Spurious Mode Generation in Nonuniform Waveguide

This paper deals with the problem of a nonuniform waveguide joining two uniform ones and the spurious modes generated by it when a pure mode is incident in one of the uniform waveguides. The generalised telegraphist´s equations are stated and transformed into a set of differential equations for the amplitudes of the forward and backward traveling waves. The expressions for the coupling coefficients between the various modes are given and analysed.