Digital time-delay beamformer for sonar systems

A method of beamforming a plurality of digital beam output signals in a sonar receiver having a multi-element symmetrical transducer array wherein each beam output signal has a direction related to at least one respective directional element in the transducer and the total number of samples to be taken is given as:

• Z=Mn
• where M is the total number of beams to be formed and n is the number of sample-sets desired to form any beam m, said method comprising the steps of:
• (A) sampling each i element symmetrically disposed to the left and right of the at least one directional element for beam m during each consecutive sampling interval, z, where i is defined as 0.ltoreq.i.ltoreq.n-1, z is defined as 0.ltoreq.x.ltoreq.Z, and m is given by:
• ##EQU10##
• where di is the time delay of the i.sup.th sample to the right and left of beam m with respect to its first sample expressed as an integer number of sampling intervals z and di is chosen such the Remainder [di/n] has a different integer value for each value of i, and i is determined from the Remainder [di/n] which remainder is equal to Remainder [z/n];
• (B) summing together each sample taken from i elements to the right and left of beam m to form a sample-set;
• (C) converting the sample-set from analogue to digital format;
• (D) multiplying the digital sample-set with weighting factors;
• (E) adding each digital sample-set to its corresponding partial sum of digital sample-sets and storing this partial sum;
• and
• (F) forming the beam from the partial sum from each beam when all n sample-sets for beam m have been summed.

A digital beamformer for a sonar receiver having a multi-element symmetrical transducer array wherein each beam output signal has a direction related to at least one directional element in the transducer and the total number of samples taken by the beamformer is given as:

• Z=Mn
• where M is the total number of beams to be formed and n is the number of sample-sets desired to form any beam m, said beamformer comprising:
• control means for sampling each i element symmetrically disposed to the left and right of the at least one direction element for beam m during each consecutive sampling interval, z, where i is defined as .ltoreq.0i.ltoreq.n-1, z is defined as .ltoreq.0z.ltoreq.Z, and m is determined by:
• ##EQU11## where di is the time delay of the i.sup.th sample to the right and left of beam m with respect to its first sample expressed as an integer number of sampling intervals z and di is chosen such that Remainder [di/n] has a different integer value for each value of i, and i is determined from the Remainder [di/n] which remainder is equal to Remainder [z/n];
• a summer for summing the samples taken from each i element to the right and left of beam m to form a sample-set;
• an A/D converter for converting the sample-set from analogue to digital format;
• a multiplier for weighting the digital sample-set;
• and
• a digital adder and memory for adding each digital sample-set to its corresponding partial sum of digital sample-sets, said memory including means for forming the beam from said partial sum when all n sample-sets for their respective beam have been summed.