Broadband/Dual-Band Metal-Mountable UHF RFID Tag Antennas: A Systematic Review, Taxonomy Analysis, Standards of Seamless RFID System Operation, Supporting IoT Implementations, Recommendations, and Future Directions

The employment of broadband/dual-band ultrahigh frequency (UHF) radio-frequency identification (RFID) tag antennas contributes to the growth of RFID technology, with many potential implications, such as the increase of international trade, and reducing costs thereof. This study presents all reported articles on RFID tags for metal objects that can work seamlessly across different countries. Moreover, it addresses all available approaches to design of wideband/dual-band metal-mountable tag antennas and showcases the techniques used to expand the tag bandwidth. The relevant works were gathered by applying a designated query '("tag antenna*" OR "RFID tag*") AND (metal*) AND ("broadband" OR "wideband" OR "dual band" OR "tri band")' in three scientific research engines (Web of Science, IEEE Xplore, and Scopus). The final set is determined on the basis of the exclusion and inclusion criteria, revealing 38 articles. The selected papers were categorized into five groups based on the tag structure, and all techniques utilized to widen the bandwidth of each specific structure. This taxonomy attempts to provide a deeper insight into the considered topic through a comprehensive presentation. The bandwidth measurement criterion, which is 3-dB return loss (RL) bandwidth is selected due to showing an adequate reading distance on the edge of the bandwidth. In addition, the criterion clarifies the operation frequencies that facilitate the worldwide operation of the RFID technology. This article fosters adaptation of suitable regulations to support the use of RFID systems, and researchers to design proper metal-mountable tags, which must be assessed based on operating frequencies, performance, size, cost, and compatibility with the targeted applications.