| 摘要 |
A chirped backscatter filter 10 compares a received signal (RSIG) to a reference signal related to a transmitted signal (TSIG) and removes from RSIG the frequency component which is equal to TSIG in frequency. This removed frequency component corresponds to the frequency of the transmitter backscatter radiation. The filter of the invention adds a frequency offset (fn) to both RSIG and TSIG in mixers 12 and 14 before substracting one from the other in mixer 22. Thus, equal frequency components in both RSIG and TSIG, such as the backscatter radiation frequency component of RSIG, will equal fn. The frequencies resulting from this subtraction are thereafter passed through a notch filter 24 which is centered on fn and which passes all frequency components except fn. The output of the notch filter thus no longer has a frequency component associated with the backscatter frequency component. The loss of the RSIG phase reference due to the phase reference between the RSIG and TSIG modulation envelopes being destroyed during the backscatter filtering process is therafter compensated for by adding TSIG to the filtered difference frequency component, thereby reestablishing the phase relationship of the original RSIG frequency components minus the backscatter frequency component.
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