Improvements to a decoy

Abstract

A decoy 1 for protecting a platform against radar-based threats comprises a case housing 2, a signal generator means 3 configured to generate an RF decoy signal and two antennas 6, 9 to transmit the RF decoy signal in two different directions. A separate amplifier 4, 7 is associated with each antenna to amplify the RF decoy signal before transmission by the respective antenna 6, 9. A first heat sink 5 is in contact with the first amplifier 4 to dissipate heat away from the first amplifier 4, and a second heat sink 8 is in contact with the second amplifier 7 to dissipate heat away from the second amplifier 7. The masses of the first heat sink 5 and second heat 8 sink differ.

Description

The invention relates to a decoy. More specifically, but not exclusively, it relates to a decoy for protecting aircraft platforms against radar-based threats. GB2516077 relates to a decoy for protecting a platform, such as an aircraft, against radar-based threats. The ejectable unit comprises memory means having predetermined information loaded on it relating to potential threats. The unit further comprises an antenna for receiving and transmitting RF signals and signal processing means for processing received RF signals. Comparing means compare the processed signals with the predetermined information and determine the presence of a threat. On determining a threat, the signal processing means transmits an altered RF signal via the antenna such that the received signal is jammed and the threat is lured away from the platform. Certain variants of active decoy comprise multiple antenna such as described in US8049656. To improve the operational performance of the decoy, it is desirous that the decoy provides a stable platform for the antenna(s) following the decoy’s ejection from the platform. The present invention was conceived in pursuit of this aim. According to a first aspect of the invention there is provided a decoy for protecting a platform against radar based threats; the decoy comprising a case housing a signal generator means configured to generate a first RF decoy signal and a second RF decoy signal; a first amplifier to amplify a first RF decoy signal from the signal generator means and a first antenna to transmit the RF decoy amplified by the first amplifier; a second amplifier to amplify a second RF decoy signal from the signal generator means and a second antenna to transmit the second RF decoy amplified by the second amplifier; a first heat sink in contact with the first amplifier to dissipate heat away from the first amplifier; a second heat sink in contact with the second amplifier to dissipate heat away from the second amplifier; and wherein the first and second heat sinks are spaced apart within the housing, and the masses of the first heat sink and second heat sink differ. The invention provides a method to set the centre of gravity of the decoy during manufacture to improve the decoy’s stability and / or flight characteristics following its ejection from the platform. Further advantageously, it may avoid the need to use a separate ballast for this purpose. One way heat sinks of different masses may be provided is through using heat sinks of different sizes and / or forming recesses or channels within the heat sink. Nevertheless, to provide at least some of the disparity in mass between the heat sinks, it is preferred that the first heat sink is primarily comprised from a first material having a first density, and the second heat second heat sink is primarily comprised from a second material having a second, density that differs to the first density. This allows the masses of the heat sinks to differ even if the effective volume occupied by each heat sink within the housing is the same. The first material and second material may be different metals selected from the following list: tungsten, copper and nickel and aluminium. For example, the first heat sink may be comprised primarily from a first metal of relatively low density, e.g. aluminium, and the second heat sink comprised primarily from a second metal with a relatively high density, e.g. copper or nickel or an alloy thereof. It will be appreciated that other materials with suitable thermal conductivity characteristics could be used. Further, selection of materials having densities that are pronouncedly different, e.g. a difference greater than 2g / cm3' will allow for a more meaningful mass disparity. Favourably the position of the first amplifier within the housing is closer to the first antenna than the position of the second amplifier is to the first antenna, and the position of the second amplifier within the housing is closer to the second antenna than the position of the first amplifier is to the second antenna. This reduces electrical losses between the amplifiers and respective antennas. The invention will now be described with reference to the figure which is a schematic representation of a decoy for protecting an aerial platform, e.g. a jet aircraft, against radar based threats. The decoy 1 comprises an elongate housing 2 carrying a signal generator 3, a first amplifier unit 4, a first heat sink 5, a first antenna 6, and a second amplifier unit 7, a second heat sink 8, and a second antenna 9. The decoy 1 also includes one or more fins, wings or vanes 10 that extend laterally outwards from the housing 2 to stabilise the orientation of the decoy 1 once airborne, following its ejection from the platform. The signal generator 3 is configured to generate a radio frequency (RF) decoy signal to lure, jam or otherwise deceive a threat. The signal generator 3 also includes a divider configured to split the RF decoy signal to provide substantially identical first and second RF decoy signals to be received by the first amplifier unit 4 and a second amplifier unit 7 respectively. Each of the first amplifier unit 4 and second amplifier unit 7 comprise an amplifying circuit to amplify the respective first and second RF decoy signals for broadcast by respective first and second antenna 6,9. The antenna 6 and 9 are spaced apart on the decoy 1 to provide broad spatial coverage around the decoy 1. To reduce losses, the first amplifier unit 4 is located as close as possible to the first antenna 6 and the second amplifier unit 7 located as close as possible to the second antenna 9. Consequently the first and second heat sinks are also spaced apart within the housing 2 in order that they sit directly against their respective amplifier units 4,7 Typically it is also desirable for the decoy 1 to receive RF signals to identify potential threats and therefore each of the amplifier units 4, 7 also includes amplifying circuitry to amplify RF signals received through their respective antenna 6,9 for processing. The amplifying circuits of the first and second amplifier units 4,7 generate significant heat during transmission of the decoy signals. To manage this, the first heat sink 5 is mounted against the first amplifier unit 4 to transfer heat away from the first amplifier unit 4, and the second heat sink 8 is mounted against the second amplifier unit 7 to transfer heat away from the second amplifier unit 7. The first heat sink 5 and second heat sink 8, which are substantially the same size, are spaced apart from one another with the first heat sink 5 positioned towards a first end 2A of the housing 2 and the second heat sink 8 positioned toward a second, opposite end 2B of the housing 2. The first heat sink 5 has a different mass to the second heat sink 8. The centre of gravity of the decoy is influenced by the position and mass of all of the component parts of the decoy 1 including the circuit boards required to implement the signal generator 3 and amplifier units 4, 7; the antenna 6, 9, the casing 2; and fins 10. There are often restrictions to the extent to which the size, weight and position of these components can be adjusted for the purpose of controlling the position of the centre of gravity. The position of the heat sinks 5,8 is also constrained for the reason of needing to be collocated with the amplifier units 4,7 whose positions are dependent on the antenna 6,9. Selection of the mass of each of the first and second heat sinks 5,8 provides an additional means to alter the centre of gravity of the manufactured decoy to stabilise the decoy 1 when airborne following its ejection from the platform. This is, at least in part, achieved by manufacturing the heat sinks 5,8 from materials with different densities. In this example the first and second heat sinks are made of different metals. The first heat sink 5 is comprised from a machined piece of aluminium; the second heat sink 8 is comprised from a machined piece of tungsten. The significantly different densities of these metals, ~2.7 g / cm3 and 19.3 g / cm3 (at standard temperature and pressure) respectively leads to heat sinks of similar sizes having noticeably different masses. 5 It will be appreciated that other materials, including non-metals, could be used for one or other of the heat sinks. Examples of other suitable materials include but are not limited to: lead, silver, copper, iron, steel, gold, tin, zinc, and alloys thereof, including brass, bronze chrome-vanadium steel, graphite, and carbon fibre. In a variant, the signal generator 3 may be configured to produce different decoy signals 10 to be transmitted through the first and second antenna 6, 9 substantially simultaneously, i.e. the first decoy signal is not identical to the second decoy signal. It is possible for the heat sinks to be of different sizes to provide, at least in part, their different masses.

