EP2887454A1 - Panel aerial system with reduced visual impact - Google Patents

Abstract

An optically transparent antenna system comprises at least one unitary antenna comprising at least one radiating element formed of at least one dipole carried by a foot placed on a reflector, the radiating element being surrounded by longitudinal and transverse partitions and connected to a feeder. The dipole, the reflector, the partitions and the feed line consist of an optically transparent substrate covered with at least one optically transparent conductive surface, the conductive surface being chosen from an optically transparent conductive film, a conductive mesh, and a combination of an optically transparent oxide conductive film and a conductive mesh.

Description

The present invention relates to the field of telecommunication antenna systems transmitting microwave radio waves. It relates more particularly to so-called "optically quasi-transparent" antenna systems for an observer.

An antenna system is composed of several unitary antennas, such as patch antennas or dipole alignments ("Antenna Array" in English) working in a given frequency band, which are intended more particularly for cell phone applications. Variable electric tilt antennas known as VET (Variable Electric Tilt) allow to vary the position of the main lobe with respect to the horizon. Adjustment of the inclination of the antenna in the vertical plane can be achieved by different techniques applied to the antenna supply network, using active and / or passive devices, mainly by means of a device for shifting the antenna. phase.

The radiating elements of the unitary antennas assigned to applications requiring a low visual impact most often have a flat layer configuration which is unfavorable to obtaining a reduced visual impact. They are made from conductive layers, which are superposed in order to increase the effective frequency bandwidth of the antennas, these conductive layers being obtained either by the deposition of thin layers of conductive oxides, or from thin wires or of conductive metal cloth. As these antennas are built from the superposition of several flat layers, the resulting transparency is reduced as the number of layers increases. This stack of multiple flat layers results in the addition of more or less transparent layers, leading to a "quasi-opaque" antenna system, or the appearance of certain non-transparent areas in the best case. Many improvements are expected in this area.

Optically quasi-transparent antenna systems are at the center of operators' interest for their visual and aesthetic qualities allowing them a better integration into the landscape. By "optically quasi-transparent" is meant a device that passes visible light in a proportion of at least 80%, so that the human eye does not identify at first glance the presence of a such device. Despite the technical choices and compromises necessary to obtain an optically near-transparent antenna system, a so-called "phased array" or "Phased Array Antenna" antenna system. in English) should nevertheless still allow an operator to select and control the position of the main lobe of the unit antennas (ie the tilt or vertical tilt), and to provide the same level of radio frequency performance as the antenna systems. unitary antennas usually used.

Until now, so-called "optically near-transparent" antenna systems use so-called "patch" technology or the slot feed technique. If the thin deposition of transparent conductive compounds, for example tin-doped indium oxide ITO (for "Indium Tin Oxide" in English), silver-doped tin oxide AgHT, zinc doped with aluminum, etc ..., represents an interesting solution to obtain a quasi-transparent conductive surface, the final conductivity of this material is not as good as that of conventional standard aluminum or copper metal surfaces. These known antenna systems can not ensure wideband use, except to increase the number of layers so significantly that it results in almost complete opacity.

• soit les fils sont minces et/ou la maille de toile est large pour améliorer la transparence, mais dans ce cas l'efficacité du blindage est faible,
• soit les fils sont épais et/ou la maille de toile est étroite pour améliorer la conductivité, mais dans ce cas l'impact visuel ne correspond pas à un système d'antennes quasi-transparent.

The use of a fabric composed of conductive wires as a ground plane may be an interesting alternative solution, but, in the current forms, it does not make it possible to achieve the objectives that one has set. Indeed :

• either the wires are thin and / or the mesh of fabric is wide to improve the transparency, but in this case the effectiveness of the shielding is weak,
• either the wires are thick and / or the mesh is narrow to improve the conductivity, but in this case the visual impact does not correspond to a quasi-transparent antenna system.

Operators are therefore waiting for an antenna system that achieves the level of radio frequency performance at least equivalent to that of known antennas, while providing the optically almost transparent desired appearance.

