Abstract: The coupling properties of an inclined narrow slot on the center lines of the broad walls between two crossed rectangular waveguides are discussed by means of the moment method. The tangential electric fields on the upper and the lower surfaces of the slot are mathematically solved with taking into account the waveguide wall thickness. Some computed curves of the important parameters of the slot, such as the tangential electric field distribution on the surfaces, the scattering fields, the scattering parameters, and the equivalent series impedance, are given. The theoritical and experimental results are in good agreement, ''