Patent ID: 7277681

Claim:
An interrogator which, together with a transponder, makes up a radio frequency identification system, comprising: a first antenna, provided for a portable wireless terminal, for radiating radio waves of a first radio frequency transmitter signal; a second antenna for receiving the radio waves radiated from the first antenna and outputting the first radio frequency transmitter signal; a divider for dividing the first radio frequency transmitter signal outputted by the second antenna; a rectifier for rectifying one of the first radio frequency transmitter signals outputted by the divider and outputting a power supply; an ASK (Amplitude Shift Keying) modulation circuit for performing amplitude modulation on the other of the first radio frequency transmitter signals outputted by the divider by information to be transmitted to the transponder and outputting the amplitude-modulated signal as a second radio frequency transmitter signal; a third antenna for radiating the second radio frequency transmitter signal outputted by the ASK modulation circuit; and a mixer for performing synchronous detection on a radio frequency receiver signal returned from the transponder which received said second radio frequency transmitter signal via the third antenna by using part of the second radio frequency transmitter signal as a carrier, and outputting data from the transponder.