Auto-tunning scanning proximity reader
First Claim
1. 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.
1 Assignment
0 Petitions
Accused Products
Abstract
A proximity reader for a radio frequency identification (RFID) system is programmed for determining and storing optimum antenna impedance values to achieve peak antenna resonance at each of multiple operating frequencies. Antenna resonance is peaked at power up and periodically during operation to compensate for environmental detuning influences. The reader scans the multiple frequencies to more effectively search for off-frequency identification tags.
-
Citations
19 Claims
- 1. 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.
- 14. A proximity reader for a radio frequency identification system, the reader having frequency generator means for generating an output frequency, an antenna circuit connected for radiating a radiofrequency field at said output frequency for a time period sufficient to receive and decode a transponder tag coded response communicated by loading down said radiofrequency field at said output frequency, a microprocessor connected to said antenna circuit for receiving and decoding transponder tag information, scanner program means operative for sequentially switching said output frequency through a plurality of discrete frequencies spaced apart from each other and waiting for a predetermined listening time at each of said discrete frequencies sufficient to receive and verify a transponder tag response at said each of said discrete frequencies, thereby to improve interrogation of transponder tags built to relatively loose frequency tolerances.
- 16. A proximity reader for a radio frequency identification system, the reader having frequency generator means for generating a center frequency and a plurality of discrete side frequencies spaced from each other, an antenna circuit connected for radiating said center frequency and said side frequencies to interrogate transponder tags, and a microprocessor connected to said antenna circuit for receiving and decoding transponder tag information, an addressable variable tuning capacitance in said antenna circuit and tuner program means operative for addressing said tuning capacitance and electrically connected to said antenna for detecting a radio frequency signal amplitude in said antenna circuit at different capacitance values of said capacitance thereby to build a table of addresses representative of capacitance values yielding an optimum signal amplitude at each of said center frequency and discrete side frequencies, thereby to optimize the operative range of the reader.
Specification