# Using AI to Improve MIMO Antennas with SRR for 26 GHz by Analyzing Data
## 4 Discussion and Future Opportunities
The SRRs act as stop-band resonators that suppress mutual coupling by redirecting and attenuating the surface currents, particularly in the coupling path between the antennas. As a result, the current distribution becomes more confined to each individual antenna element, enhancing isolation and thereby improving the decoupling and the performances of the system proposed by MIMO. Figure 27 illustrates the total gain and radiation efficiency of the proposed MIMO antenna array integrated with two SRRs structures. At the target frequency of 26 GHz, the antenna achieves a notable gain of approximately 10.22 dBi, demonstrating its capability to maintain strong radiation performance in the millimeter-wave band. Moreover, the radiation efficiency reaches up to 79%, indicating that the majority of the input power is effectively radiated, rather than lost as heat or through mismatches. These results confirm the effectiveness of the SRR-based design in enhancing both the gain and efficiency of the MIMO antenna system, which is very important for 5G and high-data-rate applications. Figure 26: Comparison of distribution current before and after adding SRR: (**a**) without and (**b**) with SRRs. Figure 25: Comparison of the reflection coefficient (S11) and transmission coefficient (S12) before and after implementing the SRR-based isolation technique. Figure 28a,b present the simulated 2D radiation patterns in the principal planes \(\varphi=0^{\circ}\) and \(\varphi=90^{\circ}\), respectively, for three configurations: a single antenna element, a two-element MIMO antenna without any isolation structure, and the same MIMO system integrated with the optimized SRR-based isolation. These radiation patterns clearly demonstrate the evolution of the gain as the design progresses toward improved MIMO integration and decoupling. In the \(\varphi=0^{\circ}\) plane (Figure 28a), the single antenna shows a relatively broad radiation lobe centered around \(\theta=0^{\circ}\), with a gain of approximately 6.64 dBi. Upon transitioning to the MIMO configuration without isolation, a slight improvement in directivity is observed due to mutual excitation between elements, raising the gain to about 8.5 dB. However, the most significant enhancement is observed when the optimized SRR isolation structure is introduced: the radiation pattern becomes more focused, the main lobe remains centered at \(\theta=0^{\circ}\), and the gain further increases to 10.22 dBi. This improvement is also confirmed in Figure 28b, where similar behavior is noted in the orthogonal \(\varphi=90^{\circ}\) plane. These results confirm that the SRR-based isolation not only mitigates mutual coupling, but also contributes to constructive radiation interference, leading to stronger beam formation and gain enhancement in both principal directions. Moreover, the radiation remains symmetric and stable across both planes, demonstrating the effectiveness of the design in maintaining pattern integrity and spatial diversity in MIMO operation. In the following, the performance of the MIMO antenna with the proposed isolation technique is evaluated in terms of key diversity and correlation metrics, including diversity gain (DG), envelope correlation coefficient (ECC), total active reflection coefficient (TARC), and channel capacity loss (CCL). Figures 29 and 30 present the performance evaluation of the proposed MIMO antenna in terms of key diversity and coupling parameters at 26 GHz. The envelope correlation coefficient is a critical metric for assessing the correlation between MIMO elements and is calculated using the scattering parameters as:  
\[ECC=\frac{|S_{11}^{*}S_{12}^{*}+\ S_{21}^{*}S_{22}^{*}|^{2}}{\left(1-|S_{11}|^{ 2}-|S_{21}|^{2}\right)\left(1-|S_{12}|^{2}-|S_{22}|^{2}\right)} \tag{5}\]  
At 26 GHz, the ECC is nearly zero, indicating excellent isolation and low correlation between ports. Consequently, the diversity gain is derived from ECC as:  
\[DG=\sqrt{1-\left(ECC\right)^{2}} \tag{6}\]  
Figure 27: Gain and efficiency of the proposed MIMO antenna array with SRRs.