A Novel Near-Field UHF RFID Reader Array Antenna for Configurable Electrically Large Reading Area

In this paper, a novel configurable loop array antenna based on resonator-loaded microstrip lines (RLML) is proposed to enlarge the interrogation zone of the reader antenna for near-field ultrahigh-frequency (UHF) radio frequency identification (RFID) system. The proposed loop array antenna is composed of a number of RLML loop units. By configuration of the RLML loop units sharing a common side with its adjacent RLML loop units which carry reverse-direction flowing current in the x-axis and y-axis directions, loop array antennas are created to generate a strong and uniform magnetic-field distribution over a large configurable interrogation area. As an example, loop array antennas with 1 × 8 and 2 × 3 RLML loop units implemented onto a piece of an FR4 printed circuit board (PCB) are designed, fabricated, and measured. The measured bandwidth ranges from 894 to 964 MHz for a 1×8 array antenna with a reading area of 570 mm × 150 mm and 917-932 MHz for a 2 × 3 array antenna with a reading area of 270 mm × 240 mm. The reading distances of an 1 × 8 array antenna for loop-like tag, dipole-like tag, and antimetal tag are achieved up to 22, 42, and 45 mm, respectively. For a 2 × 3 array antenna, the reading distances of three tags are achieved up to 23, 43, and 40 mm.