Abstract. Apertures in shielding enclosures are an important issue for determining shielding efficiencies. Various mathematical procedures and theories were employed to describe the coupling between the regions connected via an aperture in a well conducting plane. Bethe's theory describes the coupling via the equivalent problem of field excited dipole moments at the location of the aperture. This approach neglects the reaction of the dipole moments on the exciting field and therefore violates energy conservation. This work emphasizes an analytical approach for coupling between half-spaces through small apertures, inspired by the so called method of small antenna, which allows an understandable generalization of Bethe's theory.