GB2290671A

GB2290671A - Guidance of an armed flying body

Info

Publication number: GB2290671A
Application number: GB9312560A
Authority: GB
Inventors: Karl-Heinz Wilke
Original assignee: Deutsche Aerospace AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1992-06-29
Filing date: 1993-06-18
Publication date: 1996-01-03
Anticipated expiration: 2013-06-18
Also published as: FR2723191B1; GB2290671B; GB9310865D0; GB9312560D0; FR2723191A1

Abstract

A method of guiding an armed flying body (1) with a target-seeking head towards a ground or sen surface target (3) comprises the step of causing the flying body during its target approach phase to fly on a curved flight path (2), wherein the ratio of the signals reflected from the ground target to the clutter of the ground is kept constant or at least nearly constant in the mean on the curved flight path. The path vector (21) of the flying body in that case points in the direction of the ground during the target approach phase. As described FLSAR radar with aerials fixedly connected to the structure of the body is employed. Alternatively an optical system may be used. … <IMAGE> …

Description

GUIDANCE OF AN ARMED FLYING BODY The present invention relates to a method

of guiding an armed flying body with a target-seeking head towards a ground target and to a flying body provided with a target-seeking head for performance of such method.

Target-seeking guidance is utilised in, for example, rockets, guided missiles, underbody projectiles, artillery munitions and space weapons, but mostly in the field of flying bodies.

Method for the independent control of a guided flying body provided with a warhead are known from conventional flying bodies, such a guided flying body generally being a missile or an underbody projectile with an active target-seeking head. The missile or projectile is in that case used for attacking stationary and movable ground targets.

Notwithstanding the known methods, there remains scope for a method in which, for example, a flying body during a target approach phase thereof draws on the ground clutter (hereinafter referred to as clutter) for the control of its guidance system, particularly a method by which scanning of the ground and a ground target shall be possible by economic means.

According to a first aspect of the present invention there is provided a method of guiding an armed flying body with a targ-2t- seeking head towards a ground target, comprising the steps of causing the flying body to travel on a curved flight oath, with its path vector pointing towards the ground, during a target approach phase, emitting signals from the head for reflection by the target and the ground, and controlling the flight path so that the ratio of the target-reflected signal to the ground echo signal is kept substantially constant in the mean.

According to a second aspect of the invention there is provided a flying body provided with a target-seeking head for performance of the method according to the first aspect of the invention, comprising an aerial group which is composed of transmitting and receiving aerials and constructed as a rigid sub-assembly fixedly connected with the flying body and which is connected to a transmitting and receiving unit. Alternatively, a transmitting and receiving unit, which operates on an optical basis and comprises detectors and at least one illuminator, is constructed as a rigid sub-assembly fixedly connected with the flying body and the detectors are connected to an evaluating unit.

A method exemplifying and a flying body embodying the invention have the advantages that the target -ref 1 ected signal and the clutter signal (echo signal) with the greatest Doppler displacement can be processed simultaneously into a guidance signal, and that scanning of the ground and the target can take place without mechanically moved parts. In that case an economic manufacture of the target-seeking head is possible, particularly with utilisation of less complex technologies, for example from the lower gigahertz range. Moreover, the head may be highly resistant to acceleration and serviceable in 3 all weathers.

An example of the method and embodiment of the flying body will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a diagram showing a flying body, embodying the invention, during a traget approach phase thereof; Fig. 2 is a diagram showing the flying body during a target-seeking phase thereof; Fig. 3 is a diagram showing the concept of the flying body guidance with an integrated FLSAR method; Fig. 4 is a diagramshowing component resolution of the movement of a moved ground target sought by the flying body; Fig. 5 is a detail of the /% plane of Fig. 3; Fig. 6 is a diagram showing a possible target approach scenario from the view of the flying body; Fig. 7 is a block schematic diagram of a preferred embodiment of a target-seeking head in a flying body embodying the invention; and Fig. 8 is a preferred aerial configuration for the target-seeking head of Fig. 7.

Fi 9. 1 shows the flying body 1, which is, for example,a guidable rocket,during its target approach phase. The path vector 21 of the flying body 1 in this case points towards the ground 4 starting from the longitudinal axis of the flying body. The prolongation of the path vector 21 towards the ground 4 intersects this in an intersection point Z, which at an instant t = t 0 assumes a value Z 0 on the abscissa of a cartesian co-ordinate system with the ordinate which spans the flight path plane In this case t 0 is an earliest possible instant during the target approach phase. At the latest at this instant tos the flying body 1 emits signals continuously by way of a transmitting aerial (not shown) during its target approach, which signals are reflected on the one hand by the ground target 3 and on the other hand by the ground 4.

These reflected signals S (from the ground target 3) and C (from the ground 4) are received by the receiving aerials (not shown) of the flying body 1 and evaluated in a evaluating unit (not shown). In dependence on the results of this evaluation, the flying body 1 is in that case guided so that its flight path 2 is curved in such a manner that the ratio of the signal S, which is reflected by the ground target 3 and also called ground target signal, and the signal C, which is reflected from the ground 4 and also called clutter signal, is kept constant or at least nearly constant in the mean. In the case of a ground target 3 which is not moved (stationary) a flight path 2 results approximately in the form of a circular path.

