Array antenna system and algorithm applicable to rfid readers

Abstract

Embodiments of the invention pertain to Radio Frequency Identification (RFID) method and system using an antenna array, an array controller, and control algorithms. Embodiments of the invention can induce strong radio-frequency (RF) excitation, for a given level of radiated RF power, at any point within an arbitrary inhomogeneous medium. For RFID applications, one typical inhomogeneous medium is an ensemble of cases on a pallet. Another typical medium is a warehouse environment having stored goods together with shelving and other material present. An embodiment of the invention is applicable to the process of reading battery-less, or “passive” RFID tags, which rely on incident RF electromagnetic fields established by RFID readers to power the electronic circuitry within the tags.

What is claimed: 
     
         1 . An antenna system, comprising:
 an RF input port, wherein the RF input port receives an input RF signal, wherein the input RF signal is suitable for reading at least one RFID tag;   a plurality of antennas capable of producing RF fields in a region of interest;   a means for producing a corresponding plurality of antenna input signals from the input RF signal, wherein each of the plurality of antenna input signals is suitable for reading the at least one RFID tag, wherein when the plurality of antenna input signals is inputted to the plurality of antennas a corresponding plurality of RF fields is produced in the region of interest;   a state controller, wherein the state controller changes a state of the plurality of antennas by altering the plurality of RF fields, wherein the state controller produces a first state during a first period of time and produces a second state during a second period of time.   
     
     
         2 . The system according to  claim 1 , wherein the state controller alters the plurality RF fields by altering one or more of the following:
 a phase of a first at least one of the plurality of antenna input signals,   a ratio of amplitudes of a second at least two of the plurality of antenna input signals,   a radiation pattern of a first at least one of the plurality of antennas, and   a polarization of a second at least one of the plurality of antennas.   
     
     
         3 . The system according to  claim 1 , wherein the means for producing a plurality of antenna input signals suitable for reading at least one of the RFID tag comprises a power divider, wherein the input RF signal is inputted to the power divider and the corresponding plurality of antenna input signals are outputted from the power divider. 
     
     
         4 . The system according to  claim 1 , wherein the state controller alters the plurality of RF fields by altering a phase of at least one of the plurality of antenna input signals. 
     
     
         5 . The system according to  claim 1 , wherein the state controller alters the plurality of RF fields by altering a ratio of amplitudes of at least two of the plurality of antenna input signals. 
     
     
         6 . The system according to  claim 1 , wherein the state controller alters the plurality of RF fields by altering a radiation pattern of at least one of the plurality of antennas. 
     
     
         7 . The system according to  claim 1 , wherein the state controller alters the plurality of RF fields by altering a polarization of at least one of the plurality of antennas. 
     
     
         8 . The system according to  claim 1 , further comprising:
 an RFID reader, wherein the RFID reader is coupled to the RF input port and provides the input RF signal.   
     
     
         9 . The system according to  claim 1 , further comprising:
 an RF receiver, wherein the RF receiver receives a return RF signal, wherein the return RF signal is due to the plurality of the RF fields being incident on one or more of the at least one RFID tag.   
     
     
         10 . The system according to  claim 7 , wherein the receiver comprises the plurality of antennas. 
     
     
         11 . The system according to  claim 9 , wherein the received return RF signal is from the RF input port. 
     
     
         12 . The system according to  claim 8 , further comprising:
 an RF receiver, wherein the RF receiver receives a return RF signal, wherein the return RF signal is due to the plurality of the RF fields being incident on one or more of the at least one RFID tag.   
     
     
         13 . The system according to  claim 12 , wherein the received return RF signal is outputted from the RF input port to the RFID reader. 
     
     
         14 . The system according to  claim 9 , wherein the receiver comprises a second plurality of antennas. 
     
     
         15 . The system according to  claim 14 , further comprising:
 a second state controller, wherein the second state controller changes a receive state of the second antenna array by altering one or more of the following:
 a phase of a first at least one of a plurality of received return RF signals as received by the second plurality of antennas, 
 a ratio of amplitudes of at least two of the plurality of received return RF signals, 
 a radiation pattern of at least one of the second plurality of antennas, and 
 a polarization of one or more of the second plurality of antennas. 
   
     
     
         16 . The system according to  claim 15 , wherein the second state controller produces a first receive state during the first period of time and produces a second receive state during the second period of time. 
     
     
         17 . The system according to  claim 8 , further comprising:
 one or more RFID tags located in a far-field region of the plurality of antennas.   
     
     
         18 . The system according to  claim 17 , wherein the far-field region is greater than or equal to 
       
         
           
             
               
                 
                   2 
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                    
                   
                     D 
                     2 
                   
                 
                 λ 
               
               , 
             
           
         
       
       where D is the largest dimension of an antenna in a plurality of antennas normal to radiation direction and λ is the wavelength of the plurality of RF fields. 
     
     
         19 . The system according to  claim 8 , further comprising:
 one or more RFID tags located in a radiating near field of the plurality of antennas.   
     
     
         20 . A method of reading one or more RFID tags, comprising:
 positioning one or more RFID tags in a region of interest;   positioning a plurality of antennas, wherein the plurality of antennas is capable of producing RF fields in the region of interest;   receiving an input RF signal, wherein the input RF signal is suitable for reading at least one of the one or more RFID tags;   producing a corresponding plurality of antenna input signals from the received input RF signal, each of the plurality of antenna input signals suitable for reading at least one of the one or more RFID tags;   inputting each of the plurality of antenna input signals into a corresponding antenna of the plurality of antennas, such that a corresponding plurality of RF fields are simultaneously produced in the region of interest from the plurality of antennas while the plurality of RF fields are in a first state during a first period of time;   receiving a first return RF signal, wherein the first return RF signal is due to the plurality of RF fields produced during the first period of time being incident on the at least one of the one or more RFID tags;   processing the first return RF signal to determine whether the at least one of the one or more RFID tags is present in the region of interest;   inputting each of the plurality of antenna input signals into the corresponding antenna of the plurality of antennas, such that the corresponding plurality of RF fields are simultaneously produced in the region of interest from the plurality of antennas while the plurality of RF fields are in a second state during a second period of time, wherein the second state is accomplished by altering the plurality of RF fields produced in the region of interest;   receiving a second return RF signal, wherein the second return RF signal is due to the plurality of RF fields produced during the second period of time being incident on the at least one of the one or more RFID tags;   processing the second return RF signal to determine whether the at least one of the one or more RFID tags is present in the region of interest.