FR2879753A1 - - Google Patents

Abstract

The invention relates to a missile (1) equipped with a homing device comprising an antenna (7) of a synthetic aperture radar having a main detection direction (70), characterized in that the antenna is arranged in relation to to the missile so that the main direction of the antenna is fixed relative to the missile and offset by a constant angle (beta) with respect to a longitudinal axis (6) of the missile.The invention also relates to a method of guiding Attitude enslavement of the associated missile.

Description

GENERAL TECHNICAL FIELD

  The present invention relates to guided or missile-type ammunition comprising a homing device (AD). Such munitions mainly comprise an inertial unit, a GPS receiver and control surfaces for controlling the trajectory of the ammunition and its roll.

  More specifically, it relates to missile type ammunition comprising a synthetic SAR (Synthetic Aperture Radar) synthetic radar SAR (AD).

  STATE OF THE ART The use of a homing device equipped with a radar in Synthetic Aperture Radar (SAR) mode enables an all-weather metric precision guidance of a munition on a target in a complex environment, and this even in the presence of heavy rainfall.

  Radar guidance in synthetic SAR aperture radar mode is known to those skilled in the art.

  This mainly concerns the use of a lateral-aiming radar provided with a special device for processing backscattered signals, making it possible to improve the geometric resolution of the image along the axis parallel to the trajectory of the carrier of the radar, by superimposing the successive echoes of the same point identified by their Doppler effect. For SAR detection to be possible, a squint angle (or squint angle according to the English terminology generally used by those skilled in the art) is required between the propagation direction of the radar waves and the carrier velocity vector. The movement of the ammunition provides exploitable information comparable to Doppler measurements.

  This is why the SAR detection is advantageously used for an observation of the Earth in carriers of the type of reconnaissance aircraft or artificial satellite. In these cases the wearer has a well-defined and regular trajectory. The squint angle is close to 90, which is the ideal configuration.

  However, the SAR detection induces significant constraints on the trajectory of a missile type munition comprising a homing device (AD) during the acquisition of the radar signal, since the missile must move towards the target it observes.

  FIG. 1 schematically shows the projection in a horizontal plane of the trajectory 5 of a missile 1 towards a target 2 (also called the desired impact point PID).

  Remember that to allow SAR detection, there must be, during the image taking, a minimum squint angle α in the horizontal plane between on the one hand the speed vector 3 of the missile 1 and the other from the radar detection line 4 between the missile 1 and the target 2. Therefore, the velocity vector 3 of the missile 1 can not be oriented towards the target 2 during the imaging.

  However, it is also of course that the target 2 is visible on the one hand by the missile 1 when the image is taken and on the other hand that the missile moves towards the target. The squint angle should not be too big.

  The visualization of the target is complicated by the uncertainties on the relative position between the missile 1 and the target 2. These errors are due to the combination of the designation errors of the target 2 and the missile location errors 1 in position and in attitude.

  The trajectory 5 corresponds to the terminal phase of the missile path between the first radar signal acquisition and the impact. The trajectory 5 can be divided into two parts 51 and 52.

  Part 51 corresponds to the phase during which the missile can take pictures.

  Part 52 corresponds to the phase during which it becomes necessary to reach the estimated position of the target 2. Due to the need for squint, it becomes during this phase difficult or impossible to take images of the estimated target. After part 51, it is almost impossible to take images centered on the estimated target, but it may be interesting to take images by aiming at other points on the ground that are compatible with the target 2's joining by the missile 1. These ground points are offset from the target but if the munition knows the relative position of these points relative to the estimated target, this may improve the impact accuracy.

  During the entire trajectory between the drop and the terminal phase preceding the trajectory 5, it is possible for the navigation errors to derive the estimate of the position of the missile. The possibility of resetting the speed errors of the navigation thanks to the radar signal can be implemented during the part 51.

  The dilemma between the need to target the estimated target and the need for a squint angle trajectory is treatable by the use of a two-axis mobile AD that decouples the missile speed from the orientation of the target. the radar antenna.

  The SAR SAR missiles of the prior art for having both a sufficient squint angle and correct image pickup are complex and expensive.

  PRESENTATION OF THE INVENTION The invention proposes to overcome at least one of the disadvantages of the missiles of the prior art.

