Analysis of electromagnetic transmission characteristics of square loop frequency selective fabrics with different layers

Nine square loop frequency selective fabrics (FSFs) with different layers were designed, prepared, and tested in this paper. Then the electromagnetic transmission characteristics were analyzed in detail. The test results reveal that the transmission characteristics of single-layer FSFs are basically identical in two electromagnetic wave polarization modes and keep good frequency selective characteristics as the incidence angle increases. For FSFs with the same frequency selective surface (FSS) layers, the increase of FSS layer number may exert influence on the electromagnetic transmission characteristics, but the influence mode and extent are inconsistent for two kinds of FSFs. For FSFs with complementary FSS layers, the transmission coefficient curves of the double-layer sample are the combination of two single-layer FSFs, with three resonance phenomena at 7.63, 10.75, and 12.38 GHz. However, three-layer FSFs with complementary FSS layers show poor frequency selective characteristics, mainly presenting full shielding characteristics. An equivalent circuit model of multi-layer FSF is built to explore the electromagnetic transmission mechanism; many factors, such as the fabric type, structure, conductive unit type, and size, would nonlinearly affect the electromagnetic transmission characteristics. The work can provide reference value for the study of diverse multi-layer FSFs and variant electromagnetic characteristics.