Research On Directional Radiation Technique For Microwave Power Transmission System

Microwave Power Transmission(MPT)technique is one of the most promising way to realize long-distance,high-power wireless power transmission.MPT features extremely low free-space transmission loss,which can be employed to construct space solar-power station(SSPS)or high-altitude monitoring platform.However,to further improve the free-space transmission efficiency,phased array antenna should be used and directional radiation technique should be implemented.Directional radiation technique ensures maximum-possible receive power on any position the receiver is installed.The paper carrys out a preliminary exploration and research on the directional radiation technology of MPT system.A novel architecture of MPT transmitter is proposed,which is capable of generating multiple microwave power output with independent amplitude and phase control.The proposed architecture is based on quadrature modulation and demodulation techniques.One single quadrature modulator replaces both variable gain amplifier and phase shifter which are essential in traditional schemes.Also,one single demodulator is utilized to detect phase and amplitude of feedback RF signal,which provides a basis for closed-loop phase and amplitude control.The new structure overcomes shortcomings exsisting in conventional counterparts,i.e.,phase and amplitude mutual coupling between phase and amplitude control,poor consistency of RF devices.The proposed architecture achieves high performance at relatively low cost,which is a fairly good attempt in research on MPT transmitter.The architecture also provides a solid basis for hardware implemetation for directional radiation.Besides,the paper elaborates the mathematical principle of directional radiation.Firstly,the mathematical principle of linear phased array is derived.Combining theoretical analysis,calculation and simulation,mechanism of beamforming and directional radiation in 1-D and 2-D phased array is explained in detai.Based on the mathematical relationships,three practical directional radiation methods and their implementation are given.The operation principles and the proposed methods can be exploited as a software algorithm design basis for the actual implementation of MPT directional radiation.In order to verify the proposed transmitter architecture and directional radiation methods,a complete set of MPT system is constructed in the laboratory,including transmitter system,antenna arrays and receiver system.The transmitter system provides 16-channel amplitude/phase-adjustable microwave power output,working at frequency of 915 MHz,offering a maximum output power of 90 W.Antenna arrays adopt 3x3 configuration,and each array element is realized by using microstrip antenna with coupling feeding.Receiver system monitors the power received and send it back to the transmitter system via wireless communication,which is critical to the realization of closed-loop directional radiation.320 LEDs are lighted at a distance of 5m,which illustrates the feasibility of MPT technique.Also,free-space transmission efficiency is measured,which shows compliance with exsisting theory.Diretional radiation technique is verified at 2.4m distance.Experimental data obtained by three different methods are well-related,which strongly illustrates the effectiveness,feasibility and practicality of the proposed methods.