Dual Polarized Patch Antenna for UHF RFID Readers

RFID is a fast emerging automatic identification system. Its bigger data density, better security, high speed and the fact that it does not need mechanical contact or line of sight communication have made it preferable to many other identification systems such as bar code, optical character recognition, biometric identification and smart cards. Nevertheless, this fast growing technology faces some difficulties in keeping tags simple and low cost while keeping efficient and reliable communication. This thesis is among the solutions that are proposed to fulfill this goal. So far, readers usually have either linearly or circularly polarized antennas and most tags are linearly polarized. Linearly polarized reader antennas are highly sensitive to the orientation of tags. In addition, circularly polarized reader antennas have fields that rotate across a plane and thus have only 50% polarization matching with tags. Accordingly, a dual linearly polarized patch antenna is proposed, implemented and tested as a solution to reduce the power loss caused by an arbitrary orientation of RFID tags. Among the RFID technologies, passive UHF RFID, which has a bigger read range and simpler tags, working in UHF frequency, is given emphasis in this project. Thus, background information about reader antennas and dual polarized antennas has been made. In addition, a reader antenna based on a patch antenna operating in European UHF RFID band of 865 MHz-868 MHz is considered. The modeling softwares CST Microwave Studio and Empire XCcell were used in simulation. Then, the laboratory facility in Electronics department of Tampere University of Technology was used to implement and test the prototype. /Kir1