The ratio S/C of the ground target signal S to the clutter signal C is in that case described approximately by the following relationship:

S C z B S inp S v G wherein S = signal reflected from the ground target 3, R z = distance between the flying body 1 and the ground target 3 ("target distance"), = angle between the distance R z from the flying body 1 to the ground target 3 and the distance R D between the flying body 1 and the intersection point D of the velocity vector V G of the flying body 1 ("line-of-sight angle"), C = speed of light, f S = transmitting frequency of the radar of the flying body 1, B = evaluation bandwidth of the radar of the flying body 1,and v G = velocity of the flying body 1.

Insofar as the ground target 3 moves, this movement is detected by the flying body 1 and a corresponding flight path correction is undertaken. This correction can be performed in such a manner that the flying body 1 is guided to an estimated impact point which is spaced by a travel path LZ from the instantaneous target location (instantaneous location of the ground target 3). The estimation of this travel path can, for example, take place according to the formula 4 Z = T.VZ, wherein T = estimated instant of impact, v z = velocity of the ground target 3 moving on the ground 4 and A Z = travel path component traversed in the plane by the ground target 3 (compare Fig. 5).

To ascertain this ratio and the required transverse acceleration for the guidance of the flying body 1, the distance R z between the flying body 1 and the ground target 3, the distance R D between the flying body 1 and the intersection point D at the ground 4 and the line-of-sight angle 'T between the two distances R z and R D is ascertained in the flying body, for example with the assistance of the Forward-Looking-lynthetic-ApertureRadar (FLSAR) method.

The velocity of the ground target 3 is ascertained from, for example, the ratio of the radial velocity of the ground target 3 and the velocity of the flying body 1 multiplied by the cosine of the line-of-sight angle rr and taken into consideration for the flight path correction. The flight path correction can, for example, be computed on-line or read out from a stored tape.

The transverse acceleration bC which is to be exerted, of the flying body 1 is in this case described approximately by the following relationship:

nV2 G sin 0 b R z 0 7 wherein v G = velocity of the flying body 1, TO = line-of-sight angle at the instant t = t 0 of the target detection and R = target distance at the instant t = t of the target detection.

z 0 0 The line-of-sight angle r. can, for example, be ascertained by 0 Doppler frequency selection.

Fig. 2 shows the flying body 1 during the target-seeking phase.

All target points with directions of view of the same angle to the velocity vector V G of the flying body 1 result in echo signals with the same Doppler displacement relative to the transmission frequency of the radar. The curves of intersection of these directions of view with the ground 4 are describable by locus curves of constant Doppler shift, also called "isodopplers". They are approximately elliptical, wherein the spacings of the ellipses for constant frequency difference become ever closer with increasing line-of-sight angle.

Locus curves of the same distance, also called "isoranges", are circles around the projection of the flying body 1 onto the ground 4, which have about constant spacing when considered over not too large a threedimensional angle. The aerial lobe of the radar of the flying body 1 cuts out a certain part from this family of curves.

The FL5AR method consists in achieving an angular resolution by the Doppler effect instead of by the aerial lobe through narrow-band evaluation of the echo signals of each distance range.

The resolution cells are thus determined by the intersections of the "isoranges" with the "isodopplers" and not via the intersections of the I'isoranges" with the aerial lobe.

Substantial advantages by comparison with hitherto usual millimetre-wave radar concepts may be able to be achieved through application of the FLSAR method. These advantages are particularly well recognised in a comparative consideration between an FISAR method exemplifyina the present invention and the usual millimetre- wave radar method which utilises the aerial lobe for transverse resolution.

The angular resolution, which is achievable with a certain evaluation bandwith B of the radar, increases with the deviation from the vector of the velocity V G The least accurate "Doppler cell", which extends directly around the intersection point of the velocity vector through the ground 4 (earth surface) is, even with the use of the transmission frequency in, for example, the K U- band, not wider than the angular resolution of a radar target-seeking head at the same distance with a lobe width, which would be achievable only with transmission frequencies in the millimetre-wave range in the case of an aperture available in a flying body.

By contrast to such a radar, which would have to execute a scanning movement for the target search in the indicated region, an FLSAR head needs a substantially longer integration time (reciprocal of the Doppler evaluation bandwidth), which, however, is available therefor, because it surveys the entire target region at the same time.

The resolution outside the centre of the search region could also be improved in the case of a millimetre-wave radar by DopplerBeam-Sharpening (DBS) (the same resolution would be achievable at the higher frequency with the same ratio of shorter integration time) but the necessity exists as before of the sequential scanning of the search region either mechanically or by a " steered-ph ase- array" aerial which, however, is not at present realisable for applications in the millimetre- range.

For target detection or classification, no substantial difference exists to a first approximation between FLSAR and millimetre-wave radar when the resolution of angle and distance are about equal in both cases, because it is immaterial for the selection of criteria and the classificators in which manner the formation of the resolution cells takes place. The additional evaluation of the echos according to co-polarisation and cross -pol ari sati on is similarly possible through appropriate construction of the aerial system in the case of FLSAR. Great differences are, however, evident in the consideration of the target approach.

