GB2414860A

GB2414860A - Radar systems for airborne vehicles

Info

Publication number: GB2414860A
Application number: GB8214888A
Authority: GB
Inventors: Roger Voles
Original assignee: EMI Ltd
Current assignee: EMI Ltd
Priority date: 1981-07-21
Filing date: 1982-05-25
Publication date: 2005-12-07
Anticipated expiration: 2002-05-25
Also published as: GB8214888D0; GB2414860B

Abstract

An airborne vehicle in the form, of a terminally-guided sub-munition has a wing or wing-like assembly (100) which can be stowed lengthwise of the body and deployed, for flight, transversely of the body. An antenna array is mounted on the wing surface to extend across the undersurface thereof and is capable of generating a fan beam pointing forwardly of the sub-munition. A target on the ground is identified in the search phase by scanning the fan beam in azimuth and the sub-munition may then be pitched over into a dive to approach the target, so detected, in the terminal phase. The detected target may then be tracked using a linear antenna array conforming to the nose of the submunition. Scanning of the wing-mounted antenna can be achieved by rolling the vehicle, by turning the vehicle in azimuth, or by rotating the wing itself in azimuth.

Description

RADAR SYSTEMS FOR AIRBORNE VEHICLES

This invention relates to radar systems used in airborne vehicles and it relates especially, although not exclusively, to such systems used in terminally-guided sub-munitions.

Infra-red sensors are known but the sensitivity of these devices to cloud or fog, for example, tends to limit their effectiveness in operation especially in an airborne environment. In contrast, when radar frequencies are used this problem is relatively unimportant and so generally it is preferred that a radar should be used in the guidance or surveillance system of an airborne vehicle. Hitherto, a radar system used in these circumstances has typically comprised a planar antenna array, mounted in two dimensional gimbals to facilitate scanning, and the entire arrangement is normally confined within the nose of the vehicle and protected by a radome. A complex mechanical structure of this kind tends, however, to be relatively expensive and the radome, which at millimetric wavelengths should be less than 1.5 mm thick, tends to be difficult to construct with the necessary degree of robustness. Moreover, in the case of a sub-munition the available space for a radar system of the abovedescribed kind is rather restricted and it is possible that the system could limit the efficacy of a shaped charge which is also housed within the nose.

It is an object of the present invention to provide an improved radar system for use in an airborne vehicle in which the above-described difficulties are substantially avoided. : 2:

According to the invention there is provided an airborne vehicle including a radar system wherein a substantially planar antenna array is mounted on a lower surface of an aerofoil to be capable, in flight, of extending transversely of the vehicle body and generating a response pattern in the form of a beam which is narrower in azimuth than in elevation, and a circuit is associated with the antenna array to transmit and or receive a radar signal.

The airborne vehicle may be a terminally-guided sub-munition.

With a configuration of this kind it is possible to generate a fan beam, directed ahead of the vehicle, having a relatively large beam width in elevation (typically about 30) and a narrow width in azimuth (typically about 4).

In one embodiment of the invention, the antenna array is mounted on the wings of the vehicle. The wing itself may have a substantially rectangular configuration or the wing may have a different shape, the antenna array conforming to a substantially rectangular region thereof. In operation of the system the wings may be fixed relative to the body and scanning of the resulting fan beam over the terrain below is accomplished by suitably manoeuvring the vehicle. Alternatively, scanning may be achieved by moving the wings relative to the body of the vehicle.

In another embodiment of the invention, the antenna may be mounted on two members in the form of non-lifting blades, which extend, along a common axis, from either side of the nose of the vehicle so as to lie in a substantially horizontal plane during substantially level flight. The nose portion of the vehicle may be coupled for rotation about the axis of the body and may be provided with rotor blades which cause such rotation as the vehicle progresses in the forward direction along the flight track, and in this way repetitive scanning of the field of view, lying ahead of the vehicle is achieved.

In order that the invention may be more readily understood and carried into effect specific embodiments thereof are now described, by way of example only by reference to the accompanying drawings of which, Figure 1a represents a sub-munition in flight and illustrates a preferred elevation of a fan beam generated by a radar mounted thereon, Figure 1b illustrates schematically the form of the fan beam generated by a described example of a radar mounted on a sub-munition, Figures 2a and 2b represent schematically plan and side elevation views of a terminally guided sub-munition having a fixed wing in the deployed position and Figures 2c and 2d represent end elevation views showing the wing in respective stowed and deployed positions, Figure 3 shows a side elevation sectional view of a terminally-guided sub-munition with the wing assembly in the stowed position, Figures 4a to 4c show respective plan, side and end elevation views of the wing assembly and Figures Ad and he show respective sectional views through the wing assembly, Figures 5a, b and c show respective side sectional, plan and scrap views of a mounting mechanism used to deploy the wing, Figure 6 shows a side sectional view of a latching arrangement for the wing assembly, the tail fin and tail planes.

Figure 7a illustrates a plan view of the wing undersurface and shows the layout of the antenna array, Figure 7b illustrates a composite feed used in association with the antenna array, Figure 7c illustrates a single subarray used in the wing antenna, Figures 8a and 8b show different conformal nose antennas, Figure 8c shows the spatial distribution of radiating elements on the nose, Figure Ed shows a composite feed arrangement for the nose antenna, Figure Be shows a flat nose antenna, Figure 9a shows a split wing arrangement and Figures 9b and 9c show respective plan and end elevation views of the wings in the stowed position, Figure 10 shows a sub-munition having a cruciform arrangement of wings, Figure 11 shows a sub-munition having a particular form of control in roll and pitch, Figure 12 shows an arrangement having stewed wings, Figure 13 shows a swing wing arrangement, Figures 14a and 14b show two sub-munitions having non-lifting blade antennas, Figure 15 illustrates one form of nonformal nose antenna capable of rotation about the axis of the body of the sub-munition, Figures 16a to 16c show examples of linear antenna arrays suitable for use in a blade or wing radar of the present invention, Figure 17 shows a radar system for use with such an antenna.

