FR2717586A1 - Tracking radar system with laser guidance - Google Patents

Abstract

The radar tracking system includes a pedestal (1) supporting a head (2) which may be rotated by a motor (3) and gear system (4). This allows exploration in through the range of azimuth. The head contains a receiver tube (5) pivoting under the control of a further motor (6) to allow exploration of the range of elevation. A YAG laser (7), mounted on one side of the pedestal projects its light on to two mirrors (8, 9), one being mounted on the pedestal and one mounted on the head, turning when the head turns. A mirror which dissects the beam, and deflector mirrors are mounted in the lower part of the head, with a mosaic detector (15) mounted on the top of the head.

Description

 The present invention relates to tracking systems with an optical auxiliary device.

 To date, tracking systems, such as those for tracking: aircraft, have been based on methods using very short waves, such as ultra-short wave radar. The latter constitutes a very or point and very powerful instrument, suitable for this purpose. However, under certain circumstances, there are limitations which the present invention proposes to overcome.

If we consider, by hypothesis, a surface-to-air control system, at low angle, of the line of sight of a missile system using a laser radar as a differential tracking device. The use of a laser radar provides four main advantages
1) the use of a narrow beam laser illuminator eliminates the in
conveniences of parasitic signals coming from the ground and the reflexi
multiple waves accompanying the ultra-short wave radar.

2) the system offers very high security against detection by
enemy positions other than that of the target.

3) the system eliminates the difficulties arising from an overload
of the radio spectrum and interference in
resulting systems.

 4) the laser system is insensitive to known methods of scrambling.

 Taking these factors into account, it is desirable that the functions of target target and missile control are also reliable and free from interference. These requirements can be met or by means of a passive infrared surveillance system and an associated laser missile control device.

 The present invention provides a tracking system comprising organs for producing a pulsed beam of intense optical radiation in a well-defined direction, organs for collecting radiation from the visible scene in the direction of irradiation of the optical radiation beam. intense, detector bodies comprising at least two detector elements sensitive to optical radiation with a limit between the two detector elements, bodies for forming an image of the scene captured by the detecting ergenes.

means for cyclically varying the position of the image on the detector element in a direction of which at least one component is perpendicular to the limit and means for counting the number of pulses of optical radiation reflected by an object in the scene explored and detected by each of the detector elements.

 Preferably, the detection members comprise a plurality of detector segments arranged in a row.

 The tracking system may further comprise interval synchronization members separating the generation of an intense optical radiation pulse and the reception of an optical radiation pulse reflected by any object, a first counting unit counting the optical radiation pulses reflected by an object at a distance such that said time interval has a value within a first range of values, and a second counting unit enumerating the optical radiation pulses reflected by a finding object at a distance such that said time interval has a value within a second value range.

 The expression "optical radiation" designates visible radiation as well as infrared radiation.

 In one embodiment of the invention, a target and a defensive missile are separately illuminated by two laser beams. The lights returned by the target and by the missile are concentrated on a mosquito detector comprising twenty five separate elements arranged five by five. The difference separating the two received images represents an angular differential error between the trajectory of the target and the line of sight of the missile. This difference is transmitted to the missile guidance system until the images of the target and the missile scramble. As the target moves in space, the laser illuminating the target, as well as the detector, must move to follow the target and keep the image in the field of vision of the detector.

 A precise method for determining the position of the image on the detector is to nute the image received in the detector, that is to say to make describe a circle to the image. If the laser is with implusions, the nutée image will be a circle of points each of which will correspond to a received laser pulse. By counting the number of points in each panel of the detector, we can determine the position of the center of the circle.

The invention is described below in detail by means of a preferred, non-limiting example, of embodiment shown in the accompanying drawings in which; - Figure 1 is an elevational view, partially in section, of a device for
laser tracking, servo-controlled; - Figure 2 is a schematic axial section of the receiving optical system of the
device of Figure 1; - Figure 3 is an elevational view of a mosaic detector head; - Figure 4 is a schematic perspective view of the Connex3cns starting from the head
the detector; - Figures 5a and 5b are assembly drawings of a device for processing
information received by a tracking device; - Figure 6 is a truth table; and - Figure 7 is a diagram showing the derivation of an azimuth signal from ci
corn.

