A BEAM SCANNING PHASED ARRAY FOR UHF RFID READERS WITH CIRCULARLY POLARIZED PATCHES

In this paper, a circularly polarized patch array is proposed as an RFID reader antenna. Four square patches form a linear phased array to provide a scanning beam that can detect RFID tags in a larger area. The patch elements are excited with two slots placed orthogonal to each other. In order to enhance radiation efficiency, slots are extended with bent ends to avoid overlapping. The two slots are fed by microstrip lines branched from a common feed with a 90 degrees phase difference to excite circular polarization. To increase the beam rotation limit, some patch element orientations are rotated. The fabricated array antenna is measured with a phased array control system. Comparison with simulation results demonstrates that the rotating beam covers a broader region and maintains a proper circular polarization performance. Other attractive features of the antenna include simple structure, low profile, and low cost.