Constant false alarm rate with low probability of false alarms

A method of processing range cells in radar echo signals produced by a radiating source, comprising the steps of:

• (a) identifying a predetermined number of the range cells located a predetermined distance from a cell of interest in a straddle window for each of lead and lag windows;
• (b) identifying the predetermined number of the range cells, including the cell of interest, for the straddle window;
• (c) determining a power level for each of the range cells;
• (d) excluding from further calculations all of the range cells in the lead, lag and straddle windows having a saturated power level and all of the range cells containing at least a predetermined amount of interference from another radiating source;
• (e) excluding, from the range cells remaining in each of the lead, lag and straddle windows after said excluding in step (d), at least one high power range cell having the power level higher than the power level of any other of the range cells remaining;
• (f) summing, for each of the lead, lag and straddle windows, the power level of each of the range cells remaining therein after said excluding in steps (d) and (e) to produce a power sum;
• (g) applying a mean level adjustment value to the power sum of each of the lead, lag and straddle windows to produce the mean level thresholds;
• (h) selecting one of the mean level thresholds produced in step (g) as a target detection threshold;
• and
• (i) comparing the cell of interest with the target detection threshold to determine whether the cell of interest contains a target.

An apparatus for processing range cells in radar signals, comprising:

• identification means for identifying a cell of interest and a lead window, a lag window and a straddle window, associated therewith;
• calculation means for calculating mean level thresholds, each mean level threshold derived from the range cells in one of the lead, lag and straddle windows;
• selection means for selecting one of the mean level thresholds, calculated by said calculation means, as a target detection threshold, said selecting means comprising:
• lead/lag selection means for selecting one of the mean level thresholds of the lead and lag windows as a greatest side mean level threshold if larger than the mean level threshold of the other of the lead and lag windows;
• and
• straddle/side selection means for selecting the mean level threshold of the straddle window as the target detection threshold if the mean level threshold of the straddle window is larger than the greatest side mean level threshold by less than a straddle override threshold amount and otherwise selecting the greatest side mean level threshold as the target detection threshold;
• and
• comparison means for comparing the cell of interest with the target detection threshold to determine whether the cell of interest contains a target.