A specific generalized scattering matrix (GSM) approach to the analysis of a piecewise homogeneous E-plane waveguide junction with plane interfaces is presented. The object is cascaded into homogeneously filled regions, whose GSMs are found in solving two uncoupled scalar problems related to longitudinal section electric and magnetic modes, and interfaces responsible for interaction of the said modes. The GSMs of irregular constituents are determined with the help of triangular blocks. Scattering parameters of the last ones are obtained by means of the domain-product technique. The approach was successfully verified via test problems and was applied to the analysis of scattering of the TE10 mode by an E-plane slant interface between two dielectric media. Copyright © 2011 John Wiley & Sons, Ltd.