  For this purpose, the invention proposes a missile equipped with a homing device comprising an antenna of a synthetic aperture radar having a main direction of detection, characterized in that the antenna is arranged relative to the missile so that the main direction of the antenna is fixed relative to the missile and offset by a constant angle relative to a longitudinal axis of the missile.

  The invention is advantageously completed by the following features, taken alone or in any of their technically possible combination: the angle of offset between the main direction of the antenna and the longitudinal axis of the missile is between 5 and 35, preferably substantially equal to 10; the missile further comprises means able to vary the transmitting / receiving surface of the antenna, so that the detection field of the antenna also varies; the antenna is a slot antenna; the missile further comprises means capable of controlling the control surfaces of the missile in order to modify the roll angle of the missile; The invention also relates to a method for guiding and controlling a missile according to the invention.

  The guidance and control method is characterized in that it comprises a step in which the image is taken by means of the antenna, the antenna being arranged relative to the missile so that the main direction of the antenna is fixed relative to the missile and offset by a constant angle with respect to a longitudinal axis of the missile.

  The method is advantageously completed by the following steps, taken alone or in any of their technically possible combination: the main direction of the antenna of the longitudinal axis of the missile is displaced by an angle substantially equal to the squint angle minimum; the transmitting / receiving surface of the antenna is varied so that the detection field of the antenna also varies; the missile roll angle is varied to obtain a better aim of the target or to refine the slope of the missile; radar detection data is used to reset missile navigation speed errors; radar variance information is used to improve the relative position of the reconstructed radar image relative to the missile; the imaging phase is triggered as soon as the homing device detects a signal whose signal-to-noise ratio exceeds a given threshold; a calibration phase is made for altitude errors between the missile and the ground before the image is taken, in order to optimize the probability of viewing the target in the image; and when the image-taking of the target is no longer possible, images of other points on the ground are taken, the relative position of these points with respect to the estimated position of the target being otherwise known.

  The invention has many advantages.

  A missile comprising a searcher head without axis of movement relative to the missile is reliable and economical.

  2879753 5 The missile is easy to manufacture.

It is easy to guide and control.

PRESENTATION OF FIGURES

  Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which: FIG. 1, already partially commented on , schematically represents the projection in a horizontal plane of the speed vectors of a missile on a trajectory towards a target as well as the axes passing through the missile and the target; - Figure 2 schematically shows the arrangement of a main direction of an antenna in a missile according to the invention; FIG. 3 schematically represents the projection of velocity vectors in a vertical plane containing the missile / target axis for two different slopes; and FIG. 4 schematically represents the projection in the plane transverse to the missile / target axis of the roll for two angles of incidence.

  In the figures, similar elements bear identical reference numerals.

DETAILED DESCRIPTION

  FIG. 2 shows that a missile 1 according to the invention is mainly equipped with a homing device comprising an antenna 7 of a synthetic aperture radar.

  The antenna 7 has a main detection direction 70 corresponding to the direction of the main lobe of the antenna.

  The antenna 7 is arranged relative to the missile 1 so that the main direction 70 of the antenna is fixed on the one hand relative to the missile, and on the other hand offset by an offset angle R constant with respect to a longitudinal axis 6 of the missile 1.

  By construction, the offset angle R is set to a value greater than the minimum squint angle. The missile is guided in attitude so that the antenna is aimed at the estimated target while respecting the squint angle. This induces a trajectory of the missile with a maximum chance of correct correction.

  Thus, the offset angle f3 between the main direction of the antenna 70 and the longitudinal axis 6 of the missile is greater than or substantially equal to the minimum squint angle to obtain a satisfactory resolution image. The angle [3 has a value between 5 and 35, preferably substantially equal to 10.

  In the remainder of this description, we call / 3 the offset angle and / 3H the projection of this angle in a horizontal plane.

  FIG. 2 shows that when the missile is navigating on its trajectory 5, the instantaneous squint angle α is equal to the offset angle f3H plus a skid angle γ of the missile 1 on its trajectory 5. L Skid angle y reflects the fact that the velocity vector 3 of the missile is not exactly coincident with the axis 6 of the missile. pH is the offset angle of the axis 70 of the antenna relative to the axis of the missile in the horizontal plane. It is the part f3H of the angle f3 which participates in the angle of squint, with the skid y for complement.

