Abstract
A small (16.5 x 45 mm) forward-directional antenna covering the ISM bands of 2.45 and 5.8 GHz is designed for the next generation of multi-band compact handheld RFID readers. The antenna consists of a folded radiating copper strip fed by a CPW microstrip line and a ground plane. The copper strip produces surface waves at the operating frequencies that are reflected by the ground plane, producing radiation in the forward direction. Details of the antenna design and optimization are discussed by formulating closed-form equations for the resonances. Only 4 percent difference is found between the theory and simulation. The prototype exhibits 8.5 and 4 percent impedance bandwidths in the lower and upper operating bands, respectively. Measurements show forward-directed radiation patterns with good polarization purity, back radiation suppression and peak gain across the bands.