Reconfigurable antenna array

Abstract

The invention relates to a reconfigurable antenna array (14) comprising a plurality of identical elementary unit cells (10), each unit cell having at least one symmetry, in particular being a square unit cell, and comprising a radiating element (12) having: at least four ports (P1, P2, P3, P4) distributed in pairs on either side of each median (MH, MV) of one side of a unit cell (10), the antenna array additionally comprising a reconfigurable switching circuit able to generate three distinct connection states (50, 52, 54) between each port of each pair (16) of ports facing one another, each port of a pair (16) belonging to two distinct elementary unit cells (10) that are vertically stacked or horizontally adjacent within said antenna array (14).

Description

[0001] The present invention relates to a reconfigurable antenna network comprising a plurality of identical elementary meshes, each mesh having at least one symmetry, in particular a square mesh, and comprising a radiating element having: at least four ports distributed two by two on either side of each median of one side of the mesh.

[0002] The invention also relates to a ground penetrating radar comprising such a reconfigurable antenna array.

[0003] The invention lies in the field of antenna arrays, in particular miniature antenna arrays capable of meeting numerous constraints in terms of bandwidth, multi-polarization, decoupling, antenna density, etc.

[0004] More specifically, the invention relates to the family of networked antennas with reconfigurable electromagnetic properties comprising a plurality of identical elementary meshes, also called pixels of the antenna network considered, an elementary mesh or pixel corresponding to the pattern of the network reproduced identically over the entire antenna network by translation in one or two dimensions. It should be noted that a mesh is capable of being smaller in size than an antenna element (i.e. antenna) of the network as such, an antenna element capable of ensuring radiation according to one or two distinct polarizations being capable of corresponding to a combination comprising one to several elementary meshes.

[0005] For example, a dipole strand constitutes the elementary mesh of a dipole corresponding to an antenna element as such.

[0006] More specifically, the present invention aims to optimally exploit the network surface occupied by the radiating elements of each elementary mesh of the network and falls more particularly within the field of application of antenna networks with shared radiating elements to produce antennas that are reconfigurable in frequency, geometry or even polarization.

[0007] In the state of the art, antenna arrays with shared radiating elements are known, such as those described in particular in documents US 5,926,137, EP 3 105 818, and US 2012 / 0146869 A1. However, in the antenna array of document US 5,926,137 it should be noted that the excitation position of each of the radiating elements is unique, which blocks modularity and the obtaining of multiple radiation configurations from the same antenna array. The antenna array disclosed in document EP 3 105 818 discloses a possible reconfiguration in terms of geometry and position by imposing a predetermined and identical number of radiating elements forming each antenna and a common polarization, namely circular polarization obtained using an ad hoc feed network.Finally, the antenna array disclosed in document US 2012 / 0146869 A1 proposes a simultaneous dual-polarization antenna array with specific and non-reconfigurable common-mode excitation, such that such an antenna array is also not easily reconfigurable in frequency.

[0008] SONG SICHAO et al. also discloses in the article entitled "An efficient approach for Optimizing Frequency Reconfigurable Pixel Antennas Using Genetic Algorithms" a reconfigurable antenna array with a single excitation whose location is fixed and not reconfigurable, which limits its compatibility with a multi-antenna array.

[0009] In other words, current state-of-the-art solutions do not optimally exploit the available radiating surface, the number of radiating elements constituting such existing networks being fixed, which limits the number of excitable antennas, and its geometric shapes.

[0010] The object of the invention is to remedy the drawbacks of the state of the art by proposing an alternative network architecture of an antenna network to allow optimal exploitation of the available network surface of radiating elements and the synthesis of antenna networks (i.e. multi-antennas) which are both reconfigurable in frequency in order in particular to sequentially access a very wide band, for example of several octaves, and / or reconfigurable in polarization in order in particular to address two orthogonal polarizations for example along an Ox axis and an Oy axis respectively.

[0011] To this end, the invention proposes a reconfigurable antenna network comprising a plurality of identical elementary meshes, each mesh having at least one symmetry, in particular a square mesh, and comprising a radiating element having: at least four ports distributed two by two on either side of each median of one side of the mesh, the antenna network further comprising a reconfigurable switching circuit capable of generating three distinct connection states between each port of each pair of facing ports, each port of a pair belonging to two distinct elementary meshes, superimposed vertically or adjacent horizontally, within said antenna network.

