Research On Calculation Method Of Characteristic Modes Of Metal-Dielectric Models

With the development of the 5G era,the application of antennas in the field of mobile communications is becoming more and more extensive,and the requirements for antenna performance are also getting higher and higher.The traditional antenna design methods mostly rely on the experience of the antenna designer and the simulation optimization of continuous parameter adjustment.Designing an antenna in this way is often time-consuming and labor-intensive.With the development and application of characteristic mode theory in recent years,characteristic mode analysis has become a common analysis method in antenna design.It can help antenna designers intuitively analyze the inherent radiation properties of the antenna without adding excitation sources,and make targeted adjustments to the structural design of the antenna.Mode tracking is an essential technique in characteristic mode analysis.It can find and concatenate eigenvalues belonging to the same characteristic mode in a frequency band,and the eigenvectors(eigencurrents)correspond to the eigenvalues one-to-one.The process of changing with frequency in the frequency band is analyzed,and the influence of the characteristic modes on the radiation performance of the antenna is dominant at different frequency points.However,when characteristic mode analysis processes the model,it often encounters the problem of mode tracking errors,such as incomplete tracking of characteristic modes in the frequency band,mode crossing and other problems.Incorrect characteristic mode results of mode tracking affect antenna engineers’ use of characteristic mode analysis to evaluate antenna performance,so how to handle mode tracking correctly and efficiently becomes a key issue in eigenmode analysis applications.Starting from the pure metal problem,this thesis discusses the existing four mode tracking methods and introduces their respective advantages and disadvantages,after that selects the mainstream mode tracking method of current correlation coefficient among the four mode tracking methods.This thesis analyzes its specific tracking method in detail,and points out that this method will have mode tracking errors in some cases,Then,in order to mark the frequency point and mode serial number of the mode tracking error in this method,its tracking strategy is modified to generate the flag bit of the tracking error mode,and then the mode tracking method based on the change rate of eigenvalues of adjacent frequency points is introduced to correct the tracking error mode,forming a hybrid tracking mode tracking method.After that,the problem of solving the characteristic mode of the dielectric model is discussed.Because the impedance matrix of the dielectric model is antisymmetric and cannot directly establish the generalized characteristic equation,the impedance matrix of the dielectric model is symmetrized first.After symmetrizing the impedance matrix of the dielectric model,the characteristic mode is calculated by using the previously designed hybrid tracking mode tracking method.In the actual calculation,it is found that due to the introduction of matrix symmetry operation,there are many pseudo modes that do not radiate outward in the final characteristic mode results.Because eigenmode analysis usually studies outward radiation modes,it is necessary to filter out these pseudo modes that do not radiate outward.In this thesis,the characteristic far field of each characteristic mode at the end frequency point is tested for its own orthogonality to remove the pseudo mode,and only the results of the real mode are retained.Finally,the characteristic mode analysis of the medium model is realized.The correctness of this method is proved by comparing the classical cylinder with FEKO.Finally,the calculation method of characteristic mode of metal dielectric hybrid model is discussed,because the impedance matrix of metal dielectric model is similar to that of pure dielectric model.The current dimension and magnetic current dimension of impedance matrix are marked to indicate the parts that need matrix symmetry operation.Then we can apply the characteristic mode calculation method of medium model to solve the characteristic mode of metal medium hybrid model.In general,this thesis studies the mode tracking method of characteristic mode,and designs a new hybrid tracking mode tracking algorithm to improve the stability of characteristic mode solution of metal model.Then,based on this method,a characteristic mode calculation method for the mixed model of medium and metal medium is designed.Finally,a set of characteristic mode calculation method which can deal with metal,medium or metal medium mixed model is obtained.