Reconfigurable Modular Antenna for NF UHF RFID Smart Point Readers

In this paper, a reconfigurable modular antenna is presented for smart point readers employed in near-field (NF) radio-frequency identification applications at the ultrahigh frequency European Telecommunications Standards Institute band (865-868 MHz). The antenna comprises two modules sharing the same 250 × 250 mm2 aperture: a spiral-shaped traveling wave antenna and an array of four resonating slot antennas connected in series to the traveling wave antenna through a printed matching/delay network. The electromagnetic (EM) field distribution generated by the overall antenna can be controlled and shaped through an absorptive RF switch placed at the end of the spiral traveling wave antenna. Specifically, two configurations can be selected, on the basis of the particular operating scenario. In the spiral traveling-wave antenna configuration, that is, the best for tag writing operations, the EM field is maximized in the reader central area, right on its surface only (reactive NF region). In the modular antenna configuration, a field coverage is guaranteed up to a few decimeters away from the reader surface (radiative NF region). Measurements on a prototype and simulation results are in good agreement. Moreover, a system-level characterization has been carried out and compared to a numerical analysis aimed to qualitatively predict tag detection performance.