Rectifiers are essential for microwave wireless power transfer (MWPT). RF-DC conversion efficiency must be improved for the practical use of MWPT. The focus of this research is related to single shunt rectifiers. Former research explained the operations of single shunt rectifiers in the frequency domain. Currently, we are using a harmonic balance method for the circuit simulations. These analyses focus on the frequency domain and transient phenomena were not directly analyzed. Also, the differences between experiments and their simulations are still issues in designing rectifiers. Therein, we analyzed an ideal rectifier with transient analysis and simulation. We also propose a novel simulation for single shunt rectifiers. Our simulation method is based on simple theories focusing on the steady-state condition of transient phenomena. In our analysis method, the output DC voltage is a fixed parameter and the DC current with the voltage is calculated. Therefore, this method is suitable for analyzing I-V characteristics. First, theoretical solutions are compared with Advanced Design System (ADS) simulations and they show the good agreement. Next, we created the novel simulation with our analysis method. Their results are also compared with ADS simulations. These analyses showed good agreement. Therefore, our novel method is consistent with former researches and commercial simulations. As a result, this research shows a novel analysis method for single shunt rectifiers and its consistency.

Microwave power transfer (MPT) can solve certain types of problems. For example, Internet of Things requires a flexible configuration of sensor networks, which is hindered by wired-charging sensors. This problem can be overcome by MPT techniques. However, the transmission efficiency of MPT is lower than that of wired transmission. This study focuses on the operation of rectifiers having a pulse-modulated input signal. Although a pulse-modulated wave is effective for improving the RF-DC conversion efficiency, the output voltage waves of rectifiers have a high ripple content. Moreover, the harmonic balance method cannot be used to simulate the operation of a pulse-modulated rectifier. To reduce the ripple content, a smoothing capacitor should be connected in parallel to an output load. We investigated the influence of a smoothing capacitor, the general characteristics of rectifiers under pulse-modulated waves, and the effectiveness of using pulse-modulated waves for improving RF-DC conversion efficiency. In conclusion, we reveal a necessary condition of the smoothing capacitor for improvement, demonstrate the effectiveness of pulse modulation, and show that the optimum impedance with a pulse-modulated wave input is an inverse of duty ratio times as compared to that with continuous wave input.

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This study theoretically and experimentally indicates that a charge pump rectifier for lowpower rectifiers such as RF-ID can be applied to high-power rectifiers and can attain the same level of RF-dc conversion efficiency and twice as high power rectification as the single-shunt rectifiers. A high-power rectifier is primarily a single-shunt rectifier, and a charge pump rectifier that applies twice the output voltage is used in low-power applications such as RF-ID. We aim to enhance the power of charge pump rectifiers by focusing on their characteristics. A fabricated 5.8 GHz charge pump rectifier achieved an RF-dc conversion efficiency of 70.8% at an input power of 8.0 W and a load resistance of 150 . This result is also the highest efficiency for 39 dBm rectifiers in the 5.8 GHz band. Compared to a single-shunt rectifier with the same diode, the charge pump rectifier generated twice the input power and efficiency difference of 2.9% at the maximum input power. These results indicate that the charge pump rectifier has an advantage over the single-shunt rectifier in high-power rectifiers.INDEX TERMS Rectifiers, RF circuits, Schottky diodes, wireless power transmission, circuit theory.This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.