# High-Efficiency Triple-Band RF-to-DC Rectifier Primary Design for RF Energy-Harvesting Systems
## 4 Conclusions  
In this work, a Schottky diode-based triple-band rectifier was proposed. The feasible solution of the proposed system was based on an initial design of a dual-band rectifier. It consisted of an impedance-matching circuit, an RF-to-DC rectifier that converts ambient RF energy into DC voltage, and an output load. A series of shunt stubs was applied to the initial design of the dual-band rectifier to form the proposed system. The transmission lines of the triple-band rectifier were optimized by utilizing a genetic algorithm optimizer. The obtained feasible solution of the proposed system operated satisfactorily in the frequency bands of LoRaWAN networks, GSM-900 mobile communication networks, and WiFi 2.4 GHz wireless networks. The numerical results of the proposed system exhibited a triple-frequency operation (\(-29.4\) dB at 866 MHz, \(-22.13\) dB at 948 MHz, and \(-32.75\) dB at 2.423 GHz), whereas the power conversion efficiency reached up to 81% for an input power level of 0 dBm. It is worth mentioning that the DC output voltage for an RF input power level greater than \(-15\) dBm was above 0.5 V, whereas for an input power of 0 dBm, was equal to 3.24 V. The presented results of the proposed triple-band rectifier demonstrate the system's stability and durability in the frequency bands of interest. Future work includes the fabrication of the proposed system, as well as its experimental validation by combining various antenna prototypes in a rectenna system. Furthermore, knowing that, depending on the total input power of the rectifier, topologies with a reduced number of rectifying elements may lead to better RF-to-DC PCE [34], we will incorporate the above study to assess the performance of the new circuit design in our future work. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref.** & **Sub.** & **Impedance Matching** & **Efficiency @ Frequency** & **Input Power (dBm)** & **Load (kOhm)** \\ \hline
[15] \({}^{\dagger}\) & FR-4 & microstrip & 42\% @ 3-tone & 10.0 & 3.00 \\  & & lines & signal 1.95 GHz & & \\
[16] \({}^{\star}\) & Duroid & triple-stub, tuning and & \(\sim\)41\% @ 925 MHz & & \\  & 5880 & & \(\sim\)32\% @ 1.82 GHz & \(-10.0\) & 5.00 \\  & & inductor & \(\sim\)26\% @ 2.17 GHz & & \\  & & meander line, & 68\% @ 3-tone signal & & \\
[17] \({}^{\dagger}\) & FR-4 & open and & 2.0 GHz & \(-7.0\) & 1.10 \\  & & radial stubs & 2.47 GHz & & \\  & & & 3.6 GHz & & \\  & & & 61.9\% @ 0.85 GHz & & \\
[18] \({}^{\dagger}\) & Duroid & open and & 71.5\% @ 1.77 GHz & 0.0 & 2.20 \\  & 5880 & shorted stubs & 60.5\% @ 2.07 GHz & & \\  & & & 54\% @ 0.9 GHz & & \\
[19] \({}^{\star}\) & FR-4 & radial and & 51\% @ 1.8 GHz & 4.0 & 3.80 \\  & & & 48\% @ 2.45 GHz & & \\  & & & \(\sim\)42\% @ 1.85 GHz & & \\
[20] \({}^{\star}\) & Duroid & open and & \(\sim\)45\% @ 2.15 GHz & \(-10.0\) & 5.00 \\  & 5880 & shorted stubs & \(\sim\)38\% @ 2.48 GHz & & \\  & & & \(\sim\)48\% @ 3-tone signal & & \\  & & & 58\% @ 866 MHz & & \\ this work \({}^{\dagger}\) & FR-4 & shunted stubs & 68\% @ 948 MHz & & \\  & & & 47\% @ 2.423 GHz & & \\  & & & 81\% @ 3-tone signal & & \\ \hline \hline \end{tabular} \({}^{\dagger}\) simulated results \({}^{\star}\) measured results.  
\end{table} 
Table 5: Comparative results of the proposed triple-band rectifier against related work. **Author Contributions:** The conceptualization of the paper was by [PERSON] and [PERSON]; [PERSON] performed the theoretical analysis and the simulations. [PERSON], [PERSON], and [PERSON] validated the theoretical analysis and the simulation results. [PERSON], [PERSON], and [PERSON] supervised the process. [PERSON], [PERSON], and [PERSON] analyzed the results and contributed to writing the manuscript. All authors contributed to reviewing the manuscript. All authors read and agreed to the published version of the manuscript.