Theory Of Characteristic Mode And Its Application In OAM Antenna Design

The characteristic mode is the inherent attribute of the conductor structure itself,and the distribution of each characteristic mode on the conductor can be seen without the excitation.Applying the TCM to the antenna design can greatly improve the antenna design efficiency and provide a clear principle analysis.TCM can be widely applied to single conductor or multiconductor,whether planar structures or three-dimensional structures.In this paper,the Galerkin method of moment based on RWG basis function is used to calculate the impedance matrix of two-dimensional structure(ellipse,polygon)and three-dimensional structure(L-shaped square plate,sphere).Then aiming at the problem of mode crosstalk,on the basis of Galerkin method of moment of RWG basis function,a mode tracking algorithm based on characteristic mode theory is designed to realize broadband fast mdoe tracking.Finally,several microstrip patch antennas that can radiate vortex waves are designed by using the characteristic mode theory.The paper first studies the Galerkin method of moments based on RWG basis function.Using it,the impedance matrices of two-dimensional regular structure(ellipse),irregular structure(polygon)and three-dimensional structure(sphere,L-shaped square plate)are solved.The results show that the impedance matrices are diagonal matrices,which are the basis of characteristic mode analysis.Then,the generalized eigenvalue equation of the corresponding structure is constructed by using the impedance matrix,and the eigenvalues and eigenvectors of each mode are obtained to verify the mode tracking algorithm.Considering the weak influence of large eigenvalues on structural radiation,the mode tracking based on linear correlation can be fast achieved by limiting the number of eigenvectors while the accuracy of mode tracking can be ensured.Based on this,the mode arbitration method is modified to achieve fast broadband mode tracking.At the end of the thesis,the characteristic mode theory is applied to analysis of the metal patch.The paper proposes that the excitation degeneration mode of characteristic mode and adds 900°phase shift,which can realize different angular orbital momentum(OAM)beams.Based on this,a single-fed microstrip rectangular patch antenna radiating first-order OAM beams,a single-fed microstrip rectangular patch antenna radiating third-order OAM beams,a double-fed microstrip circular patch antenna radiating first-order and second-order OAM beams at different resonant frequencies,and a double-fed microstrip ring patch antenna radiating fourth-order OAM beams are designed.