Development of Kard’s theory for metal–dielectric filters

This paper discusses in detail a calculational technique for bandpass filters with a metallic layer and explains its features and limitations. It is shown that this technique is not adequate in general for calculating the structure of the filters and that there is a need to modernize it as indicated in this paper. It is shown that the electric field of the wave inside the coating is expelled from the metal layer, and this ensures that the filter will have low absorption.