In order to be able to track the target and ascertain the rotational lineof-sight velocity as a measure for the required guidance commands, the conventional millimetre-wave radar must constantly look at the ground target 3 and be decoupled, for example by a Cardan frame, from all movements of the flying body 1. For this purpose, moreover there is still required a reference system which could, for example, be realised as gyroscope platform. With respect to flying body guidance, the proportional navigation method is usually used in that case.

The Cardan frame and the gyroscope platform are exacting and therefore costly precision mechanical subassemblies which appreciably increase the price, in particular of the target-seeking head, and which in respect of the realisability of, for example, guided artillery munitions are to be regarded as very risky because of the high demands on the launching strength.

By comparison therewith, an aerial, which is fixed to the flying and of great lobe width, which is explained more closely further below, permits not only the Cardan system but also reference systems to be dispensed with, as becomes evident from the following consideration.

The course which a proportional navigation guidance method would provide for the flying body 1 would not be optimal in the approach towards ground targets 3, because the proportional navigation method in the case of a velocity of the ground target 3, which is less than the velocity V G to negligible by comparison therewith, leads to a course which leads to a straight line, i.e. with a line-of-sight angle near to zero, into the ground target 3.

The line-of-sight angle for target detection offers a certain annular resolution which together with the distance resolution supplies an adequate signal-to-cl utter ratio S/C. If the annular resolution were to reduce more rapidly than the distance from the target, the ratio S/C would corresoondingly worsen, which could lead to a loss of target and break-off of the target tracking.

In a preferred example of the method according to the invention, it is therefore provided that the flying body 1 moves on a flight path on which the ratio S/C is as constant as possible over the entire flight path. Constant S/C means that the line-of-sight angle during the guidance phase may not reduce more strongly than - 11 proportionally to the target distance.

A very good approximation to this flight path is represented by a circular path which has the vector of the velocity v G as tangent at the instant of reception and which passes through the target location. The flying body 1 is thus in this method guided not according to the principle of the proportional navigation method on a constant line-of- sight angle, but on a constant path radius.

This is possible in that a line-of-sight angle for constant S/C is preset as target value at the instant of detection in dependence on the target distance and the line-of-sight angle and compared with the actual line-ofsight angle between target direction and vector of the velocity V G The guidance is actuated by way of a regulator according to the deviations evident from this comparison.

In the case of the values which come into question for the aperture angle of the aerial diagram of the aerial, which is fixed to the flying body, between, for example, +/-10 degrees and +/-20 degrees, i.e. initial target deviations of the same magnitude or smaller, the flying of the described circular path by comparison with the straight flight path line resulting in the case of conventional proportional navigation methods means flight time prolongations of only fractions of seconds, which is inappreciable in relation to the maximum possible velocities of ground targets.

Consequently, for example, for the case that - the setting angles required for the manoeuvring of the flying body 1 are smaller than half the half-value width of the aerial lobe, - the approach flight path is so steep that the intersection of the vector of the velocity with the ground 4 still lies within the range of the radar, the flying body 1 has four receiving channels which can be combined according to a two-plane single pulse method into an azimuth difference signal, elevation difference signal and a sum signal, and the receiving channels are so stable in their properties that a reproducible characteristic "error voltage about annular deviation" is available in both planes, the following data are available to the flying body 1 simultaneously at every instant:

1. the own velocity as maximally measurable Doppler effect, 2. the ground spacing as distance from the point of maximum Doppler effect, 3. the velocity relative to the target as Doppler effect of the target, 4. the target distance, 5. the direction of the line-of-sight to the target by comparison with the path vector from the single pulse characteristic, and 6. the component of the velocity of the target in line-of-sight direction as difference between relative velocity in target direction and velocity of the flying body multiplied by the cosine of the line-of-sight angle. The line-of-sight angle between the target direction and the own velocity is measurable directly by these values independently of the setting angle of the missile. A separate reference system for the storage of the path vector can thus be dispensed with when the afore- mentioned prerequisites are fulfilled.

Fig. 3 by way of example shows a system design of the method exerrplifving the invention with the integrated FLSAR method.

After the unfolding of the aerofoils and if applicable the steering fins, the flying body 1 is guided into a flight path with an impact angle of about 45 degrees. An initial manoeuvre for horizontal flight is thus not required.

A checking of this flight path is possible with the radar constructed in the flying body 1.

The search for targets takes place, for example, onward from a height of about 1500 metres with a lobe width of the aerial of, for example, approximately 20 degrees.

For a transmission frequency of, for example, 18 gigahertz (corresponding to a wavelength of 16.7 millimetres) this 3 dB lobe width can be achieved as a product of transmission and reception diagrams with individual aerials of a diameter of about 40 millimetres.

