A COSY Antenna Incorporating a Pattern Coil for Dual-Band 2.4/5 GHz WLAN Applications

Abstract

This paper proposes a dual-band antenna for 2.4 GHz and 5 GHz wireless local area network (WLAN) applications. A pattern coil is incorporated into the COSY (COmpact and eaSY) antenna structure to enable dual-band operation without external lumped components. The proposed design maintains a simple architecture while achieving dual-band operation. The pattern coil functions as an inductor and, together with the linear element, forms a stub whose effective current path length varies with frequency. In addition, U-slots introduced in the plate and parasitic elements divide the surface current distribution and independently establish the resonant modes for the two bands. By combining these structural features, dual-band operation is achieved without the need for an external matching circuit. Simulations confirm good impedance matching and unidirectional radiation patterns in both bands, and current distribution analysis clarifies the operating principle. Furthermore, measurements of a fabricated prototype demonstrate stable dual-band performance in practical implementation, as the impedance characteristics, radiation patterns, and gains agree well with the simulation results.