UHF RFID shelf solution with cascaded reader antenna and positioning capability

Automatic goods inventory on the shelf is an important Ultra High Frequency (UHF) Radio Frequency Identification (RFID) application. Compared to other applications, it has some unique requirements: 1) Confined read region to avoid the cross reads to other tiers and shelves; 2) Positioning capability to know where along the shelf the tag is; 3) Low total system cost to support many shelves in the application. In this paper, an innovative UHF RFID solution is proposed for the RFID shelf. It contains two key technologies. First, the proposed near field (NF) shelf antenna in [1] is improved to provide the possibility to connect 5 cascaded antennas to one antenna port. It can save the system cost by reducing the number of needed readers. Second, a phase difference measurement based tag positioning method is proposed. To support different applications, it can provide both tier level and item level positioning for the goods on the shelf. Based on the measurement results, the proposed method can get the item level positioning accuracy with an average error of 4.16cm. It can also get 100% tier level positioning accuracy.