Research On Near-field Electromagnetic Focusing And Steering Of Millimeter-wave Antenna Array

Many studies pay particular attention to the radiation characteristics of antennas in the far-field(FF)region.However,in certain applications when the target is in the near-field(NF)of the antenna,such as wireless power transmission(WPT),near-field(NF)detection,radio frequency identification(RFID),NF high-speed wireless communication,microwave imaging,etc.,the radiation energy of the antenna is required to focus on specific position of the NF region to increase power density and reduce interference.Such type of antenna is defined as NF antenna.Different from the FF case,the beam-forming of NF turns into a nonlinear three-dimensional(3-D)problem due to the nonlinear spatial phase factors among different array elements in the NF antenna.The dimension of the NF beam-forming is steering away from(?,?)to(x,y,z)and the polarization is a 3-D vector(e_x,e_y,e_z).The nonlinear characteristic makes it unable to identify the common array factor of the NF antenna array,results in the failure of beam scanning through array factor manipulation in the FF case,and leads to the coupling of the transverse and longitudinal radiating area of the NF region.Therefore,the beam scanning cannot be manipulated through single factor independently.The method of independent synthesis of the orthogonal-plane cannot be applied as well.This dissertation studies the problems of nonlinear phase generation,multi-domain coupling,multi-dimensional scanning,and multi-dimensional polarization manipulation in the beam-forming of the NF antenna.The relevant mechanisms and implementation methods of the generation of the holographic amplitude-phase,the decoupling of the transverse and longitudinal area,multi-dimensional scanning,and multi-dimensional polarization manipulation of the millimeter-wave NF antenna are the main focuses.The main content and innovation of this dissertation are summarized as follows:1.There are nonlinear spatial phase factors among different array elements of the NF antenna,which require independent modulation of amplitude and phase on the antenna aperture.The nonlinear quadratic phase distribution is required for the NF-focused(NFF)problem;the Bessel function with violently fluctuating phase and amplitude distribution is required for the NF non-diffractive problem.To solve these problems,a phase-amplitude decoupling method for the NF antenna is proposed in this dissertation.The decoupling of the phase and amplitude is achieved by the independent modulation of the arrangement and the offset of the elements on the leaky-wave and standing-wave antenna arrays.Based on this phase-amplitude decoupling technology,a two-dimensional(2-D)NFF leaky-wave antenna(LWA)with high radiation efficiency and a planar Bessel beam antenna array with high transverse linear polarization purity are realized,respectively.2.To solve the coupling problem of the transverse and longitudinal area in the NF antenna radiation characteristic manipulation,a new method of the proactive conformal NF beam-forming is proposed.In this dissertation,the design for a proactive conformal array is based on the 3-D curved substrate integrated waveguide(SIW),in which the elements of the antenna array are distributed in a 3-D topology rather than a planar topology.The spatial location of each antenna element is employed as a new parameter to obtain the desired phase excitation easily.The proactive conformal beam-forming method realizes the decoupling between the transverse and longitudinal area of the NF antenna.An analysis and modulation method of propagation characteristic of 3-D cured SIW is proposed to eliminate the influence of the phase change and the impedance mismatch.On this basis,a proactive conformal NFF array with a large stable scanning range is realized,which can greatly reduce the accompanying longitudinal spatial variation phenomenon in the transverse spatial scanning of the focus.Compared with the planar case,the transverse scanning range can be expanded to 8 times of that under the same longitudinal variation.3.The nonlinear characteristic makes it unable to identify the common array factor of the NF antenna and results in the failure of beam scanning through array factor manipulation in the FF case.Meanwhile,the method of independent synthesis of the orthogonal-plane cannot be applied.To solve this problem,a holographic phase decomposition method for the NF antenna is proposed.The nonlinear holographic phase is separated into two parts,i.e.,the 2-D independent factor and the 2-D correlation factor.On the premise of generating the NF holographic phase accurately,the independent modulation of the 2-D phase distribution can be achieved,and then the 2-D steering of the focus can be realized.On this basis,the NF holographic modulated LWA and the modified passive multi-beam network are combined to realize the 2-D scanning both in NF focusing and the non-diffractive beam.4.With the increase of the antenna aperture,the nonlinear change of the NFF nonlinear quadratic phase distribution becomes much sharper,which causes the problem of sparse distribution of the antenna array elements.To overcome these weaknesses,a new modulation method using a height-modulated ridge waveguide is proposed in this dissertation to obtain a flexible phase adjustment.The modulation of the propagating phase within the waveguide is achieved through ridge height modulation.A new dimensional modulation factor is introduced to solve the problem of sparse distribution and the difficulty in the 2-D array grouping.This modulation of the ridge height is confined within the waveguide,which will not affect its application in array grouping.On this basis,combining the unequal length focused progressive phase-shifting network and the compact self-progressive phase-shifting network,two kinds of NFF full 2-D frequency scanning antenna arrays are realized.The testing information in the NF region can be directly obtained with a certain band of frequency,reducing the testing time without applying the complex SAR algorithms.5.The concerned dimension of the NF beam-forming is changed from(?,?)to(x,y,z)and the polarization is focused on the 3-D vector,i.e.,(e_x,e_y,e_z).There are difficulties in the 3-D beam-forming,e.g.,3-D polarization manipulation and 3-D scanning.To overcome these difficulties,a method of 3-D beam-forming of NFF phased array antenna is proposed.The 3-D polarization manipulation is realized through vector synthesis of orthogonal polarization elements in the NF region of the antenna.A machine learning method is employed to build the amplitude and phase prediction model of the NFF phased-array antenna,which can solve the focal shift problem and realize the instant and accurate 3-D scanning of the focus in the NF region.The 3-D polarization manipulation and accurate 3-D scanning are systematically studied with the experimental verification of the proposed NF active phased array antenna carried out.