CRLH TL-Based Compact Wideband Button Antenna for Biomedical Applications

Wearable antennas are increasingly being miniaturized and broadened in terms of bandwidth due to the increasing need for multi-standard biomedical communication and imaging capabilities. In this paper, a novel, compact and wideband button-like antenna based on composite right/left-handed transmission line (CRLH TL) theory is proposed. The antenna consists of a compact FR-4 PCB as its substrate and a semi-rigid coaxial cable is used as feed. The button dish has a dimension of π × 6 × 6 × 1.5 mm3 (π × 0.11 × 0.11 × 0.027λ3) at 5.5 GHz. The ring-shaped radiator includes two end-to-end CRLH TL unit elements on top of the substrate, which is excited by coupling with a concentric circular patch. The zeroth-order resonance (ZOR) mode and +1st order mode are generated and combined to achieve an ultra-wideband operation from 5.15 GHz to 9.35 GHz (58% fractional bandwidth). Furthermore, a spiral structure is employed in this design to decrease the negative effects of the ground plane, resulting in a high gain and a low specific absorption rate (SAR). To our best knowledge, this is the first button ZOR antenna based on CRLH TL structure designed for wearable applications with such wide bandwidth besides acceptable gain and compactness levels.