Importance

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Abstract

A radio frequency identification transponder (RFID tag) in accordance with the principles of the present includes a tag antenna having a gain and an input impedance. The tag also includes RFID circuitry, which may be in the form of an RFID tag integrated circuit, the RFID circuitry also being characterized, in part, by an input impedance. According to the principles of the present invention the tag's read distance is maximized by tuning the tag antenna impedance and gain. In general, the imaginary part of the antenna impedance is chosen as the negative of the imaginary part of the RFID circuitry's impedance. Additionally, the real part of the tag antenna's impedance is selected by tuning those geometrical antenna parameters that affect both the antenna's gain and impedance. For RFID tags wherein the geometrical parameters of the tag antenna do not affect the gain G.sub.a of the tag antenna, the antenna input impedance may tuned to establish an antenna input impedance which is the complex conjugate of the RFID circuitry's input impedance.

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First Claim