Method and system for neutralizing the effect of vibrations in a rotary-wing aircraft for airborne doppler radar

Patent metadata

Field	Value
Publication number	US-11320531-B2
Application number	US-201916716184-A
Country	US
Kind code	B2
Filing date	Dec 16, 2019
Priority date	Dec 20, 2018
Publication date	May 3, 2022
Grant date	May 3, 2022

Abstract

A method for active neutralization of the effect of the vibrations of a rotary-wing aircraft for a monostatic Doppler radar includes a first step of measuring and temporally extrapolating the vibration modes at the transmitting-receiving radar antenna, using a 3-axis vibration sensor, fixed to the antenna and near the phase centre of the antenna; then a second step of estimating the expected movements of the transmitting-receiving antenna or of the first transmitting antenna and the second receiving antenna; then a third step of compensating the expected movements of the transmission radar antenna in the transmission chain or in the reception chain of the radar transmitter, wherein the projection of the movement vector of the phase centre O on an aiming direction is calculated to determine the value of the compensation phase shift to be applied.

First claim

The invention claimed is:

1. A method for active neutralization of an effect of vibrations of a rotary-wing aircraft for a monostatic Doppler radar or a bistatic Doppler radar, the monostatic Doppler radar comprising:
a transmitting-receiving radar antenna sharing a same phase centre O, and a radar transmission chain, connected to a transmission input of the transmitting-receiving radar antenna of the monostatic Doppler radar; and
a radar reception chain, connected to a receiving output of the transmitting-receiving radar antenna of the monostatic Doppler radar, or the bistatic Doppler radar comprising:
a first transmitting radar antenna having a transmission phase centre O 1 and a second receiving radar antenna, remote from the first transmitting radar antenna, having a reception phase centre O 2 ;
a radar transmission chain, connected to a transmission input of the first transmitting radar antenna of the bistatic Doppler radar; and
a radar reception chain, connected to a reception output of the second receiving radar antenna of the bistatic Doppler radar; and
the active neutralization method being implemented by an active neutralization system comprising:
a three-dimensional vibration sensor for each of the first transmitting radar antenna and the second receiving radar antenna, fixed to said first transmitting radar antenna and the second receiving radar antenna, and at its phase centre O, O 1 , O 2 , or a single three-dimensional vibration sensor, shared by the first transmitting radar antenna and the second receiving radar antenna and at a phase centre O 1 , O 2 , when the first transmitting radar antenna and the second receiving radar antenna are strongly coupled mechanically; and
a device for estimating a movement of each three-dimensional vibration sensor and for neutralizing their movement, the active neutralization method being wherein it comprises:
a first step of measuring and temporally extrapolating vibration modes at the transmitting-receiving radar antenna or at the first transmitting radar antenna and at the second receiving radar antenna at their associated phase centre O, O 1 and O 2 ; then

a second step of estimating expected movements of the transmitting-receiving radar antenna or of the first transmitting radar antenna and of the second receiving radar antenna; and then
a third step of compensating for the expected movements of the first transmitting radar antenna in the radar transmission chain or of the second receiving radar antenna in the radar reception chain.

2. The active neutralization method according to claim 1 , wherein:
the third step of compensating for the expected movements of the phase centre O;
O 1 , O 2 comprises a fourth step of calculating at least one projection of movements in an aiming direction of the transmitting-receiving radar antenna or of the second receiving radar antenna; and
a fifth step of determining at least one compensation phase shift corresponding to an aiming direction.

3. The active neutralization method according to claim 1 , wherein, for each measurement sensor:
the first step of measuring and temporally extrapolating the vibration modes of the three-dimensional vibration sensor comprises, executed successively, a sub-step of band-pass filtering of measured triaxial acceleration signals, a sub-step of complex frequency analysis of the vibration modes, and a sub-step of interpolation of acceleration profiles by image band filtering, and temporal extrapolation to immediately subsequent instants; and
the second step of estimating the expected movements comprises, executed successively, a sub-step of integration of accelerations into velocities and a sub-step of integration of the velocities into the expected movements.

