External scattering by rectangular cavities with small apertures

The analytical description of field penetration through small apertures in good conducting screens is the topic of many earlier works. Especially Bethe´s Theory allows an easy approach to the complex problem. Bethe initially used some simplifications, which resulted in theoretical problems such as violation of power conservation. Later these problems were solved by introducing radiation reaction fields which represent the dependency of the equivalent source from the radiation conditions. In this work this dependency is identified as the main problem to be solved, to analytically calculate the backward radiation of a slotted cavity, which is irradiated by an external field. For this goal, the formalism of the Green´s functions, combined with an analytical regularization is used in contrast to the radiation reaction fields. This results in a more formal and clear representation of the solution as in earlier works.