Planar near-field RFID reader antenna using opposite-directed currents

In this paper we propose a novel planar near-field antenna for radio-frequency identification (RFID) based on the principle that two closely spaced opposite-directed currents (ODC) can generate a strong magnetic field over a broad surface area. To implement the ODC concept, the proposed antenna uses a dipole and a parasitic patch with a microstrip feedline. The proposed antenna provides an Hz field greater than −20 dBA/m in a region of 30 × 30 cm2. Measurements with a commercial RFID system show a maximum reading range of 24 cm, and a reading area of 744 cm2 for a reading range greater than 5 cm.