4. The active neutralization method according to claim 1 , further comprising a step of learning for each boresight axis, executed on the ground or in flight on known fixed beacons, and configured to provide a model for refining corrections to be applied in the radar transmission chain or in the radar reception chain, which allows for variations of vibrations correlated with an engine speed and a velocity of the rotary-wing aircraft.

5. The active neutralization method according to claim 1 , wherein:
the monostatic Doppler radar is a monostatic radar comprising a transmitting-receiving radar antenna with the same phase centre O, and
the active neutralization system comprises a three-dimensional vibration sensor, fixed to the transmitting-receiving radar antenna and at its phase centre; and
the vibration modes of the transmitting-receiving radar antenna are measured by the three-dimensional vibration sensor in the first step of measurement and temporal extrapolation; and
the expected movements of the phase centre O of the transmitting-receiving radar antenna are estimated in the second step; and
the expected movements of the phase centre O of the transmitting-receiving radar antenna are compensated during a generation of a waveform in the radar transmission chain,
by calculating a projection of the expected movements of the phase centre O on an aiming direction of the transmitting-receiving radar antenna, then
by determining a compensation phase shift Δφ corresponding to the aiming direction, equal to twice an amplitude dp of the expected movements divided by a wavelength λ of a radar signal carrier.

6. The active neutralization method according to claim 5 , wherein:
a step of learning for each boresight axis is executed on the ground or in flight on known fixed beacons, the learning step being configured to provide a model for refining corrections to be applied during a generation of a waveform in the radar transmission chain which allows for variations of vibrations correlated with an engine speed and a velocity of the rotary-wing aircraft.

7. The active neutralization method according to claim 5 , comprising a step of detecting signals from jammers that are not correlated with vibrations of the rotary-wing aircraft, the step of detecting the signals from jammers being implemented in parallel with compensation for a radar echo received, correlated with movements of the first transmitting radar antenna or the second receiving radar antenna.

8. The active neutralization method according to claim 1 , wherein:
the bistatic Doppler radar is a bistatic radar comprising a first transmitting radar antenna having a transmission phase centre O 1 and a second receiving radar antenna, remote from the first transmitting radar antenna and having a reception phase centre O 2 ;
the active neutralization system comprises a first three-dimensional vibration sensor, fixed to the first transmitting radar antenna and at its transmission phase centre O 1 , and a second three-dimensional vibration sensor, fixed to the second receiving radar antenna and at its reception phase centre O 2 ;
the vibration modes of the first transmitting radar antenna and of the second receiving radar antenna respectively are measured, in the first step of measurement and temporal extrapolation, by the first three-dimensional vibration sensor and by the three-dimensional second vibration sensor respectively; and
the expected movements of the transmission phase centre O 1 of the first transmitting radar antenna and the expected movements of the reception phase centre O 2 of the second receiving radar antenna are estimated in the second step; and
the expected movements of the transmission phase centre O 1 and of the reception phase centre O 2 are compensated during a generation of a waveform in the radar transmission chain,
by calculating a projection of the expected movements of the transmission phase centre on an aiming direction of the first transmitting radar antenna and the projection

Assignees

• Thales Sa

Inventors

• Garrec Patrick
• Cottron Rodolphe
• Veyrac Yoan

Classifications

• G01S13/60

  wherein the transmitter and receiver are mounted on the moving object, e.g. for determining ground speed, drift angle, ground track (G01S13/64 takes precedence) · CPC title

• G01S13/003 Primary

  Bistatic radar systems; Multistatic radar systems · CPC title

• G01S13/90

  using synthetic aperture techniques {, e.g. synthetic aperture radar [SAR] techniques} · CPC title

• G01S7/023

  Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques (auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36) · CPC title

• G01S7/4026 Primary

  Antenna boresight · CPC title