[0012] Advantageously, the antenna array architecture proposed according to the present invention allows, via the geometry of the elementary mesh combined with the reconfigurable switching circuit, the sequential selection of the arrangement of the excitations of each unitary radiating element located within an elementary mesh of said antenna array. In other words, the antenna array architecture proposed according to the present invention makes it possible to act on the manner of connecting the elementary meshes together to obtain the desired radiation in terms of polarization, phase center, density of radiating elements, inter-radiating element distance of the array, frequency bands, etc.More specifically, by "arrangement of the excitations of each unit radiating element", we mean that each port (also called RF radiofrequency access) is capable of being powered via the reconfigurable switching circuit, distinctly from one port to another, by an RF signal source or receiver.

[0013] The antenna network according to the present invention may also have one or more of the characteristics below, taken independently or in any technically conceivable combination: the three connection states correspond to: a short circuit; an excitation; an open circuit; the radiating element within the elementary mesh corresponds to a circular pattern; at least one antenna of said antenna array is formed of at least two vertically and / or horizontally contiguous elementary meshes, said at least two contiguous elementary meshes being connected, via said reconfigurable switching circuit, by means of a connection in the excitation state of the ports of the pair of ports opposite said at least two contiguous elementary meshes;at least one part of said antenna array is square and formed of four elementary meshes contiguous two by two, vertically and horizontally, and capable of being excited according to four distinct configurations, associated respectively, via said reconfigurable switching circuit, with a distinct arrangement from one configuration to another, of connections between each port of each pair of facing ports, each port of a pair belonging to two distinct elementary meshes superimposed vertically or horizontally within said square part formed of four elementary meshes contiguous two by two, vertically and horizontally; two of said four distinct configurations are associated with a horizontal polarization and two others of said four distinct configurations are associated with a vertical polarization;at least one antenna of said antenna array is H-shaped and comprises two identical vertical branches, each comprising at least five vertically contiguous elementary meshes, the two identical vertical branches being connected to each other by a horizontal central branch comprising at least four horizontally contiguous elementary meshes, each elementary mesh located at one of the ends of the horizontal central branch corresponding respectively to the third elementary mesh of each of the two vertical branches;said H-shaped antenna is capable of being excited, via the switching circuit, by means of a connection in an excited state of the ports of the pair of ports facing said at least two central contiguous elementary meshes of said horizontal central branch, the ports facing the other contiguous elementary meshes forming said H-shaped antenna being placed in a short-circuit state, the ports facing elementary meshes of said network external to said H-shaped antenna being placed in an open-circuit state. for each pair of ports facing each other, belonging to two distinct elementary meshes superimposed vertically or horizontally, the reconfigurable switching circuit comprises an electronic assembly comprising at least: a balun configured to transform an input electrical signal into differential mode; two single-pole switches with one input and two SPDT outputs, a single-pole single-throw SPST switch;each elementary mesh is placed in an electromagnetic cubic cavity; each electronic assembly associated with each pair of facing ports is integrated within a metal wall of said cubic cavity, said wall separating said ports of said pair.;

[0014] According to another aspect, the invention also relates to a ground penetrating radar comprising such a reconfigurable antenna array.

[0015] Other characteristics and advantages of the invention will emerge from the description given below, for information purposes only and in no way limiting, with reference to the appended figures, among which: [ Fig 1 ] there figure 1 schematically illustrates an elementary mesh and a first example of an antenna network or part of an antenna network according to an embodiment of the invention; [ Fig 2 ] there figure 2 illustrates four distinct radiation patterns associated with the same portion of an antenna array; [ Fig 3 ] there figure 3 illustrates another example of an antenna array according to an embodiment of the invention, the array comprising three types of sequentially selectable antennas; [ Fig 4 ] there figure 4 illustrates the reconfigurable switching circuit of the antenna array proposed according to the present invention; [ Fig 5 ] there figure 5 illustrates the application of the antenna array according to the present invention to a ground penetrating radar.

[0016] On side A, the figure 1 firstly illustrates schematically the geometry of an elementary mesh 10, also called a pixel, of an antenna network according to the present invention.

[0017] More precisely, each elementary mesh 10 (ie pixel) is, depending on the embodiment of the figure 1 , square and comprises a radiating element 12. According to another example not shown, each elementary mesh has a shape distinct from the square shape of the figure 1 , such a distinct shape having at least one symmetry such as a rhombus, an octagon, a disk, etc. However, it should be noted that a square elementary cell is optimal in terms of radiating surface filling.

[0018] According to the illustration of the figure 1 , the radiating element 12 within the square mesh corresponds to a conductive circular pattern. Such a circular pattern has a symmetry along the two diagonals D 1 and D 2 of said mesh square 10.

[0019] As an alternative, notably illustrated later within the figure 5 , any other form of radiating element suitable for being housed within the square elementary mesh 10 is suitable for use provided that this form also has symmetry along the two diagonals D 1 and D 2 of said mesh square 10.

