J. Shi, X. Qing and Z. N. Chen, "Electrically Large Zero-Phase-Shift Line Grid-Array UHF Near-Field RFID Reader Antenna," in IEEE Transactions on Antennas and Propagation, vol. 62, no. 4, pp. 2201-2208, April 2014. doi: 10.1109/TAP.2014.2299824
A grid-array antenna using a zero-phase-shift (ZPS) line is proposed to enlarge the interrogation zone of a reader antenna for near-field ultra-high-frequency (UHF) radio frequency identification (RFID) system. The proposed grid-array antenna is composed of a number of grid cells and a double-sided parallel-strip line feeding network. Each grid cell, namely segmented loop constructed by the ZPS line, has uniform and single-direction flowing current along the line. By configuration of the cells sharing a common side with its adjacent grid cells which carry reverse-direction flowing current, a grid-array antenna is formed to generate a strong and uniform magnetic-field distribution over a large interrogation zone even when the perimeter of the interrogation zone reaches up to (where is the operating wavelength in free space) or larger. As an example, a grid-array antenna with 1 2 segmented ZPS line loop cells implemented onto a piece of FR4 printed board (PCB) is designed and prototyped. The results show that the grid-array antenna achieves the impedance
matching over the frequency range from 790 to 1040 MHz and produces strong and uniform magnetic-field distribution over an interrogation zone of 308 mm 150 mm.
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