| Microwave Power Transfer(MPT)technology is a new way of energy transmission.It is a wireless transmission of energy between directional points in the form of microwave,which operates without cable.The concept of microwave energy transmission was proposed by Nikola Tesla in 1891.In the following years,due to the development of microwave technology and electronic components,especially the improved performance of rectifying diode,the microwave energy transmission technology became more and more possible.At present,microwave energy transmission technology has been applied in many fields,such as radio frequency identification(RFID),wireless sensors and solar satellites.Based on the above research background,this paper are focuced on new types of rectenna,which can convert microwave energy into dc energy and is a key component of the MPT system.In order to improve the sensitivity of the rectenna to the environmental electromagnetic wave power density,this paper proposes a rectifier antenna based on differential structure.Firstly,a half wave rectenna is designed based on dipole antenna and balun.Dipole antenna has a simple structure,and with omnidirectivity,which is a classical antenna in engineering.With a balun structure,the arms of the dipole antenna induce differential signal and then convert into an unbalanced signal,so that the rectifier circuit can rectify the microwave energy.In addition,due to the nonlinear characteristics of the diode,high-order harmonics will be appeared,so it is necessary to design a DC filter to prevent the harmonics and return the energy to the circuit for secondary rectification,which can further improve the rectification efficiency.The RF-DC efficiency of the half-wave differential rectenna finally designed can achieve 53.95% at the central frequency of 5.8GHz when the incident power is 33.8dBm and the load is 52.At the frequency range of 5.65 GHz ~ 6.1GHz,the RF-DC efficiency can reach more than 50%.In order to improve the efficiency of RF-DC conversion of rectenna,a balanced full-wave rectenna is designed.Firstly,in order to improve the gain of the dipole antenna,the dipole antenna is loaded with a director,and the gain of the dipole antenna with director can reach up to 8.1dBi.Furtherly,to achieve good impendace match between the rectifier bridge and the antenna,this paper designed a balanced band-pass filter based on the mixed S parameters.The range of differential mode pass-band is 1.98GHz~3.45 GHz,and the in-band common mode suppression can reach below-20 dB.In the design of rectifier circuit,this paper studies the rectifier structure based on bridge circuit and voltage multiplier circuit respectively,and realizes RF-DC conversion by using rectifier bridge instead of diode.On the other hand,it can improve the utilization rate of incident electromagnetic wave,and it can also reduce the response value of rectifier antenna to incident electromagnetic wave.The maximum rectification efficiency of the bridge rectifier circuit finally realized can reach up to 72.3%,and within the frequency range of 2.2GHz~2.8GHz,the RF-DC conversion efficiency has been above 50%.In addition,when the diode is replaced with double voltage rectifier circuit,the efficiency of RF-DC can reach up to 62.5%. |
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