High gain circularly polarized stacked circular patches loaded with a circular sector notches and vertical ground ring for UHF RFID universal reader

In this paper the design and results of circularly polarized broad band antenna covering the universal UHF RFID band (840-960 MHz) is presented. The antenna is constructed from two layers of circular patches above a circular ground plane. Each patch has two rounded circular sector notches on opposite sides. The lower circular patch is coaxially fed, and in turn is feeding a parasitic top patch. The resultant axial ratio is below 2.5 dB across the whole band with gain reaching 9 dBi. The size of the ground plane was reduced by adding a vertical ring at edge of the circular ground plane.