INTERMODULATION MITIGATION TECHNIQUE IN AN RFID SYSTEM

摘要

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.

主权项

1. A reader for supplying an interrogation signal to a transponder at a first frequency and receiving a response signal from the transponder at the first frequency, while mitigating interference effects from an interfering signal at a second frequency, the reader comprising:
an antenna for receiving the response signal from the transponder; a detector, in electrical communication with the antenna, for detecting and outputting a baseband analog signal representing the response signal received by the antenna; a frequency-selective filter, in electrical communication with the detector to receive the baseband analog signal output by the detector, for performing frequency-selective filtering of the baseband analog signal to output an analog signal with reduced interference; and signal processing circuits, in electrical communication with the frequency-selective filter to receive the analog signal with the reduced interference, for performing signal processing on the analog signal with the reduced interference to extract information from the analog signal with the reduced interference.