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Radio-frequency identification system

  • US 4,926,187 A
  • Filed: 09/26/1988
  • Issued: 05/15/1990
  • Est. Priority Date: 09/24/1987
  • Status: Expired due to Term
First Claim
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1. A radio frequency identification system, comprising:

  • a main unit, comprising;

    a main modem portion outputting a first modulation signal generated by modulating a first carrier having a first frequency with a first transmission data, a second carrier having a second frequency close to said first frequency, a starting modulation signal generated by modulating the first carrier with start data;

    a main transmission portion, operatively connected to said main modem portion, receiving the first modulation signal and the second carrier and generating a first circularly polarized wave having a first rotation, based on the first modulation signal, a second circularly polarized wave having a second rotation opposite to the first rotation, based on the second carrier and a starting circularly polarized wave, having the second rotation based on the starting modulation signal and the second carrier for initiating communication; and

    a main reception portion, operatively connected to said main transmission portion, receiving a second circularly polarized wave and outputting a second modulation signal; and

    a sub unit, radio communicatable with said main unit through a radio-communication channel, comprising;

    a small size battery;

    a sub reception portion, operatively connected to said small size battery, receiving the first circularly polarized wave and separating the first circularly polarized wave into the first modulation signal and the second carrier;

    a sub transmission portion, operatively connected to said small size battery, generating the second circularly polarized wave having a rotation equal to the first rotation on the basis of the second modulation signal;

    a sub modem portion includinga sub modulation portion, operatively connected to said sub transmission portion and said small size battery, but not supplied with power from said small size battery in a normal state; and

    a sub demodulation portion, operatively connected to said sub reception portion, for demodulating the first modulation signal, detecting the starting circularly polarized wave and triggering said sub modulation portion in response to a reception of the starting circularly polarized portion, said main modem portion demodulating said second modulation signal to recover said second transmission data.

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