[0020] Furthermore, according to the present invention, the radiating element 12 also has four ports (also called radiofrequency access RF) P 1 , P 2 , P 3 , P 4 distributed two by two on either side of each horizontal MH and vertical MV median of the elementary mesh square 10. More precisely, in the example of the figure 1 , the ports P 1 and P 3 , are located at each end, respectively left and right, of the horizontal median MH of the radiating element 12, and the ports P 2 and P 4 , are located at each end, respectively upper and lower, of the vertical median MV of the radiating element 12.

[0021] Such an elementary mesh geometry A reproduced identically over the entire antenna network by translation in one or two dimensions makes the antenna network according to the present invention modular (i.e. reconfigurable in particular in terms of radiation), because it allows a sequential selection of the radiating elements 12 to be excited via a reconfigurable switching circuit (also called power supply network of the antenna network), not shown, capable of controlling the individual connection of each RF radiofrequency access port.

[0022] By "control of the individual connection of each access port" is meant that each port can be powered by an RF signal source or receiver, which makes the application of the present invention compatible with a multi-antenna network, in particular of the MIMO type, because the location of the excitation as such is then reconfigurable.

[0023] As an optional addition, not shown, each elementary mesh (10) is placed in an electromagnetic cubic cavity, for example of dimension L 2 × L 2 × L 2 , with L 2 the dimension of one of the four sides of elementary mesh 10. According to another example, the cavity height has a cavity height distinct from the cavity length and / or width. Such placement in an electromagnetic cavity is notably implemented for an antenna network application for GPR ground radar (from the English Ground Penetrating Radar ) in order to focus the radiation of the antenna array towards the ground and avoid any interference with RF applications above the ground.

[0024] On side B, the figure 1 also illustrates a first example of an antenna network or part 14 of an antenna network according to an embodiment of the invention, this part 14 corresponds to a square antenna network formed of four elementary meshes 10 contiguous two by two, vertically and horizontally (i.e. superimposed vertically and adjacent horizontally). In other words, the antenna network corresponds to 2 × 2 elementary meshes 10.

[0025] Such an antenna network 14 formed of four elementary meshes 10 has a surface area equal to L × L , with L the dimension of one of the four sides of the antenna network 14, an elementary mesh 10 having an equal surface L 2 × L 2 , with L 2 the dimension of one of the four sides of elementary mesh 10.

[0026] Part B of the figure 1 illustrates how to connect the elementary meshes 10 (i.e. the pixels) to each other via the reconfigurable switching circuit proposed according to the present invention to obtain the desired radiation in terms of polarization, phase center, etc.

[0027] Indeed, as illustrated in part B of the figure 1 , the antenna network or part of the antenna network 14 comprises four pairs 16 of facing ports, namely: an upper horizontal pair 16 of ports P 3 and P 1 facing each other, port P 3 belonging to the upper left elementary network mesh while port P 1 belongs to the upper right elementary network mesh, a lower horizontal pair 16 of ports P 3 and P 1 facing each other, port P 3 belonging to the lower left elementary network mesh while port P 1 belongs to the lower right elementary network mesh, a left vertical pair 16 of ports P 4 and P 2 facing each other, port P 4 belonging to the upper left elementary network mesh while port P 2 belongs to the lower left elementary network mesh, a right vertical pair 16 of ports P 4 and P 2 facing each other, port P 4 belonging to the upper right elementary network mesh while port P 2 belongs to the lower right elementary network mesh.

[0028] According to an aspect not shown on the figure 1 , the reconfigurable switching circuit (also called antenna array power supply network), not shown, makes it possible to individually excite each pair 16 of ports facing the antenna array or part of the antenna array 14, so that in a modular manner from the antenna array or part of the antenna array 14, it is possible according to the present invention to excite four separate antennas as illustrated below in relation to the figure 2 , each antenna comprising two contiguous elementary meshes 10 (i.e. two contiguous pixels) being vertically superimposed, or horizontally adjacent, within the antenna network or part of the antenna network 14.

[0029] Indeed, advantageously, the reconfigurable switching circuit (also called antenna array power supply network) of the antenna array according to the present invention is specifically capable of generating three distinct connection states between each port of each pair of facing ports, each state and associated electronic circuit being described below in relation to the figure 3 .

[0030] More precisely, these three connection states correspond to a short circuit, an excitation and an open circuit.

[0031] There figure 2 illustrates four distinct radiation configurations C 1 , C 2 , C 3 , C 4 associated with the same antenna array portion 14 illustrated previously on side B of the figure 1 . In each distinct radiation configuration C 1 , C 2 , C 3 , C 4 , the antenna which is excited is represented in hatching and comprises two pixels (i.e. two elementary meshes 10) superimposed vertically, or adjacent horizontally within the antenna network or part of the antenna network 14 composed of the four elementary meshes 10 1 , 10 2 , 10 3 and 10 4 .

