US2017213056A1PendingUtilityA1

Intermodulation mitigation technique in an rfid system

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Assignee: TIERNAY ROBERT WPriority: May 26, 2005Filed: Dec 20, 2016Published: Jul 27, 2017
Est. expiryMay 26, 2025(expired)· nominal 20-yr term from priority
Inventors:Robert W. Tiernay
G01S 7/36G06K 7/10069Y10T29/49002H04B 1/10G06K 7/10019G07B 15/063G01S 13/751G06K 7/10475G06K 7/10009
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Claims

Abstract

When multiple readers for RF transponders have to be placed in close proximity, such as in adjacent lanes of a highway toll barrier, they can be set to operate at different frequencies. When signals from two adjacent ones of the readers interfere, the resulting signal includes interference terms whose frequencies equal the sum of the reader frequencies and the difference between the reader frequencies. To remove such interference terms while passing the desired terms, a tag includes a low-pass or other frequency-selective filter.

Claims

exact text as granted — not AI-modified
1 - 16 . (canceled) 
     
     
         17 . A system comprising:
 a first reader to transmit a first interrogation signal to a transponder at a first frequency and to receive a response signal from the transponder at the first frequency;   a second reader to transmit a second interrogation signal to the transponder at a second frequency,   wherein said first and second interrogation signals create intermodulation products that cause interference at the transponder;   the transponder comprising:
 an antenna; 
 a detector in electrical communication with the antenna; and 
 a frequency-selective filter in electrical communication with the detector to mitigate the interference. 
   
     
     
         18 . The system of  claim 17 , wherein the detector comprises a detector diode. 
     
     
         19 . The system of  claim 17 , wherein the frequency selective filter comprises an RC filter. 
     
     
         20 . The system of  claim 17 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         21 . The system of  claim 17 , wherein the frequency selective filter comprises a band pass filter. 
     
     
         22 . The system of  claim 17 , wherein the frequency selective filter comprises a high pass filter. 
     
     
         23 . The system of  claim 18 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         24 . The system of  claim 18 , wherein the frequency selective filter comprises a band pass filter. 
     
     
         25 . The system of  claim 18 , wherein the frequency selective filter comprises a high pass filter. 
     
     
         26 . A system comprising:
 a first reader to transmit a first interrogation signal to a transponder at a first frequency and receive a response signal from the transponder at a third frequency;   a second reader to transmit a second interrogation signal to the transponder at a second frequency and,   wherein said first interrogation signal or response signal and the second interrogation signal create intermodulation products that cause interference at the transponder;   the transponder comprising:
 an antenna; 
 a detector in electrical communication with the antenna; 
 a frequency-selective filter in electrical communication with the detector; and 
 a signal processing circuit in electrical communication with the frequency-selective filter to mitigate the interference. 
   
     
     
         27 . The system of  claim 26 , wherein the detector comprises a detector diode. 
     
     
         28 . The system of  claim 26 , wherein the frequency selective filter comprises and RC filter. 
     
     
         29 . The system of  claim 26 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         30 . The system of  claim 26 , wherein the frequency selective filter comprises a band pass filter. 
     
     
         31 . The system of  claim 26 , wherein the frequency selective filter comprises a high pass filter. 
     
     
         32 . The system of  claim 27 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         33 . The system of  claim 27 , wherein the frequency selective filter comprises a band pass filter. 
     
     
         34 . The system of  claim 27 , wherein the frequency selective filter comprises a high pass filter. 
     
     
         35 . A system comprising:
 a first reader to transmit a first interrogation signal to a transponder at a first frequency and to receive a response signal from the transponder at the first frequency;   an interference source signal received at the transponder at a second frequency,   wherein said first interrogation signal and the interfering source signal create intermodulation products that cause interference at the transponder;   the transponder comprising:
 an antenna; 
 a detector in electrical communication with the antenna; and 
 a frequency-selective filter in electrical communication with the detector to mitigate the interference. 
   
     
     
         35 . The system of  claim 35 , wherein the detector comprises a detector diode. 
     
     
         36 . The system of  claim 35 , wherein the frequency selective filter comprises and RC filter. 
     
     
         37 . The system of  claim 35 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         38 . The system of  claim 35  wherein the frequency selective filter comprises a band pass filter. 
     
     
         39 . The system of  claim 35  wherein the frequency selective filter comprises a high pass filter. 
     
     
         40 . The system of  claim 36 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         41 . The system of  claim 36 , wherein the frequency selective filter comprises a band pass filter. 
     
     
         42 . The system of  claim 36 , wherein the frequency selective filter comprises a high pass filter. 
     
     
         43 . A transponder comprising:
 an antenna;   a detector in electrical communication with the antenna;   a frequency-selective filter in electrical communication with the detector to mitigate intermodulation products created by a reader supplying a first interrogation signal to a transponder at a first frequency and an interference source signal received at the transponder at a second frequency.   
     
     
         44 . The transponder of  claim 43 , wherein the detector comprises a detector diode. 
     
     
         45 . The transponder of  claim 43 , wherein the frequency selective filter comprises and RC filter. 
     
     
         46 . The transponder of  claim 43 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         47 . The transponder of  claim 43 , wherein the frequency selective filter comprises a band pass filter. 
     
     
         48 . The transponder of  claim 43 , wherein the frequency selective filter comprises a high pass filter. 
     
     
         49 . The transponder of  claim 44 , wherein the frequency selective filter comprises a low pass filter. 
     
     
         50 . The transponder of  claim 44 , wherein the frequency selective filter comprises a band pass filter. 
     
     
         51 . The transponder of  claim 44 , wherein the frequency selective filter comprises a high pass filter.

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