| 摘要 |
The invention provides a circuit for analyzing backscatter-modulated RF signals received from a remote transponder to determine whether the transponder is stationary or moving toward the reader or away from it and, if moving, the rate at which the transponder is coming or going. The circuit of the invention can be integrated with existing readers of the type described in U.S. Pat. No. 4,739,328 and requires only a single antenna. In response to the signal received from a transponder, the invention circuit generates three signals, each having a different phase. By analyzing the pattern and frequency of signal state changes in the three signals, the invention can determine the transponder's speed and direction of movement.
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