A Yagi-Uda Antenna With Load and Additional Reflector for Near-Field UHF RFID

In this letter, a Yagi-Uda antenna with load and additional reflector is proposed to achieve strong and uniform magnetic field distribution within the antenna area for near-field ultrahigh-frequency radio frequency identification (RFID). This proposed antenna is composed of one driven dipole to emit electromagnetic (EM) wave, several directors to direct the EM wave to the desired area, a load element at the end of the director array to absorb the wave, and two reflectors at both ends to reflect the EM wave. The proposed antenna can generate a uniform magnetic field distribution within the antenna area, meanwhile keeping the field strength outside the antenna area relatively small. A prototype, as an example, that contains 13 elements is designed and fabricated, with the measured bandwidth of 880-980 MHz. The achieved interrogation area is 440 x 160 mm(2), measured by utilizing a commercial RFID reader and some near-field tags. It is worth mentioning that the interrogation area can be extended by adding more directors to the antenna.