Seen geometrically, as can be recognised by reference to Fig. 3, the following situation results:

In an earth-related co-ordinate system x, y and p, which is fixed by the projection of the instantaneous flying body location onto the ground 4 (earth surface) and the intersection point D of the velocity vector VG, which results in terms of amount from the distance R D between the flying body 1 and the intersection point D, the flight path plane ( tki) is spanned by its abscissa and ordinate tu. To be laid into this flight path plane is an approximately circular path which is tangent to the path vector and contacts the target point Z insofar as this path vector coincides with the velocity VG- As is clarified in Fig. 3, the following relationships result between the distances R D' R W and R z and the solid angles <, 13 and 1 measured on the flying body as well as between the earth-related distances x z and x D between the instantaneous flying body projection onto the ground 4 and the points Z and D. The flying body in that case has the height PG- To be understood by R D is the distance between the flying body 1 and the intersection point D of the velocity vector V G, by R W the distance between the flying body 1 and an intersection point W and by R z the distance between the flying body 1 and the target point Z. In the case of the intersection point W, there is concerned a point at the ground 4, which results from the prolongation of the longitudinal axis of the flying body and coincides with the path vector 21 according to Fig. 1. The solid angle J- lies between the path portions (M) between the flying body 1 and the intersection point W and (G7) from the flying body 1 to the intersection point Z. The solid angle [3 lies between the path portions (GU) from the flying body 1 to the intersection point D and (FA) from the flying body 1 to the intersection point W. In this case, a space point in the flying body 1 is denoted by G. In the case of the solid angle r, the lineof-sight angle decisive for the Doppler shift is concerned.

From the formation of the inner products for the path portion vectors GYGZ, WK and GW. GD, it follows at the instant of the target pick-up with the usual representation of the components that - (3.0.1) GD XD; 0; -Q -> C (3.0.2) GZ X z; YZ; -PGJ GW X; 0; -P(- -0.3) z (3 C 0 S5/ X D ' X z P G (3.1) R z R D 2 2 X + P z (3.2) c 0 S RZ R D X X P 2 (3.3) cos z ID R W R D The following relationships result for the plane anglel/"'and the above instantaneous components:

aretan YZ IXZXD X z - X D 19 1 XZ=XD 2 arctan YZ Qi (3 - -'!.3 xZ<xD ( X z X D For the solid angle 9 there applies + 1- (3.5) In this case, the solid angles 3 &j and qyrespectively lie between the path portions R_ and MU, between the path portions G7 and 7Z and between the path portions DZ and NW.

These path portions are in that case bounded by the points G, D; D, U; G, Z; D, Z; D, Z and D, W. The points G, U, D and Z are points in the flight path plane ( 1 ?D). U is the origin of the notional two- dimensional carthesian co-ordinate system of the flight path plane (9 7).

The path portion P in that case has a length 71,, the path G portion U-D a length D and the path portion U-Z a length Sz.

Furthermore, the solid angle 5 and 17"' respectively lie between the path portions (0, 0, O)D and G and between DW and R. To be understood by (0, 0, 0) is the origin of the earth-bound cartesian co-ordinate system with the components x, y and p.

Fig. 4 shows the resolution into components of the movement of the ground target 3 according to Fig. 3,insofar as this moves. In that case, the reference elements x, y, 5, U, D and 13' from Fig. 3, which are required for illustration of the ground target movement, have been taken over in Fig. 4.

If it is presupposed that the ground target 3 moves in a space direction D z the velocity of the moved ground target 3 appears resolved into components in the flying body 1.

One component D5Z lies in the flight path plane (t,7b), makes a contribution to the relative speed in target direction and thus leads to a difference between the product of the velocity of the flying body 1 and cosr as well as the measured value of the relative speed in target direction.

The angle between the target direction and the ground 4 can be computed from the target distance R z between the flying body 1 and the target 3 according to Fig. 3, the spacing R D to the intersection point D and the line-of-sight r and thus also the component of the target velocity in the flight path plane Another component D QZ lies perpendicularly to the flight path plane and appears in the flying body 1 as rotational velocity of the flight path plane in the flying body 1.

The manoeuvring accel erati on which is required for the achievement of the correct circular path, can be ascertained in the flying body 1 unambiguously in amplitude and direction from the afore-described measurement values.

In respect of the individual components, the following relationships apply, as is evident from Fig. 4:

D D 2 D 9 z YZ D,o z D z c 0 S D QZ D z s in wherein arctan D YZ D = In this case, the general movement vector D z of the ground target 3 is resolved into a component DgZ in the flight path plane and a component DQZ perpendicular thereto. The component D5Z generates a radial component in the direction towards the flying body 1 and can thus be measured. The component D QZ causes a rotation of the flight path plane about the velocity vector V G To be understood by Y is a solid angle which results from the component resolution of the movement vector DP wherein a component D YZ is parallel to the yaxis and a component D XZ is parallel to the x-axis of the co-ordinate system x and y.

Fig. 5 likewise shows a detail of the flight path plane (L/S) of Fig. 3. Here, too, reference elements from Fig. 3 have been taken over into the Figure. In this case, the reference elements)t,,5. 1, V G3 3, R D' RZI3 G, U5 D, Z,Q and 3 are concerned. In the case of the reference element L.Z, that described in Fig. 1 is applicable. As is evident from Fig. 5, the flying body 1 flies approximately in a circular arc which adjoins tangentially at the initial velocity vector here illustrated as a parallelly displaced vector V G' and passes through the target point Z.

