# Metamaterial Based Design of Compact UWB/MIMO Monopoles Antenna with Characteristic Mode Analysis
## 3 Topology and Analysis
### Modal Analysis of the MIMO Antenna  
Characteristic mode analysis was employed to the 2 \(\times\) 2 MIMO antenna without a feeding structure using a multilayer solver in CST version 2017. It conforms to the standardized amplitude of the current modes. This normalized amplitude does not depend on the feeding port but only on the conducting object's shape and size. The first three modes' modal significance at 5.2 GHz is presented in Figure 6; only mode 2 has an exactly modal significance of up to 1.0. The remaining mode has been shifted slightly; only mode 2 will dominate at this frequency response. At 10.6 GHz, only mode 2 has an exactly modal significance of nearly 1.0, mode 1 and mode 3 is not at 10.6 GHz; therefore, mode 2 will also dominate at this frequency as depicted in Figure 7. The characteristics angle for the MIMO antenna at mode 1, 2, and 3 is shown in Figure 6. A mode resonates when \(\lambda_{n}=0\) that is when the characteristic curve is 180\({}^{\circ}\). Figure 8 shows that mode 2 is almost at 5.2 GHz and remains the frequency of interest; from Figure 9, mode 2 is at 10.6 GHz or virtually at the resonance frequency of interest. It was clearly shown that, for all the two frequencies of interest, the characteristic angle is closer to 180\({}^{\circ}\), which signifies that the  
Figure 4: Evolution stages of the proposed UWB/MIMO antenna. Figure 5: Effect of slot radius on the resonant frequency, \(R_{s}\) (mm). mode is a good radiator. Figures 10 and 11 present the eigenvalues for the three modes at the resonant frequency of interest. The results clearly showed that the three modes are resonant \(\lambda_{n}=0\), but mode 2 is more dominant. For a more physical insight into the MIMO antenna design, Figure 12 shows the modal significance of three modes at 5.5 GHz, mode 2 being the dominant mode is at precisely 1.0. The characteristic angle of three modes at 5.5 GHz is also shown in Figure 13, and the eigenvalues for the three modes at 5.5 GHz is also presented in Figure 14.  
At 7 GHz, mode 2 has an exactly modal significance of 1.0, as depicted in Figure 15. The characteristic angle at 7 GHz for the three modes is shown in Figure 16. With mode 2 being the dominant mode, the value of 180\({}^{\circ}\) is significantly closer compared to other modes. Figure 17 presented the eigenvalues of three modes at 7 GHz; all three modes are resonant. Figure 6: Modal significance at 5.2 GHz. Figure 7: Modal significance at 10.6 GHz. Figure 8: Characteristic angle curve of three modes at 5.2 GHz. Figure 6.0 Eigenvalues of three modes at 5.2 GHz. Figure 6.1 Characteristic angle curve of three modes at 10.6 GHz. Figure 6.2 Eigenvalues of three modes at 10.6 GHz. Figure 6.3 Modal significance at 5.5 GHz. Figure 6.4 The characteristic angle of three modes at 5.5 GHz. Figure 6.5 Characteristic angle for three modes at 7 GHz. Figure 6.6 Eigenvalues of three modes at 5.5 GHz. Figure 6.7 Modal significance at 7 GHz. the metamaterial structure helps concentrate the surface waves within the decoupling frame, bringing about high isolation between the MIMO components. The \(S_{21}\) with and without decoupling network can be seen in Figure 6.8 The current distribution with and without the metamaterial and perturbed stubs at 10.6 GHz is depicted in Figure 6.9 Gain is one of the basic parameters of the antenna. The MIMO antenna's gain and total efficiency appear in Figure 25, and the efficiency is calculated as gain divided by directivity, as shown in Figure 4:0 The maximum value of 5.5 dBi is at 5.5 GHz and a total efficiency of 89%. The measured and simulated far-field patterns have emerged for two different frequencies, i.e., 5.2 GHz and 10.6 GHz. The xz-plane and yz-plane radiation characteristics for 5.2 GHz are shown in Figure 26,  
Figure 4:1 Simulated S-parameter with and without metamaterial. Figure 4:2 Measured and simulated \(S_{11}\) of the designed antenna. Figure 4:3 Measured and simulated \(S_{21}\) of the designed antenna. Figure 4:4 The measured and simulated far-field pattern for E and H plane at 5.2 GHz.