Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With beam steering – scanning – or focussing
Patent
1979-08-29
1981-06-16
Farley, Richard A.
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With beam steering, scanning, or focussing
343100SA, 367105, 367900, 367904, 367905, G01S 380
Patent
active
042741483
ABSTRACT:
There is described a digital sonar receiver having a novel beamformer, own doppler nullifier (O.D.N.), and adaptive time varied gain controller. The beamformer interrogates a multi-element transducer by utilizing an interleaved sampling scheme which samples the elements in the trandsducer array sequentially, in such a fashion that continuous, uniformly spaced samples are obtained. The samples are subsequently converted into digital format, weighed and summed. The O.D.N. eliminates the own ship's doppler effect on the beam output signal resulting in a half beam output signal representative of the target doppler. The O.D.N. offsets the frequency of the beam output signal and a digital generated signal representative of the own ship's doppler. The O.D.N. multiplies these two offsetted signals resulting in a signal lying in each of the sum and difference frequency bands for which the signal lying in the difference frequency band corresponds to the target doppler. The adaptive time varied gain controller varies the gain of preamplifiers at the input of the sonar receiver to be inversely proportional to the momentary average reverberation level of the medium in which the receiver operates. The adaptive time varied gain control apparatus initially sets the gain of the preamplifiers to be inversely proportional to a standard reverberation curve during the first ping-cycle and subsequently updates the gain of the preamplifiers during each successive ping-cycle by computing a gain correction from the average value of a predetermined number of beam output signals.
REFERENCES:
patent: 4107685 (1978-08-01), Martin et al.
Farley Richard A.
Fox Robert H.
Oldham Edward H.
Westinghouse Canada Limited
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