| Wireless Microwave Power Transmission(MPT)can be widely used in commerce and military.The rectifying antenna is the key subsystem of the MPT that determines the efficiency of the entire microwave transmission system.A rectifying antenna system consists of the receiving antenna and the rectifying circuit.The receiving antenna with the harmonic suppression can eliminate the insertion loss introduced by the input filter and suppress the high order harmonics generated by the rectifier diodes,then improve the system efficiency.The output DC filter in the rectifying circuit can also affect the system rectifying efficiency.In this paper,the receiving antenna for harmonic suppression and the rectifier circuit of output filter are designed and analyzed.Firstly,the development and application of microwave energy transmission technology are introduced,and the present research level in the rectifying circuit and the receiving antenna is summarized.As the effect of the patch shape and the feeding point on the resonant modes of the microstrip patch antenna has been analyzed,the patch of open slot and the suitable feeding point is used to suppress the second and third harmonic for the directional patch antenna.This antenna structure can also suppresses the parasitic modes accompanying the harmonics while,currently,the parasitic modes of the patch antenna is mostly suppressed by the band-stop unit in the feedline.Based on the rectangular slot ring,the bi-directional slot antenna with the harmonic suppression is realized by loading the band-rejected narrow slot in the microstrip feedline.This antenna shows a wider working frequency band.In order to reduce the radiator size,two slots are loaded in both sides of the rectangular slot ring,which can work like a H-shaped slot antenna.However,the working bandwidth for this antenna also reduces.In order to further improve the working bandwidth,a single slot is asymmetrically loaded in one side of the rectangular slot ring.This harmonic-suppressed antenna has the relative bandwidth of 47%.To discuss the rectifying efficiency at low and high input power,the components of the rectifying circuit,including input filter,matching circuit,rectifier diode and output DC filter are analyzed.It is pointed out that the reason for the low rectification efficiency at low power is that the power signal fails to meet the requirements of the best conditions for rectifier diodes.At the same time,a rectifying circuit based on distributed parameter output filter is designed,and its conversion efficiency is close to 70%.The designed antennas and rectifying circuits in this paper can provide the structure reference for the microwave rectenna system,and also have the application value. |
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