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Doppler complex FFT police radar with direction sensing capability

  • US 6,646,591 B2
  • Filed: 11/07/2001
  • Issued: 11/11/2003
  • Est. Priority Date: 07/21/1998
  • Status: Expired due to Term
First Claim
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1. A method for carrying out a stationary, strongest target search for targets travelling in one selected direction only in a Doppler police radar having a quadrature front end receiver that generates two quadrature shifted channels of digital sample data from Doppler shifted reflected radar signals, and having at least a single antenna, said method for searching comprising the steps of:

  • acquiring a buffer full of digital sample data for each said quadrature shifted channel;

    applying a Hamming window or other DFT window to the data to minimize end effects;

    performing a complex Fast Fourier Transform (FFT) on said sample data from said buffer for reach said quadrature shifted channel using a sample from one buffer as the real axis magnitude and a paired sample from the other buffer as the imaginary axis magnitude of each complex number input vector to said complex FFT so a to generate a Fourier spectrum with a first half with frequency components that define the speed of only approaching targets and a second half with frequency components that define the speed of only receding targets;

    searching the appropriate half spectrum defining speeds of targets travelling in the selected direction relative to said police radar for one or more frequency component(s) defining the speed of the strongest magnitude target travelling in a selected direction corresponding to the direction of targets the speeds of which re defined by the frequency components in said half spectrum searched by said searching step and converting the frequency of said component(s) to a speed and displaying said speed.

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