An analysis is presented of the shielding effectiveness (SE) of a rect
angular enclosure with an aperture in one face. The enclosure is treat
ed as a length of rectangular waveguide and the aperture as a length o
f coplanar strip transmission line. Theoretical values of SE agree wit
h measurements for a range of enclosures, apertures and frequencies. T
he variation of SE with position in the enclosure is also correctly pr
edicted.