It is usually desirable that a radar used, for example, in the guidance system of a terminally guided sub-munition (TGSM) should be capable of searching for a target within a roughly circular region on the ground typically 500 metres in radius and to have acquired a target at a range of at least 1 km. The sub-munition itself is usually aerodynamically shaped so as to glide, and maintain altitude during a search phase until the target has been identified and subtends a depression angle of around 45. The sub-munition then enters the terminal phase and pitches over into a steeper descent to track, and home in on the target.

As illustrated in the schematic side elevation view of Figure la, it is possible to scan the target region (500 metres in radius), during the search mode, with a single sweep in azimuth of a fan beam having a width in elevation of about 30. Moreover, it has been found by the inventor that a system of this kind has an adequate detection range and resolution, especially if the aperture of the antenna is sufficiently large. A linear antenna array having an aperture : 6: 500 mm wide, for example, proves to be particularly suitable over a wide range of operating frequencies; at 9.4 GHz, 35 GHz and 94 GHz, for example, the resulting fan beam has a width in azimuth of 4.4, l.l and 0. 44 respectively.

Alternatively dimensioned arrays can, of course, be used but it has been found that generally an array required to generate a fan beam, commensurate with an acceptable detection range and resolution, tends to have an aperture which is wider than the body diameter of conventional terminally-guided sub-munitions (e.g. relatively large sub-munitions have diameters typically in the range 80-100 mm). It will be appreciated that by using a fan beam of this kind scanning may be accomplished relatively slowly in a single, or small number of sweeps, and this obviates the need for a complex scanning system of the kind conventionally used hitherto.

In one embodiment of the present invention, illustrated! schematically in Figure 2, the antenna array used to generate the fan beam is mounted on the substantially flat undersurface of the wing lO of the sub-munition. As shown in the plan view of Figure 2a, the wing lO spans about 500 mm, in this example, and so at an operating frequency of 9.4 GHz generates a fan beam having an azimuthal width of about 4.4. To form a beam having a width in elevation of about 30, the antenna array may have an effective aperture of about 2 (where ifs the wavelength of the radiation used) and when projected onto the plane of the wing this corresponds to an antenna width of about 4\ for a depression angle of 30 with respect to the wing.

As illustrated in Figure 2a, therefore, a wing of the above-described dimensions preferably has a chord, C, of about mm (for = 30 mm).

In this embodiment of the invention a single wing 10 is pivotally mounted, for rotation about an axis X, to the underside 11 of the body 12 of the sub-munition and may be stowed prior to launch along the length of the body, as shown in Figure 2c. After launch the wing may be turned through an angle of 90 and then locked into the deployed position, as shown in Figure 2d, and in these circumstances a fan beam is directed ahead of the sub-munition along the line of flight.

By mounting the wing below the body in this manner interference spoiling of the fan beam by reflection from the body is minimised. Moreover, if for example, the mean angle of depression of the centre of the radar beam during the search phase, is about 25 relative to the horizontal and the sub-munition is pitched up, relative to the horizontal, at an angle of about 5 say, then the upper "edge" of the fan beam remains typically 15 below the underside of the body 12, assuming, as before, a fan beam 30 in elevation.

An example of fixed wing arrangement of the above-described kind is now described in greater detail by reference to the scale drawings of Figures 3 to 7. As before, the wing spans 500 mm and the body of the TGSM is 650 mm long and 100 mm in diameter. The wing is designed in this example to provide sufficient lift to allow a gliding range of between 3 and 5km when the TGSM is deployed from a height of 500 metres. The : 8: antenna mounted on the undersurface of the wing is capable of generating a response pattern giving an elevation coverage of about 26 and a width in azimuth of about 4.4 at about 10 GHz which points ahead of the sub-munition at an angle Is in elevation of about 60 . As illustrated in Figure 1b the beam will then illuminate a region on the ground about lkm long at a height of 500 metres.

Referring initially to Figure 3, which illustrates a cross-sectional side view of the sub-munition, the wing assembly shown at 100 is mounted on the underside of the body 120 by means of a mounting mechanism 130 which, as will be described hereinafter, facilitates rotation of the wing through 90 from the stowed position (shown in the drawings) in which the wing extends lengthwise of the body to the deployed position in which the wing extends transversely of the body. As is usual in a TOSS the body 120 houses a gyro unit 121, an electronic processing pack 122 for the radar and system controller, a power supply 123 and a shaped warhead 124 mounted to the fore of the body. The body also houses a main r.f. head 125 which supplies the wing antenna, and a monopulse r.f. head 126, the purpose of which will become evident hereinafter.

The sub-munition is manoeuvred in flight by means of a vertical tail fin shown at 127 and two tail planes (not shown) which extend, in the deployed position, on either side of the body. The fins are controlled in flight by a servo driver 128 mounted at the rear of the body and are housed, in the stowed position, within respective slotted cavities in the body 120. o - .

A common mechanism for latching the tail plane, fins and the wing in the stowed position is described hereinafter by reference to Figure 6.

The wing assembly is shown in detail in the scale plan, side and end elevation views of Figures 4a to 4c and in the sectional views of Figures Ed and Me taken along XX and [Y respectively in Figure 4a.

