In this article, we present a new methodology in spectral domain to study a novel, complex canonical electromagnetic problem constituted of perfectly electrically conducting (PEC) wedges immersed in complex environments. In particular, we present an arbitrarily flanged dielectric-loaded waveguide that resembles practical structures in scattering analysis, radar applications, antenna’s design, and electromagnetic compatibility. The proposed method is based on the recently developed semianalytical method known as the generalized Wiener–Hopf technique that extends the applicability of classical Wiener–Hopf method to a new variety of problems constituted of different geometries and materials. In this article, the method is further extended and it is now capable of handling piecewise constant inhomogeneous dielectric layers by resorting to the application of characteristic Green’s function procedure starting from the wave equation. The method has the benefit to be a comprehensive mathematical model and to be quasi-analytical, thus allowing us to investigate the true physics of the problem in terms of field’s components. The proposed solution is also of interest in computational electromagnetics to benchmark numerical codes. Validation through numerical results is reported in terms of engineering quantities such as geometrical theory of diffraction (GTD)/uniform theory of diffraction (UTD) coefficients, total far fields, and modal fields.