Abstract:
The invention relates to a radiofrequency antenna comprising a chassis ( 26 ) and an emission surface supporting a set of radiating antenna elements, each radiating in a unique emission direction, characterized in that each antenna element is at least partially movable relative to the emission surface to modify its specific emission direction and in that it comprises means for moving the antenna elements in a coordinated manner along said surface to form, from the elementary waves produced by the antenna elements, a coherent wave propagating in a direction that is angularly offset relative to the normal to the emission surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority to French patent application no. FR1005125, filed Dec. 27, 2010, the disclosure of which is herein incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    The present invention relates to a radiofrequency antenna, of the type comprising a chassis and an emission surface supporting a set of radiating antenna elements, each radiating in a unique emission direction. 
         [0003]    Array antennas with helical transmitting elements are known, in particular from U.S. Pat. No. 6,115,005. Likewise, this type of compact antenna is capable of transmitting very high peaking capacities, as for example described in the document by Li, X. Q.; Liu, Q. X.; Zhang, J. Q.; Zhao, L.; Zhang, Z. Q.; , “The high-power radial line helical circular array antenna: Theory and development,” Microwave and Millimeter Wave Technology (ICMMT), 2010, International Conference on , vol., No., pp.671-674, 8-11 May 2010, doi: 10.1109/ICMMT.2010.5525020. However, the possibilities for aiming such a very high-power antenna remain limited due to the direct connection, generally in a vacuum, between the power source and the antenna. Generally, a radial line helical circular array antenna is made up of a radial transmission line, which can be powered through its center or its periphery, and an array of regularly distributed radiating antenna elements. Each antenna element comprises a helical radiating wire protruding on the emitting face. The wire is connected to a pickup loop present within the radial transmission line of the antenna, on the other side of the emission surface. Each of the helical radiating wires is positioned with an initial angle so as to form, for example, a coherent electromagnetic field whereof the direction of propagation is perpendicular to the emission surface. 
         [0004]    The angle of departure for the helices of each antenna element is set for good so that the phase shift between the different antenna elements allows the coherent addition in the desired emission direction. 
         [0005]    In order to change the emission direction of the antenna, it is known to mount the antenna on an articulated and motorized support making it possible to move the entire antenna, in particular its emission surface and all of the antenna elements present, as well as the support chassis of the emission surface. 
         [0006]    The electromagnetic radiation source used to power the very high-power antenna is generally made up of a relativistic source (high-power magnetron, magnetically insulated line oscillator (MILO), backward-wave oscillator, relativistic klystron, for example). The source, connection guide, antenna assembly must then be kept in a vacuum and is very difficult to deform, due to the breakdown risks limiting the technologies and architectures making it possible to aim the antenna in a particular direction, other than by moving the assembly. 
       SUMMARY 
       [0007]    The invention aims to propose a radiofrequency antenna that can be used in an arrangement where the direction of the field radiated by the antenna is angularly mobile in one or two directions, without requiring complex deformable guide elements or the movement of substantial masses. 
         [0008]    To that end, the invention relates to a radiofrequency antenna of the aforementioned type, characterized in that each antenna element is at least partially movable relative to the emission surface to modify its specific emission direction and in that it includes means for moving the antenna elements in a coordinated manner along said surface to form, from the elementary waves produced by the antenna elements, a coherent wave propagating in a direction that is angularly offset relative to the normal to the emission surface. 
