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A multi-protocol RFID interrogating system employs a synchronization technique (step-lock) for a backscatter RFID system that allows simultaneous operation of closely spaced interrogators. The multi-protocol RFID interrogating system can communicate with backscatter transponders having different out

A multi-protocol RFID interrogating system employs a synchronization technique (step-lock) for a backscatter RFID system that allows simultaneous operation of closely spaced interrogators. The multi-protocol RFID interrogating system can communicate with backscatter transponders having different output protocols and with active transponders including: Title 21 compliant RFID backscatter transponders; IT2000 RFID backscatter transponders that provide an extended mode capability beyond Title 21; EGO™ RFID backscatter transponders, SEGO™ RFID backscatter transponders; ATA, ISO, ANSI AAR compliant RFID backscatter transponders; and IAG compliant active technology transponders. The system implements a step-lock operation, whereby adjacent interrogators are synchronized to ensure that all downlinks operate within the same time frame and all uplinks operate within the same time frame, to eliminate downlink on uplink interference.

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1. An interrogator system to read active RFID transponders and backscatter RFID transponders comprising at least two transceivers,each transceiver covering a respective capture zone, the two capture zones being in proximity to each other, wherein said transceivers are adapted to use time division mu

1. An interrogator system to read active RFID transponders and backscatter RFID transponders comprising at least two transceivers,each transceiver covering a respective capture zone, the two capture zones being in proximity to each other, wherein said transceivers are adapted to use time division multiplexing to read the active RFID transponders in a first capture zone during a first time period, to read the active RFID transponders in a second capture zone during second time period and to simultaneously read the backscatter RFID transponders in both capture zones during a third time period, wherein a synchronization signal is shared between said transceivers, and wherein the read of the backscatter RFID transponders in the third time period by each transceiver comprises a downlink transmission, the downlink transmission comprising plural bits, and wherein each bit of the backscatter downlink transmission of each transceiver occurs at substantially the same time. 2. An interrogator system to read active RFID transponders and backscatter RFID transponders comprising at least two transceivers,each transceiver covering a respective distinct capture zone, the two capture zones being in proximity to each other, wherein said transceivers are adapted to use time division multiplexing to read the active RFID transponders in a first capture zone during a first time period, to read the active RFID transponders in a second capture zone during a second time period and to simultaneously read the backscatter RFID transponders in both capture zones during a third time period, wherein a synchronization signal is shared between said transceivers, and wherein during a fourth time period each transceiver transmits a downlink transmission to the active RFID transponders in its respective capture zone and wherein each bit of the active RFD transponder downlink transmission of each transceiver occurs at substantially the same time. 3. An interrogator system using at least a first and second protocol to read RFID transponders comprising: at least two transceivers, each transceiver covering a respective capture zone, the respective capture zones being in proximity to each other; and a synchronization circuit adapted to synchronize the two transceivers such that said at least two transceivers operate the first protocol simultaneously with each other during a first time period and operate the second protocol simultaneously with each other during a second time period, wherein each of said at least two transceivers transmits a respective downlink transmission as part of the first protocol, each downlink transmission comprising plural bits, with the first bit of each downlink transmission of each transceiver occurring at substantially the same time. 4. The system of claim 3 wherein the two protocols operate at different frequencies. 5. The system of claim 3 wherein a synchronization signal is shared between the transceivers. 6. The system of claim 5 wherein a first transceiver generates the synchronization signal and a second transceiver receives the synchronization signal. 7. The systems of claim 5 wherein one or more active RFID transponders are read during the first time period. 8. The system of claim 7 wherein two or more active RFID transponders are read in turn during the first time period. 9. The system of claim 8 wherein the two or more active RFID transponders read in turn during the first time period are read using different communications protocols. 10. The system of claim 7 wherein two or more active RFID transponders are read simultaneously. 11. The system of claim 7 wherein one or more backscatter RFID transponders are read in turn during the second time period. 12. The system of claim 11 wherein the two protocols operate at different frequencies. 