  The angle is often greater than zero but with low values, which still contributes to the squint. The angle y can of course be zero at given times.

  We then have: a = JJH The roll angle of the missile is controlled so that 13H is substantially equal to R. For this reason, by construction f3 is set to a value greater than the minimum squint angle .

  A method of guiding a missile according to the invention uses guiding and driving laws which enslave the position of the axis 6 of the munition in the space so that the main axis 70 of the antenna is aimed at zone containing target 2 during the image capture phase. This guide mode / aiming control makes it possible both to ensure the presence of the target 2 in the main lobe of the antenna 7 and to maintain the squint angle a during the acquisition of the radar signal.

  FIG. 1, already partially commented, represents an example of a trajectory 5 of a missile 1 towards a target 2. In FIG. 1, the velocity vector 3 is parallel to the axis 6 of the missile 1.

  The trajectory 5 corresponds to the terminal phase of the missile between the first radar signal acquisition and the impact.

  Part 51 corresponds to the phase during which images can be taken.

  Part 52 corresponds to the phase during which it becomes necessary to reach the estimated position of the target 2. Due to the need for squint, it becomes during this phase difficult or impossible to take images of the estimated target.

  The position 11 of the missile 1 corresponds to the first acquisition of the radar signal (image). The position 12 of the missile 1 corresponds to the last acquisition of the radar signal (image) and corresponds to the transition between the first and the second part.

  At a position 11 of the missile 1 on the first part 51 of the trajectory 5, the squint angle α1 is measured between the velocity vector 31 and the axis 41 missile 1 - target 2. The axis 41 coincides with the axis 70. Preferably, during the first part 51 of the trajectory, a coordinate attitude aiming law is used, with control of the roll angle. At a position 12 of the missile 1 before its entry on the second part 52 of the trajectory 5, the squint angle a2 is measured between the velocity vector 32 and the axis 42 missile 1 - target 2. The axis 42 corresponds again to the axis 70.

  Overall, the guidance / steering of the missile is to enslave its attitude so that the direction of the radar antenna is directed at the estimated target, and that the roll of the missile is controlled such that the ammunition meets the minimum squint angle during the part 51 of the terminal trajectory (which leads the munition to follow the trajectory 51).

  Preferably, during the second part 52 of the trajectory, a proportional navigation law is used, for example.

  The angle of approach of the velocity vector with respect to the horizontal is between 20 and 45 for example. The angle of the velocity vector with respect to the vertical at impact is between 70 and 45 for example.

  The guide / control laws are known to those skilled in the art and are not described in more detail in the following description. In addition, other guide laws / steering than those mentioned here are possible.

  The criteria advantageously used as end of pursuit criteria are as follows. The instant squint angle must be less than the minimum squint angle of approximately 10. The viewing angle of the target 2 should be greater than about 45. The true target must be located off the main lobe of antenna 7. The missile must reach the estimated target.

  Furthermore, the missile further preferably comprises means capable of varying the transmitting / receiving surface of the antenna 7.

  The detection field of the antenna also varies. Thus, the surface of the antenna can be reduced at the beginning of the first part of the trajectory 5 to have a very large main lobe. The chances of finding the target 2 are increased, in the case where inaccuracies on the position of the missile 1 relative to the target 2 are important. The inaccuracies may be due to a misidentification of the target, and / or strong misalignment errors of the missile 1 in position and attitude due for example to a jamming of the GPS and a drift of the missile on the trajectory between the release and the first image in position 11.

  Once the target 2 is located, the antenna surface is increased to obtain a finer detection of said target. Several types of SAR antennas are usable, but advantageously, the antenna 7 is a slot antenna. The width of the main lobe of the antenna is for example substantially equal to 7.5 and the radar range at the beginning of search is for example 2500 m.

  It will be recalled that the missile advantageously comprises means capable of controlling the control surfaces of the missile in order to modify, in particular, the angle of roll of the missile on the trajectory. You can get a better aim of the target or refine the slope of the missile.

