Near field phased array DOA and range estimation of UHF RFID tags

This paper presents a near field localization system based on a phased array for UHF RFID tags. To estimate angle and range the system uses a two-dimensional MUSIC algorithm. A four channel phased array is used to experimentally verify the estimation of angle and range for an EPC gen2 tag. The system is calibrated for phase offsets introduced by hardware as simulations show the sensitivity to these offsets. Experiments with this calibrated receiver array give inaccurate ranging estimates. A solution is to calibrate the system for every angle, allowing meaningful range estimates. Experiments in a different environment show a reduced result, indicating the need for extensive calibration.