Abstract: It is critical to sense orientation of target objects for radio frequency identification (RFID) applications, such as supply chain, equipment management, and so on. Based on the principles of ultra high frequency radio frequency identification (UHF RFID) and the theory of antenna scattering, a link budgets model of RFID is provided. Utilizing the technology of RFID and polarization diversity, a novel method for sensing the orientation is presented. The method requires standard RFID equipment and assumes that each object is attached by two RFID tags. Based on the received signal strength of the tag reply, orientation of the target object is obtained by using of a simple statistical estimator. The performance of the method proposed is evaluated via experimental measurements, and the results show that the mean estimated error of orientation sensing is 10.1^{\circ}

Key words: orientation sensing, radio frequency identification, polarization diversity;statistical analysis