Radar/Antennas Technical Session

Near-Field Antenna for RFID Tag Inspection


Eastern Time September 11, 2019 11:30 am - 12:00 pm

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Scott Best

RFID Tags are commonly inspected using Far-Field Antennas with a Reader, so multiple RFID Tags are simultaneously illuminated by the antenna beam, which permits each RFID Tag to respond and be counted.  However, it is important to realize that RFID Tags are relatively inexpensive to fabricate and deploy onto packages for inventory control, security, and other purposes.  These RFID Tags are not commonly inspected before they are deployed, so both Working and Defective RFID Tags are placed onto packages, which creates inventory errors and security losses when packages containing Defective RFID Tags cannot be correctly counted by a Far-Field RFID system.

Hence, RFID Tag inspection systems are often used to sort Working from Defective RFID Tags to mitigate this problem.  RFID Tags are mass produced and distributed on tape spools that contain hundreds, and at time thousands of RFID Tags on a single tape spool.  It is obvious that a Far-Field Antenna cannot be used to identify individual Defective RFID Tags on a tape spool, so a Near-Field Antenna was developed for this inspection system.  The Near-Field Antenna permits identification of individual Working and Defective RFID Tags on a tape spool, permitting only Working RFID Tags to be deployed onto packages and the Defective RFID Tags are subsequently destroyed.

The Near-Field Antenna is also used to locate a single package with a specific RFID Number when a Far-Field Antenna has isolated the location of the package to a container or box containing multiple RFID Tags located on separate packages.  Each package can then be inspected with the Near-Field Antenna to identify the package containing the desired RFID Number.

The Near-Field Antenna operates at 915 MHz, and was fabricated as a CPW Meander Line yielding a Return Loss of -14 dB across the IMS band.  The CPW Near-Field Antenna was designed to be less than 5-mm away from the RFID Tag, mitigating excitation of more than one RFID Tag by a Reader.