Doppler radar for the detection and localizing of helicopters

• US 5,081,459 A
• Filed: 11/16/1990
• Issued: 01/14/1992
• Est. Priority Date: 11/17/1989
• Status: Expired due to Term

• Current Assignee: Thomson-CSF
• Original Assignee: Thomson-CSF
• Inventors: Guillerot, Jean-Claude, Chanot, Claude, Girou, Thierry, de Grancey, Patrick
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US07/614,135
• Time in Patent Office: 424 Days
• Field of Search: 342/192, 342/90
• US Class Current: 342/90
• CPC Class Codes: G01S 13/5246 post processors for coherent MTI discriminators, e.g. residue cancellers, CFAR after Doppler filters
• CPC Class Codes: G01S 7/415 Identification of targets based on measurements of movement associated with the target

Abstract

This Doppler radar for the detection and localization of helicopters through blade flashes works in a band located between 300 MHz and 20 GHz and identifies the blade flashes by the width of their frequency spectrum and their duration. It uses, at reception, a multilobe antenna associated with several parallel signal processing chains specialized in the detection of helicopters, enabling detection over a widened zone as well as precise localization. Each chain has a phase amplitude detector PAD (10, 10'"'"') followed by a Doppler filter MTI (20, 20'"'"') selecting the wide frequency spectrum, a module computing circuit (30, 30'"'"'), a contrast circuit (40, 40'"'"') eliminating excessively long echoes, a threshold circuit (50, 50'"'"') and a false alarm reduction circuit FAR (60, 60'"'"') eliminating excessively short echoes. The chains lead to a relative bearing computation circuit (100) performing angle measurements when this is possible.

Claims

1. A Doppler radar for the detection and localization of helicopters blade flash echoes, generating at least two interrogation pulses in the duration of a blade flash during the time taken by the transmission antenna lobe to pass through a given direction, having an ambiguous Doppler speed of the order of 450 m/s and comprising:

wideband Doppler filtering means matched with a wide spectrum of the blade flashes, including at least one cell comprising two identical parts operating in parallel, a first part operating on an in-phase component of the instantaneous echo signal for a given distance window and another part operating on a quadrature component of said instantaneous echo signal for a given distance window, each said part comprising a subtractor receiving, at its two inputs, the corresponding component in phase or in quadrature of said instantaneous echo signal for a given distance window, directly at one of its inputs, and by means of a delay circuit at its other input, said delay circuit introducing a delay of two periods of recurrence of the interrogation pulse; and

means for selecting the echoes as a function of their duration, said means for selecting operating on a module of the signal having its components in phase and in quadrature delivered by said wideband Doppler filtering means, including means for eliminating excessively long echoes, said means eliminating echoes with a duration that corresponds to the time taken for the transmission antenna lobe of the antenna to pass through a fixed direction, and means for eliminating excessively short echoes with a duration that does not go beyond a period of recurrence of the interrogation pulse.

2. A radar according to claim 1 wherein said wideband Doppler filtering means includes two identical cells which are cascaded, each said cell comprising two identical parts operating in parallel, the one on the in phase component of the instantaneous echo signal for a given distance window and the other on the quadrature component of said instantaneous echo signal for a given distance window, each part comprising a subtractor receiving, at its two inputs, the corresponding component in phase or quadrature of said instantaneous echo signal for a given distance window, directly at one of its inputs, and by means of a delay circuit at its other input, said delay circuit introducing a delay of two periods of recurrence of the interrogation pulse.

3. A radar according to claim 1, comprising at least two reception channels, antenna patterns of which are offset in relative bearing and partially overlapping, and a relative bearing computation circuit performing an angle measurement on the basis of the in-phase and quadrature components of the instantaneous echo signals on the two reception channels when they occur simultaneously, wherein said radar further comprises a device for tracking based on discontinuous information, said device associating, with the directions of the detected targets, angular correlation window widths and information on detection quality, for improving target designation precision on the basis of different intercepted blade flashes corresponding to one and the same helicopter.