Patent ID: 7084739

Claim:
An interrogator for use in a communication system including, in addition to the interrogator as a first interrogator, a second interrogator, a first transponder, and a second transponder, the first interrogator comprising: a carrier wave transmitter which transmits a first carrier wave toward the first transponder, so that the first transponder receives the first carrier wave, modulates the first carrier wave based on first information, and returns the modulated first carrier wave as a first reflected wave, toward the first interrogator; a reflected wave receiver which receives the first reflected wave returned from the first transponder; a demodulator which demodulates the first reflected wave received by the reflected wave receiver, into a demodulated signal; an information obtaining device which obtains said first information from the demodulated signal; a second carrier wave transmission judging device which judges, before the carrier wave transmitter transmits the first carrier wave, whether the second interrogator is transmitting a second carrier wave toward the second transponder so that the second transponder receives the second carrier wave, modulates the second carrier wave based on second information, and returns the modulated second carrier wave as a second reflected wave toward the second interrogator; a reflected wave reception judging device which judges, when the second carrier wave transmission judging device judges that the second interrogator is transmitting the second carrier wave, whether the reflected wave receiver can receive, as a third reflected wave, a modulated second carrier wave that has been modulated by the first transponder based on said first information and returned therefrom; and a transmitter and receiver controller which controls, when the reflected wave reception judging device judges that the reflected wave receiver can receive the third reflected wave returned from the first transponder, the carrier wave transmitter not to transmit the first carrier wave, and additionally controls the reflected wave receiver to receive the third reflected wave.