Radiation generator

Abstract

A crossed-dipole antenna comprises first and second dipoles, each dipole having two arms, wherein the arms of the first and second dipoles each define a truncated elongated ellipse. An electrical feed arrangement is provided for electrically feeding the arms of the first and second dipoles to cause the crossed dipole antenna to generate radiation.

Description

[0001]RADIATION GENERATORFIELD This specification relates to a radiation generator such as an antenna orantenna array. In particular, but not exclusively, it relates to a radio-frequency(RF) directed energy weapon (DEW).BACKGROUND Known RF DEWs comprise an antenna or antenna array to generate radio-frequency radiation. The antenna array may comprise a phased array to permitsteering of the generated radiation.SUMMARY According to a first aspect of the present disclosure, there is provided acrossed dipole antenna, comprising: first and second dipoles, each dipole havingtwo arms, wherein the arms of the first and second dipoles each define atruncated elongated ellipse, and an electrical feed arrangement for electricallyfeeding the arms of the first and second dipoles to cause the crossed-dipoleantenna to generate radiation.The electrical feed arrangement may be configured for electrically feedingthe arms of the first and second dipoles such that the crossed-dipole antennagenerates radiation having a peak power of 1 kW or higher.The major axis of each ellipse may be at least 1.5 times as long as theminor axis of the ellipse.In some examples, the major axis of each ellipse may be at least twice aslong as the minor axis of the ellipse.Each of the arms of the first and second dipoles may include an outeredge, wherein the distance along the major axis of the respective ellipse from aninner vertex of the ellipse to the outer edge is less than half of the distancebetween the inner vertex of the ellipse and an outer vertex of the ellipse.Each truncated elongated ellipse may be truncated along it major axis. Anelongated ellipse may be truncated to exclude the co-vertices of the ellipse.The electrical feed arrangement may comprise an electrical connectionhub. A major axis of each ellipse may extend outwardly from the electricalconnection hub.The major axis of the ellipse of the first arm of the first dipole may becollinear with the major axis of the ellipse of the second arm of the first dipole.The major axis of the ellipse of the first arm of the second dipole may be collinearwith the major axis of the ellipse of the second arm of the second dipole.The first and second dipoles may be arranged in a perpendicularorientation with respect to one another.Each arm may be printed on a common substrate.For each dipole, the arms of the dipole may be printed on opposite sidesof the common substrate.The electrical feed arrangement may be configured for electrically feedingthe arms of the first and second dipoles to cause the crossed-dipole antenna togenerate circularly polarized radiation.The electrical feed arrangement may be configured to provide a 90° phaseshift between a first arm of the first dipole and a first arm of the second dipole,and a 90° phase shift between a second arm of the first dipole and a second armof the second dipole.The electrical feed arrangement may comprise a first phase shiftcomponent to provide the 90° phase shift between a first arm of the first dipoleand a first arm of the second dipole, and a second phase shift component toprovide the 90° phase shift between a second arm of the first dipole and a secondarm of the second dipole.According to a second aspect of the present disclosure, there is provideda radiation generator comprising an antenna array having a plurality of arrayelements, each array element comprising a crossed-dipole antenna according tothe first aspect.The radiation generator may further comprise a radiation reflector spacedfrom the antenna array to redirect a portion of the radiation generated by theantenna array into a desired direction.The radiation reflector may be spaced from the antenna array by adistance less than or equal to a third of a wavelength of the radiation that isgenerated by the array.The radiation reflector may be spaced from the antenna array by adistance less than or equal to a quarter of a wavelength of the radiation that isgenerated by the array.The arms of the first and second dipoles of the array elements may beprinted on a common substrate.The radiation reflector may comprise a metallic sheet which is parallel tothe common substrate.The gap between the radiation reflector and the antenna array may be freespace only.In some examples an RF absorber component is not present between theradiation reflector and the antenna array.The radiation generator may further comprise control electronics to controlthe relative phase of the radiation generated by the array elements so as togenerate a steerable output radiation beam.According to a third aspect of the present disclosure, there is provided aunidirectional radiation source comprising the radiation generator of the secondaspect. According to a fourth aspect of the present disclosure, there is provided aradio-frequency directed energy weapon comprising the radiation generator ofthe second aspect, the unidirectional radiation source of the third aspect, or thecrossed-dipole antenna of the first