Design Of Rectenna For Internet Of Things System

With the wide applications of wireless Internet of Things（IoT）technology and the rapid development of new generation communication technology,there is an increasing demand for wireless energy charging devices applied to IoT systems.Rectenna is the core device of wireless energy reception and recovery,and its performance directly affects the effect of energy recovery,so it is of practical significance to study the design and implementation method of high-performance rectenna.In this thesis,rectennas applied to IoT systems are studied,and the following main results are achieved:（1）A four-polarization receiving antenna capable of covering 4G and 5G communication frequency bands and receiving horizontal（90°）,vertical（0°）,+45°and-45°line polarization waves simultaneously is proposed and designed for IoT systems.The antenna realizes four broadband dipole antennas on two metal patches and is fed by a single microstrip line,which has the advantages of compactness,simplicity and low cost,and is suitable for applications in harvesting systems that recover RF energy from the environment.The measured results show that,in the frequency band of 2.5～3.5 GHz,|S₁₁|<-14.6 dB,the antenna can receive four line polarization waves,and the maximum gains in the four planes ofφ=90°,0°,+45°and-45°are1.04 dBi,2.07 dBi,1.85 dBi and 1.2 dBi,respectively,which meet the requirements of the rectenna to the receiving antenna.（2）A dual circularly-polarized antenna at 2.45 GHz band and a dual-band dual circularly polarized antenna at 2.45 GHz/2.1 GHz band are designed using defective ground structure excited by microstrip line and artificial magnetic conductor metamaterial and multiple-input multiple-output technology.2.45 GHz band（2400-2484.5 MHz）is the license-free band for WLAN,Bluetooth,Zig Bee and other systems,and 2.1 GHz band is widely used in the field of narrowband IoT,so the dual circularly-polarization antenna working at 2.45 GHz/2.1 GHz bands can widely collect RF energy from the environment,and can also combine energy recovery and send IoT signals.The measured results show that the dual circularly polarized antenna at 2.45 GHz band can transmit and receive left-handed and right-handed circularly polarized waves at 2.45 GHz frequency with a gain of about 4.5 dBic,a bandwidth of about16%for|S₁₁|less than-10 dB,a cross-polarization discrimination ratio of more than 20 dB,and a front-to-back radiation ratio（0°and 180°radiation ratio）of more than 24 dB,the unidirectional radiation characteristic is good.The dual-band dual circularly-polarized antenna can transmit and receive both left-handed and right-handed circularly polarized waves at 2.45GHz and 2.1 GHz.the measured gain of the antenna is about 7.8 dBic at 2.1 GHz,and the measured gain of the antenna is about 7.2 dBic at 2.45 GHz.the cross-polarization discrimination rate is above 20 dB,and the front-to-back radiation ratio is above 25 dB,which has good dual-band dual circular polarization characteristics and unidirectional radiation characteristics.（3）A rectifier circuit is designed to work at 2.45 GHz frequency band.HSMS285C is selected as the rectifier diode,and the circuit structure of voltage doubling is used for the design.The rectifier circuit is simple,compact and easy to integrate with the receiving antenna in the IoT device.Measured results show that the maximum DC conversion efficiency is 56%,occurring at an input power level of 10dBm and a load of 1.2 kΩ.At the center frequency of2.45 GHz,|S₁₁|is less than-20 dB,and the input impedance is close to 50Ωin the input power range of 0～10 dBm,which is well matched.