Electromagnetic Field Expansions in Loss‐Free Cavities Excited through Holes

摘要

It is shown that the electromagnetic field in a loss‐free cavity excited through holes cannot be completely expressed in terms of the short‐circuit modes of the cavity satisfying the condition that the tangential component of the electric field is zero on the boundary of the cavity including the openings. For a complete expansion it is necessary to add an irrotational magnetic field, which contributes a term inversely proportional to the frequency, to the usual admittance matrix. If the cavity is presumed to include a reasonable portion of the guides feeding the openings, this irrotational component becomes almost diagonal.