aspect.BRIEF DESCRIPTION OF THE FIGURESEmbodiments of the invention will now be described by way of exampleonly with reference to the figures, in which:Figure 1 shows a crossed-dipole antenna in accordance with a firstexample; Figure 2 shows the electrical connection hub of the crossed-dipoleantenna;Figure 3 shows a radiation generator comprising an antenna array.DETAILED DESCRIPTIONFigure 1 schematically illustrates a crossed-dipole antenna 100 inaccordance with a first example. The crossed-dipole antenna 100 comprises afirst dipole 110, a second dipole 120, a planar substrate 130, and an electricalfeed arrangement comprising an electrical connection hub 140. As shown, thefirst and second dipoles 110, 120 are provided on the planar substrate 130 in agenerally perpendicular orientation with respect to one another. As explainedbelow, the crossed-dipole antenna is adapted for generating high power REoutput. Referring again to Figure 1, the first dipole 110 comprises a first arm 112(shown as a solid line) formed on a top side of the substrate 130. The first dipole110 further comprises a second arm 114, which is shown as a dotted line toindicate that it is formed on the underside of the substrate 130. It will beunderstood that the terms “top side” and “underside” are used herein relative tothe perspective of Figure 1 and do not imply any preferred orientation of theantenna 100.Thus, the first and second arms 112, 114 are disposed on opposite sidesof the substrate 130. The first and second arms may comprise a suitableconductive material, and may be printed on the respective side of the substrate130, for example using known etching techniques. The substrate 130 maycomprise a suitable insulating material such as FR4.Similarly, the second dipole 120 comprises a first arm 122 printed orotherwise formed on the top side of the substrate 130, and a second arm 124printed or otherwise formed on the underside of the substrate 130. Thus, the firstarm 112 of the first dipole 110 and the first arm 122 of the second dipole 120define a layer on the top surface of the substrate 130, and may be referred toherein as the “top layer” arms. Similarly, the second arm 114 of the first dipole110 and the second arm 124 of the second dipole 120 define a layer on thebottom surface of the substrate 130 and may be referred to herein as the “bottomlayer” arms.The electrical connection hub 140 is configured to electrically drive thearms 112, 114, 122, 124 of the first and second dipoles to generate radiation. Inone example, the electrical connection hub may be connected to a single coaxialcable (not shown) having an inner pin and an outer conductor. The top layer armsmay be connected to the inner pin, while the bottom layer arms may be connectedto the outer conductor.As shown in more detail in Figure 2, the electrical connection hub 140includes a phase shift line 150 in the form of a ¼ ring, which is disposed on thetop side of the substrate 130 and provides a 90° phase shift between the signalsdelivered to the top layer arms 112, 122. The electrical connection hub 140 furthercomprises a similar phase shift line (not shown) disposed on the underside of thesubstrate; this provides a 90° phase shift between the signals delivered to thebottom layer arms 114, 124. In this way, pairs of the crossed dipole arms are fedin quadrature so as to generate circularly polarized radiation. Advantageously,the arrangement of Figure 2 allows this to be achieved with a signal coaxial cable.As shown in Figure 1, the general shape of each arm 112, 114, 122, 124is that of a truncated elongated ellipse, with the major axis 113, 115, 123, 125 ofeach respective ellipse extending outwardly from the electrical connection hub140. This allows a configuration in which the gaps between the dipole arms arelarge enough for high power operation, whilst also allowing for strong mutualcoupling and thus a wide bandwidth. If the ellipse were not elongated (i.e. if theratio between the major and minor axes were close to 1), then this would resultin ‘fat” arms with small gaps between them; such a configuration is unsuitable forhigh power operation due to the risk of breakdown (i.e. arcing). In variousexamples, the major axis of the ellipse may be at least 1.5 times as long as theminor axis of the ellipse, for example twice as long as the minor axis of the ellipse,for example three times as long as the minor axis of the ellipse, for example fourtimes as long as the minor axis of the ellipse. It will be understood that that theterms “major axis” and “minor axis” as used herein in relation to an ellipse, referto the larger and smaller diameters of the ellipse, respectively.As shown in Figure 1, in this example, the major axis of the ellipse of thefirst arm 112 of the first dipole 110 is collinear with the major axis of the ellipse ofthe second arm 114 of the first dipole 110. Similarly, the major axis of the ellipseof the first arm 122 of the second dipole 120 is collinear with the major axis of theellipse of the second arm 124 of the second dipole 120. In the illustrated example,the major axes of the ellipses of the first dipole 110 are perpendicular to the majoraxes of the ellipses of the second dipole 120.As described above, each arm in Figure 1 is formed as a layer on thesubstrate, and thus forms a truncated elongated ellipse in a plane parallel