Fractal Antenna for Passive UHF RFID Applications

This paper addresses the design of fractal antennas placed onto dielectric object in the UHF RFID band and introduces a tag antenna conflguration of simple geometry having impedance tuning capability. Through the paper, the dimensions of the fractal antenna are optimized to improve the impedance matching with the chip impedance. The tag performance changes are studied when it is placed on difierent objects (e.g., cardboard boxes with various content), or when other objects are present in the vicinity of the tagged object. It has been shown that a tag antenna can be designed or tuned for optimum performance on a particular object. Using the flnite element method the open circuit voltage and the polarization mismatch factor against the operating frequency are calculated. The input impedance, re∞ection coe-cient, power transmission coe-cient and the read range as a function of frequency are illustrated. The performance of the tag antenna in the presence of the dielectric box and difierent object materials inside the box is illustrated. The efiect of the objects that are placed in the center of the dielectric box didn't have a signiflcant efiect on the performance of the tag antenna; there is a small shift in the resonance frequency but still within the operating frequency band. Both the power transmission coe-cient and the read range change with the object material. The backscattering properties of the tag antenna have been studied. The difierential radar cross-section of the tag antenna is calculated for difierent antenna loads.

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