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Device for the detection of the signals of transponders interrogated by a secondary radar in the presence of multiple-path phenomena

  • US 5,063,386 A
  • Filed: 10/23/1990
  • Issued: 11/05/1991
  • Est. Priority Date: 11/03/1989
  • Status: Expired due to Term
First Claim
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1. A device for detecting transponder signals generated by transponders interrogated by a secondary radar in the presence of multiple-path phenomena, wherein each of said transponder signals is formed by a pulse train arranged in a determined format with formatting pulses that identify the position of data pulses, wherein said device comprises:

  • a format identification circuit for identifying the format of a transponder signal including means for detecting said formatting pulses contained in a reception signal;

    a time base synchronized by said format identification circuit and including means to generate timing signals for identifying time intervals in said reception signal that may possibly be occupied by data pulses of a transponder signal, and for identifying a middle of said time intervals and zones centered on said middles of said time intervals;

    a presumed pulse determining circuit for determining presumed data pulses in said reception signal, said presumed pulse determining circuit having its timing rate set by said time base and including means to set up a correlation between a first, a second and a third sample of respective levels of said reception signal, wherein said first sample is taken at said middle of each said time interval that may possibly be occupied by a data pulse of a transponder signal, and said second sample and said third sample are taken during each said time interval at instants surrounding an instant when said first sample is taken, said presumed pulse determining circuit further including means to generate a weighting coefficient which is associated with each level determined by said first sample, and represents a probability of the presence of a data pulse in said time interval that may possibly be occupied by a data pulse of a transponder signal, wherein a value of said weighting coefficient corresponds to a level of correlation of said first sample, said second sample and said third sample;

    a circuit for determining a reference level of said reception signal, thereby determining a reference amplitude level of pulses for each of the signals of said transponder whose format has been identified in said reception signal by said format identification circuit, said circuit for determining a reference level having its timing rate set by said time base and including means to select said reference level of said reception signal based on a maximum value of a frequency of occurrence of a level of said reception signal taken in the middle of each said time interval that may possibly be occupied by data pulses of a transponder signal wherein each said level considered is weighted by the weighting coefficients prepared by said circuit for determining presumed data pulses; and

    ,a circuit for detecting data pulses in said reception signal for each transponder signal whose format has been identified in the reception signal by said format identification circuit, said circuit for detecting data pulses including means for the recognition of a data pulse whenever a level of said reception signal at the middle of a time interval that might possibly be occupied by a data pulse belongs to a range of values centered on said reference level determined by said circuit for determining the reference level of the reception signal.

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