Influence of substrate on shielding effectiveness of metallic mesh under oblique incidence condition

A double film method was employed to accurately estimate the influence of substrate on shielding effectiveness. By using the equivalent film model of free-standing mesh and preparing a thin mesh film on its substrate, this paper considers its influence on substrate interference to overcome the uncertainty of Konin's method that merely considers the interference of the substrate itself, and to a-void the inaccuracy of Kohin's transmission formulas of free-standing mesh at high frequency and large incident angle. To identify its validity, the metallic mesh with line width of 4.5 μm and period of 320 μm was fabricated on quartz glass by UV-lithography. The measuring results show that the shielding effectiveness is greater than 16 dB under 30° S-polarized incidence at 12-18 GHz, it is slightly below the theoretical value and has the same change trend with that. The analysis using the new method shows that for S-polarization, the shielding effectiveness decreases with oblique incidence; for P-polarization, it decreases also when incident angle is less than Brewster angle θ_B but it increases abnormally when incident angle is larger than θ_B, and the largest alteration value varies with incident angle. Optimal shielding effectiveness can be obtained by optimizing substrate thickness without affect on the transparent property.