BY way of example, let it be considered that the velocity V Z of the ground target 3 in the target point Z is equal to zero. Consequently, it follows R Z r R 0 wherein and R are the measurement values r and R at the instant 0 Z 0 Z t = t 0 = 0. The guidance transverse acceleration b q, which is to be exerted, of the flying body 1 follows the relationship v 2 b G (5.2.0) q r 0 or with equation (5.1.1) 9 2v- G (5.2.1) b s inr q R z 0 0 and results, when b q is constant, in the circular path to be flown.

To be understood by r 0 in that case is the radius r at the instant t = t 0 = 0 with the centre M 0 of the flight path of the flying body 1. The centre M 0 is in this case displaced by a spacing Lr on the path portion or GM, wherein the path portion point M MO is to be found between the points G and M 0 of the path portion GM 01 M lies at the intersection between the path portion GMO and a line which orthogonally intersects the distance R z and has approximately minimum distance from the target Z.

The cross-resolution Q in the region of a detected ground target thus results as R- Q 2f ZI V_ sinr B in which case R z = direct distance between the flying body 1 and the ground target 3 in the target point Z f S = transmitted signal frequency, c = speed of light, v G = velocity of the flying body 1, B = evaluation bandwidth of the radar of the flying body 1 and = line-of-sight angle.

From this, it follows for the target resolution at the instant t t 0 = 0 at which the ground target 3 is recognised by the flying body 1 that R z f 5. v G (5.2) s in c It is symbolised by the index 0 at the variables according to equation (5. 2) that those variables which are mentioned further above at the instant t = t = 0 are concerned; for example T, stands for 0 0 the line-of-sight angle at the instant t 0.

It follows generally from 5.2 that R z x(t) - sir, (t) = - (5.3) r and from R Z(t) r = constant (5.4) s i t that C(t) = c 0 (5.5) The variables mentioned in the equations (5.3) to (5.5) are identical with the variables discussed further above. In other words, the above result means that C and thereby S/C remains constant over the entire flight path insofar as the flying body 1 flies a circular path.

Fig. 6 by way of example shows a possible target approach scenario from the view of the flying body.

Let is be assumed within the scope of this scenario that the target is detected, the target moves and a component of the target velocity lies in the flight path plane, the velocity vector of the flying body points in the direction of its intersection point and a guidance manoeuvre is initiated so that the main axis of the flying body momentarily no longer points in the direction of the intersection point. Starting from this scenario, there can be recognised in the figure a cartesian co-ordinate system, which is individual to the flying body, with its vertical and horizontal axes Ver. and Hor. and with its axis RH, which stands perpendicularly thereon and preferably coincides with the main axis of the flying body. The velocity vector V G points in the direction of its intersection point D, around which locus curves of constant Doppler shift are drawn in. The intersection point D and the afore-mentioned target Z in that case lie on the -axis of the flight path plane ( -p,) according to Figs. 1 and 3 to 5, of which only the 3 -axis is drawn in. When the target Z is moving, one component of the target velocity now lies in the flight path plane and in that case makes a contribution to the relative velocity in the target direction, as is also evident, for example, from Fig. 4. Ifone now transfers this - 22 scenario for illustration to the generally known single-pulse method (description of a manner of representation, for example, for the evaluation of received radar signals, which is not to be confused wi th the single-pulse method from the field of radar signal generation), then the described illustration in Fig. 6 enlarges by two co-ordinate systems, in which horizontal and vertical error signals are entered into this two- dimensional cartesian co-ordinate system as respective functions of the horizontal and vertical deviations, wherein the target Z as well as the intersection point D are shown in both co-ordinate systems in known manner as points Hor. Z and Hor. D or Ver. Z and Ver. D as has occurred within the scope of Fig. 6 for the scenario present therein, wherein the points Hor.Z, Hor. D' Ver. Z and Ver. D can change their position in the further course of the target approach and each lie approximately in the origin of the stated co-ordinate systems in the case of direct alignment of the main axis F0 of the flying body onto the target Z (towards the end of the target approach phase).

A preferred embodiment of the arrangement in a flying body for the performance of a method exemplifying the invention is shown in Fig. 7. The arrangement consists of a radar target-seeking head, also called radar search head. It contains an aerial group 77, which consists of a transmitting aerial s and four receiving aerials a to d. The transmitting aerial s and the receiving aerials a to d are of about the same size and mounted in the flying body 1, as can be recognised, for example, from Fig. 7. An alternative embodiment (not shown) consists in that the receiving aerials a to d are grouped around the transmitting aerial s externally at the flying body 1. The choice of the transmission - 23 frequency is in principle not subject to any restriction; however, it advantageously lies in the low gigahertz range, for example, at about 18 gigahertz.

The aerial group 77 is connected to a transmitting and receiving unit 79. This transmitting and receiving unit 79 is formed of further subassemblies 78, a target-recogni sing logic system 7, a geometry computer 8 and a regulator 9. In that case, the individual aerials s and a to d are connected by way of the further subassembly 78 to the target- recognising logic system 7. This target-recognising logic system 7 is followed (seen electrically) by the geometry computer 8 and the regulator 9 for the guidance of the flying body 1.

