Tunable Near-Field Focused Circular Phase-Array Antenna for 5.8-GHz RFID Applications

Abstract : An RFID-compatible focused circular phase-array antenna working at 5.8 GHz is proposed, which is theoretically analyzed and experimentally demonstrated. It consists of 24 half-wavelength dipole antennas placed on three circles. Using only two phase-shifters, a tunable focal spot in the range of 0.4–1 m (10 lambda) is obtained. The antenna system is analyzed using the Huygens–Fresnel theory, which is compared to the experimental results. At a focal distance of 0.9 m, the measured beamwidth and focal depth are given by 0.75 lambda and 5 lambda, respectively, which are in agreement with the calculated results.