High-efficiency microwave rectifier with wide operating power range

Wireless power transmission (WPT) is a promising technology that can be employed as an alternative power source for electronic circuits. Actually, the receiving power generally cannot remain constant due to different transmission environment and distance. The variation of the input power levels leads to the diode impedance change, and then causes impedance mismatch and rectifier performance degradation. In this work, two kinds of network have been placed between the input port and the rectifiers, extending the operating power range. Firstly, a branch-line coupler is used as a power recycling network to improve the matching performance and conversion efficiency when the input power varies. In this case, two types of rectifiers can be designed by using the branch-line coupler. Both the two rectifiers include two identical sub-rectifying circuits and a branch-line coupler. The isolation port of the coupler in the proposed Type I rectifier is directly connected to the ground, in order to re-inject the reflected power back to the sub-rectifiers for recycling. As for that in the proposed Type II rectifier, it is connected to the third rectifier, which can rectify the reflected power. Thereby, the power reflected from the two sub-rectifiers due to impedance mismatch can be reused by the two types of proposed rectifier. The RF-dc conversion efficiency can be improved and the operating power range for high efficiency can be widened. Moreover, a complex impedance compression network (ICN) is also proposed and applied to the design of rectifying circuits for extending operating power ranges. The proposed ICN is connected to the microwave input of two parallel sub-rectifiers. It reduces the variation range of the rectifier input impedance which changes with input power. Thus the loss due to impedance mismatch is therefore reduced and subsequently high efficiency can be obtained over a wider input power range. Compared with the resistance compression network (RCN), the proposed ICN is able to compress the variation range of the complex impedance rather than that of the resistive load, featuring design flexibility. For demonstration, the ICN is applied to the design of single-band and dual-band microwave rectifiers. Theoretical analysis and performance comparison are carried out. The results indicate that the proposed topologies are able to realize high efficiency with wide input power dynamic range.