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Transponder for vehicle identification device

  • US 5,311,186 A
  • Filed: 06/04/1993
  • Issued: 05/10/1994
  • Est. Priority Date: 09/27/1989
  • Status: Expired due to Fees
First Claim
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1. A transponder used in a mobile body identification system in which an interrogator generates a query radio wave to a mobile body and receives a radio wave including mobile body information returned from a transponder provided on said mobile body, said transponder comprising:

  • an antenna for receiving a query radio wave transmitted from said interrogator to activate a code signal generating means and to modulate a signal, and for transmitting a modulated radio wave to said interrogator;

    a detection device for detecting said query radio wave received by said antenna and for generating a detection signal;

    coded signal generating means for generating a coded signal train output previously stored in response to said detection signal, andbias controlling means for varying an amount of bias of said detection device in accordance with said coded signal train output and for varying a reflection coefficient of said detection device in accordance with said coded signal train output so that said coded signal train output is returned to said interrogator as a responding radio wave generated by modulating said reflected wave of said query radio wave;

    an electric power source controlling means for supplying the electric power to said coded signal generating means when a detection output having a level exceeding a predetermined set level is detected; and

    a circuit for eliminating a modulated component modulated by said bias controlling means and which is superimposed on said detection output generated from said detection device to preclude transmitting the modulated wave, such as a second harmonic wave.

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