[0032] In particular, according to the radiation configuration C 1 , the antenna 18, shown in hatching, is composed of the elementary meshes 10 1 and 10 3 superimposed (i.e. contiguous) vertically within the antenna network or part of the antenna network 14, and connected, via said reconfigurable switching circuit, by means of a connection in the excitation state 20 of the ports of the pair of ports facing said at least two contiguous elementary meshes 10 1 and 10 3 , this excited pair 20 corresponding to the left vertical pair 16 of ports P 4 and P 2 facing each other, the port P 4 belonging to the upper left elementary network mesh 10 1 while the port P 2 belongs to the lower left elementary network mesh 10 3 .

[0033] According to this radiation configuration C 1 , the other pairs 22 of ports facing each other within the antenna network or part of the antenna network 14 are maintained via said reconfigurable switching circuit in an open circuit state.

[0034] The excitation activated by the reconfigurable switching circuit at the pair of facing ports 20 produces an antenna 18 polarized vertically along the axis Oy represented via the arrows 24 on the figure 2 , the excitation activated by the reconfigurable switching circuit corresponding to the application of a potential difference between, for example, the potential V A − associated with port P 2 of mesh 10 3 and the potential V A + associated with port P 4 of mesh 10 1 .

[0035] According to the radiation configuration C 2 , the antenna 26, shown in hatching, is composed of elementary meshes 10 1 and 10 2 horizontally adjacent (i.e. horizontally contiguous) within the antenna network or part of the antenna network 14, and connected, via said reconfigurable switching circuit, by means of a connection in the excited state 28 of the ports of the pair of ports facing said at least two contiguous elementary meshes 10 1 and 10 2 , this excited pair 28 corresponding to the upper horizontal pair 16 of ports P 3 and P 1 facing each other, the port P 3 belonging to the upper left elementary network mesh 10 1 while the port P 3 belongs to the upper right horizontally adjacent elementary network mesh 10 2

[0036] According to this radiation configuration C 2 , the other pairs 22 of ports facing each other within the antenna network or part of the antenna network 14 are maintained via said reconfigurable switching circuit in an open circuit state.

[0037] The excitation activated by the reconfigurable switching circuit at the pair of facing ports 28 produces an antenna 26 polarized horizontally along the axis Ox represented via the arrows 30 on the figure 2 , the excitation activated by the reconfigurable switching circuit corresponding to the application of a potential difference between, for example, the potential V A + associated with port P 3 of mesh 10 1 and the potential V A − associated with port P 1 of mesh 10 2 .

[0038] According to the radiation configuration C 3 , the antenna 32, shown in hatching, is composed of the elementary meshes 10 2 and 10 4 superimposed (i.e. contiguous) vertically within the antenna network or part of the antenna network 14, and connected, via said reconfigurable switching circuit, by means of a connection in the excitation state 34 of the ports of the pair of ports facing said at least two contiguous elementary meshes 10 2 and 10 4 , this excited pair 34 corresponding to the right vertical pair 16 of ports P 4 and P 2 facing each other, the port P 4 belonging to the upper right elementary network mesh 10 2 while the port P 2 belongs to the lower right elementary network mesh 10 4 .

[0039] According to this radiation configuration C 3 , the other pairs 22 of ports facing each other within the antenna network or part of the antenna network 14 are maintained via said reconfigurable switching circuit in an open circuit state.

[0040] The excitation activated by the reconfigurable switching circuit at the pair of facing ports 34 produces an antenna 18 polarized vertically along the axis Oy represented via the arrows 36 on the figure 2 , the excitation activated by the reconfigurable switching circuit corresponding to the application of a potential difference between, for example, the potential V A − associated with port P 2 of the 10 4 mesh and the potential V A + associated with port P 4 of mesh 10 2 .

[0041] According to the radiation configuration C 4 , the antenna 38, shown in hatching, is composed of elementary meshes 10 3 and 10 4 horizontally adjacent (i.e. horizontally contiguous) within the antenna network or part of the antenna network 14, and connected, via said reconfigurable switching circuit, by means of a connection in the excitation state 40 of the ports of the pair of ports facing said at least two contiguous elementary meshes 10 3 and 10 4 , this excited pair 40 corresponding to the lower horizontal pair 16 of ports P 3 and P 1 facing each other, the port P 3 belonging to the lower left elementary network mesh 10 3 while the port P 3 belongs to the lower right horizontally adjacent elementary network mesh 10 4 .

[0042] According to this radiation configuration C 2 , the other pairs 22 of ports facing each other within the antenna network or part of the antenna network 14 are maintained via said reconfigurable switching circuit in an open circuit state.

