# Novel MIMO Antenna System for Ultra Wideband Applications
## 3 Fabrication and Measured Results  
A prototype of the four-element MIMO antenna was fabricated (see Figure 8) to verify the simulations. For measurement purposes, a Precision Network Analyzer (PNA) E836 SC by Agilent Technologies is utilized. The measured S-parameters are shown in Figure 9. Due to symmetry, the reflection coefficients of antenna-1 and antenna-2 are presented. From Figure 9, it is evident that the measured S-parameters matched well with the simulated ones (see Figure 6). The measured impedance bandwidth is 9.23 GHz in the frequency range of 2.77-12 GHz. As demonstrated in Figure 9, the observed isolation is \(>\)15 dB for both neighbouring and parallel antenna elements. The discrepancies between the results are due to SMA connector losses and fabricationtolerances.  
Figures 10-13 demonstrate the radiation parameters of the proposed MIMO antenna for all ports at frequencies of 3 GHz, 6 GHz, and 9 GHz. In case of port-1, for 3 GHz (see Figure 10a), omnidirectional pattern is observed for \(xz\)-plane (\(\phi=0^{\circ}\)), while for \(yz\)-plane (\(\phi=90^{\circ}\)), antenna exhibits typical monopole like pattern. For 6 GHz, a quasi-omidirectional pattern is noted for \(xz\)-plane and a monopole like pattern is observed for \(yz\)-plane, as shown in Figure 10b. For higher frequencies, such as 9 GHz, a quasi-omidirectional pattern with some ripples is observed for both the planes, as illustrated in Figure 10c. For port-2, the same kinds of patterns are observed, but in this case, antenna-1  
Figure 7: Surface current distribution of the proposed UWB MIMO antenna when port-1 is excited. (a) 3 GHz. (b) 6 GHz. (c) 9 GHz.  
\(xz\)-plane radiation pattern is equal to antenna-2's \(yz\)-plane radiation pattern, and vice versa. This effect can clearly be observed from the patterns in Figure 11. From Figure 12, one can observe that antenna-3 offers the same radiation characteristics as antenna-1. In this case, the \(yz\)-plane of antenna-3 provides pattern diversity for the reported frequency bands. The same is the case with antenna-4, whose \(yz\)-plane offers pattern diversity in comparison to antenna-2's characteristics. As a whole, from the results of Figures 10-13, one can observe that all the antenna elements have the ability to exhibit pattern and polarization diversity. Furthermore, from Figures 10-13, one can also observe that the simulated and measured radiation characteristics are in good agreement. Some discrepancies are observed between the simulated and measured data, especially at higher frequencies (9 GHz), which could possibly arise due to fabrication tolerances at higher frequencies and far  
Figure 11: Radiation characteristics of the proposed UWB MIMO for port-2. (**a**) 3 GHz, (**b**) 6 GHz. (**c**) 9 GHz.  
Figure 10: Radiation characteristics of the proposed UWB MIMO for port-1. (**a**) 3 GHz. (**b**) 6 GHz. (**c**) 9 GHz.  
Figure 12: Radiation characteristics of the proposed UWB MIMO for port-3. (**a**) 3 GHz. (**b**) 6 GHz. (**c**) 9 GHz.  
Figure 13: Radiation characteristics of the proposed UWB MIMO for port-4. (**a**) 3 GHz. (**b**) 6 GHz. (**c**) 9 GHz.