US 4,398,274 AGranted

Within-pulse doppler scanning

AssigneeThe Secretary of State for Defence in Her Britannic Majesty's Government of the United Kingdom of Great Britain and Northern Ireland

InventorPornchai Chotiros

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Abstract

The invention concerns a method and apparatus for detecting Doppler-shifted waveforms in electrical signals. A replica is derived from the waveform prior to Doppler shift and stored in a storage device as a non-uniform profile having progressively increasing distortion along its length. The replica storage device is connected non-uniformly to correlating means such that the correlated replica profile has a degree of uniform distortion varying with storage position simulating varying degrees of Doppler shift. The electrical signal is uniformly correlated with the replica while the replica storage position is varied. An output signal is generated indicating correlation variation. The electrical signal is repetitively sampled and a maximum correlation is detected when the waveform occurs in the electrical signal with a degree of Doppler shift matching that simmulated by the correlated replica. The invention also includes apparatus for performing the method.

Claims19

Dependent claims

A method of detecting a Doppler-shifted waveform in an electrical signal including the steps of:

(a) generating a replica signal derived from the waveform prior to Doppler shift;
(b) sampling the replica signal at intervals changing in accordance with a first geometric progression;
(c) storing the replica samples in successive storage positions of a first storage means whereby the profile of the stored replica samples has a progressively increasing distortion along its length compared to the replica signal;
(d) storing a sample of the electrical signal in a second storage means by sampling means arranged for sampling at uniform sampling intervals;
(e) correlating the samples of the electrical signal at uniformly spaced storage positions in the second storage means with stored samples of the replica signal profile at storage positions in the first storage means selected such that the ratio of the numbers of storage positions between successive correlated samples in said first storage means is substantially a geometrical progression in the same sense as said first geometric progression so as to cancel the progressively increasing distortion of the replica signal profile;
(f) performing a correlation scan by moving the stored replica signal profile through a range of stored positions;
(g) deriving a correlation output signal indicating degree of correlation between the correlated signals during a scan;
and
(h) repeating steps (d) to (g) to build up and subsequently refresh a uniform stored profile of the electrical signal while performing successive correlation scans.

6 more elements

Apparatus for detecting a Doppler-shifted waveform in an electrical signal including:

(a) means for generating a replica signal derived from the waveform prior to Doppler shift;
(b) means for storing samples of the electrical signal comprising a first storage device having a plurality of storage positions and a sampling clock connected to the storage device and arranged for sampling the electrical signal at uniform sampling intervals;
(c) means for storing samples of the replica signal comprises a second storage device having a plurality of storage positions and a sampling clock connected to the second storage device and arranged for sampling the replica signal at intervals changing in accordance with a first geometric progression such that the profile of the stored replica samples has a progressively increasing distortion along its length compared to the replica signal;
(d) scanning means connected to the second storing device for cyclically moving the stored replica signal profile through a range of storage positions;
and
(e) correlating means including an array of multipliers connected to respective selected storage positions of the first and second storage devices, the connected storage positions being uniformly spaced in the first signal storage device and being spaced in the second replica profile storage device such that the ratio of the numbers of storage positions between successive multiplier connections to said first storage device is substantially a geometric progression in the same sense as said first geometric progression so as to cancel the progressively increasing distortion of the replica signal profile.

3 more elements

Dependencies are inferred from the claim text.