 As shown in Figure 1, the laser tracking device has a foot 1 on which a head 2 is rotatably mounted. The head 2 is rotated to explore in azimuth by a motor 3 and a gear 4. In the head 2 is disposed a receiving tube 5, pivotally mounted in said head for exploring in elevation under the control of a motor d elevation 6.

 On one side of the foot is mounted a yttrium-aluminum-garnet laser 7 projecting its light on two mirrors 8, 9 I'one mounted in the foot and the other in the head and arranged to rotate in elevation when l 'the receiver tube is rotated. A beam dissecting mirror and deflecting mirrors, not shown, are mounted at 10.

 Inside the receiving tube 2 (Fig. 2) is placed a mirror 11, with a focal length of 60 cm, concentrating the laser light received on a small nutator mirror 12 hampered in rotation by a small motor 13. The plane of the mirror nutator 12 is inclined on the axis of the motor 13 so as to make the received light describe the shape of a cone passing through the lens 14 and forming a circle of light on a mosque detector 15 shown, on a larger scale, on Fig. 3. The marking mirror is adjusted so as to produce a circle of dots with a diameter corresponding approximately to the width of one of the detector panels.

 A pilot clock (not shown) generates signals driving, by dividers and power amplifiers, the nutator motor as well as a framing clock, also by a separate divider, to drive the laser clock. By adjusting the dividers feeding the nutator motor appropriately, the laser will pulsate at the frequency required by nutation, for example at 16 pulses by nutation. This last value could be an integer, and in this case the circle of points on the detector will appear motionless, or a fractional number, in this case the circle will seem to rotate and thus reduce its instability.

 When using a laser beam with a small divergence, for example around 5 milliradians (mrad), it is essential, at least at the start of a missile's flight, to illuminate the target and the missile separately by means of two guided laser beams separately if the angular separation is greater than the width of a laser beam. This is achieved by projecting the laser output radiation onto a partially reflecting mirror which will deflect 50% of the beam on the target and transmit 50% of it to a second mirror which will deflect it on the missile.

The reflections of the missile as well as the target are reproduced on the detector in the form of circles 16 for the target and 17 for the missile, visible on the
Fig. 3.

 In a variant of the device, the missile is provided with allows reflectors.

both correct reception of the signal with much less than 50% of the laser output radiation. In this case, the reflectivity of the partially reflecting mirror is adjusted so as to project most of the output radiation from the laser onto the target.

 As shown in Fig. 4, the mosque detector 15 comprises a photodiode 18, with 25 silicon elements arranged in 5 rows of 5. These 25 photodiodes 18 control a matrix of 25 low noise video amplifiers 19 having an appearance time of approximately 100 nanoseconds . The outputs of the amplifiers are coupled together by threshold detectors 20, 21 set above the peak noise level.

 These detectors 20, 21 operate like a digital "OR" gate and couple the individual outputs in five rows 20A and in five columns 21A. Therefore, ten output lines transmit the instantaneous address of one: return pulse to the 25-element mosque.

 In order to simplify the description, only the processing of the output signals from the columns (azimuth) will be described, the processing of the output signals from the rows (elevation) being identical.

 The exact positions of a target and missile circle on the mosque detector 15 are determined by counting the number of pulses received in each column, but this gives a position relative to a boundary between columns. The position of the target and the missile on the detector can be determined ep by first establishing a marker for each circle and then counting the number of pulses to the left and right of this marker.

 To establish a benchmark, the columns are explored electronically to ensure the possible presence of pulses in these columns; it is therefore not essential to know the exact number of pulses in the columns.

The marks are defined by the center of the columns and by the boundary between adjacent columns; there are therefore nine marks if one neglects the outer edges of the detector or if one assigns them the value zero.

 When pulses occur in only one column, the frame will be the center of that column; when pulses occur in two adjacent columns, the reference will be the line separating the two columns; and when pulses occur in three columns, the mark will be the center of the central column.

 Fig. 6 represents a truth table giving the exit code produced by a landmark generator (which will be described below), in binary form, for a certain number of possible positions of a target or missile circle.

 The five columns on the left side of the table represent the columns of the detector. The black point represents a center of a target or missile circle, a 0 indicates the absence of pulses in a given band, the sign I represents one or more pulses in a given band, and the sign X represents pulses repeated in a given band.