The transmitting aerial s is driven from a control unit 64 by way of a modulator 63, a control stage 62 connected therebehind and a power output stage 61.

The control unit 64 furthermore controls the target-recogni sing logic system 7.

The receiving aerials a to d are each respectively connected by way of an amplifier 51, a filter 52, a regulable amplifier 53, an anal og-to-di gi tal converter 54, a distance filter bank, a velocity filter bank, preferably realised as Fast-Fourier-Transformation in a given case with focussing, for the compensation for non-linearities in the echo frequencies, in the subassemblies R-M 55 and V-FFT 56 to the targetrecognising logic system 7.

As is evident from this figure, the afore-mentioned subassemblies are connected serially one with the other. The function of the arrangement embodying the invention is therefore as follows:

The transmission power is produced in two stages and radiated by way of the transmitting aerial s. The modulator 63 in that case L produces a sawtooth-shaped frequency modulation under the control of the control unit 64 of the target-seeking head of the flying body 1.

This radar operates by the frequency-modulated carrier wave method. Alternatively thereto, a radar operating by a pulse method with or without additional modulation for increase in the distance resolution can also be used. In the case of the FM-CW method the spectrum of the echo signals is substantially narrower than for a pulse method, for which reason a homodyne mixing is possible and the digitisation of the echo signals can take place very far forward in the signal train. The four parallel analog branches each consist only of a respective receiving mixer (in a given case with highfrequency pre-amplifier connected in front), a filter with an attenuation course (SRC-filter, also called sensitive-range-control filter) matched to the proportionality of echo frequency and distance attenuation and, for example, an AGC amplifier (also called automatic-gain-control amplifier).

The simplicity and narrow bandwidth facilitates the observation of the requirement for stability and synchronism of the signal branches and permits the formation of the sum and difference diagrams to be performed only in the geometry computer 8 instead of a comparator arranged in the high-frequency plane, wherein also asymmetric digrams with zero places ("adaptive zero guidance") can be produced in an intended direction by choice of the correct coefficients.

A significant increase in the immunity to interference of the radar search head thereby results.

In the target-recogni sing logic system 7, the sum signals are formed for each resolution cell as well as the algorithms for target recognition and target classification are applied to cell groups matched to the respective kind of target. The algorithms for an Hadaptive-zero guidance", which is installed in a given case, can likewise be integrated in this subassembly.

After the target detection, the signals (for example own velocity, ground spacing, radial velocity in target direction, deviations in azimuth and elevation of the target and intersection points), available in the radar search head are passed on to the geometry computer 8. During the target tracking, the targetrecognising logic system 7 runs in parallel, so that the correct resolution cells are always also evaluated as target.

The geometry computer 8 corresponds to the autopilot of the otherwise usual target seeking heads of flying bodies. The geometry computer 8 translates the measured data in accordance with the guidance method, which is to be realised, into control signals for the guidance regulator 9.

An example of a Particularly favourable mission course of the flying body is described in the following:

- launch and ballistic flight into the target region, - reconfiguration of the flying body into the guided flying body, - pivotation into a flight path suitable for searching, - target search, target recognition and target detection, and - guidance into the target.

The launch and the ballistic flight concern the target-seeking head in the flying body to the extent that it must be up to the extreme mechanical and thermal stresses arising in that case. For this purpose, appropriate constructional measures are to be taken, which, however are, - as already mentioned - facilitated appreciably by the omi ss ion of the otherwise usual precision mechanical subassemblies of Cardan and gyroscope reference.

The reconfiguration into the guided flying body includesthe release of the radome, which must be protected appropriately against mechanical and thermal damage during storage, launching and ballistic flight, as well as the moving-out of the lift surfaces and guidance devices (fins). The requirements in respect of manoeuvrability in a flying body embodying the invention are less than for a flying body with a millimetre-wave targetseeking head of the flying body, since - the requirement of an horizontal search flight disappears and - the detection ranges are greater and more time is therefore available for manoeuvres for the reaching of targets at the edge of the field of sight.

Pivotation into a flight path suitable for searching means that a rectilinear course with an angle of incidence of about 45 degrees to the surface of the earth is taken from the ballistic course. As soon as a sufficiently low height is reached (according to reflectivity of the ground, for example, between 2000 and 3000 metres), the target-seeking head of the flying body can detect the ground and determine the path angle in relation to the flying body axes. The angle of the incidence can be ascertained and corrected from the distance distribution along a certain lineof-sight angle (Doppler effect):

The locus curve of a specific Doppler effect at the ground is an ellipse along which the distance varies more or less greatly according to the angle of the incidence. In the distance-velocity diagram (R-V diagram), this ellipse is pictured as a line of distance cells displaced downwardly from the maximum velocity by the factor cos '.

Because of the long integration time necessary for Doppler analysis, the target search, target recognition and target detection require a compensation for own movement, because the projectile typically moves through 12 to 19 metres, thus a multiple of the distance cell depth, during an integration time of, for example, 64 milliseconds. This componensation for own movement takes place, illustrated in simplified manner, by the modulation of the received signals by a "chirp" signal which counteracts the modulation caused by the own movement.

