore, it will leak some amount of current toward the neighboring antenna elements [65]. To avoid this effect the antenna is thus loaded with MTM structure.