[0043] The excitation activated by the reconfigurable switching circuit at the pair of facing ports 40 produces an antenna 38 polarized horizontally along the Ox axis represented via the arrows 42 on the figure 2 , the excitation activated by the reconfigurable switching circuit corresponding to the application of a potential difference between, for example, the potential V A + associated with port P 3 of mesh 10 3 and the potential V A − associated with port P 1 of mesh 10 4 .

[0044] In other words, the antenna array or part of the antenna array 14 is capable of providing two separate antennas 26 and 40 polarized along the Ox axis and two other separate antennas 18 and 32 polarized along the Oy axis, which provides polarization reconfigurability (i.e. polarization modularity) of the antenna array or part of the antenna array 14 by means of a sequential selection of the arrangement of the excitations between the radiating elements of each elementary mesh constituting said antenna array or said part of the antenna array 14. Thus, the antenna array or part of the antenna array 14 makes it possible, from four separate elementary meshes 10 1 , 10 2 , 10 3 and 10 4 to selectively obtain four separate antennas 18, 26, 32 and 38, two of which antennas 18 and 32 are associated with a vertical polarization, while two other antennas 26 and 38 are associated with horizontal polarization.

[0045] Such modularity is advantageous and allows optimal exploitation of the surface area of ​​the antenna network or said part of the antenna network 14, in particular compared to the technical solutions disclosed in documents US 5,926,137 and EP 3,105,818 which require in particular the use of four distinct elementary meshes to create a single antenna.

[0046] In other words, in the antenna network structure according to the present invention, the principle of the shared radiating element is implemented, the radiating element of the elementary mesh 10 being for example shared between the antenna 18 and the antenna 26 respectively associated with the configurations C 1 and C 2 . With the right choice of the pixel (i.e. elementary mesh 10) and the access points (i.e. ports) excited specifically and selectively via the reconfigurable switching circuit of the antenna network according to the present invention, it is thus possible to exploit the radiating surface in a more optimal manner.

[0047] Such modularity allows the creation of other examples of antenna networks such as the one illustrated by the figure 3 , of enlarged dimension 4L × 4L, an elementary mesh 10 (ie network pixel) having an equal surface L 2 × L 2 , with L 2 the dimension of one of the four sides of elementary mesh 10, and therefore comprising eight elementary meshes 10 along Ox, and eight elementary meshes 10 along Oy.

[0048] As illustrated according to the figure 3 , such an antenna network is versatile in terms of possible antenna configurations and comprises for example at least three distinct types of antennas 44, 46, 48, synthesizable simultaneously or preferentially, in order to avoid the use of the same pixel on two different antennas, or a coupling between antennas due to their proximity, such a coupling being capable of modifying the performance of each antenna, sequentially selectable, via the reconfigurable switching circuit of the antenna network according to the present invention, each antenna being composed of at least two network pixels (i.e. elementary mesh 10), the antenna 44 being formed of eight vertically superimposed pixels, the antenna 46 being formed of two vertically superimposed pixels, and the antenna 48 having an H shape and comprising two identical vertical branches, each comprising at least five elementary meshes (i.e.pixels) vertically contiguous, the two identical vertical branches being connected to each other by a horizontal central branch comprising at least four horizontally contiguous elementary meshes, each elementary mesh located at one of the ends of the horizontal central branch corresponding respectively to the third elementary mesh of each of the two vertical branches.

[0049] It should be noted that the example of the figure 3 aims to illustrate the possibility according to the present invention of producing a plurality of antenna shapes and / or geometries by combining elementary meshes and reciprocal adaptation of the switching circuit, which corresponds to an optimal exploitation of the proposed elementary meshes. In other words, the present invention allows the production of any antenna shape or geometry meeting a specific need, including shapes / geometries distinct from those presented and illustrated as examples within the figures 2 And 3 .

[0050] Each of these antennas 44, 46, 48 are produced by applying to each port of each pair of ports facing each other elementary meshes of the entire antenna network of the figure 3 one of the three distinct connection states capable of being selected by the reconfigurable switching circuit implemented specifically according to the present invention, namely a short-circuit state 50, an excitation state 52 or an open-circuit state 54.

[0051] In particular, for the antenna 44, an excitation 52 is applied between the opposite accesses (i.e. ports) of the fourth and fifth vertical pixels, a short circuit 50 is applied between the other pixels constituting the antenna 44, while all the accesses not concerned (i.e. adjacent to pixels of the antenna network external to the antenna 44) are left in open circuit 54. On the figure 3 , for reasons of clarity, the set of open circuits 54 are not shown, but according to the present invention it is obvious that the ports P 3 (as shown in the figure 1 ) of each of the eight vertical pixels constituting the antenna 44 are in an open circuit state 54 with the ports P 1 of the horizontally adjacent set of the eight vertical pixels following in a horizontal direction Ox.