A central portion of the wing, represented by the shaded area in Figure 4a carries a rectangular mounting plate 131 of lo aluminium alloy which is shown in the partial side sectional view of Figure 5a. The wing assembly is shown (again in part) at 100 in the stowed position. A first cylindrical support member 132 is fixedly mounted on plate 131 for rotation about the axis of a second, complementary support member 133 fixedly mounted on the body of the sub-munition. A ball race 134 allows rotation of the support member 132 (and so the wing assembly also) relative to the body. The wing assembly is biassed resiliently towards the deployed position by a tension spring 135 shown in the plan sectional view of Figure 5b through the body. The tension spring is fixed to the support member 133 at one end and is coupled at the other end to a pin 136 mounted on the wing assembly. The pin can move along an arcuate slot 137 in response to the action of the tension spring and is locked in the deployed position by a latch shown at 138 in the scrap view of Figure 5c.

As described hereinbefore, to maintain the wing assembly in the stowed position against the biassing action of the spring a : 10: latching mechanism common to the wing assembly, tail fin and tail planes is used and this is shown in the partial side view of the rear of the submunition in Figure 6. The latch mechanism is shown at 150 and comprises a support portion 151 pivotally mounted on the body of the sub-munition and projections 152, 153 which, in the stowed position are respectively located in notches NF, NW in the tail fin and wing assembly to maintain them in the stowed position. The latching mechanism has a pair of similar projections (not shown) which are located in slots in the tail planes to maintain them in the stowed position also. An explosive motor 156 is fired to force the latching mechanism back (into position 150') to simultaneously release the wing assembly, tail fin and planes which may then assume their respective deployed positions. A motor used to control the tail fin in flight, in response to control signals from the servo control is shown, by way of

example, at 157.

Referring now in more detail to Figures 4a and 4b it will be seen that the wing assembly 100 spans 500 mm and has a width varying from 100 mm at its centre to 80 mm at its tips. The wing profile which is shown clearly in Figures 4c to he has been designed in this example to have zero angle of incidence since aerodynamic studies have shown that optimum gliding performance can then be achieved. As described hereinbefore, the wing is capable of providing sufficient lift to allow a gliding range of between 3 and 5km when deployed at a height of 500 m.

The wing is formed of a high density (approx. 0.25 g/cc) : 11: foam and supports an antenna panel P of 1/16" RT duroid set into the undersurface. As is evident from the sectional views of Figures Ad and Me panel P conforms generally to, and has the same dimensions as, the wing undersurface. The antenna panel P bears an antenna array in the form of a printed circuit and a further panel F bearing the azimuth power divider is provided on the side of panel P remote from the undersurface to feed r. f. to the antenna array. The feed panel is also formed of 1/16" RT duroid and is mounted close to the trailing edge of the wing.

The azimuth power divider is coupled to the r.f. head shown at in Figure 3.

Figure 7a shows a plan view of the underside of the wing and illustrates the layout of both the antenna array itself and the elevation power dividers which distribute radiation to the array.

In this example, the array comprises 24 identical sub-arrays E1, E24 each comprising six radiating elements in the form of proximity coupled patch resonators R of microstrip printed onto the 1/16" RT duroid panel P. The patch radiators are roughly square (of 9.5 mm side) and the sub-arrays are spaced apart by 20 mm along the wing (along axis y), this spacing being sufficient to accommodate the elevation feed lines L1 L24 which extend alongside the radiators forming a respective sub-array.

An enlarged view of a sub-array and its associated feed line is shown in Figure 7c. The feed line is end fed in this example and is also formed of microstrip printed on the antenna : 12: panel. By suitably choosing the relative spacings lengthwise of the feed line (along axis x) the phase distribution across the wing can be tailored to generate a response pattern of the required width in elevation ( -- 26 Figure 1b) pointed at an angle s in elevation of about 60. Moreover, it is possible to generate a response pattern which is relatively uniform over angles exceeding (3 = 60, to permit good illumination of the target region in the terminal phase when the sub-munition is pitched over into a dive. The spacing of elements across the wing is around 12 mm in the example.

The azimuth power divider comprises a 24-way corporate feed, shown in Figure 7b, which is also of microstrip printed on the feed panel. Each limb 1 to 24 of the corporate feed is connected through the feed panel F to a respective elevation feed L1...L24. The input I is connected to the main r.f. ' head shown at 125 in Figure 3.

The antenna gain of the above-described arrangement, which takes into account losses in the feeds, is expected to be about dB.

It will be appreciated that alternative feed arrangements could be used. In particular, each elevation feed may be a six way corporate feed connected directly to the patch resonators forming a respective sub-array. The azimuth feed on the other hand may comprise a centre fed power divider extending along the feed panel. 80th the corporate feed and the centre feed may be of microstrip or strip line. Alternatively end fed elevation or azimuth power dividers of microstrip or strip line could be : 13: used. Furthermore, slot radiators rather than patch radiators could be used to form the antenna array.

Although a single wing of the above-described kind, may conveniently be stowed lengthwise of a relatively large sub-munition 650 mm long and lOO mm in diameter, say, this is clearly not possible in the case of relatively small sub-munitions - 400 mm long and 80 mm in diameter, say. In these circumstances, the wing could be divided into two parts 20, 21 which are separately pivoted to the body 22 and may be stowed sideby-side along the underside of the sub-munition, as shown in the plan and end elevation views of Figures 9b and 9c respectively. As shown in Figure 9a, however, the overall span of the wings, when deployed, remains at 500 mm although the width of each wing is only 40 mm which is adequate to generate a fan beam of the optimum width in elevation (30 in this case) at operating frequencies down to about 35 GHz.

With fixed wing arrangements of the above-described kind i.e. arrangements in which the wing is deployed in a fixed position on the body of the TGSM, scanning of the fan beam in azimuth, during the search phase, is accomplished by suitably manoeuvring the sub-munition in flight. In one example, a "twist and steers (sometimes known as a "roll and steers) technique is used whereby the sub-munition rolls about an axis of the body to effect scanning of the radar beam in azimuth and, in response to received radar returns, is steered in the direction of the target. Initially a relatively wide sweep (typically + 22} ) in azimuth is performed but once the target : 14: has been located the sub-munition is steered towards it and so the extent of the scan can be reduced.

