| 摘要 |
<p>PURPOSE: To obtain a communication apparatus which judges whether a responder is situated within a prescribed distance with reference to an interrogator or which can indicate a point of time when the responder is situated within the prescribed distance. CONSTITUTION: An interrogator 10 sends out modulated signal waves, for distance measurement, which have been modulated by a reference signal 14. A responder 60 receives the modulated signal waves for distance measurement, it demodulates the reference signal so as to be 1/2- frequency-divided 76, and the modulated signal waves for distance measurement are demodulated further by a frequency-divided signal so as to be sent out as response modulated signal waves for distance measurement. The interrogator 10 receives and demodulates the response modulated signal waves for distance measurement, and the phase difference between the demodulated frequency-divided signal and a frequency-divided signal which has 1/2- frequency-divided the reference signal inside the interrogator 10 is detected by a phase difference detector 40. In the phase difference, a phase delay according to the distance between the interrogator 10 and the responder 60 is added to a phase delay due to the circuit constitution of the interrogator 10 and the responder 60. The phase delay due to the circuit constitution is constant, the distance between the interrogator 10 and the responder 60 can be operated on the basis of the phase delay, it is judged whether, the responder is situated within a prescribed distance or not, and a point of time when the responder is situated within the prescribed distance can be indicated on the basis of a change in a discrimination signal.</p> |
