A generalised scattering matrix (GSM) of the generalised 2-port discontinuity is proposed for use in the analysis of multiportmultidiscontinuity structures. This gives the GSM of the discontinuity in a simple way and with a number of algebraic manipulations independent of the number of discontinuity ports. Moreover, they can be cascaded with the same procedure as two-port discontinuities. This leads to a simplification in the analysis of structures with multiple discontinuities and with more than 2 ports. An application to short-circuited E-plane septum and E-plane reaction cavities is considered. The results show that these structures can be used to obtain waveguide stop-band filters of small size and low cost.