Can a slot act as a band pass aperture?

The paper discusses the performance of slots in a shielded enclosure, with special emphasis on slots in thick walls. A special "anomaly" is presented, where, in contrast to acceptable shielding theory of dots, provided a lower shielding effectiveness (SE) at lower frequencies that at higher frequencies, while waveguide below cutoff conditions were barely valid. The paper presents the analytical concept of coupling of RF signals through slots, as applicable to the specific problem and presents actual test results from a tactical S280/G shelter, where the effect was identified.