Performance comparison between an UHF RFID antenna for portable reader and its UHF RFID/WLAN dual-band version

A low-cost single-band circularly polarized antenna for the UHF RFID band and its extended dual-band configuration for UHF RFID/WLAN applications are here compared, in terms of both electromagnetic parameters (reflection coefficient, axial ratio and gain, in the UHF band) and operational performances when used in a commercial RFID reader (Received Signal Strength Indicator, RSSI, and reading range). Thanks to their high compactness and low-profile (60mm×60mm×7mm), both antennas can be easily integrated into a commercial portable UHF RFID reader. An array composed by four inverted-F meandered monopoles appears in both antennas, which covers the 902-928 MHz frequency band. In the dual-band configuration, a miniaturized patch has been added on the same FR4 substrate, in the middle of the four monopoles, so providing the portable reader with an extra wireless functionality, namely a WLAN connectivity (2400-2480 MHz). Results in terms of reflection coefficient, gain, axial ratio, as well as measured RSSI values are shown in this paper. The dual-band antenna performances are comparable with those of the original singleband version, despite of the remarkable mutual coupling between the RFID array and the WLAN patch, which are very close to each other and printed on the same side of the FR4 substrate.