Waveguide Antenna Topologies for Distributed High-Frequency Near-Field Communication and Localization

High-frequency (HF) near-field communication (NFC) is an inherently short-range technology. However, the total capture volume can be increased with traveling-wave antennas. Here, we report on the analysis, design, and measurements of flexible waveguide antennas and discuss their performance for NFC and localization. The antennas comprise sections of coaxial transmission lines loaded periodically with field-generating inductive networks. Several topologies were compared to each other theoretically, and the best-performing candidate was selected to fabricate antennas between 5 and 48 m long, each containing 15 read nodes. Waveguiding properties of the antennas were measured and agreement with the theory was demonstrated. Afterward, each antenna was integrated with a custom NFC reader and shown to be capable of communication with and localization of commercial off-the-shelf transponders compliant with ISO/IEC 14443 Type A protocol. The transverse detection range was 10 cm with 1 W input RF power. Both 1-D and quasi-2-D configurations were tested. The proposed antennas are flexible, scalable, have low loss, and could be used for NFC, identification, and tracking of distributed and mobile tags.