An Annular Microstrip Antenna with Sectoral Slots for RFID Reader

This paper presents an annular microstrip antenna with two sectoral slots fed by a coaxial probe on a square vertical ground plane. The proposed microstrip antenna can support the dual-band operation (UHF and microwave RFID bands). From the results, the antenna has the magnitude of S-11 less than -10 dB along the bandwidth of 32 MHz (3.51%) for UHF band and 140 MHz (5.76%) for microwave band. The unidirectional beam can be achieved by the proposed microstrip antenna. The beamwidth in xz- and yz-planes is 82.8 and 89 degrees at the center frequency of 922.5 MHz and beamwidth in xz- and yz-planes is 39.8 and 28 degrees at the center frequency of 2.45 GHz, respectively. This antenna has efficiently high directivity for both bands. The simulation and measurement results are shown.