         [0009]    According to specific embodiments, the radiofrequency antenna comprises one or more of the following features: 
         [0010]    the antenna elements are distributed by groups of antenna elements, the elements of a same group being present in a strip of the emission surface extending perpendicular to the projection of the emission direction on the surface, the antenna elements of a same group being positioned to produce elementary waves having a same phase shift relative to the waves produced by the antenna elements of another group, 
         [0011]    the means for moving the antenna elements can position the antenna elements so that they each produce an elementary wave phase shifted by a phase shift          φ relative to the other antenna elements defined by: 
         [0000]                φ=2 πh tgθ/λ 
 
         [0012]    where θ is the incline angle of the emission direction relative to the normal to the emission surface, λ is the wavelength of the electromagnetic radiation, and h is the distance of the antenna element from a reference axis measured along the emission direction on the emission surface, 
         [0013]    the antenna elements each include an emission wire rotatably mounted relative to the emission surface and the means for moving the antenna elements are capable of rotating the antenna elements, 
         [0014]    the movement means include racks mounted slidingly relative to the emission surface and the emission wires are integral with driving pinions engaged with the racks, and in that the movement means include a mechanism for synchronized movement of the racks, 
         [0015]    the synchronized movement mechanism includes a rotary control crown relative to the chassis and provided with control cams of the racks, the racks each being equipped with at least one cam follower cooperating with a cam, and a motor for rotating the crown, 
         [0016]    the antenna elements comprise a deformable emission wire, and in that the movement means comprise a mechanism designed to ensure the deformation of each emission wire to modify the specific emission direction, 
         [0017]    the antenna elements each comprise a focusing lens for the elementary electromagnetic wave produced by the antenna element, and in that the movement means comprise an angular movement mechanism for each focusing lens, 
         [0018]    the emission surface supporting the radiating antenna elements is rotary relative to the chassis, and in that it comprises means for rotating the emission surface, 
         [0019]    the chassis delimits a closed vacuum space in which the antenna elements are contained, and in that it comprises force-reacting guide pins between the chassis and the emission surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention will be better understood upon reading the following description, provided solely as an example and done in reference to the appended drawings, in which: 
           [0021]      FIG. 1  is a cross-sectional view of an antenna according to the invention, in top view, along line I-I of  FIG. 2 ; 
           [0022]      FIG. 2  is a transverse cross-sectional view of the antenna according to the invention along line II-II of  FIG. 1 ; 
           [0023]      FIG. 3  is a detailed cross-sectional view of an antenna element of the antenna according to the invention; and 
           [0024]      FIGS. 4 ,  5  and  6  are elevation views of alternative embodiments of antenna elements according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    The antenna  20  according to the invention is shown in top view and cross-section in  FIG. 1  and in transverse cross-section in  FIG. 2 . It assumes the general shape of a disk with axis X 1 -X 1 . According to the invention, each antenna  20  is capable of emitting in a direction T-T angularly offset by an angle θ relative to the axis X 1 -X 1  of the antenna. 
         [0026]    Its planar emission surface is formed by a circular plate  22  rotatably mobile around the axis X 1 -X 1  and on which a set of radiating antenna elements  24  regularly distributed on the surface of the plate  22  is positioned. The antenna elements are each able to produce an elementary wave, each along a unique emission direction and with a unique phase shift such that the addition of the elementary waves produces a coherent wave in direction T-T. 
         [0027]    These antenna elements each have an axis X 2 -X 2  normally perpendicular to the plate  22 . 
         [0028]    According to the invention, the antenna is equipped with means  25  for moving the antenna elements relative to the emission surface to modify their emission direction and/or their phase. In the embodiment described here, the means  25  are capable of producing a rotational movement around themselves of all or part of the antenna elements. 
         [0029]    The plate  22  is supported by a chassis  26  in the general shape of a bell gradually flaring from an inlet  27  for collecting the magnetic radiation coming from the source  12  to an outlet mouth  28  for the radiation coming from the antenna elements  24 . This mouth is covered by an airtight protective wall  30  making it possible to create the vacuum inside the chassis  26 . The wall  30  is transparent to the electromagnetic radiation and forms a radome. 
         [0030]    The inlet end  27  of the chassis  26  is formed by a tube extended by a crown  34  forming the bottom of the chassis. This crown has axis X 1 -X 1 . The bottom is extended by a first peripheral wall  36  having, at its end turned toward the mouth  28 , a divergent shoulder  38  forming a support. This shoulder is bordered by a second peripheral wall  40  supporting the protective wall  30 . 
         [0031]    The plate  22  bears on an inner peripheral rim  44  of the side wall  34 . This rim  44  forms a bearing for guiding the rotation of the plate  22  around the axis X 1 -X 1 . To that end, it is advantageously equipped with a ball bearing  46 . 