to theplane of the substrate 130. It will be understood that in some examples, the armmay also include other elements. Even so, it can generally be said that each armgenerally defines a truncated elongated ellipse, for example in a plane and / orprinted on the substrate 130.It is convenient herein to describe the shape of the arms 112, 114, 122,124 in relation to the ellipse on which the shape is based, for example by referringto the axes of the ellipse, and / or its vertices and co-vertices. However, it will beunderstood that the shape that each respective arm 112, 114, 122, 124 definesmay not necessarily include every part of the respective ellipse on which it isbased. This is because the shape that each arm defines is generally that of atruncated ellipse.For example, in Figure 1, the ellipse on which each arm 112, 114, 122,124 is based is truncated in both directions along its major axis. In particular,each ellipse is truncated inwardly (i.e. towards the connection hub 140) to forman integral connection between the respective arm and the connection hub 140.Each ellipse is also truncated outwardly to form an outer edge 112a, 114a, 122a,124a of the respective arm. Thus, in the example of Figure 1, each arm 112, 114,122, 124 does not include either vertex of the ellipse on which it is based.Moreover, since the ellipse is truncated prior to its co-vertices, the arm does notinclude the co-vertices of the ellipse either.For each arm 112, 114, 122, 124, the distance along the major axisbetween the outer edge 11 2a, 114a, 122a, 124a and the closest (i.e. inner) vertexof the respective ellipse may be less than half of the distance between thevertices of the ellipse, for example less than a third of the distance between thevertices of the ellipse, for example less than a quarter of the distance betweenthe vertices of the ellipse, for example less than a fifth of the distance betweenthe vertices of the ellipse, for example less than a sixth of the distance betweenthe vertices of the ellipse.The antenna 100 may be of any suitable size dependent on thewavelength of the radiation to be generated. For RF radiation, the distancebetween the edge 122a and the edge 124a may for example be between 100 mm -1-and 200 mm. The distance between the edge 112a and the edge 114a may bethe same.The electrical feed arrangement may further comprise appropriateelectrical signal generation equipment to drive the crossed-dipole antenna togenerate radiation having a peak power of 1 kW or higher, such as 2kW or higher.Suitable electrical signal generation equipment is well known to those skilled inthe art and will not be described here. Figure 3 shows a radiation generator 300 in accordance with a secondexample. As shown, the radiation generator comprises an antenna array havinga plurality of array elements 310. In some cases, appropriate control electronicsmay be provided to control the relative phase of the radiation generated by thearray elements so as to generate a steerable output radiation beam. That is, theradiation generator may comprise a phased array.Each array element 310 comprises a crossed-dipole antenna 100according to the first example. In Figure 3, a 2x2 array of elements 310 is shown;however it will be appreciated that more generally, the array may be formed ofany N x M array of array elements, where N and M are appropriately selectednumbers. The radiation generator 300 of Figure 3 is configured to operate over a30% bandwidth (Sil <-10dB, axial ratio <3dB) with peak powers of 2-3kW percrossed dipole antenna 100.As shown in Figure 3, the arms of the first and second dipoles of each ofthe array elements are printed on a common substrate 330, which may be formedof any suitable insulating material such as FR4. The radiation generator is madeunidirectional by way of a radiation reflector (ground plane) 340, which ispositioned behind the array, parallel to the substrate. The radiation reflector maycomprise a metal plate. Advantageously, to increase efficiency of the radiationgenerator, no absorber is present between the substrate and the radiationreflector. That is, the gap between the substrate and the radiation reflector maybe free-space only.The radiation reflector 340 may be positioned at a distance less than orequal to 0.8 wavelengths from the substrate 330, for example at a distance lessthan or equal to 0.5 wavelengths from the substrate 330, for example at adistance less than or equal to a third of a wavelength from the substrate. In oneparticular example, the radiation reflector may be positioned 0.25 wavelengthsbehind one face of the array.The array of the radiation generator may be of any suitable size. Forexample, the substrate 330 of Figure 3 may be 300 mm square. It will beappreciated that larger arrays may be provided for increased power.Radiation generators according to exemplary implementations of thisdisclosure may, for example, be applied in ground-based air defence, forceprotection, check point protection systems, counter-UAS (unmanned aerialvehicle), counter-mobility, or e-bike, e-scoater or electric car stopping.Although several embodiments have been shown and described, it wouldbe appreciated by those skilled in the art that changes may be made in theseembodiments without departing from the principles of this disclosure, the scopeof which is defined in the claims.

