Abstract: Provided are a tag, interrogator, and system for performing position measurement based on backscatter in a millimeter-wave band. In detail, provided is a tag including a planar Van Atta array antenna, a frequency-shift keying (FSK) modulator connected to the planar Van Atta array antenna, and at least one bias circuit connected to the FSK modulator, wherein the FSK modulator is configured to, based on an interrogation signal being received by the planar Van Atta array antenna, modulate the interrogation signal based on a control signal supplied through the at least one bias circuit, and output the modulated interrogation signal in a direction from which the interrogation signal is received, through the planar Van Atta array antenna.