         [0032]    Positioned between the plate  22  and the bottom  34  is an intermediate separating wall  48  extending parallel to the plate  22  and separating the annular space delimited by the side wall  36  into two adjacent spaces. The wall  44  is supported, like the plate  22 , by a rim forming a bearing  50  advantageously equipped with a ball bearing  52 . 
         [0033]    Connecting and force-reacting guide pins  54  are positioned between the plate  22  and the wall  48 . They extend parallel to the axis X 1 -X 1  and are equidistributed along one or more circles of axis X 1 -X 1  on the surface of the plate so as to ensure the mechanical strength of the assembly when the antenna is in vacuum. These guide pins rigidly connect the plate  22  and the wall  48 . 
         [0034]    Guide pins  56  extending the guide pins  44  extend between the wall  48  and the bottom  34  in the extension of the guide pins  54 . The guide pins  56  are connected to the wall  48  at one of their ends and have a sliding contact  58  at their other ends bearing on the surface of the bottom  34 . 
         [0035]    Likewise, guide pins  60  extend the guide pins  54  from the plate  22  to the protective wall  30 . These guide pins are fixed to the plate  22  and bear along a sliding contact  62  on the wall  30 . 
         [0036]    The sliding bearing of the guide pins  52  and  60  on the bottom  34  and the wall  30  is for example ensured by positioning a freely rotating ball at the end of each guide pin. 
         [0037]    The intermediate wall  48  supports, opposite the conduit  32 , along axis X 1 -X 1 , a metal cone  70  able to modify the propagation mode of the electromagnetic flow, going from a TM01 mode flow along the axis X 1 -X 1  to a TEM mode centripetal flow extending from the axis X 1 -X 1  outward in the direction of the arrows  72 . 
         [0038]    The intermediate wall  48  is provided with traversing loops  74  regularly distributed along a circle centered on axis X 1 -X 1 . These loops  74  are formed by a metal conductor closed on itself and have two lobes  74 A,  74 B protruding on either side of the intermediate wall  48 . The antenna elements  24  are shown on a larger scale in  FIG. 3 . According to the invention, these antenna elements are capable of turning on themselves around their axis X 2 -X 2  parallel to the axis X 1 -X 1 . 
         [0039]      FIG. 3  shows the plate  22  supporting the antenna element  24 . Each antenna element comprises an emission wire  80  positioned on the antenna emission loop side and a pickup loop  82  positioned between the panel  22  and the intermediate wall  48 . 
         [0040]    The loop  82  is rigidly and fixedly connected to the wall  22  by one of its ends while remaining electrically isolated from the wall  22  in its crossing toward the emission wire  84 . The loop has a shape known in itself and is obtained by curving a metal conductor on itself. 
         [0041]    The wire  80  has an emission part  84  made up of a solid metal wire in the shape of a helix. This wire is extended by a core  86  engaged inside the hollow conductor forming the loop  82  while ensuring an electrical connection. 
         [0042]    A sliding contact  88  is ensured between the conductor  83  and the core  86  using any adapted type of arrangement thereby allowing the emission wire  80  to rotate relative to the loop  82  while ensuring an electrical connection. 
         [0043]    A drive pinion  90  is positioned around the wire  80  at the connection between the helical emission part  84  and the core  86 . This pinion extends perpendicular to the axis X 2 -X 2  of rotation of the emission wire and is positioned along the panel  22  on the emission mouth  28  side. It is integral in rotation with the wire  80 . 
         [0044]    As illustrated in  FIG. 1 , the mechanism  25  for rotating the antenna elements  24  around themselves includes a set of racks  102  positioned parallel to one another on the surface of the plate  22  turned toward the mouth  28 . These racks thus extend along chords of the disk forming the plate  22 . They are perpendicular to the component of direction T-T along the emission plane defined by the plate  22 . 
         [0045]    These racks have, on either side, rectilinear toothings engaged with the pinions  90  of the adjacent antenna elements. In this way, the antenna elements associated with a same rack are alternately distributed on either side of the rack. 
         [0046]    The racks  102  are mounted to be slidingly mobile along the surface of the plate  22 . They are maintained laterally by the antenna elements positioned on either side. 
         [0047]    The drive mechanism  25  also comprises a crown  104  for controlling the racks and a motor  106  for driving the control crown  104 . 