[0052] For the antenna 46 composed of two pixels, an excitation 52 is applied between the opposite accesses (i.e. ports) P ​​2 and P 4 belonging respectively to the lower pixel and upper pixel of the antenna 46, the other ports being in open circuit state 54 (not shown so as not to load the figure).

[0053] The H-shaped antenna 48 is adapted to be excited, via the reconfigurable switching circuit implemented specifically according to the present invention, by means of a connection in an excited state 52 of the ports of the pair of ports facing said at least two central contiguous elementary meshes of the horizontal central branch of the H, the ports facing the other contiguous elementary meshes forming said H-shaped antenna 48 being placed in a short-circuit state 50, the ports facing elementary meshes of said network external to said H-shaped antenna 48 all being placed in an open-circuit state 54 (although this is not explicitly shown on the figure 3 to avoid overloading the figure 3 ).

[0054] There figure 4 illustrates the reconfigurable switching circuit of the antenna array proposed according to the present invention. Such a reconfigurable switching circuit allows a high degree of reconfigurability and involves only three connection states (i.e. mode) at the ports (i.e. access) of each elementary mesh (i.e. pixel). These three modes correspond to short circuit 50, excitation 52 and open circuit 54. For this, a switching circuit is connected between each corresponding access (i.e. port). The architecture of the switching circuit presented on the figure 4 illustrates that the reconfigurable switching circuit according to the present invention comprises an electronic assembly comprising at least: a 58 balun configured to transform an input electrical signal into differential mode; two single-pole switches with one input and two SPDT outputs 62 (from English Single Pole double Throw ), a single pole single throw switch SPST 66 (from English Single Pole single Throw ) .

[0055] More precisely, on the figure 4 , an input signal 56 is transformed into differential mode thanks to the balun 58, each of the two differential outputs V C + And V C − is respectively transmitted, via a transmission line 60, to the input of each single-pole, single-input, two-output SPDT switch 62.

[0056] Each single-pole, single-throw, single-input, single-output SPDT switch 62 has two outputs, one connected via a resistive load 64, for example 50 Ohm to ground, and the other connected both to the input of the single-pole, single-throw SPST switch 66, and to the potential V A + for the single-pole, single-input, double-output SPDT 62 switch connected at the input to the differential output V C + , and respectively to the potential V A − for the single-pole, single-input, double-output SPDT 62 switch connected at the input to the differential output V C − .

[0057] According to the present invention, in the short-circuit state 50, the differential outputs V C + And V C − are directed to the resistive loads 64, and the single-pole, single-throw SPST switch 66 is closed.

[0058] In excitation state 52, the differential outputs V C + And V C − are directed respectively towards the potentials V A + And V A − , and the SPST 66 single pole single throw switch is open.

[0059] In the open circuit state, the differential outputs V C + And V C − are directed respectively to the resistive loads 64, and the single-pole single-throw SPST switch 66 is open.

[0060] There figure 5 illustrates the electromagnetic simulation environment 68 of the application of the antenna array according to the present invention to a ground penetrating radar.

[0061] More precisely, according to the figure 5 , a power supply 70 feeds such a ground penetrating radar 72 GPR (from the English Ground Penetrating Radar ) suitable for allowing the study of the composition and structure of the soil, and especially the detection and location of objects buried in the soil. Such a radar being placed at a distance 74 suitable for emulating a GPR scenario, for example equal to 15 mm from the ground 76 whose permittivity is for example ε r = 15, and the loss tangent tan δ = 0.1, the ground penetrating radar 72 being capable of generating an electric field E within the soil as illustrated by the figure 5 .

[0062] According to this example the radiating element 12 of the figure 1 corresponding to a circular pattern is replaced by an alternative quasi-rectangular shape, the pixel geometry having, in this example, been optimized to minimize the reflection coefficient S11 of the antenna 80 seen from above shown in hatching and composed of two pixels each comprising such a quasi-rectangular radiating element shown with a dotted texture within the pixel (i.e. elementary mesh) of square shape whose side measures for example 100mm so that an antenna network 78 consisting of four elementary meshes contiguous two by two, in a similar manner to the antenna network of the figure 2 , vertically and horizontally, occupies a flat surface equal to 200 mm x 200 mm.

[0063] According to this example of the figure 5 dedicated to the application 68 of the antenna array to a ground penetrating radar, each elementary mesh is advantageously placed in an electromagnetic cubic cavity, in order to focus the radiation of the antenna array towards the ground and avoid any interference with RF applications above the ground. For example, the cavity height measures 100 mm.

