倾斜入射条件下衬底对金属网栅屏蔽特性的影响

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

提出了双层膜系分析方法，该方法采用独立网栅等效薄膜模型，将网栅对衬底干涉的影响引入分析，克服了Kohin方法仅考虑衬底干涉的不精确性，并避免了其分析独立网栅的透波率公式在高频和大入射角时存在的不准确性。用紫外光刻在石英衬底上制备了周期为320μm，线宽为4．5μm的网栅，测得S波30°入射时12～18GHz的屏蔽效率大于16dB，略低于理论值但变化趋势一致，证实了双层膜法的有效性。进而分析衬底影响表明：入射为S波及小于衬底布儒斯特角θB的P波时屏蔽效率降低，而入射为大于θB的P波时屏蔽效率反常增加；屏蔽效率变化最大值随入射角变化；优化衬底厚度可在不影响网栅透光能力的同时获得最佳屏蔽效果。

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 avoid 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 θB, but it increases abnormally when inciclent angle is larger than θB ,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.