         [0048]    The crown  104  bears on the shoulder  38  and is laterally guided by the peripheral wall  40 . The crown has axis X 1 -X 1 . It is angularly movable relative to the plate  22  around its axis along an angular travel in the vicinity of 60°. 
         [0049]    The motor  106  is fixed to an extension of the plate  22  denoted  108 . The extension extends to the outside of the closed space delimited by the chassis  26  and the protective wall  30 . The output shaft of the motor is equipped with a pinion  110  received in a groove  112  of the crown  104 . This groove is in the shape of an arc of circle centered on the axis X 1 -X 1  and has, on a cylindrical surface, a toothing  114  engaged with the pinion  110  to drive the crown under the action of the motor  106 . 
         [0050]    Each rack  102  extends in the space delimited between the shoulder  38  and the crown  104 . At both of its ends, each rack has a driving finger  120  received in a groove  122  forming a cam of the control crown  104 . 
         [0051]    The grooves  122  forming a cam have a curved shape and have a width equal to the thickness of the driving finger  120 . They generally extend along an angular opening around the crown  104  equal to the angular travel of the crown  104  relative to the plate  22 . 
         [0052]    The grooves  122  are symmetrical to one another for a same rack relative to a diameter of the disk forming the plate, this diameter extending perpendicular to the racks  102 . 
         [0053]    The profile of the grooves forming a cam  122  is such that, for a given rack situated at a distance R-h from the center of the plate  22 , R being the radius of the plate, the movement of the rack is such that it produces an angular movement of the antenna element  24  meshed with it equal to          φ according to the formula: 
         [0000]                φ=2 πh tgθ/λ   (1)
 
         [0054]    where θ is the incline angle relative to the normal to the emission direction T-T of the antenna and λ is the wavelength of the electromagnetic radiation to be emitted. In general, the incline of the grooves forming the cam  22  increases from one side denoted A to the other side of the crown in the direction of the arrow F as shown in  FIG. 1 . 
         [0055]    The antenna elements are thus distributed by group while being associated with a same rack. All of the antenna elements of a same group are thus situated in a strip extending in the plane of the plate  22  perpendicular to the emission direction T-T. These antenna elements are all able to be moved by a same angular offset when the associated rack is moved. The initial angular offset of the helices is calculated to allow the coherent addition in the main axis of the antenna for centered positioning of that rack to allow travel of the beam on either side of said axis. One alternative, only conducive to travel by a single side, would correspond to an initial adjustment of the helices to allow the coherent addition along the main axis for abutting positioning of the racks. 
         [0056]    The antenna lastly comprises a mechanism  150  globally rotating the plate  22  and the set of antenna elements around the axis X 1 -X 1  relative to the chassis  26 . This mechanism comprises a motor  152  supported by the chassis  26 . It has, on its output shaft, a pinion  154  capable of driving the plate  22 . To that end, the plate  22  has, in the extension  108 , a semi-circular slot  156  centered on the axis X 1 -X 1  whereof one wall  158  has a toothing  160  engaged with the pinion  154 . 
         [0057]    During operation, in such an antenna, the electromagnetic flow arriving along axis X 1 -X 1  through the inlet  27  is distributed along the surface of the intermediate wall  28  by the mode converter  70 . 
         [0058]    The then-centripetal flow is picked up by the lobes  74 A of the loops and re-emitted by the lobes  74 B in the space between the plate  22  and the intermediate wall  48 . The loops  82  of the antenna elements  24  again pick up the electromagnetic wave, inducing a current up to the emission wire  84 , which re-emits the electromagnetic wave in a direction and with a phase that are specific to the angular positioning of the antenna elements. 
         [0059]    When the crown  104  is in an extreme position, all of the antenna elements are oriented in the same direction, so that they produce elementary electromagnetic waves with zero relative phase shifts. 
         [0060]    When, under the action of the motor  106 , the control crown  104  is moved angularly, the racks  102  are moved parallel to one another while being driven by both of their ends by the drive fingers stressed by a wall of the grooves  122  forming a cam. 
         [0061]    The amplitude of the movement applied to each rack is defined by the shape of the groove forming a cam  122  present at each end so that the further the rack is from the point A, the greater the amplitude of its movement. 
