Patent ID: 6317027
Filing Date: 2001-11-13
Classification: G06K,H03J

Abstract:
A proximity reader for a radio frequency identification system wherein identification tags have transponder circuits powered by a radio frequency transmission of the reader at a resonant frequency of the tags for inducing a coded response, the reader having frequency generator means for generating a center frequency and a plurality of discrete side frequencies spaced from each other and from said center frequency, an antenna circuit connected for radiating each of said center frequency and said side frequencies in a sequence to interrogate transponder tags, and a microprocessor connected to said antenna circuit for receiving and decoding transponder tag information communicated by loading down a radiofrequency field radiated by said antenna circuit at any single one of said center and side frequencies, antenna resonance tuning means including a selectable impedance in said antenna circuit and tuner program means operative in step with said sequence for selecting discrete values of said impedance corresponding to each of said center frequency and said discrete side frequencies to substantially optimize the reactance of said antenna circuit for maximum radiated signal at each of said center frequency and side frequencies thereby to maximize operative range of the transmitter and for storing said values for reference by said tuner program means.