A longitudinal slot at the centre of the broad wall of a rectangular waveguide in the presence of one or two vertical strips has been analysed. The combination is excited by the dominant TE01mode, and the slot radiates externally. The effect of finite thickness of the waveguide walls has been taken care of by treating the slot as a stub waveguide. The coupled integral equations are solved using Galerkin's technique. The resultant coefficients are used to compute the dominant mode scattering parameters and hence the equivalentT-network. The possibility of obtaining a resonant condition for the radiating centred slot–strip combination has been established. Design data derived in this study eliminate the need to gather initial input data experimentally.