Coupling of rectangular waveguides having a common broad wall which contains uniform transverse slots

A theoretical and experimental study is presented of the coupling of two identical rectangular waveguides. The coupling is by means of a uniform array of transverse slots in a common broad wall, using narrow and closely spaced slots. The objectives were to solve the electromagnetic boundary value problem of two waveguides coupled in this manner, to determine the characteristics of the two dominant normal modes, and to verify the results experimentally. A solution giving the propagation constant is obtained from two formulations of the boundary conditions. One formulation is derived by assuming an approximate distribution for the tangential electric field in the plane of the slotted septum. The second expression is deduced by assuming a distribution for the tangential magnetic field in the plane of the septum. By minimizing the difference between the two formulations, an equation which determines the propagation constant results. The values calculated from this equation are in good agreement with those determined experimentally.