Ultra-thin electromagnetic bandgap backed fractal geometry-based antenna for 24 GHz ISM band WBAN

Abstract

A compact, ultra-thin electromagnetic bandgap (EBG) backed antenna is presented for the 24 GHz ISM band for WBAN applications. The proposed antenna has Koch fractal geometry-based bow-tie slots, designed with an overall dimension of 0.91 (Formula presented.) × 0.84 (Formula presented.) × 0.01 (Formula presented.) and backed by a 5 × 5 element 0.01 (Formula presented.) thick EBG structure; it is fabricated on a flexible Rogers 5880 substrate (thickness = 0.127 mm and dielectric constant (Formula presented.) = 2.2, tanδ = 0.0009). In comparison to the previously published K band prototype antennas, our presented fractal antenna has a more compact and ultra-thin form factor. The low profile, via-less EBG unit cell structure with dimensions of 0.254 (Formula presented.) × 0.254 (Formula presented.), possesses both Artificial Magnetic Conductor (AMC) and EBG characteristics. It is straightforward to fabricate at a millimeter-scale. The performance parameters of the design are investigated in terms of on-body reflection coefficient and free-space radiation patterns with and without structural bending. The EBG structure enhances the antenna's front-lobe gain by 2.3 dB, decreases back-lobe radiation by 12.6 dB and decreases the specific absorption rate (SAR [1 g]) from >50.9 W/kg to <6.14 W/kg, significantly reducing the potential harm to the human body. Experimental investigations revealed high insensitivity of the proposed antenna to body proximity, and the performance is preserved with structural deformation.