Scanning of the antenna over the relatively wide sweep angle is generally only required for one or two scans, after which a suitable target should have been located. For this manoeuvre it is preferred to use a "barrel roll" whereby the sub-munition is caused to rotate through 360 about an axis parallel to, but offset from, the longitudinal axis of the body. Control of roll is achieved in this case by suitably adjusting the tilt of the tail planes.

When the sub-munition has been manoeuvred to a position in which the target subtends a depression angle of about 45 it is caused to enter the terminal phase by pitching over into a relatively steep descent. The target can then be tracked using a receive antenna conforming to the hemispherical nose portion of the sub-munition, the antenna on the wing being used as the transmit antenna to illuminate the target area. By suitably feeding the conformal antenna, monopulse operation can be achieved to obtain measurements of both range and angle error (in azimuth or elevation depending on the form of antenna array used). Monopulse techniques are described in "Introduction to Radar Systems" Skolnik International Student Edition p. 176-179 McGraw Hill.

As is shown in the end-on view of the nose in Figure 8a the conformal array may lie in the horizontal plane of the sub-munition to enable monopulse tracking in azimuth or alternatively as shown in Figure 8b the array may lie in the : 15: vertical plane to enable monopulse tracking in elevation. The elements forming the array may be proximity coupled patch radiators of microstrip, for example, fed either in parallel or series.

Alternatively directly coupled radiators could be used.

To generate an antenna response pattern pointing along the axis of the sub-munition it is necessary to introduce phase shifts at respective elements thereby to compensate for the curvature of the nose. Figure 8c illustrates a section through the nose portion in the horizontal plane and the antenna array, in this example, comprises six elements referenced at E'1....E'6 distributed on the nose at equal intervals along the y-axis, normal to the longitudinal axis (x) of the body. The diameter of the nose is assumed to be 100 mm and the spacing d of the elements (along axis y) is assumed to be 15 mm. For a parallel feed arrangement the phase shifts are given by h, to give a toward pointing beam where h is the distance (along x-axis) of the respective element from the centre of the nose and in these circumstances the elements E1' to E6' are subjected to respective phases 203.2, 64.2, 6.8, 6.8, 64.2 and 203.2 for a frequency of 10 GHz. The antenna may be used for transmitting and or receiving.

Figure Ed shows a corporate power divider suitable for feeding a vertical array at its centre point for operation in monopulse.

The divider would include appropriate delays or phase shifters to obtain the required phase distribution. The hybrid junction HJ could be printed on the antenna substrate itself in which case separate cables would carry the sum and difference signals to : 16: the r.f. head (shown at 126 in Figure 3) or alternatively separate antenna halves could be provided, the hybrid junction being mounted on the r.f. head.

It may be desirable to use crossed horizontal and vertical nonformal antenna arrays to provide a measure of angle-error both in elevation and azimuth.

In an alternative arrangement, shown in Figure Be, a planar antenna array mounted on a flat substrate within the nose is used. Again either a corporate or series feed arrangement can be used. It is likely that the conformal and flat nose antennas of the above-described kind will have a gain of about 9 to 12 1B at an operating frequency of 10 GHz.

The above-described arrangements relate to monopulse tracking. However, by suitably feeding the nose antenna a squinted response pattern may be generated which can be scanned conically by spinning the rapidly descending sub-munition about its body axis as it homes in on the target. Alternatively the nose portion only of the body can be made to rotate the means by which this is achieved will be described hereinafter by reference to Figure 15. Alternatively target tracking could be achieved using a radiometer or IR seeker mounted on the nose and in another example a radar may be provided to generate three or four fixed pencil beams to permit tracking in the terminal phase using the known sequential robing technique - it is not then necessary to spin the TGSM.

The nose antenna could be used both to transmit and receive and in yet a further example it is possible to operate the wing : 17: antenna array in monopulse by feeding it centrally using a hybrid junction, thereby to provide a measure of the angle-error in azimuth of the target in the terminal phase.

The "twist and steer control" described hereinbefore is relatively simple to implement but has the disadvantage that the action of steering the submunition towards a target causes the fan beam to move away from the target.

In an alternative technique, an additional vertical aerofoil 25 is provided, as shown in the respective end and plan views of Figure 10a and 10b, to form a cruciform arrangement.

This additional aerofoil carries no antenna and is used, in conjunction with the tail plane or rudder, solely to steer the aircraft to effect azimuthal scanning without roll. The wing and aerofoil are mounted on the body of the vehicle for rotation about offset, mutually orthogonal pivot points 26, 27 and may be stowed, prior to launch, along the sides of the body. When deployed, however, the vertical aerofoil is used in conjunction with the tail plane or rudder to steer the vehicle and has the advantage that when a target is detected the vehicle is pointing in the desired direction, the vehicle being maintained in the horizontal attitude during steering.

It will be appreciated that an airborne vehicle (e.g. a terminally-guided sub-munition) using a "twist and steer" form of control should be especially responsive in roll and this can be achieved using the fins provided on the vehicle.

In another embodiment of the invention, however, illustrated in Figure 11, improved response in roll is achieved : 18: by removing control from the tail planes and instead providing each wing 15, 16 with a respective moveable end portion 17, 18.

In such an arrangement control of roll can be achieved by counterrotating the moveable wing portions while control of lift is achieved by co-rotation. As shown in Figure 11 the outer two-thirds of each wing is moveable, although the actual fraction adopted would depend upon the overall design considerations and could, in principle, be any value up to unity.

