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

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 (10λ) 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 beam width and focal depth are given by 0.75λ and 5λ, respectively, which are in agreement with the calculated results.