Communications – electrical: acoustic wave systems and devices – Echo systems – Distance or direction finding
Patent
1992-10-06
1993-10-05
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Echo systems
Distance or direction finding
367100, 367105, G01S 1500
Patent
active
052511863
ABSTRACT:
A device is provided for processing an echo received by an array of N receiving elements from a target at range R ensonified by an LFM signal of bandwidth B transmitted for a duration T. The device receives each elements output f.sub.n (t) over the elements total receiving time and selects time window element outputs f'.sub.n (t), which are discrete portions of f.sub.n (t), each time window extending from an arbitrary initial time T.sub.0 to time T.sub.f and is spaced from T.sub.0 no more than T and, if there is a target within the window, an echo is received at time T.sub.n. Further the device produces element frequency difference outputs g.sub.n (t) from the frequency difference between a replica of at least a portion of the transmitted LFM signal and the time window element outputs f'.sub.n (t), the outputs g.sub.n (t) being tones with frequencies directly proportional to the time T.sub.n of the target from the time T.sub.0 so that the target range R=(c/2)(T.sub.0 +T.sub.n)+.DELTA.R.sub.n, where c is the speed of sound, and .DELTA.R.sub.n is the distance by which R exceeds each element's range to the target. With this arrangement range and bearing of the target from the array can be more easily ascertained by dealing with parameters of cw, rather than broadband signals. This arrangement facilitates the application of adaptive beamforming techniques in a manner similar to their application to narrowband signals.
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"The Use of Fast Fourier Transform for the Estimation of Power Spectra: A thod Based on Time Averaging Over Short, Modified Periodograms" by Peter D. Welch, pp. 70-73.
"Adaptive Beamforming for Coherent Signals and Interference" by Tie-Jun Shan and Thomas Kailath, Fellow, IEEE, pp. 527-536.
Fendelman Harvey
Keough Thomas Glenn
Pihulic Daniel T.
The United States of America as represented by the Secretary of
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