Finite element/moment method analysis of waveguide coupling by means of apertures or slots

An equivalence principle is invoked to divide the problem into three separate regions which are then coupled by enforcing the continuity of magnetic fields at the interfaces of these regions. A coupled set of equations are derived by invoking appropriate boundary conditions, dyadic Green´s functions and variational approaches, to find the tangential electric field on the upper and the lower surfaces of the aperture or slot. A finite element method is adopted to discretize the aperture or slot region. In order to overcome the singularity at conducting corners and edges, edge-based expansion functions are chosen. The predominant advantage of this approach is that it is no longer necessary to know the dyadic Green´s functions in the aperture region. Hence the technique can be employed to analyse waveguide coupling problems involving complex slots or apertures. The method has been successfully applied to the coupling problem comprising two identical waveguides containing a slot in the common broadwall. Comparisons between the results obtained from this method and those from a moment method are presented