In this paper, a generalized deembedding technique is presented. It provides a multimodal characterization for microwave devices fed with planar guiding structures of arbitrary configurations. Instead of the conventional scattering matrix, the proposed technique leads to the multimodal scattering matrix. This matrix describes all possible kinds of mutual coupling between the different modes present on the feeding ports. In order to achieve this task, the feeding planar guiding structures are analyzed a priori using a full-wave two-dimensional solver. The generalizability of the proposed deembedding technique is demonstrated by characterizing a couple of coplanar-waveguide-based discontinuities. The results show that the proposed technique provides a rigorous and a detailed characterization.