  Transmission through a slot in a an infinite metallic shield of finite
thickness, inhomogeneously loaded with dielectric material, is modeled using an
analytical approximation based on the slot being small compared to a free space
wavelength. Resonances of relatively broad bandwidth (Fabry-Perot) as well as
of very narrow bandwidth (Fano) are found. We show that by introducing a gap of
different dielectric constant within the slot, we can control the separation
between the broad bandwidth resonances, and the locations and magnitudes of the
very narrow bandwidth resonances. The influence of grooves on both kinds of
resonances is considered using the same analytical model. The effect of losses
in the dielectric slot is also considered, using data for commercially
available dielectrics.