During the search phase the vehicle may typically be required to roll through about 1 radian in about 1 second. As the forward velocity of the vehicle will typically be of the order of 200 m/s it follows that, for a vehicle having a total wing span of 0.5m, the incremental wing pitch will be about 0.06 (i.e. 0.25m x 1 radian/200m). The differential pitch between the moveable wing portions will then only be about 0.12 which will involve a negligible effect upon the form and direction of the fan beam generated by the antenna array extending across the entire undersurface of both wings 15, 16.

It will be appreciated that in practice the actual differential pitch required to achieve roll at 1 rad/sec would be somewhat smaller than 0.12 on account of the fact that the wing consists of three flat sections, the pitch being correct at two positions only across the span.

During the terminal phase, when the vehicle is caused to dive to approach a detected target, it may be desirable to spin the vehicle through as many as ten rotations in the last 100 metres of flight. In that case, the required incremental wing : 19: pitch, necessary to achieve rotation, would be about 9 (i.e. 0.25m x 2rCrad/10m) corresponding to a differential pitch of 18. Insofar as this will result in relatively good forward illumination from the "pitched-up" sections of the antenna a coning guidance system becomes feasible and it may then be possible to dispense with the nonformal nose antenna of the kind described hereinbefore. Since relatively large differential pitch angles are used in the terminal phase it is preferable to design the airframe and antenna array so that the moveable sections 17, 18 of the wing rotate about an axis R-R lying immediately above the position, in the chord of the wing,of the antenna array phase centre. Clearly alternative methods of tracking a target could be adopted in the terminal phase. A conformal nose antenna operating in monopulse, or by conical scanning could be used, as described hereinbefore.

Although the above-described embodiment is especially applicable to terminally-guided sub-muntions (TGSM's) the use of moveable wing sections to achieve radar scanning control is also applicable to other forms of winged vehicles.

Having described in detail a fixed wing embodiment of the present invention a number of alternative arrangements will now be described by reference to Figures 12 to 15.

In the embodiment shown in Figure 12, the azimuthal scan is accomplished in the search phase by stewing a single wing 30, which is again pivotally mounted on the underside of the body 31, through an azimuthal angle of + 22} relative to the axis of the body. As indicated in the drawing slowing occurs in the : 20: plane of the wing which in this example has a chord of 40 mm and is suitable for operation at frequencies down to about 35 GHz.

The arrangements described hereinbefore, having one or two substantially flat wings mounted on the underside of the sub-munition may tend to be rather unstable in flight and may require active stabilization. If scanning of the fan beam is achieved by manoeuvring the sub-munition then a suitable dihedral angle of the wings would be used to provide stabilization. With an arrangement of this kind a mechanism is provided to set the dihedral angle as the wing rotates to the deployed position. In addition, the inclination of the major axis of each wing could be adjusted relative to the axis of the body to ensure that the correct antenna aperture is presented in the beam direction. The antenna radiating elements are suitably designed so as to be commensurate with the expected inclinations of the wings. Alternatively a "swing wing" arrangement, of the kind illustrated in Figure 13a, can be used in which separate wings 40, 41, each having its own antenna array operable during alternate pulses of the radar, are mounted to either side of the body 42 so as to be capable of swinging, in a scanning movement, in the horizontal plane. This arrangement permits mounting either on the centre or the top of the body and this configuration provides for greater stability in flight, although some reduction in radar performance may occur due to the reduced antenna aperture and possible reflections from the body. To provide even greater stability the dihedral angle of the wings can be varied as appropriate in dependence on the swing angle. : 21:

The wings may be folded back to lie along the length of the body so as to be stowed either centrally, as shown in the alternative configurations of Figures 13b and 13c, or in a "high wing" configuration against the upper surface of the body, as shown in Figure 13d. Since each wing has a relatively small span - 250 mm in this case, stowage is readily facilitated.

Since the antennas mounted on the wings operate independently their respective fan beams have a relatively wide azimuthal spread and this leads to a reduction in the target detection range by a factor of about and a reduced signal to clutter ratio of about 3 dB.

In operation, once the target has been detected, the wings are gradually returned toward their forward position, but are halted at a position just short (by about half the azimuthal beam width) of the extreme in-line position. Since the antennas operate on alternate radar pulses the system then acts as a sequential-robing homing radar suitable for steering the sub-munition towards the target.

Although the arrangements described hitherto have comprised an antenna array conforming to the wings of an airborne vehicle - a sub-munition, for example - it is also possible to mount the array on "non-lifting" members in the form of blades which extend from the body of the vehicle in a common plane but which are mounted towards the nose as shown, for example, in Figures 14a and 14b. These figures illustrate sub-munitions respectively 650 mm and 400 mm long and each blade 50, 51 is about 200 mm long resulting in an overall span of 500 mm. : 22:

Prior to deployment the blades may be folded back to lie flat against the body 52 of the sub-munition, or alternatively they may be housed within slots also extending along the length of the body. Although each blade is locked into the deployed position, as shown in Figures 14a and 14b, it is freely mounted to a shaft for rotation about a longitudinal axis located towards the leading edge thereof. In this way the blades are feathered and are incapable of providing lift which might otherwise have resulted in vehicle instability. As in the case of an antenna array conforming to the wings of a sub-munition, an array conforming to blades, of the abovedescribed kind, may be used to scan the terrain in azimuth during the search mode.

Furthermore, since the blades are mounted towards the front of the submunition it is also possible to use them for scanning in the terminal phase, by rotating the entire sub-munition about the axis of its body.

In an alternative approach, scanning in the terminal phase is achieved by switching the radar to a conformal nose of the kind described hereinbefore by reference to Figures 8a to 8c.

