| 摘要 |
An interrogating station includes apparatus for transmitting a frequency modulated signal having a relatively low modulation rate to a plurality of uniquely tagged targets and for receiving therefrom a further modulated reply signal at a relatively high modulation rate, a mixer for mixing the transmitted and reply signals, to produce range modified tag modulation frequencies for all tagged targets, a voltage controlled filter for selectively passing the mixer output signal corresponding to any one of the tagged targets and a sweep and hold circuit for providing the frequency selecting voltage to the filter. The frequency selecting voltage is caused to change when no signal is passed by the filter and is fixed at the voltage corresponding to the signal frequency when a signal is passed by the filter. The magnitude of the frequency selecting voltage when fixed is used to determine the identity of the tag and the signal passed by the filter is further processed to determine range and/or range rate of the associated target.
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