Circularly Polarized Single-Fled Wide-Slot Antenna for UHF RFID Reader

This paper presents a design of the universal reader antenna applied for the radio frequency identification (RFID) system with the operating frequency from 840 MHz, to 960 MHz. The antenna structure consists of a rectangular loop and a rectangular feeding patch which are the important elements to produce the circular polarization. The total size of the reader antenna is 120 mm x120 mm fabricated on the FR4 substrate with thickness of 3.18 mm and with the dielectric constant of 4.3. From the measured results, it is obvious that the proposed reader antenna radiates a bidirectional pattern with the circular polarization, covering the operating frequency from 750 MHz to 1150 MHz with axial ratio bandwidth of 42%. The axial ratio and gain at the boresight direction are 1.03 dB and 3.62 dBic, considering at 900 MHz which the center frequency hand of universal RFID standard.