Method of and apparatus for long distance reading of passive tags in radio frequency identification systems
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Abstract
A method and an apparatus for reading passive tags affixed to objects to be identified and tracked by a radio frequency identification system are disclosed. An interrogating station sends radio-frequency inquiry signals toward the passive tags through an antenna array and receives the response signals from the tags through the same array. Electronic circuitry for processing such response signals has a phase conjugator submitting each received signal to phase conjugation, and the phase-conjugated signals are back transmitted to the passive tags. Retrodirectivity of the antenna array obtained through the phase conjugation allows a precise object identification and tracking also at relatively long distances.
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Citations
42 Claims
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1-21. -21. (canceled)
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22. A method of reading passive tags in a radio-frequency identification system, wherein an interrogating station comprising an antenna array sends radio-frequency inquiry signals toward passive tags to be identified, and each tag associates information stored thereon with the received inquiry signal to form a response signal that is reflected toward the interrogating station and is processed therein, comprising detecting at the interrogating station an absolute value and a phase of each response signal received at each antenna in the array;
- submitting each received response signal to phase conjugation, thereby generating a respective phase-conjugated signal; and
transmitting the phase conjugated signals back to the passive tags. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31)
- submitting each received response signal to phase conjugation, thereby generating a respective phase-conjugated signal; and
- 32. An apparatus for reading passive tags in a radio frequency identification system comprising an interrogating station sending radio-frequency inquiry signals toward the passive tags and receiving from the tags response signals each consisting of an inquiry signal reflected toward the interrogating station after having been associated with information carried by a respective tag, the interrogating station comprising a control unit for controlling the transmission of the inquiry signals and for processing the response signals, the interrogating station comprising an antenna array controlled by the control unit and transmitting the inquiry signals and receiving the response signals, the control unit being arranged to detect and temporarily store an absolute value and a phase of each response signal received at each antenna of the array, and being connected with a phase conjugator submitting each received signal to phase conjugation to generate respective phase-conjugated signal and supplying the phase conjugated signals to a radio frequency generator connected to the antenna array, for back transmission of the phase conjugated signals to the passive tags.
Specification