Formula for the Field Excited in a Faraday Cage With a Graphite–Epoxy Closeout

A simple, nearly exact, formula is derived for the fields excited in a rectangular metallic cavity by a plane wave incident on a graphite–epoxy (GrEpx) panel that replaces one wall. It is used to assess the accuracy of an approximate formula for the fields for the case where a GrEpx access panel covers a small aperture in a wall.