Claims

1. A decoy for protecting a platform against radar based threats; the decoy comprising a case housing a signal generator means configured to generate a first RF decoy signal and a second RF decoy signal;a first amplifier to amplify a first RF decoy signal from the signal generator means and a first antenna to transmit the RF decoy amplified by the first amplifier;a second amplifier to amplify a second RF decoy signal from the signal generator means and a second antenna to transmit the second RF decoy amplified by the second amplifier;a first heat sink in contact with the first amplifier to dissipate heat away from the first amplifier;a second heat sink in contact with the second amplifier to dissipate heat away from the second amplifier; andwherein the first and second heat sink are spaced apart within the housing, and the masses of the first heat sink and second heat sink differ.

2. A decoy according to claim 1 wherein the first heat sink is primarily comprised from a first material having a first density, and the second heat sink is primarily comprised from a second material having a different density to the first density.

3. A decoy according to claim 2 wherein the first material and second material are different metals selected from the following list: r tungsten, copper and nickel and aluminium.

4. A decoy according to claim 1, 2 or 3 wherein the housing is elongate having a first end and a second end, and in which the first heat sink is located nearer the first end and the second heat sink is located nearer the second end.

5. A decoy according to any previous claim wherein the first amplifier is located 5 at a position within the housing that is nearer the first antenna than the secondantenna, and in which the second amplifier is located at a position within the housing that is nearer the second antenna than the first antenna.

6. A decoy according to any previous claim wherein the first RF decoy signal and second RF decoy signal are identical.

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