Design and Experiment of a Wideband Circularly Polarized Stacked Patch Antenna for Universal UHF RFID Readers

This paper presents a wideband circularly polarized stacked patch antenna for universal UHF RFID readers. The proposed antenna consists of a slanted elliptical microstrip patch layer, corner truncated patch layer, a horizontally meandered strip (HMS) layer, and a corner truncated ground plane. A slated elliptical patch, which is the main radiating patch, is etched on one side of a FR4 substrate in order to achieve circular polarization. The slated elliptical patch is fed through the HMS. This HMS is placed below the slanted elliptical patch to improve the impedance bandwidth. One end of the HMS is connected to the ground plane via SMA connector, while the other end is connected to the main radiating patch by the probe. In order to further enhance the bandwidth, the parasitic truncated patch is placed above the main radiating patch. In addition, the truncation of the ground plane is used to control the AR bandwidth. The proposed antenna has an overall size of 250 x 250 x 54 mm3. The measured results show that the proposed antenna can provide the impedance bandwidth of about 149 MHz (817 – 966 MHz) or 16.7%, a 3-dB axial ratio (AR) bandwidth of about 170 MHz (830 – 1000 MHz) or 18.5%, and maximum gain of about 8.4 dBi. The proposed antenna can operate at the UHF band of 840 – 960 MHz, which covers the bandwidth of universal UHF RFID readers.