Microwave shielding effectiveness of EC-coated dielectric slabs

Correct formulas for the microwave shielding effectiveness (SE ) of a thin metallic layer deposited on top of a dielectric slab are derived. For coatings much thinner than the skin depth, the following holds: (a) in a half-wave geometry, SE is a function of a sheet resistance only, SE (in dB)=20×log(1+188.5/R_s) if R_s is in ohms per square; (b) in a quarter-wave geometry, SE (in dB)=20×log[(1+ε_r)/(2√ε _r)+188.5/(√ε_rR_s)], where ε_r refers to the dielectric constant of the substrate. These formulas provide upper and lower limits for the effective shielding performance of an electroconductive coated dielectric slab