 If we consider the first position shown (a) of a centrotde, we only see pulses in the first band, the exit code is dopc 0001 and represents a mark halfway between the sides of column 1 If we now consider the position (d) in which the circle is at the limit separating columns 2 and 3, the exploration of the columns from the left will reveal that there is no impulse in the column 1 but pulses in column 2; no other column will be explored from the left. The columns are then explored from the right and reveal the absence of pulses in columns 4 and 5 and the presence of pulses in column 3. The output signal is therefore 100, in binary form. The same output signal is obtained when the pulses in columns 1 and 4 are recorded, the pulses in columns 2 and 3 being repeated pulses. This last reading would occur if the pulse circle had enough diameter to span four columns.

 If the center point of the circle is located in the center of the detector (e), four readings are possible on the columns, giving a binary output of 0101. These readings are as follows. readings in column 3 only, readings in columns 2 and 4, and readings in columns 1 and 5. You can see that the position of the marks is only a rough indication of the position of the centrotde and is not precise only about half the width of a column. The nine positions of the marks, written in binary numbers, form four bits indicating the position of the marks or the approximate position of the centers of the target and missile circles.

 Once a reference has been established, the pulses of each column are counted down to further define the center of a target or missile circuit. Fig.

7 shows a portion of the five columns on which three circles are drawn to show the derivation of a position of the circles.

 The circle 22 on the left has pulses in columns 1 and 2 therefore, according to a reading of the truth table of FIG. 6, the reference position is the limit between columns 1 and 2, represented by the binary number 0010.

If we first read this circle from the left, we find twelve pulses in column 1, and if we then read it from the right, there are four pulses in column 2. If D is the coordinate system binary, L the binary number of pulses read from the right, the exact position of the left circle in Fig. 7 will be given by the formula D + R - L in which D represents the first four bits of an eight-bit binary number and R - L represents the last four bits of this eight-bit binary number. In the example represented by the left circle 22 of FIG. 7, the eight-bit number representing the center of the circle is 0001 1000
For the example represented by the central circle 23, the reference will be 0100 as shown by the truth table of FIG. 6. The number of pulses is eight in column 2 when reading from the left, and eight in column 3 when reading from the right. So by adding D + R - L = 0100 0000 which represents the exact position of the center of the circles.

For the example represented by the right circle 24, the reference is 0011 because there are pulses in columns 3 and 5. The number of pulses is one in column 3 by reading from the left and two in column 5 reading from the right. The pulses in column 4 are not counted because only the pulses in the leftmost and rightmost columns are essential. The exact position of the center of the right circle is 0111 0001
The above shows how we determine the position, in azimuth, of a circle on the monarch detector. The elevation position is determined in the same way.

 If we now refer to the diagrams of Figs. 5a and 5b, it can be seen that the output signals of each of the columns of FIG. 4 are transmitted to separate threshold amplifiers 25 where they are amplified before passing to a target distance discriminator 26 and to a distance discriminator missile 27, suitably determined by a distance discriminator group 28 separating, over time, the signals received from the target and the missile. From discriminators 26 and 27, the signals pass through target and missile counters 29 and 30, i respectively, counting down the signals received in each of them to form a four-bit word.

 The two counters, target 29 and missile 30, are disconnected by a common line by means of a control element 31 comprising the frame clock. The signals, in the form of four-bit words, pass into input memories for the target and for the missile, 32 and 33, where they are retained before passing to a first target / missile duplexer switch 34.

 From the duplexer switch 34, the four-bit words pass to a routing circuit 35 which directs them to a data generator 36, to a left buffer memory 37 or to a right buffer memory 38. The three series of four-bit words then pass into an arithmetic unit 39 which forms the word D dan; the first four bits of an eight bit word then add the three words to form an eight bit word giving the precise position, on the detector, of a target or missile circle center. The output signal from the arithmetic unit 39 is sent to a second duplexer switch 40 having a single input and two outputs. From this second switch-duplexer 40 the eight-bit words pass the target or missile output buffers 41 or 42. The use of two switch-duplexers 34 and 40 allows the circuit which separates them to function timeshare, which reduces its material complexity.

