Surface Integral Equation-Based Characteristic Mode Formulation For Patch Antenna Structures

In recent years,the theory of characteristic mode has received significant attention because it just depends on the properties of the electromagnetic objects and has no connection with any exterior excitations.It is becoming a popular and commonly method to characterize the modal resonant behavior of electromagnetic objects with arbitrarily shaped such as antennas and scatterers.In this letter,the characteristic mode theory of perfect electric conductor bodies is derived from the electric field integral equation of perfect electric conductor bodies,and the physical meaning of the characteristic mode is proved by Poynting theorem.Then two typical characteristic mode theory of dielectric structures based on Poggio-Miller-Chang-HarringtonWu-Tsai(PMCHWT)equation are introduced and the numerical results of the two formulations are compared in the third chapter.In the end of the thesis,we propose a novel theory of characteristic mode based on the surface integral equation.Because of the particular structures of patch antennas,which are often composed of a metallic surface touched on the finite dielectric substrate,the electric field integral equation coupled PMCHWT(EFIE-PMCHWT)are commonly chosen as the governing equation to model the electromagnetic property.Conventional surface integral equation(SIE)-based characteristic mode formulation for the patch structure is susceptible to the nonphysical modes produced by the dielectric part.To conquer this difficulty of the spurious mode,the volume-surface integral equation(VSIE)based TCM is proposed for the printed patch antenna structures.However,the volume discretization of the substrate will also lead to tremendous computational cost.To reduce the computational requirements,in this letter,a novel surface integral equation(EFIE-PMCHWT)based CM analysis method is proposed for printed patch antenna structures.In this novel method,we split the integral operator of EFIE-PMCHWT into interior(material-related)integral operator and exterior(radiation-related)integral operator.According to the theory of the characteristic mode about the electric field integral equation(EFIE)and the magnetic field integral equation(MFIE),we choose the real part of the impedance and admittance operator and j times the imaginary part of the rotation operator in the exterior radiation operator as the right weighting operator of the generalized eigenvalue equation,the spurious mode can be avoided,also with clear physical interpretations.To further reduce the computational cost,the symmetrical EFIE-PMCHWT equation(sEFIE-PMCHWT)is also developed and it has the same numerical performance as the nonsymmetrical equation.This formulation can avoid nonphysical modes effectively,so no post-processing is required.Numerical results compared with the volume-surface integral equation(VSIE)to validate the accuracy of the proposed formulations.