A conformal nose antenna of this kind generates a fan beam directed ahead of the sub-munition and scanning can be achieved either by spinning the rapidly descending sub-munition about the axis of the body as it homes in on the target or by using monopulse scanning. Since the range of the target is considerably less than in the search mode a relatively short antenna aperture of this kind proves to be sufficient. As before, in a further arrangement three or four fixed pencil : 23: beams are generated to permit homing by means of the known technique of sequential robing - no spinning of the sub-munition is required in this case and in yet further embodiments a radiometer or IF seeker could be mounted within the nose for scanning in the terminal phase.

When feathered blades are used scanning in the search phase can be accomplished, as before, either by manoeuvring the body of the submunition or alternatively by moving the blades relative thereto. Alternatively the blades could be used in a repetitive scanning mode in which case the nose shown at 61 in Figures 15a and 15b is coupled to the main part of the body 62 by a bearing which permits free rotation about the axis of the body. Rotor blades or tabs 63 are mounted on the nose to cause such rotation as the sub-munition advances in flight and typically the nose rotates at a speed of about l rev/see when the forward velocity is about 200 metres/sec, thereby providing a repetitive azimuthal scanning capability during the search mode. This coupling arrangement can also be used to facilitate scanning in the terminal phase using either the blade antenna or the conformal nose antenna, as described earlier, although the rotation speed should preferably be about ten times that required in the search mode. This can be achieved by increasing the pitch of the rotor blades mounted to the nose.

Although patch resonators have been described in relation to the embodiments of Figures 3 to 7 a conformal linear antenna array mounted on wing or blade may alternatively be of the form illustrated schematically and by way of example only in Figures : 24: 16a, b and c. The radiating elements shown at E1... En in Figure 16a, for example, can be printed on microstrip and fed by an appropriate arrangement of transmission lines T1 Tn' which may again be formed of microstrip or a dielectric guide, for example. This arrangement is shown more clearly in the array of Figure 16b having eight radiating elements. Figure 16c shows an end fed array in which the radiating elements E1"...En" are formed of microstrip or strip line slot radiators, for example, and the feed F could be formed from a dielectric guide, metal waveguide strip line or fin line, for

example.

When relatively high operating frequencies are used (94 GHz say) the width of the wing antenna, commensurate with a beam width in elevation of about 30 is a mere 13 mm (i.e. 4> = 4 x 3.2 mm) which is much smaller than the chord of most a structurally and aerodynamically stable wings. This surplus wing area can be exploited to improve the range detection of the system. In one embodiment this is achieved by using two linear antenna arrays mounted one behind the other over the chord of the wing. Each array has a width of 8> and this results in the generation of two fan beams, each 15 wide in elevation, (at a depression of 30 ) which abut one another to provide an overall coverage of 30 in elevation. In operation the antenna arrays are energised alternately, resulting in an increase in system gain of 6 dB and a 40% increase in the free space range detection. With an arrangement of this kind, using two antenna arrays the wing has a chord length of at least l6\ : 25: (i.e. 51 mm at 94 GHz) which is a practical proposition even for relatively small sub-munitions. In another embodiment a single antenna aperture 16\ wide is used and this generates a beam 7} wide in elevation. Four separate beams, each 7} wide could be generated to give the desired 30 elevation coverage by using a beam former such as a Butler matrix.

The linear antenna arrays decribed above could be used in conjunction with a radar system of known kind as shown by way of example in the block schematic diagram of Figure 17. Signals, indicative of a target, generated by a radar circuit of this kind are used to control the servo driver to the tail planes to steer the sub-munition in flight towards the target. By duplexing the system the same antenna can be used for both the receiver and the transmitter, although alternatively as described hereinbefore an additional antenna, conformally distributed over the nose of the sub-munition could be provided, to generate a pencil beam pitched at an appropriate angle. If the radar is scanned by moving the wings or blades of the vehicle relative to the body, it is necessary for the pencil beam to move in synchronism, and this could be achieved by rotation of the nose as described above. Either antenna, however, could be used as the transmitter and the other used as the receiver.

The arrangements described above provide a radar system which is particularly convenient for use in a terminally-guided sub-munition. It will be appreciated, however, that the invention is applicable to other forms of airborne vehicle, such : 26: as a "parawing" vehicle, for example. In this case the radar antenna is incorporated in the wing and the shaped charge, and the radar and control apparatus are suspended below the wing by a control rod which serves to steer the vehicle by shifting its centre of gravity. Alternatively an autogyro arrangement could be used. Other forms and applications of the invention will also be envisaged by persons skilled in the art. In particular, as explained earlier, it will be appreciated that the wings need not have an elongate shape. They could, for example, have a "delta" shape, the antenna array conforming to an elongate region towards to leading edge thereof. : 27:

Claims

What we claim is: 1. An airborne vehicle including a radar system wherein

a substantially planar antenna array is mounted on a lower surface of an aerofoil to be capable, in flight, of extending transversely of the vehicle body and generating a response pattern in the form of a beam which is narrower in azimuth than in elevation, and a circuit is associated with the antenna array to transmit and or receive a radar signal.
2. An airborne vehicle according to Claim 1 wherein the antenna array is mounted on a lower surface of a wing which extends, in substantially level flight, along a horizontal axis extending transversely of the vehicle body, the vehicle being manoeuvrable in flight to scan the response pattern, generated by the antenna array, in azimuth across the field of view to be capable of detecting therein a target.
3. An airborne vehicle according to Claim 2 wherein the wing is mounted pivotally on the underside of the vehicle body and is capable of being stowed lengthwise of the body and being deployed, for flight, transversely of the body.
4. An airborne vehicle according to Claim 3 wherein the wing is arranged for pivotal motion in substantially level flight to scan the said response pattern, generated by the antenna array, in azimuth across the field of view to be capable of detecting therein a target.
5. An airborne vehicle according to any one of Claims 2 to 4 wherein the said vehicle body carries a further aerofoil mounted to extend, in level flight, along a vertical axis to assist in steering : 28: the vehicle towards a target detected in the field of view.
6. An airborne vehicle according to Claim 1 wherein the antenna array is mounted on respective lower surfaces of a pair of wings, the wings being mounted pivotally on opposite sides of the vehicle body and being capable of being stowed, lengthwise of the body, and being deployed, for flight, transversely of the body on opposite sides thereof.
7. An airborne vehicle according to Claim 6 wherein each said wing is arranged for pivotal motion, in substantially level flight, about a respective vertical axis and carries at a lower surface thereof a respective antenna array capable of generating a respective fan beam, the wings being caused to execute said pivotal motion to scan the respective fan beams, in azimuth, across the