Buffers 41, 42 the eight bit words pass to an exploration / or blocking, target or missile switch, 43 or 44, then in digital-analog, target or missile converters, 45 or 46. Part of the output signals of each converter 45, 46 is transmitted, by a amplifier amplifier, target or missile, 47 or 48, and a power amplifier, target or missile, 49 or 50, to a azimuth beam deflector
laser illuminating the target or the missile, 51 or 52. The rest of the output signals from the two converters 45 and 46 pass through a difference amplifier 53 and an am-.

difference-conforming plifier 54 to provide a differential error 55 which will be transmitted to the missile control members.

 An identical circuit is used to process the signals coming from the row thresholds 20 of the detector of FIG. 4, to give differential elevation error signals which will be transmitted to the missile, as well as laser beams of deflection of elevation of the target and the missile.

If therefore we assume that a target has been captured and illuminated by the beam
target laser, the resulting signal received appears on the detector 15 of FIG. 3 in the form of a circle of points 16. The missile launched and illuminated by the beam
missile laser will give a signal appearing on the detector in the form of a
dot circle 17.

The differential error between the two circles and therefore between the target and the
missile is proportional to the difference between their exact coordinates on the
detector 15. Eight-bit words will therefore be formed to represent the position
azimuth of the target, the azimuth position of the missile, the elevation position
of the target, and the elevation position of the missile.

If you specifically consider the target circle, the exit signals from
each column 21 of detector 15 represents the number of target pulses
received on each column, are sent by the distance discriminator of
target 26, in target counters 29 to form a four-bit word in
each counter. On an order received from the control element 31, each of the
counters write their four-bit word into the target input buffer
32. The control element then selects the target channel in the first
switch-duplexer 34 and the memories 32 register in the routing circuit
35. The latter explores the five columns from the left and then from the
right, see the presence of pulses in columns 1 and 2, and transmit these
data to the data generator 36 so that it produces the word "D" 0010. The ex-
ploration from the left also reveals twelve pulses in the column:
1, which makes it possible to form the word "L"1100; and exploration from the right
reveals four impiZ4sions in column 2, which makes it possible to form the word "R"
0100. The control element 31 switches these three words in the arithmetic unit
39 where the eight bit word 0001 1000 is formed. The second duplexer switch 40 is connected, by the control element 31, to the target channel and the word to
eight bits corresponding to the azimuth of the target is entered in the buffer
target exit 41.

The eight-bit word corresponding to the azimuth of the missile is treated the same
by the control element 31 which admits the signals from the missile column
to counter 30 and connects the two duplex switches 34, 40 to the channel
missile. Therefore, at some point, the output, target and missile buffers, 41 and 42 will contain eight-bit words representing the
azimuth position of the target and the missile. Each of these two eight-bit words
is then sent, on order received from the control element 31, by the switches
exploration and enslavement torques 43, 44, to its digital-to-ana converter
respective logic 45 or 46. The output signals from the two converters 45,46
pass through the difference amplifier 53 and into the shaping amplifier 54 after which the differential error signal 55 is used, to control the missile, to successively reduce this differential error until it is? zero, the target and missile circles then dovetail on detector 15 and the missile is directed straight at the target.

In addition, the output signals from the target and missile converters 45, 46 pass separately through the conforming amplifiers 47, 48 and by the power amplifiers 49.50 whose output signals are used to control
the laser beams to follow the target and the missile. The target output signal is also used to control the laser tracking head 2 (Fig. 1) to place
the target circle 16 in the center of the detector 15. The control, in elevation, of
the tracking head 2, and of the target and missile laser beams is identical to the azimuth command which has just been described.

To start the illumination of the target, we make sweep by the beam
target laser the field represented by the detector. This scanning is essential because the viewing angle of the detector is approximately 20 mrad while the laser beam is smaller, for example 5 mrad. This scanning is carried out by
control element 31 generating eight-bit words which are transmitted to the target exploration / blocking switch 43. These words represent a position on the detector and it is therefore possible to generate a succession of eight-bit words representing each element 18 of turn detector. As the words are transmitted to the target exploration / blocking switch 43, they are processed by the digital-analog converter 45 and then transmitted to the target laser beam which moves while the field covered by the detector 15. Once the target is illuminated and the detector 15 receives a signal, the exploration / target blocking switch 43 is blocked by the control element 31 and the production of words ordering the exploration is interrupted. The target is now picked up and the target laser beam is controlled as described.

