# A Dual-Polarized Omnidirectional Rectenna Array for RF Energy Harvesting Harvesting
## 3 Power-Combining Scheme for the Rectenna Array
### Design of an RF Power-Combining Network  
Based on the aforementioned mechanism, an RF power-combining network is proposed to integrate the RF power components of different polarizations received by the dual-polarized antenna array. Figure 10a shows the structure of the proposed RF power-combining network. The yellow parts in Figure 10a are all metal layers, and the red parts indicate isolation resistors with a resistance of 100 \(\Omega\). The RF power-combining network consists of a 1-to-2 Wilkinson power divider, a 1-to-4 Wilkinson power divider, and a 3-dB hybrid coupler. After optimization, the network was fabricated and measured, and a photograph is provided in Figure 10b. It is printed on a 30-mil-thick Rogers RO4350B substrate. Table 3 gives the detailed dimensions of the RF power-combining network.  
Figure 11 plots the phase simulation results for the corresponding ports of the RF power-combining network. It can be seen that the network has an equal phase difference between the two Wilkinson power dividers' input ports and the coupler's output ports. In addition, there is a phase difference of about 90 degrees between either input ports and the two output ports of the coupler, which proves the effectiveness of the RF power-combining network design.  
As shown in Figure 12, the simulated reflection coefficients of the 1-to-2 and 1-to-4 Wilkinson power dividers in the RF power-combining network are both below \(-20\) dB at 2.45 GHz, which means that the Wilkinson power dividers in the network have good impedance matching. Moreover, the insertion loss of the 1-to-4 Wilkinson power divider is 6.1 dB, while the insertion loss of the 1-to-2 Wilkinson power divider is 3.2 dB.  
The simulated and measured \(S\)-parameters of the RF power-combining network are given in Figure 13. As shown in Figure 13a, the simulated and measured reflection coefficients of the network are below \(-20\) dB at the center frequency of 2.45 GHz. In addition,  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Parameter** & **Value (mm)** & **Parameter** & **Value (mm)** & **Parameter** & **Value (mm)** & **Parameter** & **Value (mm)** \\ \hline \(w_{0}\) & 1.6 & \(l_{0}\) & 5 & \(l_{6}\) & 4.6 & \(l_{12}\) & 7.5 \\ \(w_{1}\) & 0.9 & \(l_{1}\) & 5.2 & \(l_{7}\) & 37.6 & \(l_{13}\) & 5 \\ \(w_{2}\) & 73.1 & \(l_{2}\) & 6 & \(l_{8}\) & 4 & \(l_{14}\) & 23.6 \\ \(w_{3}\) & 1.6 & \(l_{3}\) & 16.2 & \(l_{9}\) & 18.2 & \(l_{15}\) & 16.7 \\ \(w_{4}\) & 2.8 & \(l_{4}\) & 7.2 & \(l_{10}\) & 4 & \(l_{16}\) & 15.4 \\ \(w_{5}\) & 1.6 & \(l_{5}\) & 4 & \(l_{11}\) & 5 & \(l_{17}\) & 5.8 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Dimensions of the proposed RF power-combining network (unit: mm).  
Figure 10: Schematic and photograph of the proposed RF power-combining network: (**a**) Schematic; (**b**) Photograph.  
the simulated and measured reflection coefficients within the operating bandwidth of the corresponding antenna array are below \(-12\) dB. As shown in Figure 13b, the measured isolation performances of the network at 2.45 GHz are better than 25 dB. The measured insertion performance from the 1-to-4 Wilkinson power divider's input port to the coupler's output port of the network is 9.2 dB, while the one from the input port of the 1-to-2 Wilkinson power divider to the output port of the coupler is 6.4 dB.  
Figure 11: Phase simulation results of the proposed RF power-combining network.  
Figure 12: Simulated reflection coefficients and insertion losses of the Wilkinson power dividers.  
Figure 13: S-parameters of the proposed RF power-combining network: (**a**) Reflection coefficients; (**b**) Insertion and isolation performances.