Modern RFID Reader Antennas: A Review of the Design, State-of-the-Art, and Research Challenges

The internet of things (IoT) paradigm aims to make the world smarter by reducing human intervention and promoting automated interactions. A radio frequency identification (RFID) reader is a necessary component for automated object identification and data transfer in an IoT network. Its performance is primarily determined by the characteristics of the integrated or externally connected antennas. This article provides a review of the state-of-the-art reader antenna designs, as well as research challenges. The RFID reader antennas are investigated based on their operating frequency bands, gain, and polarization. Generalized procedures for designing specific antenna configurations, which are useful and widely used by readers, are illustrated and explained. Several design challenges have been investigated and analyzed, including narrow bandwidth, bidirectional radiation pattern, low gain, linear polarization, and a larger footprint. Subsequent solutions have also been provided. Cross-dipole configurations are one method for achieving a compact footprint and circular polarization characteristics without using complicated feeding circuitry. Low antenna gain has a direct impact on the read range of the reader. Therefore, increasing the gain of the reader antennas is an essential requirement. One of the gain-enhancing techniques is to use an artificial magnetic conductor (AMC) surface beneath the antenna. This reduces backward radiation of the antenna-AMC integrated configuration, increasing the antenna peak gain. The AMC also helps in the achievement of unidirectional radiation.