A numerical method to determine mode content in circular waveguide based on an integral identity equation

According to the orthogonality of circular waveguide modes, an orthogonal integral identity equation is proposed among plane-wave spectrum of different modes, under the same azimuthal angle index. By using this identity equation, a simple method, which can determine components of different modes, is proposed. In the end, some numerical experiment results are also reported, which show that the proposed method is efficient.