Printed symmetric inverted-F antenna with a quasi-isotropic radiation pattern

This article presents a tag antenna with a quasi-isotropic radiation pattern operating in the UHF band to eliminate the shadow zone in RFID systems. The proposed tag antenna has a symmetric inverted-F structure with a bent section and is printed on a 50 mu m-thick PET substrate for easy and low-cost fabrication. The detailed design parameters of the antenna were optimized using a Pareto genetic algorithm in conjunction with the IE3D EM simulator. The optimized antenna shows 3.2% fractional bandwidth for S-11 < - 10 dB, more than 87% efficiency in the operating frequency band, and less than 6 dB gain deviation. The measured reading range between the tag and reader is between 1.4 and 2.2 m. (C) 2008 Wiley Periodicals, Inc.