An RFID interrogator includes a signal processing module for converting a transmission signal transmitted from an RFID tag into an input signal; a first matched filter coupled to the signal processing module for generating a first matched signal according to the input signal and a first predetermined signal pattern; a second matched filter coupled to the signal processing module for generating a second matched signal according to the input signal and a second predetermined signal pattern; a control unit for generating a control signal according to the input signal; and a decision unit, coupled to the first matched filter, the second matched filter and the control unit, for comparing the first matched signal with the second matched signal according to the control signal to generate a read-back signal.