## 4 Antenna Performance Measurements
### Antenna Parameters Analysis  
For the antenna to be resonating at 1.8 and 2.6 GHz, two orthogonal modes have to be excited simultaneously. Port 1 excites dominant TE\({}^{x}\)s\({}_{11}\) and higher order TE\({}^{x}\)s\({}_{21}\) modes whereas port 2 excites TE\({}^{y}\)181 and TE\({}^{y}\)281 modes, respectively. Because of the symmetry of both ports, the E-field distribution for both modes is shown in Figure 8 for port 1 only. The prototype of the proposed antenna is shown in Figure 9. The ground plane is etched on FR4 substrate and the DR is made up of Eccostock HK-10 material with tan\(\delta\) = 0.002. Microstrip feed lines are placed at the opposite side of the substrate to feed DR through two slots of equal dimensions. Figure 10 demonstrates the comparison of both the simulated and measured S-parameters. S-parameters for reference level \(-10\) dB are measured.  
Figure 7: E-field Magnitude plot.  
Measured fractional bandwidth at 1.8 GHz is 18% (1.71-2.05 GHz) and at 2.6 GHz is 8% (2.5-2.7 GHz) through ports 1 and 2, respectively. Figure 10 indicates a good agreement between measured and simulated results. The antenna is well matched at both resonances, covering four LTE bands as mentioned earlier.  
Simulated total radiation efficiencies through ports 1 and 2 are the same i.e., 94.42% at 1.8 GHz and 96% at 2.6 GHz, respectively. These values are calculated using Equations (3) and (4) [13].  
Figure 10: Measured and simulated S-parameters.  
Figure 9: Prototype of the proposed MIMO antenna (**a**) 3-D view (**b**) Bottom view.  
\[\mu_{1,tot}= \mu_{1,rad}(1-|s_{11}|^{2}-|s_{21}|^{2}) \tag{3}\] \[\mu_{2,tot}= \mu_{2,rad}(1-|s_{22}|^{2}-|s_{12}|^{2}) \tag{4}\]  
Figure 11 shows the simulated and measured gain and efficiency plots of the proposed MIMO DRA. The measured gain and efficiency is shown only at the bands of interest. It can be easily seen that the measured gain at 1.8 GHz for ports 1 and 2 is 5.5 dBi and 5.2 dBi, respectively. While at 2.6 GHz, the measured gain for ports 1 and 2 is 5.4 dBi and 5.3 dBi, respectively. Similarly, the measured efficiency at 1.8 GHz for ports 1 and 2 is 90% and 89% while at 2.6 GHz for ports 1 and 2 is 93% and 91%, respectively.  
Figure 12a-d shows E-plane views and Figure 12e-h shows the H-plane views of the measured and simulated radiation patterns at 1.8 and 2.6 GHz through ports 1 and 2, respectively. Radiation patterns shown in Figure 12a,b point in broadside directions for both ports 1 and 2 at 1.8 GHz. Similarly, radiation patterns shown in Figure 12 c,d point in +45\({}^{\circ}\) and 315\({}^{\circ}\) for ports 1 and 2 at 2.6 GHz, respectively. The cross polarization values in all the plots are well below the co polarization values. The same is true for the H-plane patterns. These results clearly indicate pattern diversity operation of the presented MIMO antenna. The 3-D radiation pattern plots of the proposed dual-band MIMO antenna are presented in Figure 13. The 3-D patterns are shown for both the ports at 1.8 GHz and 2.6 GHz, respectively.  
Figure 11: Simulated and measured (**a**) Gain; (**b**) Efficiency.  
Figure 12: _Cont._  
Figure 12: Measured and simulated radiation patterns. (**a**) E-Plane Port 1 at 1.8 GHz; (**b**) E-Plane Port 2 at 1.8 GHz; (**c**) E-Plane Port 1 at 2.6 GHz; (**d**) E-Plane Port 2 at 2.6 GHz; (**e**) H-Plane Port 1 at 1.8 GHz; (**f**) H-Plane Port 2 at 1.8 GHz; (**g**) H-Plane Port 1 at 2.6 GHz; (**h**) H-Plane Port 2 at 2.6 GHz.