field of view.
8. An airborne vehicle according to Claim 7 wherein said circuit is coupled, for operation, to each said antenna array whenever the respective wing executes said pivotal motion.
9. An airborne vehicle according to any one of Claims 1 to 8 comprising control means for causing the vehicle to fly at a selectable angle of pitch to approach a target detected in substantially level flight, and means for tracking said target while flying at said selectable angle of pitch.
10. An airborne vehicle according to Claim 9 wherein said tracking means comprises a further antenna mounted on, and conforming to, a surface of the nose of the vehicle body and being capable of forming a further forwardly directed fan beam, said nose being rotatable about the longitudinal axis of the body while flying : 29: at said selectable angle of pitch to scan the further fan beam so formed.
11. An airborne vehicle according to Claim 9 wherein said tracking means comprises a further antenna mounted on, and conforming to a surface of the nose of the vehicle body and means for feeding said further antenna array in accordance with monopulse operation thereby to track said target while flying at said selectable angle of pitch.
12. An airborne vehicle according to Claim 11 wherein said further antenna comprises an array of radiating elements extending in the horizontal or vertical plane of the body of the vehicle to be capable of generating respective vertical and horizontal fan beams.
13. An airborne vehicle according to Claim 9 wherein said tracking means comprises an array of radiating elements mounted in a common plane in the nose of the body of the vehicle and being capable of generating a forwardly directed fan beam.
14. An airborne vehicle according to Claim 1 wherein the antenna array is mounted on a lower wing surface of said vehicle which, in flight, extends transversely of the vehicle body, respective end portions of the wing being rotatable about a common axis of the wing to manoeuvre the vehicle in flight.
15. An airborne vehicle according to Claim 14 wherein said end portions of the wing are rotatable in opposite respective senses to cause the vehicle to roll, in substantially level flight, about an axis extending lengthwise of the vehicle body to scan the fan beam, in azimuth, across a field of view to be capable of detecting therein a target without substantially affecting the form of said fan beam. : 30:
16. An airborne vehicle according to Claim 15 capable of flying at a selectable angle of pitch to approach a target, detected in substantially level flight.
17. An airborne vehicle according to Claim 16 wherein one of said end portions is rotatable in the clockwise sense about said axis of the wing and the other end portion is rotatable in the anticlockwise sense about said axis of the wing to cause the vehicle, while flying at said selectable angle of pitch, to rotate about the longitudinal axis of the vehicle body, whereby the antenna array mounted on an end portion is capable of generating a fan beam which is scanned across the field of view to track a target detected in level flight.
18. An airborne vehicle according to Claim 17 wherein a further antenna is mounted on the nose portion of said vehicle body to generate a further, forwardly directed response pattern, the nose portion being capable, while flying at said selectable angle of pitch of rotating about the longitudinal axis of the body to scan said further response pattern across the field of view to track a target detected in level flight.
19. An airborne vehicle including a radar system wherein an antenna array is mounted on respective surfaces of a pair of non-lifting members mounted to extend, in flight, on respective sides of the vehicle body along respective axes lying in a common plane, the antenna arrays being capable, in flight, of generating respective response patterns in the form of fan beams which extend forwardly of the vehicle and a circuit is provided to transmit and or receive a radar signal. : 31:
20. An airborne vehicle substantially as hereinbefore described by reference to and as illustrated in the accompanying drawings.

20. An airborne vehicle according to Claim 19 wherein said non-lifting members are mounted pivotally on said body to be capable of being stowed lengthwise of the body and being deployed, for flight, transversely of the body.

21. An airborne vehicle according to Claim 19 or Claim 20 wherein said members extend, in substantially level flight, along a common horizontal axis, the vehicle being manoeuvrable in flight to scan said response patterns, in azimuth, across the field of view to be capable of detecting therein a target.

22. An airborne vehicle according to Claim 20 wherein said members are arranged for pivotal motion, in level flight, about respective vertical axes, the members being arranged to execute said pivotal motion alternately, to scan the respective fan beams, in azimuth, across the field of view to be capable of detecting therein a target.

23. An airborne vehicle according to Claim 20 wherein said non-lifting members are mounted on a nose portion of the body, the nose portion being capable, in substantially level flight, of rotating about the longitudinal axis of the body to scan the respective fan beams, in azimuth, across the field of view to detect therein a target.

24. An airborne vehicle according to Claim 19 capable of flying at a selectable angle of pitch towards a target detected, in substantially level flight, and being capable, while flying at said selectable angle of pitch, of rotating about the longitudinal axis of the body to scan the respective fan beams across the field of view to track said target. : 32:

25. An airborne vehicle according to Claim 23 capable of flying at a selectable angle of pitch towards a target detected in level flight, said nose portion being capable, while so flying, of rotating about the longitudinal axis of the vehicle body to scan the respective fan beams across the field of view to track said target.