[0064] Not shown, because within a GPR system the antenna must have the lowest time dispersion in order to avoid the overlap between the direct coupling between the transmitting antenna Tx and the receiving antenna Rx and also the echo from the target, to reduce the time dispersion, four resistive loads not shown on the figure 5 are notably added between the pixel and the four upper corners of the cavity surrounding it.

[0065] As previously described in connection with the figures 1 And 2 , from an antenna network consisting of four elementary meshes contiguous two by two, vertically and horizontally according to the present invention, it is possible to create four antenna configurations (two polarized horizontally along Ox and two polarized vertically along Oy).

[0066] According to this example of the figure 5 corresponding to an optional aspect of the present invention, each electronic assembly of the reconfigurable switching circuit specifically proposed according to the present invention, and associated with each pair of facing ports is integrated within a metallic wall of said cubic cavity, said wall separating said ports of said pair, as illustrated in the side view 82 of the wall of the figure 5 where the reconfigurable switching circuit 84 specifically proposed according to the present invention and its power supply 86 are integrated. Such use of cavity walls makes it possible to produce transmission lines.

[0067] According to another aspect, not shown in the figure 5 representing, in a similar manner to the figure 2 , a dual-polarization antenna array comprising four elementary meshes (2x2) allowing four distinct antenna configurations to be obtained, namely two horizontally polarized antennas and two vertically polarized antennas, such an application 68 of the antenna array to a ground-penetrating radar is likely to require an ultra-wideband ULB multi-antenna system enabled by an antenna array according to the present invention comprising other antenna configurations (in polarization and / or in geometry). For example, another antenna array according to the present invention comprising three distinct antenna geometries not shown, namely vertical with two pixels, vertical with four pixels, and H-shaped with two identical horizontal branches, each comprising at least five elementary meshes (i.e.pixels) horizontally contiguous, the two identical horizontal branches being connected to each other by a vertical central branch comprising at least four vertically contiguous elementary meshes, is suitable for use as an alternative to meet other needs. These three geometries are sequentially selectable via the reconfigurable switching circuit of the antenna array according to the present invention. These three distinct antenna geometries are in fact suitable for exhibiting ULB behaviors useful for the application targeted by the . figure 5 while exhibiting distinct efficiencies, the four-pixel vertical antenna and the aforementioned H-shaped antenna with two horizontal branches, due to their larger electrical size, being notably more efficient in the low frequency bands allowing the detection of deep targets for a GPR application and exhibiting an improvement in gain level compared to a two-pixel vertical antenna.

[0068] It should be noted that the antenna array according to the present invention has an architecture that can be reconfigured as desired, depending on the application, to obtain a desired resolution or detection direction. In particular, depending on the needs, the aforementioned H-shape is not optimal and is indicated above just as an example, the architecture of the antenna array according to the present invention making it possible to exploit other antenna configurations having, for example, higher performances than the aforementioned H-shape on predetermined low-frequency bands.

[0069] It should be noted that the size of the antenna (formed by a plurality of elementary meshes according to the activated configuration) is a key element that defines its operating frequency, which is an important parameter for the GPR application. With the solution proposed according to the present invention, it is possible to reduce or increase the operating frequency of the antenna by changing the number of mesh(es) that form(s) this antenna

[0070] Also, the geometric reconfiguration obtained thanks to the present invention, and as previously illustrated also by the figure 3 , is capable of significantly contributing to improving the performance of a GPR system, this reconfiguration providing a degree of freedom to synthesize the performance of the antenna in accordance with the instantaneous needs of the system, and allowing to create even more antennas whose geometry is not limited to a specific number of pixels.

[0071] Those skilled in the art will understand that the invention is not limited to the embodiments described, nor to the particular examples of the description, the embodiments and variants mentioned above being suitable for being combined with each other to generate new embodiments of the invention.

[0072] The present invention thus makes it possible to reconfigure the antenna geometry according to the system requirement corresponding for example to the need and / or to move its operating frequency to enlarge the electrical size (height and / or width) of the antenna to increase its radiation efficiency and its gain, to the need to move the phase center of the excited antenna on the surface of the network, to the need to multiply the number of sources to densify (reduce the inter-element space (i.e. the elementary mesh size in order to reduce the space between the antennas, the reduction of the elementary mesh size implying a reduction in the inter-element space)) in the high frequency bands, to the need to change the polarization of the elementary meshes to exploit the polarization properties, to the need to load antenna ends to attenuate the phenomena of internal reflections at the end of the line likely to distort the emitted signals (from the English ringing) in time (useful in ground radar applications) but also to attenuate inter-element coupling (i.e. between elementary meshes), while remaining reconfigurable at the request of the telecommunications or radar system capable of integrating the antenna network according to the present invention.

