Dual Printed Dipole Reader Antenna Design For UHF RFID Near-Field Applications

Radio frequency identification is a non-contact identification technology that provides automatic identification and data switch on moving and static objects by radio signal. In recent years, as RFID deployment moves from pallet level to item level, near-field UHF RFID technology has received a lot of attention, and it is considered as a possible solution for item level tagging (ILT) in pharmaceutical and retailing industry. Antenna is an important component of the RFID system, which has a direct effect on the RFID system performance.This paper is committed to study the UHF-band RFID near-field antenna. In most near-field applications, RFID reader and tag antennas are made of circular loops. The mutual inductance between these two loops is mainly influenced by the loop diameter. Commonly, a loop antenna with a perimeter much less than its operated wavelength has constant current phase along the loop line which have the capability to generate a strong magnetic field along its axis, but the field falls rapidly when the sensing coil is moved more than approximately one diameter above the loop. And the read range is very short. But if we enlarge the antenna, make the size of the loop to be significant compared to a wavelength, the current is not in phase and shifts to produce a change in sign of the current flow, which results the antennas produce relatively little magnetic field on axis. In this paper, a novel dual printed dipoles reader antenna is proposed for UHF near-field RFID applications. The dual dipoles structure is designed to replace the electrical large loop. As each dipole is shorter than one wavelength, the current flow will keep in the same direction. The proposed antenna shows a small dimension of 80x70x30mm3 for the special small size industry application requirement. The measured bandwidth is 205MHz (765MHz-970MHz) under the condition of Voltage Standing Wave Ratio (VSWR) less than 1.5, which can cover the Europe and FFC standards. And the measured reading range is 37mm and no reading nulls 15mm above it. In addition, the antenna has a low far-field gain less than-20dBi, which make it suitable for pure near-field industry applications.