Claims

CLAIMS 1. A crossed-dipole antenna, comprising:first and second dipoles, each dipole having two arms, wherein thearms of the first and second dipoles each define a truncated elongatedellipse, andan electrical feed arrangement for electrically feeding the arms ofthe first and second dipoles to cause the crossed-dipole antenna togenerate radiation.

2. The crossed-dipole antenna of claim 1, wherein the electrical feedarrangement is configured for electrically feeding the arms of the first andsecond dipoles such that the crossed-dipole antenna generates radiationhaving a peak power of 1 kW or higher.

3. The crossed-dipole antenna of claim 1 or claim 2, wherein the major axisof each ellipse is at least 1.5 times as long as the minor axis of the ellipse.

4. The crossed-dipole antenna of claim 3, wherein the major axis of eachellipse is at least twice as long as the minor axis of the ellipse.

5. The crossed-dipole antenna of any one of the preceding claim, whereineach of the arms of the first and second dipoles includes an outer edge,and wherein the distance along the major axis of the respective ellipsefrom an inner vertex of the ellipse to the outer edge is less than half of thedistance between the inner vertex of the ellipse and an outer vertex of theellipse.

6. The crossed-dipole antenna of any one of the preceding claims, whereineach truncated elongated ellipse is truncated along it major axis, whereinthe elongated ellipse is truncated to exclude the co-vertices of the ellipse.

7. The crossed-dipole antenna of any one of the preceding claims, whereinthe electrical feed arrangement comprises an electrical connection hub,wherein a major axis of each ellipse extends outwardly from the electricalconnection hub.

8. The crossed-dipole antenna of any one of the preceding claims, whereinthe major axis of the ellipse of the first arm of the first dipole iscollinear with the major axis of the ellipse of the second arm of the firstdipole, andthe major axis of the ellipse of the first arm of the second dipole iscollinear with the major axis of the ellipse of the second arm of the seconddipole.

9. The crossed-dipole antenna of any one of the preceding claims, whereinthe first and second dipoles are arranged in a perpendicular orientationwith respect to one another.

10. The crossed-dipole antenna of any one of the preceding claims, whereineach arm is printed on a common substrate.

11. The crossed-dipole antenna of claim 10, wherein for each dipole, the armsof the dipole are printed on opposite sides of the common substrate.

12. The crossed-dipole antenna of any one of the preceding claims, whereinthe electrical feed arrangement is configured for electrically feeding thearms of the first and second dipoles to cause the crossed-dipole antennato generate circularly polarized radiation.

13. The crossed-dipole antenna of any one of the preceding claims, whereinthe electrical feed arrangement is configured to provide a 900 phase shiftbetween a first arm of the first dipole and a first arm of the second dipole,and a 90° phase shift between a second arm of the first dipole and asecond arm of the second dipole.

14. The crossed-dipole antenna of claim 13, wherein the electrical feedarrangement comprises a first phase shift component to provide the 90°phase shift between a first arm of the first dipole and a first arm of thesecond dipole, and a second phase shift component to provide the 90°phase shift between a second arm of the first dipole and a second arm ofthe second dipole.

15. A radiation generator comprising an antenna array having a plurality ofarray elements, each array element comprising a crossed-dipole antennaaccording to any one of the preceding claims.

16. The radiation generator of claim 15, further comprising a radiation reflectorspaced from the antenna array to redirect a portion of the radiationgenerated by the antenna array into a desired direction.

17. The radiation generator of claim 16, wherein the radiation reflector isspaced from the antenna array by a distance less than or equal to a thirdof a wavelength of the radiation that is generated by the array.

18. The radiation generator of claim 17, wherein the radiation reflector isspaced from the antenna array by a distance less than or equal to a quarterof a wavelength of the radiation that is generated by the array.

19. The radiation generator of any one of claims 15 to 18, wherein the arms ofthe first and second dipoles of the array elements are printed on a commonsubstrate.

20. The radiation generator of claim 19 when dependent on claim 16, 17 or18, wherein the radiation reflector comprises a metallic sheet which isparallel to the common substrate.

21. The radiation generator of any one of claim 16 to 20, wherein the gapbetween the radiation reflector and the antenna array is free space only.

22. The radiation generator of any one of claims 16 to 21, therein an RFabsorber component is not present between the radiaUon reflector and theantenna array.

23. The radiation generator of any one of claims 15 to 22, further comprisingcontrol electronics to control the relative phase of the radiation generatedby the array elements so as to generate a steerable output radiation beam.

24. A unidirectional radiation source comprising the radiation generator of anyone of claims 15th 23.25 A radio-frequency directed energy weapon comprising the radiationgenerator of any one of claims 15 to 24, or the crossed-dipole antenna ofany one of claims 1 to 14.

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