Dependences of reflecting factor of electromagnetic radiation on thicknesses of a flat absorbing layer of dielectric drawn on ideal metallic support have been studied. It has been established that extremes of these dependences lie at thicknesses of a layer covering of great values four times over a wave in a covering substance; with this at relatively weak fading of wave in the substance of covering under these dependences there emerge anomal and normal areas, differing by the character of change of their experimental values.