[0073] Indeed, as seen previously, from a unit pixel (i.e. elementary mesh) with four accesses (i.e. ports), a part of an antenna network comprising, according to a first example, 2x2 pixels can be designed in particular according to the present invention, from which it is possible to configure the excitation of the neighboring (i.e. facing) accesses (i.e. ports), thanks to the integration of an RF switching circuit (otherwise called a power supply network) to create four antennas polarized either along Ox or along Oy.

[0074] Such an RF switching circuit makes it possible to impose a specific excitation mode on each access (i.e. port) to excite antennas of larger electrical size and thus makes it possible to optimally use the surface occupied by radiating elements, in particular for an application to an antenna network for ground radar (GPR), or to an antenna network for spectrum monitoring and direction finding, or even for any telecommunications or radar application where the spectrum is scanned by successive sub-bands or using multiple polarizations successively.

Claims

1. A reconfigurable antenna array (14) comprising a plurality of identical elementary meshes (10), each mesh having at least one symmetry, in particular a square mesh, and comprising a radiating element (12) having: at least four ports (P1, P2, P3, P4) distributed in pairs on either side of each median (MH, MV) of one side of a mesh (10), the antenna array being characterised in that it further comprises a reconfigurable switching circuit capable of imposing a specific excitation mode on each port by being capable of generating three distinct connection states (50, 52, 54) between each port of each pair (16) of facing ports, each port of a pair (16) belonging to two distinct elementary meshes (10), vertically superimposed or horizontally adjacent, within said antenna array (14).

2. The antenna array according to claim 1, wherein the three connection states correspond to: - a short circuit (50); - an excitation (52) - an open circuit (54).

3. The antenna array according to claim 1 or 2, in which the radiating element (12) within the elementary mesh (10) corresponds to a circular pattern.

4. The antenna array according to any one of the preceding claims, in which at least one antenna (18, 26, 32, 38, 46) of said antenna array is formed by at least two vertically and / or horizontally contiguous elementary meshes (10), said at least two contiguous elementary meshes being connected, via the said reconfigurable switching circuit, by means of a connection in the excitation state (52) of the ports of the pair of facing ports of said at least two contiguous elementary meshes.

5. The antenna array according to any one of the preceding claims, in which at least one part (B) of said antenna array is square and formed of four elementary meshes contiguous in pairs, vertically and horizontally, and suitable for being excited according to four distinct configurations (C1, C2, C3, C4), associated respectively, via the said reconfigurable switching circuit, with a distinct arrangement, from one configuration to another, of connections between each port of each pair (16) of facing ports, each port of a pair (16) belonging to two distinct elementary meshes superimposed vertically or horizontally within said square part formed of four elementary meshes (10) contiguous two by two, vertically and horizontally.

6. The antenna array according to claim 5, wherein two (C1, C3) of said four distinct configurations (C1, C2, C3, C4) are associated with horizontal polarisation and a further two (C2, C4) of said four distinct configurations are associated with vertical polarisation.

7. The antenna array according to any one of the preceding claims, in which at least one antenna (48) of said antenna array is H-shaped and comprises two identical vertical branches, each comprising at least five vertically contiguous elementary meshes, the two identical vertical branches being connected to one another by a horizontal central branch comprising at least four horizontally contiguous elementary meshes, each elementary mesh located at one of the ends of the horizontal central branch corresponding respectively to the third elementary mesh of each of the two vertical branches.

8. The antenna array according to claim 7, in which said H-shaped antenna is adapted to be excited, via the switching circuit, by means of a connection in the excitation state (52) of the ports of the pair of facing ports of said at least two contiguous central elementary meshes of said horizontal central branch, the facing ports of the other contiguous elementary meshes forming said H-shaped antenna being placed in short-circuit state (50), the facing ports of elementary meshes of said array external to said H-shaped antenna (48) being placed in an open-circuit state (54).

9. The antenna array according to any one of the preceding claims in which, for each pair of facing ports belonging to two distinct elementary meshes superimposed vertically or horizontally, the reconfigurable switching circuit comprises an electronic assembly comprising at least: - a balun (58) configured to transform an input electrical signal into differential mode; - two single-pole switches with one input and two SPDT outputs (62), - a single-pole single-throw SPST switch (66).

10. The antenna array according to any one of the preceding claims, in which each elementary mesh (10) is placed in an electromagnetic cubic cavity.

11. The antenna array according to claims 9 and 10, in which each electronic assembly associated with each pair of facing ports is integrated within a metal wall of said cubic cavity, said wall separating said ports of said pair.

12. A ground-penetrating radar comprising a reconfigurable antenna array according to claim 10 or 11.

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