Research On Near-field Focusing Array Antenna Technolog

With the rise of wireless power transmission,microwave hyperthermia,radio frequency identification and other applications,more and more attention has been paid to focusing antennas working in the near field(Fresnel zone).Although there are many techniques and methods to study near-field focusing,there are few researches that can realize tunable focus scanning.In addition,a conformal antenna can be fitted on the surface of various carrier platforms without affecting the aerodynamics of the carrier.If the near-field focusing technology is combined with conformal antenna technology,it will provide the possibility of further optimization for the application of near-field focusing.Compared with a single focus,shaped focusing technology can focus electromagnetic energy into a special shape area,which has become a hot research topic in near-field electromagnetic focusing.Therefore,this paper uses a microstrip array antenna to carry out the detailed analysis and design of the above near-field focusing technology.The main work completed in this paper includes:1.A feed network and U-slot antenna unit with a one-minute eight-point Wilkinson power divider loaded with a digital phase shifter are designed.The ability of focal length tunable focus scanning in the near field is discussed by using a planar array antenna with 16 elements.Finally,the simulation and measurement verify that the planar array antenna can generate electromagnetic waves focusing at the ideal position in the near field.2.A cylindrical conformal array antenna is proposed for near-field focusing.Firstly,an antenna unit with 11% bandwidth and 7.8d Bi gain is designed.Then the performance of focus scanning in the near field is analyzed by using a cylindrical conformal array with 64 elements.Finally,simulation and experimental results show that the proposed cylindrical conformal array antenna can flexibly realize two-dimensional focus scanning in the near field.In addition,by activating a certain number of antenna elements in different sections of the cylindrical array,the omnidirectional scanning effect with good stability can be obtained.3.A synthesis method for forming special focusing patterns on the focal plane is proposed,and an amplitude-modulated feed network is designed based on the phasemodulated feed network.Firstly,the performance of 8×8 planar array antenna to produce a four-angle star focusing pattern in the focal plane is analyzed by using the method of equal amplitude phase regulation.Then,the performance of 8×8 planar array antennas to generate square and triangle focusing patterns in the focal plane is analyzed through amplitude and phase simultaneous regulation.Finally,the simulation and measurement results show that when the phase and amplitude distribution of the array antenna are controlled simultaneously,the focusing pattern of low sidelobe can be formed on the focal plane.This method can provide a reference for radio frequency identification,microwave imaging,high-efficiency wireless power transmission and other applications.