Research And Design Of The Rectenna For RF Energy Harvesting System

As a way of wireless energy harvesting,Radio Frequency(RF)energy harvesting technology,which mainly uses electromagnetic energy as its energy source,is being widely concerned by the academic community,and has been widely used in Wireless sensor devices,such as personal health care,radio frequency identification,intelligent traffic management,environmental monitoring and so on.As a critical part of RF energy harvesting system,the rectifying antenna(rectenna)is usually a combination of a receiving antenna and a rectifying circuit.The function of the rectenna is to convert the ambient RF power into usable direct current(DC)power.The energy harvesting efficiency of the whole system is directly determined by the overall performance of the rectenna.This paper mainly focuses on the application requirements of the broadband compact rectenna in the low input power environment.The RF energy receiving antenna and rectifying circuit are studied deeply,and finally completed the design of the rectenna.Firstly,the theory of microstrip antenna and several typical rectifying circuits are discussed,based on the structural model of RF energy harvesting system and its principle.In addition,the comparison and analysis of half wave rectifying circuit and single stage voltage doubler rectifying circuit are given.It is concluded that the single stage voltage doubler rectifier circuit is the ideal choice for the low input power rectifying circuit.Secondly,the RF energy distribution in the environment is analyzed,and the initial operating frequency band of the designed rectenna is determined.For the RF energy receiving antenna,which is firstly based on a fan shaped cross dipole linearly polarized antenna.Its second harmonic and third harmonic are effectively suppressed in the 4.5GHz and 6.5GHz bands,by cutting a flower-shaped slot on each pole and an H-shaped slot on the ground plane respectively.The measured results of the antenna are basically consistent with the simulated results,and its impedance bandwidth is up to 800 MHz.In order to further increase the bandwidth of the antenna,a broadband circularly polarized antenna which based on a symmetrical trapezoidal tooth with logarithmic periodic structure is designed,because of the limitation of the direction of the RF signal received by the linearly polarized antenna.The feed structure of the antenna is simplified by introducing a 90 degree phase delay line,and a 1000 MHz impedance bandwidth and a 350 MHz axis ratio bandwidth are realized.Subsequently,the closed circuit is used to analyze the rectifier diode,and three kinds of commonly used schottky diodes are simulated and analyzed by ADS based on the single stage voltage doubler rectifying circuit at the same time.The final selected rectifying element of the rectifying circuit is HSMS-285 C.The optimized value of chip capacitors and load resistance are selected as 100 pF,700? respectively.The two kinds of low input power rectifying circuit with different frequency bands are designed.Their power sensitivity reached-26 dBm,and the maximum RF-to-DC conversion efficiency are 70% and 76.5% respectively.Finally,the in-kind production,welding and measurement of the rectenna are completed.The maximum RF-to-DC conversion efficiency of the multi-band rectifying circuit is about 75%,and a good agreement between the simulated and measured results has been reached.The output voltage of 108.5mV and 139.6mV are obtained at the load of the harmonic suppression rectenna system and the broadband circularly polarized rectenna system,by connecting the multi-band rectifying circuit with the two RF energy receiving antennas respectively.