Different representations of dyadic Green's functions for a rectangular cavity

A detailed derivation is presented of several alternative representations of the dyadic Green's functions of both the vector potential type and electric type, for a rectangular cavity. Differentiation of discontinuous series expressions for evaluating the fields in a source region can be obviated through the use of the electric type function. Eigenfunction expansions of the dyadic Green's functions are worked out for a rectangular cavity, with three different but equivalent representations worked out for the electric type function. A triple sum form for the functions, already available for cylindrical and spherical cavities, can be reduced to a double sum in the case of cylindrical cavities.