The Research Of Retrodirective Array Used In Wireless Power Transfer

In recent years,with the development of various technologies such as the mobile Internet,the Internet of Things,and small unmanned aerial vehicles,the demand for wireless charging by mobile devices has been continuously expanding.Microwave wireless power transmission(WPT)is a promising technology for solving long-range power supply of electronic devices for it has a long-distance effect.However,electromagnetic waves will be attenuated in space,so wireless power transmission efficiency is low,and higher antenna gains and precise beam control techniques are needed to make up for these deficiencies.Therefore,at present,researches on WPT mainly focus on point-to-point microwave transmission.There is less research on power transfer to mobile targets.The retro-directive array has the property of automatically emitting a beam to the direction of arrival without knowing the position of the source of the arrival wave.This adaptive beam tracking can be implemented using pure analog circuits without cumbersome digital processing techniques or expensive phase-shifting networks.Therefore,it has the characteristics of low cost,high reaction speed and high gain.Also,it has great application potential in WPT systems.At present,researches on retro-directive array mainly focus on low-power applications such as communications and radio frequency identification.There has been little research on retro-directive arrays for wireless power transmission.This is due to the large transmit power of the WPT,which requires high isolation between transmit and receive channels.However,ordinary retro-directive array designs rarely consider this aspect.Based on the research of domestic and foreign related literature,this paper focuses on the research of the retro-directive arrays for wireless power transmission.The main work and innovations are as follows:1: The principle of phase conjugation is analyzed,and the implementation methods and key technologies of different kinds of retro-directive arrays are explained.Various factors that affect the beam pointing error are studied,including antenna element pattern,antenna element number,antenna element spacing,channel amplitude and phase error,and array mutual coupling.2: Based on theoretical analysis,it is illustrated that the retro-directive array used for wireless power transmission requires high channel isolation.Based on this,a phase conjugated mixer with high channel isolation and low conversion loss was designed.At the same time,IF amplifier and local oscillator power divider were also designed.3: A microstrip antenna with high ports isolation and low cross-polarization was designed and used to form an antenna array.The array has low mutual coupling characteristics.4: The designed circuit module and antenna array were assembled into a retro-directive operating at 2.45 GHz,and the adaptive tracking ability of the array was tested.