Research On High-performance Microwave Source And Rectenna For Microwave Power Transmission

Wireless power transfer(WPT)is a way to supply energy through radio wave directly from the source to the powered end.It changes the traditional way of transfering energy by using electrical conductors.It aims to eliminate all power cables connected to the electronic equipment.Microwave power transmission(MPT)is one kind of WPT using microwaves as a carrier.The MPT system mainly comprises a transmitter composed of a microwave source and a transmitting antenna,and a receiver/rectenna composed of a receiving antenna and a rectifier.The RF-DC conversion efficiency of the rectenna plays an important role in the performance of the system.On the one hand,the efficiency of the rectenna is limited by the loss of the rectifying diode.On the other hand,due to the nonlinear characteristic of the rectifying diode,the matching between the rectifier and the receiving antenna is affected by the variation of the input power,frequency,and load.Thus it is difficult to maintain high rectifying efficiency.In view of the above problems,a high-power integrated antenna-source capabling of generating pulse signals is proposed at the transmitting end.Compared with the sinusoidal signal,the high peak-to-average pulse signal reduces the energy loss caused by the threshold barrier of the diode in the rectenna,consequently realizing higher rectifying efficiency.Then,several high-efficiency rectifiers,as well as a rectenna with wide input power,frequency and load range are designed at the receiving end.Specially,the main research contents are as follows:(1)An integrated microwave source based on self-resonant antenna array is proposed to generate pulse signal with high peak-to-average ratio.In the design of simulation and physical structure,two kind of basic units of the integrated microwave antenna-source are proposed.Both of them simultaneously serve as energy storage system,pulse generator and radiator,which are used to construct the first-order,second-order and fourth-order integrated microwave antenna-source.The proposed integrated microwave antenna-source has a more compact and simple structure than the transmitter in the conventional MPT system which connects the microwave source and transmitting antenna in series.The experimental results show that the output waves of multiple units are in phase and the power can be added.Therefore,a multi-stage integrated antenna-source can be designed by placing a plurality of integrated antenna-source units to output high-power pulse.Compared with the existing high-power microwave source,the proposed microwave source can output pulse with higher power by placing multiple units,featuring strong expandability.(2)The concept of reflcted power recycling network is proposed to extend the input power,frequency and load dynamic ranges of rectifiers.The reflcted power recycling network is inserted between the receiving antenna and rectifier.When the input power,operating frequency and output load vary,resulting in impedance mismatch,the reflected power recycling networks are able to recycle the reflected power,consequently improving the RF-dc conversion efficiency.Based on the above concept,two reflected power recycling networks are designed.The first reflected power recycling network has a wide frequency bandwidth,while the second one has a more compact and simple structure.The simulated results show that the first reflcted power recycling network is able to extend the operating power,frequency and load range of the rectifier.The second reflcted power recycling network can reduce the sensitive of the recrifying efficiency to the variation of the input power,as well as working at a higher input power level.Measured results agree well with the simulated ones.(3)Two novel complex impedance compression networks(ICNs),including a single-band and a dual-band networks,are proposed and applied to the design of rectifying circuits for efficiency improvement.The proposed ICNs are connected to the microwave input of two parallel sub-rectifiers.They reduce the variation ranges of the rectifier input impedance which change with input power,consequently improving the impedance matching performance.Thus the loss due to impedance mismatch is reduced and high conversion efficiency can be obtained over the input power ranges.Compared with the resistance compression networks(RCNs),the proposed ICNs are able to compress the variation range of the complex impedance rather than that of the resistance,featuring design flexibility.Detailed analysis is carried out.For demonstration,a 2.45 GHz rectifier and a dual-band one working at 2.45 GHz and 5.8 GHz for WLAN and ISM bands are implemented based on the ICN.The experimental results show that,in comparison to the counterparts without the ICN,the proposed rectifiers with the ICN can improve the efficiency at low input power levels without degrading the maximum conversion efficiency,and extend the operating power range.Besides,the ICN-based rectifiers have a more compact and simple circuit structure than the RCN-based ones.(4)A wideband rectenna with a dynamic operating power range is proposed.Firstly,a wideband circular polarization antenna working at the frequency band of 1.68-2.72 GHz is designed with a relative frequency bandwidth of 47.3%.Then a wide-dynamic-range input matching network is designed,which composes of an impedance manipulation network and a wideband resistance compression network,in order to improve the impedance matching performance of the rectifiers within wide input power and frequency ranges.The working principle is analyzed in detail,and the design formulas are derived.According to the above theoretical analysis,a rectifier based on the wideband resistance compression network is designed.The simulation and measurement results show that,compared with a rectifier based on the traditional resistance compression network and an ordinary wideband rectifier,the proposed rectifier achieves impedance compression in a wider frequency bandwidth.In other words,when the input power varies,it improves the impedance matching performance and rectifying efficiency in a wider frequency band.Finally,a wideband rectenna with dynamic operating power range is designed based on the proposed wideband circular polarization antenna and rectifier.Moreover,a complete WPT system is built to measure the efficiency of the rectenna within a wide input power and frequency range.