# Multiband Frequency Tuneable Antennas for Selection Combining Strategy in White Space Applications
## 3 Simulation Results  
To verify the reconfigurable scheme, the proposed antenna performance was analyzed and optimized using ANSYS EM software. The simulated antenna reflection coefficients are shown in Figure 5, with S11 lower than \(-6\) dB in the white-space frequency band. According to the result, instead of using all the states of the DTC, only States 4 to 21 were applied.  
To verify the performance of multiple resonances, these antennas were set to operate at different frequencies. In addition to checking the reflection coefficients, isolation between ports should be considered. Thus, three configurations were simulated with the specifications shown in Table 2.  
The simulated results of the S parameter are reported in Figures 6-8 for Configurations 1-3, respectively. According to the figures, the antennas were matched with a reflection coefficient lower than \(-6\) dB for all cases. In Configurations 1 and 2, the isolation values at 470 and 700 MHz were about \(-27\) and \(-18.5\) dB, respectively. These results confirm that the influence between antennas could be reduced. However, in Configuration 3, the isolation was \(-6.5\) dB, which is an acceptable value while the distance between two antennas is relatively close (0.188 of wavelength at 470 MHz).  
In terms of far-field radiation properties, the realized gain of the antennas is reported in Figures 9-11 for Configurations 1-3, respectively. In general, the radiation patterns were omnidirectional, and the principal radiated planes were different. These depend on the  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Configuration Type** & **Ant.1 Frequency** & **Ant.2 Frequency** \\ \hline Config. 1 & 470 MHz & 700 MHz \\ Config. 2 & 700 MHz & 470 MHz \\ Config. 3 & 470 MHz & 470 MHz \\ \hline \hline \end{tabular}
\end{table}
Table 2: Configuration of multiple resonances.  
Figure 5: Simulated antenna reflection coefficient.  
radiated antenna and the resonant frequency. According to the results, the realized gains of the antennas were \(-2.2\) dBi and \(1.87\) dBi at frequencies of \(470\) and \(700\) MHz, respectively.  
Figure 8: Simulated S-Parameters of antennas with Configuration 3.  
Figure 6: Simulated S-parameters of antennas with Configuration 1.  
Figure 7: Simulated S-Parameters of antennas with Configuration 2.  
According to the results shown in Figures 9-11, the proposed antennas had a quasi-nidirectional pattern for the different configurations. Furthermore, despite the antenna operating at the same frequency, there were differences in the antenna radiation patterns, which shows the independence of the antenna performance, and contributed to reducing the antenna power.  
Figure 11: Realized gain of the antennas with \(\phi=0^{\circ}\) (solid line) and \(\phi=90^{\circ}\) (dashed line) for Configuration 3.  
Figure 10: Realized gain of the antennas with \(\phi=0^{\circ}\) (solid line) and \(\phi=90^{\circ}\) (dashed line) for Configuration 2.  
Figure 9: Realized gain of the antennas with \(\phi=0^{\circ}\) (solid line) and \(\phi=90^{\circ}\) (dashed line) for Configuration 1.  
the ECC value. This can be explained by the effects of the ground plane on antennas when their positions were placed at the board corners.