A four-port selective differential feeding network for high precision UHF near-field sectional localization systems

Depending on magnetic fields caused by phase differences between the adjacent transmission lines for high precision UHF near-field sectional localization systems, a four-port selective differential feeding network is presented. The proposed four-port feeding network consisting of four quadrature hybrid couplers and 90° phase delay lines can selectively generate a differential phased current on a particular transmission line. The maximum insertion loss within the authorized UHF RFID frequency band (902-928MHz) has a 7.1dB loss including the theoretical 6dB power distribution loss, and the maximum amplitude imbalances and phase error have less than ±0.5dB and ±10°, respectively. By switching the input ports, the sectional identification with regard to tag positions on the 10 mm height away from parallel transmission lines can be achieved. The proposed system using a four-port selective differential feeding network makes it possible to utilize a near-field position detection application such as a smart shelf.