A 3D finite element scheme for nonuniformly loaded waveguides

A finite element scheme for modelling three dimensional cavities and waveguides is described. The formulation used is an extension of the AV scheme (A is the magnetic vector potential and V is the electric scalar potential) which is a subset of the formulations hitherto used in the MEGA program for modelling 2 and 3D low frequency eddy current problems. The scheme allows cavities of general 3D shape, which may be loaded with arbitrary dielectrics or metallic objects to be modelled. Travelling or standing waves can be supported. Special boundary conditions are used for travelling wave problems, when it is required for instance to model scattering in a dielectric loaded section connected to two or more waveguides. These boundary conditions are obtained from the analytic expressions for fields in an ideal waveguide