  The use of the roll angle of the missile 1 makes it possible to increase or refine the area 8 displayed on the ground. The enslavement of the aiming direction of the missile then corresponds to a polar coordinate system whose variable is the roll of the ammunition.

  Figure 3 shows that the roll may also be useful in adjusting a slope of the munition.

  It is possible to refine the slope of the missile by choosing the torque (incidence of the ammunition, roll) to hold the desired squint angle and the desired slope E1 or E2. The choice of the slope facilitates the formation of the trajectory and avoids having to compensate for the vertical errors during the part 52 of the trajectory.

  So we have the constraints: RH + y> minimum squint angle; OH being a function of the torque (R, roll), and the slope being a function of the incidence of the munition.

  Figure 4 shows that the roll d can also be used to control the altitude of the missile and its incidence.

  Roll control techniques and their influences on the trajectory are known to those skilled in the art.

  Advantageously, radar detection data are also used to readjust errors in the navigation speed of the missile.

  Similarly, radar deviation information is used to improve the relative position of the reconstructed radar image relative to the missile.

  Preferably, the image-taking phase is triggered as soon as the homing device detects a signal whose signal-to-noise ratio exceeds a given threshold.

  Advantageously, a altitude error registration phase is performed between the missile and the ground before the image is taken, in order to optimize the probability of viewing the target 2 in the image.

  After part 51, it is no longer possible to take images centered on the estimated target, but it may be interesting to take images by aiming at other points on the ground, compatible with the meeting of the target by the ammunition. These ground points are offset relative to the target but if the munition knows the relative position of these points relative to the estimated target, it improves the impact accuracy.

Claims (1)

11 CLAIMS   1. Missile (1) equipped with a homing device comprising an antenna (7) of a synthetic aperture radar having a main direction of detection (70), characterized in that the antenna is arranged with respect to the missile of so that the main direction of the antenna is fixed relative to the missile and offset by an angle ((i) constant with respect to a longitudinal axis (6) of the missile.   2. Missile according to claim 1, wherein the offset angle between the main direction of the antenna and the longitudinal axis (6) of the missile is between 5 and 35, and preferably substantially equal to 10.   3. Missile according to claim 1 or 2, further comprising means 15 adapted to vary the transmitting / receiving surface of the antenna (7), so that the detection field of the antenna also varies.   4. Missile according to claim 3, wherein the antenna is a slot antenna.   5. Missile according to one of claims 1 to 4, further comprising means adapted to control the control surfaces of the missile to change the roll angle of the missile and also the trajectory of the missile.   6. A method for guiding and controlling a missile equipped with a homing device towards a target, the homing device comprising an antenna (7) of a synthetic aperture radar having a main detection direction (70), characterized in that it comprises a step in which the image is taken by means of the antenna, the antenna being arranged relative to the missile so that the main direction of the antenna is fixed relative to the missile and offset a constant angle ((3) with respect to a longitudinal axis (6) of the missile.   7. The method of claim 6, wherein shifting the main direction of the antenna of the longitudinal axis (6) of the missile by an angle between 5 and 35 and substantially equal to 10.   8. The method of claim 6 or 7, wherein enslaving the attitude of the missile so that the direction of the radar antenna is directed at the estimated position of the target, and that the roll of the missile is controlled as the ammunition respects the angle of minimal strabismus during the shots.   9. Method according to one of claims 6 to 8, wherein the transmitting / receiving surface of the antenna (7) is varied so that the detection field of the antenna also varies.   10. Method according to one of claims 6 to 9, wherein radar detection data is used to reset errors in navigation speed of the missile.   The method according to one of claims 6 to 10, wherein radar discrepancy information is used to improve the relative position of the reconstructed radar image with respect to the missile.   12. The method as claimed in one of claims 6 to 11, in which the image-taking phase is triggered as soon as the autodirector detects a signal whose signal-to-noise ratio exceeds a given threshold.   13. The method as claimed in one of claims 6 to 12, in which a altitude error registration phase is carried out between the missile and the ground before the image is taken, in order to optimize the probability of viewing the target ( 2) in the picture.   14. Method according to one of claims 6 to 13, wherein, when the image of the target is no longer possible, we take images of other points on the ground, the relative position of these points with respect to the estimated position of the target being otherwise known.