If the detector 15 does not receive any signal from the target, the control element 31 starts again to produce signals ordering the exploration from the point of reception of the last signal until capture of the target.

When the target has been picked up, a missile can be launched, which requires its illumination by the missile laser beam. The control element 31 resumes producing missile exploration / blocking orders 44 so that the laser beam of the missile scans until the missile is illuminated, after which the signals received by the detector 15 control the missile laser beam, and the control element 31 ceases to produce exploration orders
The initial operation of tracking the head 2 in order to capture a target in the field of the detector 15 can be carried out by means of a conventional infrared ray monitoring device.

 The tracking system described above uses a YAG-Nd illuminator with a high pulse repetition frequency, for example 3 kHz, a peak output power greater than 10 kW, and a minimum missile control speed of 100 Hz.

The detector described with reference to FIG. 4 used twenty-five elements
A variant of this detector uses a hundred elements arranged in rows of ten, to give a field of vision of 40 mrad.

 The present invention can be used in various other ways. For example, the illuminating laser, the detector and the target information processing devices can be used without the illuminating laser and the missile's information processing organs. A target can therefore be identified with great precision by the target illuminator laser so as to block on it (an extremely powerful laser beam which will cause its fusion, therefore its destruction. In another mode of use, the laser illuminator of target may be used to point cannons at a target.

Claims (12)

 1. Laser tracking system characterized in that it comprises organs for producing a pulsed beam of intense optical radiation in a well-defined direction, organs for collecting radiation from the visible scene in the direction of irradiation beam of intense optical radiation, detector bodies comprising at least two detector elements sensitive to optical radiation with a limit between the two detector elements, bodies for forming an image of the scene captured by the detector bodies of the organs varying cyclically the position of the image on the detector element in a direction of which at least one component is perpendicular to the limit, and of bodies for counting the number of pulses of optical radiation reflected by an object being in the explored scene and detected by the detecting elements.  2. Laser tracking system according to claim 1, characterized in that the detector members comprise at least four detector elements arranged in rows of two.  3. Laser tracking system according to claim 2, characterized in that the members for cyclic variation of the position of the image on the detector element comprise a surface which can be rotated and arranged so as to move the position of the image along a circular path on the detector elements.  4. Laser tracking system according to claim 3, characterized in that it further comprises members for producing a signal representing the position of the image received on the rows of detector elements.  5. laser tracking system according to claim 3, characterized in that the organs for producing a pulsed beam of intense optical radiation comprise organs producing two beams of intense optical radiation which can be independently controlled in order to illuminate two objects separated.  6. Laser tracking system according to claim 5, characterized in that it further comprises members for synchronizing the time interval separating the production of a pulse of intense optical radiation from the reception of a pulse of optical radiation reflected by any object, a first counting member counting the optical radiation pulses reflected by an object at a distance such that said time interval has a value located in a first range of values, and a second counting member count counting the pulses of optical radiation reflected by an object at a distance such that said time interval has a value located in a second range of values.  7. laser tracking system according to claim 6, characterized in that it comprises members generating a signal representing the differential error of two images received on the set of detector elements from the two illuminated objects.  8. laser tracking system according to claim 4, characterized in that the organs for producing a signal representing the position of the image received on all of the detector elements comprise organs producing a signal for guiding the beam of intense optical radiation.  9. laser tracking system according to claim 1, characterized in that it further comprises organs communicating an exploration movement to the beam of intense optical radiation until reception of an image by the detector organs.  10. Laser tracking system according to claim 1, characterized in that the intense optical radiation is produced by a laser.  11. Laser tracking system according to claim 4, characterized in that the members for producing a signal representing the position of the image received on the set of detector elements comprises members for connecting the elements in rows and in columns, counting units for the number of pulses received in each column and in each row to provide a reference mark on the set of elements as well as an exact position of the center of the image in a row and in a column , and members supplying a digital signal in which the marker forms the first part of a binary number and in which the exact position forms the second part of said binary number.  12. A laser tracking system essentially constructed, arranged, and suitable for operating essentially as described above with reference to the accompanying drawings.