Compact diversity antenna for UHF RFID readers

A diversity antenna combining four inverted-F antennas (IFAs) is evaluated for UHF RF identification (RFID) readers. Polarisation and pattern diversities are obtained for a sequentially rotated configuration of the IFAs. Mutual coupling between ports is minimised by etching quarter-wavelength slots into the ground plane. The resulting envelope correlation coefficient is less than 0.003 in the working band. A switching diversity scheme is then applied to evaluate the tags readability in a lab environment. It is shown that the antenna diversity enhances the reading range compared to a circularly or a linearly polarised antenna of the same size.