The methods for target identification and false target rejection, which have hitherto been used in the millimetre-wave target-seeking head of the flying body, can be used in similar manner here, because the dimensions of the resolution cells are comparable.

Fig. 8 by way of example shows a possible configuration of the aerial group 77, which consists of four receiving aerials a to d and a transmitting aerial s and which altogether requires a diameter of, for example, 120 millimetres. The remote radiation diagrams of the individual aerials are not displaced relative to each other and the obtaining of the angular error signals takes place on the basis of the phase differences of the signals (phase single pulses).

Because of the low transmission frequency f S and since the diagrams are pivoted relative to the flying body axes, the structuring of the radome can be adapted substantially better to the aerodynamic requirements than for a conventional millimetre-wave radar target-seeking head.

By reason of the arrangement of the individual receiving aerials a to d in the flying body 1, the azimuth and the elevation respectively result through received signal addition to azimuth a c b d a c b d a b c d elevation a b + c d (7.2.) In the case of moved targets, a correction for flying time and thereby flight path is necessary. For this purpose, the flying time to the moved target is to be estimated, as indicated in Fig. 1.

The flying time towards the moved target can, for example, be estimated as follows:

The estimated relative speed between the flying body and the moved target is:

V V cosy - V COS0i Z In this case, V G is the velocity of the flying body 1 measured according to Fig. 3, for example in the direction of the intersection point D. r is the measured line-of-sight angle and W is the solid angle according to Fig. 3. v Z is the velocity of the ground target 3 moving on the ground, according Figs. 1 and 5.

The estimated values of the respective variables, which are not estimated when the ground target is stationary, are denoted by With respect to Fig. 5 it follows from (8.1):

v- - v COSI, v r G (8.2) z c 0 S Cal A flight path towards Z can be computed from the measured val ues or the estimated values R, R and This flight path is Z D characterised by 6j and time derivative of according to T) and the internal relationship between '' and 3 according to (3.5), which in the case of the movement of the ground target can be converted into an equation of the form 5 = ú., + T. In respect of this flight path, the target velocity can be resolved into a tangential component V tz contacting the flight path and a radial component V Z v V- - cos (8.3) tz 11 Belonging to this tangential component is an angular velocity b (by M):

v tz (8.4) The estimated time results from:

T- + 2 8 - into - z T' (8.6) v z The estimated position at the instant of impact is then displaced by L Z = T.V z according to equation (8.6). For the position of the target, 23L. is computed anew in a further step and drawn upon as target value. This target value is corrected by AZ in order that the line- of-sight does not point towards the impact point, but towards the ground target 3. The line-of-sight deviation,&' arising in this case by reason of the movement of the ground target 3 according to Fig. 5 by the travel portion AZ is computed by AZ 2 R 2 R 2 2R R (8.7) D Z D z into 2 R2 R A-- OS D z (8.8) arc 1) R R, D Z_ This line-of-sight deviation h' can in that case be drawn upon in alternative manner to the flight path correction in the case of a moving ground target 3 in place of the flight path correction on the basis of the travel portion component change A Z.

Flying time correction or the flight path correction can take place continuously for the duration of the entire target approach phase.

It is self-evident that the invention is not restricted to the described examples of embodiment, but can in fact be transferred to further ones. Thus, it is, for example, possible in place of the described microwave signals to use optical signals from the ultraviolet to the infra-red range, for example, signals of a laser, as transmitted signals of the flying body. Accordingly, the spectral sensitivity of the receiving aerials is then also to be matched to the transmitted spectrum of the transmitting aerial s. This can, for example, lead to photo- transistors having to be used as receiving aerials.

It is to be noted that a target (for example a ship) floating on water can be concerned in the case of the ground target and that water is therefore to be understood as ground in the sense of the invention.

32 -

Claims

CLAI MS

1 A method of guiding an armed flying body with a target-seeking head towards a ground target, comprising the steps of causing the flying body to travel on a curved flight path, with its path vector pointing towards the ground, during a target approach phase, emitting signals frem the head for reflection by the target and the ground, and controlling the flight path so that the ratio of the target-reflected signal to the ground echo signal is kept substantially constant in the mean.

2. A method as claimed in claim 1, wherein the step of controlling comprises ascertaining the distance between the flying body and the target, the distance between the flying body and the point of intersection of the ground by the velocity vector of the body, and the angle between the two distance vectors by means of forwardlooking synthetic aperture radar in the head.

3. A method as claimed in claim 2, wherein said angle is determined by a single pulse procedure.

4. A method as claimed in any one of the preceding claims, wherein the target is stationary and the flight path of the flying body is controlled to be substantially circularly arcuate.

5. A method as claimed in claim 4, comprising the step of determining the signal ratio by the equation 33 R c B sin f v G wherein S is the target-reflected signal, R z is the distance between the flying body and the target, ris the angle between the vector of the distance R z and that of the distance between the flying body and the point of intersection of the ground by the velocity vector of the body, c is the speed of light, f S is the transmission frequency of radar for emitting the signals from the head, B is the evaluation bandwidth of the radar and V G is the velocity of the flying body.

