Coverage and read range comparison of linearly and circularly polarised radio frequency identification ultra-high frequency tag antennas

This study presents a comparison between two dipoles acting as representatives of ultra-high frequency radio frequency identification (RFID) circularly polarised (CP) and linearly polarised (LP) tag antennas, respectively. As the CP dipole is derived from the LP dipole, they have equivalent reflection coefficient and radiation efficiency values, allowing the comparison to be focused on polarisation and radiation pattern. Then, a comparison of RFID angular and read range is investigated. This is conducted by combining the interrogation of CP and LP tags emulators by CP and LP readers with regulated power. The emulators are made up of the CP and LP dipoles embedded onto RFID tags with analog front-ends. A methodology is described for measuring the maximum angular and read ranges, involving maximum power allowed by European regulation. A 17.9% extra range is achieved by the CP tag and the CP reader compared to the LP tag with any kind of reader. Furthermore, null cancellation is observed in the former case in the region of interest.