Research On High-Efficiency Rectifying Circuit And Antenna For Microwave Power Transmission

Microwave power transmission（MPT）technology is one of the wireless power transmission（WPT）technologies and it is widely used in space solar power station（SSPS）,space aerocraft energy supply,wireless sensor network（WSN）and so on.Rectenna is a vital component of the MPT system and it is used to receive the electromagnetic power and convert it into DC power.The obtained DC power can be used to supply the energy for some other electronic equipment.Rectenna is composed of antenna and rectifier.Because of the nonlinear characteristic of the microwave diode,it is difficult to design high efficiency multiband rectifier and high efficiency wide input power range rectifier circuit.In addition,the radiation of the harmonic components of the diode and the polarization mismatch between the transmitting antenna and the receiving antenna also can lead to the efficiency of the rectenna decreased.Therefore,high efficiency multiband rectifier,wide input power range rectifier and high efficiency rectenna are mainly studied in this dissertation.Specially,the main research contents are as follows:（1）In terms of high-efficiency multiband rectifying circuit,a high efficiency dual-band rectifier working at 0.915 GHz/2.45 GHz and a compact triple-band rectifier working at 0.85GHz/1.77 GHz/2.07 GHz are designed,respectively.In the process of designing dual-band rectifier,a novel dual-band impedance matching network is proposed and its theoretical analysis is carried out.The proposed matching network can transform a pair of complex impedance to a real resistance at two arbitrary frequencies.For validation,the dual-band rectifier is designed and measured.The measured results show that the maximum power conversion efficiencies at the two operating frequencies are 77.2%and 73.5%,respectively.Furthermore,a compact triple-band impedance matching network is proposed and its design equations are derived.For validation,a compact rectifier operating at 0.85 GHz,1.77 GHz and 2.07 GHz is implemented and measured.The measured results show that the maximum efficiencies at the three operating bands are 61.9%,71.5%and 60.5%,respectively.Compared with some other related designs,the proposed dual-band and triple-band rectifiers feature high efficiency and compact in size.（2）In terms of wide input power range rectifying circuit,two dual-band rectifiers with different frequency-spacing are designed.One works at 0.915 GHz/2.45 GHz and the other one works at 1.8 GHz/2.4 GHz.In the process of study the dual-band wide input power range rectifier,a dual-band transmsission-line resisitance compression network（TLRCN）is proposed and it can be used to reduce the sensitivity of the rectifier to the variation of the input power level and load resistance at two frequencies.The analytical expressions for the dual-band TLRCN are derived.For comparison,their counterparts without the dual-band TLRCN are also designed and implemented.The measured results have validated the proposed idea.That is,the proposed dual-band TLRCN can be employed to extend the input power ranges of the rectifier at two bands without decreasing the maximum efficiency.（3）A 2.45 GHz rectenna with harmonic suppression characteristic is designed.Compared with the conventional rectenna,the proposed rectenna no longer need the low pass filter.This characteristic is beneficial for enhancing the efficiency and reducing the physical size of the rectenna.In the rectenna,the antenna is a microstrip patch antenna and it is fed by gap coupling.The measured results show that the S₁₁ of the antenna at the second harmonic（4.9 GHz）and the third harmonic（7.35 GHz）are-1.12 dB and-1.77 dB,respectively.That is,the proposed antenna has good harmonic suppression characteristic.When the input power level is 15 dBm,the measured maximum efficiency of the proposed rectenna is 66.1%at 2.45GHz.（4）A 2.45 GHz broadband circular polarized rectenna is designed and it has two substrates and they are connected by the probe.In this rectenna,the antenna is a microstrip patch antenna.And it is fed by a coupler.In addition,a balanced rectifier is proposed by a quadrature coupler and two identical sub-rectifiers are connected with the two output ports,respectively.Here,the quadrature coupler can be used to extend the bandwidth of the rectifier and reduce the sensitivity of the rectifier to the variation of the input power level and output load.When the input power is 15 dBm,the measured maximum efficiency of the proposed rectenna is 63.4%at 2.45 GHz.