# Dual-Band RF Wireless Power Transfer System with a Shared-Aperture Dual-Band Tx Array Antenna
## 4 Conclusions  
In this paper, a dual-band RF WPT system that includes a shared-aperture 2.4 and 5.8 GHz Tx array antenna with 2.4 GHz RHCP patches and 5.8 GHz RHCP patches is developed. The Tx array antenna combining a 2.4 GHz thinned array and a 5.8 GHz thinned array is optimally designed to obtain high transmission efficiency for various WPT scenarios. The aperture size of the proposed shared-aperture dual-band array antenna is reduced by 15% compared to that when implementing 2.4 GHz and 5.8 GHz arrays individually with equivalent performance and stacking them. WPT experiments according to the operating frequency are conducted in order to validate the developed dual-band RF WPT system. As a result of the WPT experiments when varying the distance and position of the Rx at 2.482 and 5.73 GHz, the measured received power was in good agreement with the calculated result. In adddition, transmitting wireless power with the focused beam improves the received power compared to when applying beam-forming. When the distance was varied from 1 m to 3.92 m and RF wireless power of 10 W was transmitted to the Rx by applying the beam-focusing, the received power (WPT efficiencies) at the 2.482 GHz and 5.73 GHz were distributed as 24.75-13.5 dBm (2.985-0.224%) and 19.25-6.8 dBm (0.841-0.050%), respectively. It was verified that wireless power with frequencies of both 2.482 and 5.73 GHz can be simultaneously transmitted. Furthermore, dual beams of 2.482 and 5.73 GHz can be generated to different receivers separately. Consequently, it is proven that the proposed dual-band RF WPT system is differentiated in \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Frequency** & **Polarization** & \begin{tabular}{c} **Size of** \\ **Tx Antenna** \\ \end{tabular} & \(\mathbf{P_{T}}\) & **Distance** & \
\begin{tabular}{c} **Size of** \\ **Rx Antenna** \\ \end{tabular} &
\begin{tabular}{c} **P\({}_{R}\)** \\ **(WPT Efficiency)** \\ \end{tabular} \\ \hline
[7] & 5.8 GHz & \begin{tabular}{c} \
\begin{tabular}{c} LP \\ (linear polarization) \\ \end{tabular} & \(1\times 1\) m\({}^{2}\) \\ \end{tabular} & 500 W & 10 m & \(1\times 1\) m\({}^{2}\) &
\begin{tabular}{c} 209.26 W \\ (41.85\%) \\ \end{tabular} \\ \hline
[8] & 2.45 GHz & LP & \(1\times 0.122\) m\({}^{2}\) & 0.25 W & 1 m & \(0.5\times 0.122\) m\({}^{2}\) &
\begin{tabular}{c} 0.0125 W \\ (5.01\%) \\ \end{tabular} \\ \hline
[37] & 2.08 GHz & LP & \begin{tabular}{c} \begin{tabular}{c} 0.28 \(\times\) 0.1 m\({}^{2}\) \\ (guess) \\ \end{tabular} & 1 W & 0.5 m & \
\begin{tabular}{c} 0.07 \(\times\) 0.1 m\({}^{2}\) \\ (guess) \\ \end{tabular} &
\begin{tabular}{c} 0.014 W \\ (1.4\%) \\ \end{tabular} \\ \hline
[38] & 5.8 GHz & LP & \(0.217\times 0.217\) m\({}^{2}\) & 0.1 W & 0.4 m & \(0.16\times 0.16\) m\({}^{2}\) & \begin{tabular}{c} 0.0332 W \\ (0.332\%) \\ \end{tabular} \\ \hline This study & 2.482 GHz & \begin{tabular}{c} \begin{tabular}{c} CP \\ (circular polarization) \\ \end{tabular} & \(0.44\times 0.44\) m\({}^{2}\) \\ \end{tabular} & \begin{tabular}{c} 10 W \\ 1-3.92 m \\ 10 W \\ \end{tabular} & \
\begin{tabular}{c} 0.063 \(\times\) 0.063 m\({}^{2}\) \\ 1-3.92 m \\ 0.031 \(\times\) 0.031 m\({}^{2}\) \\ \end{tabular} &
\begin{tabular}{c} 0.2985 W–0.0224 W \\ (2.985–0.224\%) \\ 0.0841 W–0.005\% W \\ (0.841–0.05\%) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparisons of previous studies of RF WPT. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Rx(1): 2.4 GHz Patch**} & \multicolumn{2}{c}{**Rx(2): 5.8 GHz Patch**} \\ \cline{2-5}
**Beam-Focusing** & \multicolumn{2}{c}{**2.482 GHz**} & \multicolumn{2}{c}{**5.73 GHz**} \\ \cline{2-5}  & **Calculated** & **Measured** & **Calculated** & **Measured** \\ \hline
**Received power** & 16.57 dBm & 15.57 dBm & 11.47 dBm & 10.58 dBm \\ **(WPT efficiency)** & (0.454\%) & (0.361\%) & (0.140\%) & (0.114\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Experimental result of the dual-band received power when transmitting a dual beam separately to two receiving antennas.