Calculation of Orthogonal Decomposition of Scattered Far Field

Orthogonal mode decomposition is a useful tool in the analysis of electromagnetic field, such as representation of Green's function, microwave device analysis and etc. In recent research on quantum electromagnetics, the normal mode approach needs the orthogonal mode decomposition as well. To study the quantum scattered field, a method to calculate the orthogonal decomposition of scattering far field is proposed in this paper. The scattering far field can be calculated from the surface current on the target and expanded under the spherical harmonic function basis. Then a fast method based on orthogonal decomposition of exponential function is applied to get the coefficients under such basis. Numerical examples verify the accuracy and efficiency of the proposed method.