Research On Generalized Eigenvalue Equation And Antenna Q-factors Based On Theory Of Characteristic Modes

In recent years,the theory of characteristic modes(TCM)has become attractive in the field of antenna design,and is widely used to investigate the modal resonance characteristics of radiators or scatterers of arbitrary shapes.The characteristic mode is only determined by the geometry and material property of the radiator or scatterer,which is independent of the feeding sources.This theory makes the antenna design process free from the dependence of the knowledge and previous experience of designers,and gives a physical explanation from the radiation mechanism of the antenna,which has guiding significance for the antenna design.Based on the TCM,a new generalized eigenvalue equation,which is used to directly reflect the radiation ability of a specific mode,is proposed in this paper.The influence on the modal parameters of antennas in the presence of PEC obstacles is also discussed,which provides a feasible method for broadband antenna design.The main work and innovations in this paper are summarized as follows:1.A new generalized eigenvalue equation based on the matrix of inner product of basis functions(Gram Matrix)is proposed.The eigenvalue obtained by the equation is directly proportional to the radiation power of the corresponding mode.By comparing with the conventional generalized eigenvalue equation,the validity and superiority of the novel equation are proved.The process of comparing the radiation abilities of different modes is simplified by applying this equation.2.Combining the theory of sub-structure characteristic modes with the method for computing Q-factors proposed by G.Vandenbosch,we study the influences on antenna modal significance(MS),modal Q-factors and total Q-factors when there are PEC obstacles near the antenna.The integrals for Q-factors in this paper are directly based on the surface currents of the conductor.The stored energies are revised by introducing modified terms,which are equivalent to subtracting the contribution of the radiation fields.The integral derivation process is not approximate,which is accurate and easy to implement.The influence on MS and Q-factors of the antenna is also investigated in this paper when the size and distance between the antenna and obstacles change.This work provides a reference for the design of wideband antennas.