Wideband high gain circularly polarized UHF RFID reader microstrip antenna and array

This paper presents a wideband and high gain circularly polarized ultra-high- frequency (UHF) radio frequency identification (RFID) reader microstrip antenna and array. Such antenna unit is composed of one main radiation patch and one parasitic radiation patch with air as the dielectric spacer. Two feeding lines connect to the main radiation patch with 90 deg phase difference. Numerical optimizations and experimental demonstrations are performed to investigate the performances of the proposed antenna unit and good agreements are obtained. This antenna unit can cover the whole UHF band (860-960 MHz) with gain of 9.7 dBi. Then two antenna arrays of 1×4 and 2×2 based on previously demonstrated antenna unit are numerically investigated. The array performances, including the gain, beam scanning and low side-lobe are discussed. The obtained results in this paper indicate that the proposed antenna and array are suitable for the universal UHF RFID applications.