Radio Frequency Identification (RFID) is becoming an important identification technology in applications such as inventory management, security access, personnel identification, factory automation, automotive toll debiting, and vehicle identification to name just a few. RFID systems utilize an RFID transmitter-receiver unit (usually referred to as a base station or interrogator) to query an RFID transponder or tag which maybe located at a distance from the transmitter-receiver unit. The RFID tag detects the interrogating signal and transmits a response signal containing encoded data back to the receiver.
RFID systems provide identification functions not found in identification technologies such as optical indicia (e.g., bar code) recognition systems. For example, RFID systems may employ RFID tags containing read/write memory of several kilobytes or more. The RFID tags may be readable at a distance and do not require direct line-of-sight view by the reading apparatus (e.g., base station or interrogator). Further, several such RFID tags may be read by the RFID system at one time.
To improve the reliability of RFID tags and to prevent the distribution of RFID tags which do not function properly due to a manufacturing defect, it is desirable to test or screen each RFID tag (or a representative number thereof) during assembly. Tests may be performed on RFID tag components (i.e., wafer sorting, board screening, etc.) to verify operation of the components before they are assembled into the RFID tag. Fully assembled RFID tags may also be tested to verify their operation (e.g., a "field test"). Such field tests allow fully assembled RFID tags to be tested within an RF field rather than probed on a test bench. Thus, field testing has many advantages over component screening alone. For example, circuits whose operation can only be verified in the RF field may be tested. Further, RFID tags typically function only when all components (the RFID circuits, the antenna, the battery, the packaging, etc.) are correctly assembled. Field testing, unlike component screening, allows verification of correct assembly.
Field testing of assembled RFID tags may be accomplished using a base station having a normal read range. The base station generates an RF interrogation field which activates and interrogates the RFID tag to determine if it is functioning properly. At present, only the RFID tag which is being tested is placed within the read range of the base station during the test so that RFID tags which are not being tested are not activated. Inadvertent activation of other RFID tags could cause them to provide return signals which would be received by the base station. These return signals would interfere with the return signal produced by the RFID tag being tested resulting in incorrect test results and, in the case of a read/write tag, undesirable information being written to the tag.
Consequently, it is necessary to physically separate RFID tags during testing by a distance at least as great as the read range of the RFID system. As methods for assembling RFID tags are automated (i.e., via assembly line processes), the time needed to produce a typical RFID tag is decreased to the point where testing of the RFID tags may significantly slow production. Thus, it would be advantageous to provide a method and apparatus for testing RFID tags wherein multiple tags may be sequentially tested while in close proximity to each other (e.g., within the normal read range of the RFID system).