         [0062]    When the racks are moved, the associated antenna elements are angularly moved, the rack driving the pinion  90  integral with the emission wire  80 . Under these conditions, it will be understood that all of the emission wires associated with a same rack and belonging to the same group are moved angularly by the same amplitude, thus producing a phase shift between the elementary electromagnetic waves emitted by those antenna elements and those of the antenna elements associated with other racks that undergo a different movement. 
         [0063]    It will be understood, due to formula (1), that the phase shifts applied to the antenna elements are such that according to their position, the antenna elements produce an electromagnetic wave whereof the phase shift corresponds to the phase shift existing between the wave actually emitted and the wave that would have been emitted by antenna elements situated in a plane angularly offset by an angle θ relative to the plane of the plate  22 . Thus, the electromagnetic wave resulting from the elementary waves produced by the elements is coherent, the elementary waves being in phase in a plane perpendicular to the propagation direction T-T and that coherent antenna wave propagating in direction T-T is angularly offset by an angle θ relative to the normal to the plate  22 . 
         [0064]    It will be understood that such an arrangement makes it possible to modify the direction of propagation of the wave by an angle θ that depends on the position of the control crown  104 , which is controlled by the motor  106 . Upon a 360° rotation of the crown  104 , the direction of propagation T-T describes a cone of revolution along axis X 1 -X 1  and with half-cone angle θ. The angle θ is adjustable independently of the overall movement and thus makes it possible to achieve two-dimensional aiming over a solid angle with half-cone angle θmax (θmax being the angle during maximum travel of the racks). 
         [0065]    Likewise, the motor  152 , through action on the plate  22  through the pinion  154  meshed with the toothing  158 , enables an overall movement of all of the antenna elements with a same angular offset around their axis X 2 -X 2  by moving the plate  22 , thereby making it possible to phase shift all of the antenna elements and therefore the antenna. This phase shifter can operate over a wide frequency range and at very high powers. 
         [0066]    The antenna thus formed therefore makes it possible, without an articulated element in the wave inlet guide conduit, to emit an angularly offset wave. 
         [0067]    This angular offset is obtained without it being necessary to move the chassis of the antenna and its randome angularly. 
         [0068]    According to one alternative embodiment, illustrated in light of  FIG. 4 , each antenna element  24  is formed by a radiating wire  184  fixedly mounted in rotation relative to the panel  22 . All of the wires are identical and are oriented identically. Each wire is associated with a focusing lens  186  positioned at the corresponding wire. This lens can focus the electromagnetic wave produced by the wire. 
         [0069]    These lenses are associated with a mechanism  188  for angularly moving each lens  186  around two axes  188 A,  188 B extending perpendicular to one another and parallel to the plate  22 . The mechanism  188  is such that all of the lenses have a same orientation, thereby allowing a deviation by an angle θ of all of the elementary electromagnetic waves initially emitted normally to the plate  22  by each of the wires  184 . 
         [0070]    One can see that with such an arrangement, the coherent wave produced by the addition of the elementary electromagnetic waves produced by each antenna element propagates along a predefined angle θ relative to the normal to the plate  22 . 
         [0071]      FIG. 5  shows still another alternative embodiment. In this embodiment, the antenna wire denoted  284 , corresponding to the radiating wire  84 , is wound in a helix around an elastically deformable pylon  286 . In the absence of stress, the pylon  286  extends perpendicular to the plate  22 . 
         [0072]    As before, the pylon  286  is connected to a mechanism  188  for moving its end, thereby allowing bending of the axis of the helix of the wire  284  by deforming the pylon  286 . In this way, the mechanism  188  ensures an emission of the elementary wave produced by each wire in a direction angularly offset relative to the normal to the wall  22 . 
         [0073]    In the embodiment illustrated in  FIG. 6 , a focusing lens  288  is added to the arrangement described in  FIG. 5 . This lens is placed at the free end of the pylon  286 . 
         [0074]    According to an alternative of the embodiment described in  FIG. 1 , the wall  48  is eliminated and the antenna elements are then powered from the center. The mode converter  70  is supported by the inner surface of the wall  22 .