US 4,839,652 AGranted

Method and apparatus for high speed digital phased array coherent imaging system

AssigneeGeneral Electric Company

InventorsMatthew O'Donnell, William E. Engeler, Thomas L. Vogelsong, Steven G. Karr, Sharbel E. Noujaim

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Abstract

A method for generating an output stream of digital data words, with each data word representing the amplitude of an analog signal at one of a multiplicity F samples each second and with substantially equally spaced time intervals T therebetween, is obtained from a digital baseband demodulation system used for array beam forming. A data stream, formed of interleaved ADC output digital data words acquired from a set of converters, is at a rate of F total samples/second. Subsequent digital demodulation, filtration, and decimation provides digital output signals which need less delay resolution prior to the formation of coherent sum signals, thereby reducing overall channel memory requirements. The output baseband data stream has enhanced dynamic range, thereby reducing the ADC bit density requirements.

Claims16

Dependent claims

A method for digitally forming a beam of energy substantially focussed at a range R at an angle .theta. with respect to a transducer array having a plurality N of transducers, each in a separate channel and receiving a portion of the beam energy, comprising the steps of:

(I) separately generating for each j-th channel, where 1.ltoreq.j.ltoreq.N, a stream of digital baseband data signals comprised of consecutive data words occurring at a first rate of F' samples per second with a substantially equally spaced first time interval T' between any sequential pair of data words, with each digital baseband data signal stream representing the amplitude and phase for an analog signal, from the associated j-th transducer, sampled at a second rate of F samples per second, where F is greater than F', and with a substantially equally spaced second time interval T between any sequential pair of samples, where T is less than T', by the steps of:
(a) separately converting the amplitude of that j-th analog signal to a stream of digital data words each responsive to a sample strobe S signal at a maximum conversion rate equal to the second rate of F samples per second;
(b) separately digitally demodulating the stream of data words for that j-th channel to obtain a stream of j-th channel baseband data words;
(c) separately digitally lowpass filtering each j-th channel stream of baseband data words;
and
(d) separately decimating the j-th channel stream of filtered data words by a selected decimation factor D, which is substantially constant with respect to both time and channel number, to obtain a j-th channel output stream of data words each occurring at the reduced first rate of F' samples per second;
(II) separately delaying each j-th channel output data word stream by a selected channel delay time interval, which may be different for each different channel, responsive to the predetermined range R and angle .theta.;
and
(III) coherently summing all N of the separately-delayed decimated output data word streams to obtain a single set of digital baseband data words representing at least amplitude information from the formed energy beam.

6 more elements

Apparatus for digitally forming a beam of energy substantially focussed at a range R and angle .theta. with respect to a transducer array having a plurality N of transducers, each in a separate channel and receiving a portion of the beam energy, comprising:

(I) means for separately generating for each j-th channel, where 1.ltoreq.j.ltoreq.N, a stream of digital baseband data signals comprised of consecutive data words occurring at a first rate of F' samples per second with a substantially equally spaced first time interval T' between any sequential pair of data words, with each digital baseband data signal stream representing the amplitude and phase of an analog signal, from the associated j-th transducer, sampled at a second rate of F samples per second, where F is greater than F', and with a substantially equally spaced second time interval T between any sequential pair of samples, where T is less than T' and including:
(a) means for separately converting the amplitude of that j-th analog signal to a stream of digital data words each responsive to a sample strobe S signal at a maximum conversion rate equal to the second rate F of samples per second;
(b) means for separately digitally demodulating the stream of data words for that j-th channel to obtain a stream of j-th channel baseband data words;
(c) means for separately digitally lowpass filtering each j-th channel stream of baseband data words;
and
(d) means for separately decimating the j-th channel stream of filtered data words by a selected decimation factor D, which is substantially constant with respect to both line and channel number, to obtain a j-th channel output stream of data words each occurring at the reduced first rate of F' samples per second;
(II) means for separately delaying each j-th channel output data word stream by a selected channel delay time interval, which may be different for each different channel, responsive to the predetermined range R and angle .theta.;
and
(III) means for coherently summing all N of the separately-delayed decimated output data word streams to obtain a single set of digital baseband data words representing at least amplitude information from the formed energy beam.

6 more elements

Dependencies are inferred from the claim text.