Design of planar RFID tag antenna for metallic objects

Proposed is a novel RFID tag antenna consisting of an inner spiral dipole, an outer bent dipole and a double T-matching network that is suitable for attaching to metallic objects. For low-cost fabrication, the antenna is printed on a single-layer substrate without a ground plane or shorting pins. The detailed design parameters of the antenna were optimised using the Pareto genetic algorithm so that the antenna would operate adequately both in fiee space and on metallic objects. The antenna was fabricated, based on the optimised design, and the performance in fiee space and on a metallic surface were measured. The half-power matching bandwidth (VSWR < 5.8) and the reading range of the antenna in fiee space were 7.6% and 2.8 m, while on a metallic surface the corresponding values were 0.8% and 1.8 m. For non-metallic surfaces (i.e. low dielectric targets, 2 < epsiv_r < 4), the antenna exhibited the reading range of 2-3 m.