Reduction of Proximity Effects on UHF Passive RFID Systems by Using Tags with Polarization Diversity

A new technique that enables passive ultra high fre- quency (UHF) radio frequency identification (RFID) tags to be read when they are placed in close proximity in an array is pre- sented. This paper demonstrates that, in a linear tag array with a tag separation of 1 cm, the interaction between the backscat- tered waves and incident wave causes a significant degradation in tag sensitivity. It is found that the use of tags that have polariza- tion diversity can improve the read performance when they are placed in close proximity to one another compared with conven- tional linear tags. Two ways of achieving polarization diversity are studied in this paper, namely: 1) using a circularly polarized tag and 2) using a cross-polarized tag pair. Both methods show an improvement in close proximity read performance and it is exper- imentally demonstrated that by using cross-polarized tag pairs in an array, one achieves on average a 2.6-dB increase in read power margin for a 57-tag array with 1 cm separation compared with using conventional linearly polarized tags.This work has been supported by UK Engineering and Physical Science Research Council via the COPOSII project.This is the final published version. It first appeared at http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7042269