26. An airborne vehicle according to Claim 19 capable flying at a selectable angle of pitch towards a target detected in the field of view, and comprising a further antenna array mounted on, and conforming to a surface of the nose of said vehicle body to generate a further response pattern, said nose being capable, while flying at said selectable angle of pitch, of rotating about the longitudinal axis of the vehicle body to scan said further pattern across the

field of view to track said target.

27. An airborne vehicle according to Claim 19 capable of flying at a selectable angle of pitch towards a target detected in substantially level flight and comprising a further antenna array mounted on and conforming to a surface of the nose of said vehicle body to generate a further response pattern and means for feeding said further antenna array in accordance with monopulse operation thereby to track said target while flying at selectable angle of pitch.

28. An airborne vehicle according to any preceding claim in the form of a terminally guided sub-munition.

29. An airborne vehicle substantially as hereinbefore described by reference to and as illustrated in the accompanying drawings. : :

Amendments to the claims have been filed as follows 1. An airborne vehicle including a radar system wherein a substantially planar antenna array is mounted on a lower surface of an aerofoil to be capable, in flight, of extending transversely of the vehicle body and generating a response pattern in the form of a beam which is narrower in azimuth than in elevation' and a circuit is associated with the antenna array to transmit and or receive a radar signal.

2. An airborne vehicle according to Claim 1 wherein the antenna array is mounted on a lower surface of a wing which extends, in substantially level flight, along a horizontal axis extending transversely of the vehicle body, the vehicle being manoeuvrable in flight to scan the response pattern, generated by the antenna array, in azimuth across the field of view to be capable of detecting therein a target.

3. An airborne vehicle according to Claim 2 wherein the wing is mounted pivotally on the underside of the vehicle body and is capable of being stowed lengthwise of the body and being deployed, for flight, transversely of the body.

4. An airborne vehicle according to Claim 3 wherein the wing is arranged for pivotal motion in substantially level flight to scan the said response pattern, generated by the antenna array, in azimuth across the field of view to be capable of detecting therein a target.

5. An airborne vehicle according to any one of Claims 2 to 4 wherein the said vehicle body carries a further aerofoil mounted to extend, in level flight, along a vertical axis to assist in steering : A: the vehicle towards a target detected in the field of view.

6. An airborne vehicle according to Claim 1 wherein the antenna array is mounted on respective lower surfaces of a pair of wings, the wings being mounted pivotally on opposite sides of the vehicle body and being capable of being stowed, lengthwise of the body, and being deployed, for flight, transversely of the body on opposite sides thereof.

7. An airborne vehicle according to Claim 6 wherein each said wing is arranged for pivotal motion, in substantially level flight, about a respective vertical axis and carries at a lower surface thereof a respective antenna array capable of generating a respective fan beam, the wings being caused to execute said pivotal motion to scan the respective fan beams, in azimuth, across the

field of view.

8. An airborne vehicle according to Claim 7 wherein said circuit is coupled, for operation, to each said antenna array whenever the respective wing executes said pivotal motion.

9. An airborne vehicle according to any one of Claims 1 to 8 comprising control means for causing the vehicle to fly at a selectable angle of pitch to approach a target detected in substantially level flight, and means for tracking said target while flying at said selectable angle of pitch.

10. An airborne vehicle according to Claim 9 wherein said tracking means comprises a further antenna mounted on, and conforming to, a surface of the nose of the vehicle body and being capable of forming a further forwardly directed fan beam, said nose being rotatable about the longitudinal axis of the body while flying : it: at said selectable angle of pitch to scan the further fan beam so formed.

11. An airborne vehicle according to Claim 9 wherein said tracking means comprises a further antenna mounted on, and conforming to a surface of the nose of the vehicle body and means for feeding said further antenna array in accordance with monopulse operation thereby to track said target while flying at said selectable angle of pitch.

12. An airborne vehicle according to Claim 11 wherein said further antenna comprises an array of radiating elements extending in the horizontal or vertical plane of the body of the vehicle to be capable of generating respective vertical and horizontal fan beams.

13. An airborne vehicle according to Claim 9 wherein said tracking means comprises an array of radiating elements mounted in a common plane in the nose of the body of the vehicle and being capable of generating a forwardly directed fan beam.

14. An airborne vehicle according to Claim 1 wherein the antenna array is mounted on a lower wing surface of said vehicle which, in flight, extends transversely of the vehicle body, respective end portions of the wing being rotatable about a common axis of the wing to manoeuvre the vehicle in flight.

15. An airborne vehicle according to Claim 14 wherein said end portions of the wing are rotatable in opposite respective senses to cause the vehicle to roll, in substantially level flight, about an axis extending lengthwise of the vehicle body to scan the fan beam, in azimuth, across a field of view to be capable of detecting therein a target without substantially affecting the form of said fan beam. : Up:

16. An airborne vehicle according to Claim 15 capable of flying at a selectable angle of pitch to approach a target, detected in substantially level flight.

17. An airborne vehicle according to Claim 16 wherein one of said end portions is rotatable in the clockwise sense about said axis of the wing and the other end portion is rotatable in the anticlockwise sense about said axis of the wing to cause the vehicle, while flying at said selectable angle of pitch, to rotate about the longitudinal axis of the vehicle body, whereby the antenna array mounted on an end portion is capable of generating a fan beam which is scanned across the field of view to track a target detected in level flight.

18. An airborne vehicle according to Claim 17 wherein a further antenna is mounted on the nose portion of said vehicle body to generate a further, forwardly directed response pattern, the nose portion being capable, while flying at said selectable angle of pitch of rotating about the longitudinal axis of the body to scan said further response pattern across the field of view to track a target detected in level flight.

l9. An airborne vehicle according to any preceding claim in the form of a terminally guided sub-munition.