Abstract: Systems and methods are disclosed for radiolocation using backscatter RFID tags and a special-purpose reader that produces a stepped-frequency continuous wave (SFCW) radio frequency (RF) interrogation signal comprising N carrier frequencies. A backscattered interrogation signal from a backscatter RFID tag is down-converted using at least a portion of the generated SFCW RF interrogation signal. Received signal phases (RSP) corresponding to the N carrier frequencies are determined. Received signal strength (RSS) may be determined to improve performance. A distance between the RFID reader and the backscatter RFID tag may be estimated based on at least a summation of differences between RSPs corresponding to adjacent carrier frequencies.