On filling up the grooves of a perfectly-conducting grating with a dielectric material

In order to protect them from environmental degradation, as well as to increase their reflection efficiency in some instances, metallic gratings are often coated with dielectric materials. This practice introduces the effects of waveguide modes in the reflection characteristics. Here, we study the alteration of the plane wave reflection characteristics of a perfectly conducting grating whose grooves are filled up to the brim by a dielectric material. The method of analysis is synthesized from an improved T-matrix method. From the numerical results for sinusoidal gratings, it is shown that the dielectric material in the grooves does affect the reflection characteristics; however, the effect of waveguide modes is avoided.