A moment method (MoM) model of a rectilinear edge slot in rectangular waveguide is developed using entire domain trigonometric basis functions. This model has been found to provide an optimum trade-off between computational efficiency and accuracy. The intention behind the analysis is to provide an accurate, computationally fast model for the inclined edge slot radiator for incorporation into an array synthesis program. The basis functions for the 'three-dimensional' slot geometries involved in the analysis are generated using a simple transmission line representation of the slot field distribution to identify the resonant 'slot modes'. The results obtained are compared with alternative modelling approaches to this problem, based on finite element method and finite difference time domain techniques, and also with measurement.