## 2 Antenna Design and Performance
### Dual-Polarization P-Band Dipole Antenna Design and Performance  
As shown in Figure 10a, two half bow-tie dipole antennas are assembled orthogonally to achieve dual-polarization characteristics. However, as shown in Figure 10b, the simulated \(-10\) dB reflection coefficient performances are slightly shifted to a higher band in comparison with the performance of a single half bow-tie dipole antenna. In the case of a single half bow-tie dipole antenna (\(d_{1}\) = 20 mm and \(d_{2}\) = 6 mm), the simulated \(10\) dB \(|S_{11}|\) band covers from 440.92 to 787.96 MHz. On the other hand, in the case of the antenna shown in Figure 10a, the simulated \(-10\) dB reflection coefficient band covers from 447.7 to 800.91 MHz. It is considered that the operating band was changed due to the influence of antennas located nearby. Therefore, additional bandwidth enhancement in the lower band is required to cover the target band stably.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Frequency (MHz)**} & **Gain (dBi)** & \multirow{2}{*}{**FBR (dB)**} \\  & **(@ \(\theta\) = 0°)** & \\ \hline
450 & 4.49 & 7.42 \\
580 & 2.62 & 2.37 \\
700 & 4.23 & 3.04 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Simulated radiation performances when \(d_{1}\) = 20 mm and \(d_{2}\) = 6 mm.  
Figure 10: _Cont._  
Figure 9: Half bow-tie dipole antenna: (**a**) geometry of antenna with various \(d_{1}\) values, (**b**) simulated reflection coefficient performances for various \(d_{1}\) values, (**c**) geometry of antenna with various \(d_{2}\) values (\(d_{1}\) = 20 mm), (**d**) simulated reflection coefficient performances for various \(d_{2}\) values (\(d_{1}\) = 20 mm), (**e**) simulated E-field distribution at 677 MHz when \(d_{1}\) = 20 mm and \(d_{2}\) = 6 mm, (**f**) simulated radiation performances versus frequency when \(d_{1}\) = 20 mm and \(d_{2}\) = 6 mm, (**g**) simulated radiation patterns at 450 MHz when \(d_{1}\) = 20 mm and \(d_{2}\) = 6 mm, (**h**) simulated radiation patterns at 580 MHz when \(d_{1}\) = 20 mm and \(d_{2}\) = 6 mm, and (**i**) simulated radiation patterns at 700 MHz when \(d_{1}\) = 20 mm and \(d_{2}\) = 6 mm.  
To shift the operating band to the lower band side slightly, we widened the width of the upper dipole arms, as shown in Figure 11a. However, the slope of the half bow-tie structure was unaltered (\(d_{2}=6\) mm). As a result, as shown in Figure 11b, the simulated \(-10\) dB reflection coefficient band covers from 435.43 to 788.83 MHz; this is sufficient to cover the target band. Figure 11c shows the simulated radiation performance of the optimized dual-polarization half bow-tie dipole antenna. Because the radiation performances of the two antennas are identical, only the simulated result for the case of Port 1 excitation is shown. At 580 MHz, the simulated radiation gain is 2.51 dBi at \(\theta=0^{\circ}\) and FBR is 2.06 dB.  
Figure 11: Optimized dual-polarization half bow-tie dipole antenna: (**a**) geometry of antenna, (**b**) simulated reflection coefficient performances, and (**c**) simulated radiation patterns at 580 MHz when Port 1 is excited.  
Figure 10: Dual-polarization half bow-tie dipole antenna: (**a**) geometry of antenna and (**b**) simulated reflection coefficient performances.