Application of Quasi log-periodic antenna for UHF passive RFID tag design featuring constant power transmission coefficient over broadband operation

Quasi log-periodic antenna configuration was adopted to design passive UHF RFID tag for the first time. With proper adjustment of the physical parameters which in turn adjusted the induced coupling levels to the dipole-based radiator, the designed antenna was capable of providing constant reactance from 860 MHz to 960 MHz covering the whole spectrum of UHF passive RFID system. In addition to the omni-directional radiation pattern and good overall radiation efficiency provided by the antenna, the proposed design features constant power transmission coefficient over 860 MHz to 960 MHz which is essential to guarantee consistent read range in passive RFID systems.