Design And Research Of Rectifying Antenna For Wireless Energy Harvesting

With the development of the Internet of Things(Io T),the wireless sensor network will be extensively deployed as the basis for perceiving the environment.The large number of sensors poses a challenge for the power supply.The traditional battery-based power supply will lead to time-consuming and labor-intensive maintenance,and thus cannot meet the needs of the future development.Due to the reduction of power consumption of sensors and wireless communication,and the increasing dependence of modern society on radio frequency(RF)technology,the wireless RF energy harvesting has become a promising method for power supply.As the key component of RF energy harvesting,the rectifying antenna(rectenna)has attracted great attention.However,there are two factors that restrict the efficiency of RF energy harvesting.On the one hand,the RF emitters are usually not optimized for wireless power supply or transmission,which results in the low RF power densities in the ambient environment.On the other hand,the rectifying circuit exhibits an efficiency bottleneck when the input RF power is low.The rectenna designs in recent years have demonstrated that the multi-beam rectenna can be an effective solution for elevating the received RF power and improving the rectification efficiency.In the multi-beam rectenna,the multi-port multi-beam antenna or multiple antennas are adopted to enhance the RF power receiving capability through multiple highgain beams with different polarizations and different spatial coverage;the multi-branch rectifier is utilized to convert the RF power received by the multiple beams and combine the DC products in the conversion.From the perspective of further improving the efficiency of the multi-beam rectenna under low RF power densities,this dissertation mainly studies the simplification of the antenna feeding networks and the optimization design of the multi-branch rectifier.The main contributions of this dissertation are as follows.1.A novel design scheme that utilizes the traveling-wave antenna to simplify the feeding structure is proposed,considering the problem that the multi-beam rectenna based on the array antenna relies on the beam-forming feeding network.The traveling-wave radiation characteristic of the dual-port antenna is exploited to directly obtain two beams covering different spatial range,so the beam forming can be realized without extra feeding networks.Based on the design scheme,the traveling-wave characteristic of the grid-array antenna is investigated,and the effect of its structural parameters on the beam direction and isolation between ports is elaborated.The coplanar stripline(CPS)structure is employed to integrate the rectifier circuit and the grid array of antenna.The proposed high-gain dual-beam rectenna design has a simple structure,which makes it easy to expand the aperture and to fabricate.2.The conventional traveling-wave array antenna relies on a large size to ensure good isolation between ports due to its slow radiation attenuation.To solve this problem,a novel design method that utilizes the coupling between array elements to enhance the traveling-wave attenuation is proposed.This method enables the dual-beam rectenna design to eliminate the beam-forming network and maintain a small size in the meantime.In the method,an equivalent circuit model based on the coupled lossy resonators is proposed,and the effect of the circuit parameters on the traveling-wave attenuation and phase shift is analyzed.On this basis,a traveling-wave antenna consisting of a seriescoupled patch array is proposed.Compared to the convectional traveling-wave series-fed patch array,it presents a significantly shorter array length,and thus can be applied to the cases where a trade-off between the size and gain exists.With the proposed design method,the scope of application of traveling-wave antennas is expanded.In addition,in view of the equivalent circuit similar to the coupled-resonator filter topology,it also lays the foundation for the designs integrating the traveling-wave antennas and filters.3.The multi-beam rectenna based on the beam-forming circuit can achieve a more compact structure since it does not rely on the array antenna size.However,since the coupling between array elements needs to be avoided in the separate design of the array antenna and circuit,the spacing between array elements is large and the circuit structure is redundant.To solve these problems,a novel design scheme integrating the coupled patch array antenna and hybrid coupler circuit is proposed.Through comparative analysis,the feasibility of the antenna to replace part of the circuit is demonstrated.The design scheme employs the complex J inverter to accurately characterize the coupling between the single-ended patches,thereby clarifying the effect of the coupling on the antenna beam.On this basis,the coupling between antennas is exploited,which enables the reduction of antenna spacing,the simplification of beam-forming circuit and the streamlining of design process.Consequently,a compact quad-beam dual-polarized rectenna is presented.4.The Yagi antenna can exhibit high aperture utilization,and thus can improve the compactness of multi-beam rectenna.However,it usually occupies a large space in the radiating or receiving direction.To solve this problem and realize a compact rectenna harvesting RF waves in the front and rear spaces,a novel quasi-Yagi array antenna with a thin linear profile is proposed.The collinear antenna is introduced to replace the traditional driven part of the Yagi array antenna—the dipole array.With the collinear antenna,the feeding networks like the power divider and balun can be eliminated,and the Yagi antenna can be arrayed in the vertical direction while maintaining a narrow profile.Besides the narrow profile,the proposed quasi-Yagi array also realizes high antenna gain and wide bandwidth while keeping high aperture utilization.By combining two such thin quasi-Yagi arrays,a rectenna with dual back-to-back beams achieves a relatively small width,and thus can be applied in scenarios with high requirements for horizontal space utilization.5.In view of the lack of research on the multi-branch rectifier circuit for multi-beam harvesting,a figure of merit is proposed to comprehensively evaluate the harvesting performance of the multi-beam rectenna in a range of incident angle of RF waves.Based on the figure of merit,a method optimizing the impedance matching is presented.Then,the circuit topologies that combine the DC power from multiple beams are discussed and analyzed,and the negative effect of the inactive rectifying branch is demonstrated.In addition,the rectifier of CPS structure,which is commonly used to integrate the antenna and circuit,is analyzed,and the important role of the balance in the CPS circuit is pointed out.