Directly-fed single-layer wideband RFID reader antenna

A wideband circularly-polarised (CP) antenna with a simple structure is proposed for universal ultra-high frequency (UHF) radio-frequency identification (RFID) reader applications. The antenna is composed of two patches, an L-shaped ground and an SMA connector. The main patch which is truncated to generate CP radiation is fed directly by the SMA connector oriented in the same plane via the vertical part of the L-shaped ground. The parasitic patch used to enhance the bandwidth is placed at the same layer of the main patch. These two schemes realised a directly-fed single-layer structure. The 3 dB axial ratio bandwidth and impedance matching bandwidth for 14 dB return loss overlap within the universal UHF RFID band (840 960 MHz), while high gain with an average level of 7.3 dBi is achieved. Simulation and measurements are in good agreement.