A Near-Field Focused Polling Antenna Array Working With 1-Bit Reflectarray for RFID Reader Applications

In this letter, a radio frequency identification (RFID) near-field focused polling antenna array working with insensitive polarization 1-bit reflectarray is proposed for semi-open metal shelf applications. Composed of two 3 × 2 focused antenna arrays and two polling feeding networks, the antenna array is designed to realize multiple focal points, and generate the electric field distribution in accordance with the shape of the shelf, which contributes to avoiding error reading tags outside the interrogation zone. The reflectarray controlled by pin diodes is used to deal with the interference of shelf board in the near-field application. Standing waves will occur due to the reflection of shelf board when the antenna array is working. By switching the work states of the pin diodes, the nodes/antinodes of the standing waves in metal shelf are moved. Then, the miss reading problem of the tags in the nodes of standing waves is solved. Measurement results show that the RFID near-field antenna array working with 1-bit reflectarray can achieve 100% reading rate inside the shelf and no error reading outside.