6. A method as claimed in any one of claims 1 to 3, wherein the target is moving and the flight path of the flying body is corrected to compensate for the target movement.

7. A method as claimed in claim 6, comprising the step of correcting the flight path by guiding the flying body towards an estimated target impact point spaced from the instantaneous target location by a travel increment determined as the product of the target velocity and the estimated instant of impact with the target.

8. A method as claimed in claim 7, comprising the step of determining the target velocity from the ratio of the radial velocity of the target and the velocity of the flying body multiplied by the cosine of the angle between the vector of the distance between the flying body and the target and the vector of the distance between the flying body and the point of intersection of the ground by the velocity vector of the body.

9. A method as claimed in any one of claims 6 to 8, wherein the flight path correction is obtained by on-line computation or by reading out from a stored table.

10. A method as claimed in any one of the preceding claims, wherein the step of controlling comprises determining transverse acceleration of the flying body by the equation nV2 sind R z 0 wherein VG is the velocity of the flying body, -ro is the angle, at the instant of target detection, between the vector of the distance between the flying body and the target and the vector of the distance between the flying body and the point of intersection of the ground by the velocity vector of the body, and R z is the distance between the flying body and the target at the instant of target detection.

11. A method as claimed in claim 6, comprising the step of correcting the flight path in dependence on change in the angle between the vector of the distance between the flying body and the target and the vector of the distance between the flying body and the point of intersection of the ground by the velocity vector of the body.

12. A method as claimed in claim 1 and substantially as hereinbefore described with reference to Figs. 1 to 6 of the accompanying drawings.

13. A flying body provided with a target-seeking head for performance of the method claimed in claim 1, comprising a group of transmitting and receiving aerials in the form of a rigid subassembly fixedly connected with the structure of the body and a transmitting and receiving unit connected to the aerial group.

14. A flying body provided with a target-seeking head for performance of the method cliamed in claim 1, comprising a transmitting and receiving unit in the form of a rigid sub-assembly connected with the structure of the body, the unit comprising optical signal transmission means and optical signal receiving means and an evaluating unit being connected to the signal receiving means.

15. A flying body as claimed in claim 13, wherein the aerials comprise one transmitting aerial and at least three receiving aerials.

16. A flying body as claimed in claim 14, comprising four receiving aerials.

17. A flying body as claimed in claim 15 or claim 16, wherein the aerials are of substantially the same size.

18. A flying body as claimed in any one of claims 15 to 17, wherein the receiving aerials are arranged around the transmitting aerial and disposed internally of the flying body.

19. A flying body as claimed in any one of claims 15 to 17, wherein the receiving aerials are arranged around the transmitting aerial and disposed externally of the flying body.

20. A flying body as claimed in any one of claims 13 and 15 to 19, wherein the aerial group has wide lobes.

20. A flying body as claimed in any one of claims 12 and 15 to 19, wherein the aerial group has wide lobes.

21. A flying body as claimed in any one of claims 13 to 20, wherein the transmitting and receiving unit comprises a target-recognition logic device, a geometry computing device connected to the logic device and a regulator connected to the computing device, the computing device and regulator being operable to provide signals for control of the flight path of the flying body.

22. A flying body as claimed in claim 21 when appended to any one of claims 15 to 20, wherein the transmitting and receiving unit comprises a control device arranged to control the transmission aerial by way of a modulator, a control stage and a power output stage.

23. A flying body as claimed in claim 22, wherein the control device is arranged to generate single pulse sionals and to drive the logic device.

24. A flying body as claimed in clai m 22 or claim 23, wherein each of the receiving aerials is serially connected to the logic device by way of a first amplifier, a first filter, a second, regulable amplifier, an analog-to-digital converter, a second filter for distance and a third filter for velocity.

25. A flying body as claimed in claim 24, wherein the second filter and the third filter are an R-M filter and a V-FFT filter, respectively.

26. A flying body as claimed in claim 14, the optical signal transmission means comprising at least one laser.

27. A flying body provided with a targetseeking head substantially as hereinbefore described with reference to Figs. 7 and 8 of the accompanying drawings.

131d Amendments to the claims have been filed as follows 13. An armed flying body provided with a target-seeking head for performance of the method claimed in claim 1, the head being arranged to control the flying body for travel on a curved flight path, with its path vector pointing towards the ground, during a target approach phase, to emit signals for reflection by the target and the ground, and to so control the flight path that the ratio of the targetreflected signal to the ground echo signal is kept substantially constant in the mean, and the head comprising a group of transmitting and receiving aerials in the form of a rigid sub-assembly fixedly connected with the structure of the body and a transmitting and receiving unit connected to the aerial grouD.

14. An armed flying body provided with a target-seeking head for performance of the method claimed in claim 1, the head being arranged to control the flying body for travel on a curved flight path, with its path vector pointing towards the ground, during a target approach phase, to emit signals for reflection by the target and 'the ground, and to so control the flight path that the ratio of the targetreflected signal to the ground echo signal is kept substantially constant in the mean, and the head comprising a transmitting and receiving unit in the form of a rigid sub-assembly connected with the structure of the body, the unit comprising optical signal transmission means and optical signal receiving means and an evaluating unit being connected to the signal receiving means.