The potential use of waveguides with a dielectric grating is explored. It is shown that the selective behavior is modified by introducing dielectric slabs in its characteristic cell. The analyses also show that this behavior changes by changing the incidence angle of the plane wave that excites the structure, the height/period ratio of the periodic region and the electric characteristics of the medium that confines the periodic layer. In addition, an expression is presented for an analytical estimation of how many times and the corresponding frequency values for which the fundamental mode is reflected by the structure with maximum intensity.3 18741877