13. An interrogator system for reading RFID transponders comprising: at least two transceivers and a synchronization circuit, each of the at least two transceivers covering a respective capture zone and being arranged for transmitting a downlink signal in its respective capture zone, and each of the downlink signals comprising plural bits, wherein the respective capture zones overlap at least partially, creating an overlap capture zone in which an RFID transponder may be located, and wherein the synchronization circuit synchronizes the downlink signals from each of the two transceivers such that each bit in the downlink signals starts at substantially the same time. 14. The system of claim 13 wherein a synchronization signal is shared between the transceivers. 15. The system of claim 14 wherein a first transceiver generates the synchronization signal and a second transceiver receives the synchronization signal. 16. The systems of claim 13 wherein the RFID transponders are active RFID transponders. 17. The systems of claim 13 wherein the RFID transponders are backscatter RFID transponders. 18. An interrogation system for communicating with a plurality of transponders having different communication protocols, the interrogation system comprising a plurality of interrogators anda synchronization signal,each of the interrogators comprisinga transmitter anda receiverthe transmitters being arranged for transmitting downlink signals in accordance with different communication protocols over a downlink communications link to the transponders,the receivers being arranged for receiving respective uplink signals over an uplink communications signal link from the transponders,the synchronization signal being arranged for synchronizing the downlink signals for each of the plurality of interrogators, each of the interrogators operating in response to the synchronization signal to simultaneously transmit the downlink signals to the transponders to enable the transponders to provide their respective uplink signals after the transmission of the downlink signals, thereby enabling communication between respective ones of the interrogators and transponders without interference between the uplink signals from the transponders and the downlink signals from the interrogators, wherein the transponders comprise backscatter transponders. 19. The system of claim 18, wherein the transponders comprise backscatter transponders that are beam powered. 20. The system of claim 18, wherein the transponders comprise backscatter transponders that are beam powered and backscatter transponders having a battery power supply. 21. The system of claim 18, wherein the transponders comprise backscatter transponders that are beam powered and active transponders that transmit at a fixed frequency. 22. The system of claim 18, wherein the transponders comprise backscatter transponders that are beam powered, and backscatter transponders having a battery power supply, and active transponders that transmit at a fixed frequency. 23. The system of claim 18, wherein at least two backscatter RFID transponders are communicated with at the same time. 24. The system of claim 18, wherein at least three backscatter RFID transponders are communicated with at the same time. 25. An interrogation system for communicating with a plurality of transponders having different communication protocols, the interrogation system comprising a plurality of interrogators anda synchronization signal,each of the interrogators comprisinga transmitter anda receiverthe transmitters being arranged for transmitting downlink signals in accordance with different communication protocols over a downlink communications link to the transponders,the receivers being arranged for receiving respective uplink signals over an uplink communications signal link from the transponders,the synchronization signal being arranged for synchronizing the downlink signals for each of the plurality of interrogators, each of the interrogators operating in response to the synchronization signal to simultaneously transmit the downlink signals to the transponders to enable the transponders to provide their respective uplink signals after the transmission of the downlink signals, thereby enabling communication between respective ones of the interrogators and transponders without interference between the uplink signals from the transponders and the downlink signals from the interrogators,wherein the system establishes a tag communication signal sequence, said signal sequence comprising first and second said sequence portions, said signal sequence being arranged to enable said system to read at least one active RFID transponder in a first capture zone during said first sequence portion, and to read at least one active RFID transponder in a second capture zone during said second sequence portion. 26. The system of claim 25, wherein said signal sequence further comprises comprising and third sequence portion, said signal sequence being further arranged to enable said system to read at least one active RFID transponder in a third capture zone during said third sequence portion. 27. The system of claim 26 wherein at least two backscatter RFID transponders are communicated with at the same time. 28. The system of claim 26 wherein at least three backscatter RFID transponders are communicated with at the same time. 29. the system of claim 27 wherein said two transponders are communicated with using different commands. 30. The system of claim 28 wherein at least two of said three transponders are communicated with using different commands.