Segmented spiral antenna for UHF near-field RFID

A segmented spiral antenna is proposed for ultra-high frequency (UHF) near-field radio frequency identification (RFID) reader applications. The invented antenna comprises two open-circuited arms which are wrapped at different clockwise to form a square enclosure. The segmented configuration does not accumulate the phase delay of the current flowing along the arms so that the current along the arms keeps nearly in phase and thus produces uniform magnetic field distribution in the interrogation region. As an example, an antenna printed onto an FR4 printed circuit board (PCB) with an interrogation zone of 154 mm × 154 mm (the perimeter is 1.85λ at 900 MHz) is designed. The antenna prototype achieves 10-dB return loss and exhibits the uniform magnetic field distribution over an operating bandwidth 770-1025 MHz.