The object of the present invention is therefore to propose a phased array antenna system comprising at least one VET variable tilt panel antenna simultaneously having a very low visual impact for an observer who would be placed in front, and radio frequency performance equivalent to those of a known VET panel antenna.

Another object is to provide such an antenna system which is further configured in a plane and well suited for mounting on a tubular support (such as a mast or pylon) or a flat surface, such as the wall of a building.

The object of the present invention is an optically transparent antenna system comprising at least one unitary antenna comprising at least one radiating element formed of at least one dipole carried by a foot placed on a reflector, the radiating element being surrounded by longitudinal and transverse partitions and connected to a power line. The dipole, the reflector, the partitions and the supply line consist of an optically transparent substrate covered with at least one optically transparent conductive surface, the conductive surface being chosen from an optically transparent conductive film, a conductive mesh, and a combination of an optically transparent conductive film and a conductive mesh.

According to a first variant, the mesh is formed of a set of vertical and horizontal conductor wires forming approximately parallelepipedal meshes, or a set of vertical, horizontal and diagonal conductor wires forming approximately triangular meshes.

According to a second variant, the mesh is formed of a set of conductive tracks printed on an optically transparent substrate.

According to a first aspect, the dimensions of the conductive wires or conducting tracks vary according to the zones as a function of the current density in these zones.

According to a second aspect, the pitch of the mesh of the mesh varies according to the zones as a function of the current density in these zones.

In a third aspect, the feed line is disposed on the face of the substrate opposite the dipole.

According to a fourth aspect, the dipole, the reflector, the partitions and the power supply line consist of an optically transparent substrate covered with an optically transparent conductive film, the conductive film being itself covered with a mesh fabric made of lead wires.

According to a fifth aspect, the optically transparent conductive film is a film of an optically transparent conductive oxide selected from tin doped indium oxide, silver doped tin oxide, aluminum-doped zinc, indium doped zinc oxide and gallium-doped zinc oxide.

According to a sixth aspect, the optically transparent conductive film is a film of an optically transparent conductive polymer containing a polyaniline or poly (3,4-ethylenedioxythiophene).

According to a seventh aspect, the optically transparent conductive film is a film of an optically transparent conductive nanomaterial chosen from a fullerene, a graphene, a carbon nanotube and a nanometal, especially in the form of nanowire or nanoparticle.

According to an eighth aspect, the optically transparent oxide conductive film is deposited on the substrate by a mechanical, physical or chemical process.

According to a ninth aspect, the conductive son consist of a metal selected from copper, aluminum, silver and gold.

According to a tenth aspect, the optically transparent substrate is selected from a glass, an acrylic polymer, polyethylene terephthalate PET, polycarbonate PC, a composite material based on glass fibers bonded with a polyester resin.

According to one embodiment, the antenna system comprises two unitary antennas whose radiating elements are aligned in parallel rows separated by a longitudinal partition.

According to another embodiment, the antenna system comprises two unitary antennas whose radiating elements are formed of a first dipole belonging to the first unitary antenna and a second dipole belonging to the second unitary antenna, the two dipoles being crossed with orthogonal polarization.

According to yet another embodiment, the antenna system comprises at least two unitary antennas, each operating in a different frequency band. For example, the antenna system may comprise several unitary antennas (3, 4, 5, 6, etc.) whose radiating elements are aligned in parallel rows separated by a longitudinal partition. For example again, the antenna system may comprise several unitary antennas of which at least two unitary antennas comprise radiating elements formed of a first dipole belonging to the first unitary antenna and of a second dipole belonging to the second unitary antenna, the two dipoles being crossed with orthogonal polarization. The radiating elements belonging to the other antennas may, depending on the case, be in the same configuration or aligned.

Advantageously, the radiating elements are arranged perpendicularly on vertical surfaces, such as walls, etc. Thus only a few "small lines" will be visible in front view of the antenna. Therefore, even if the final thickness of the panel antenna may be greater than those using patch-type or slot-type radiators, the volumetric design option ultimately leads to a lower overall visual impact for an observer who would be placed in front.

Moreover, by combining the advantages of an optically transparent conductive film and of a mesh fabric composed of conducting wires, the overall conductivity of the conductive surface is improved while not substantially reducing its transparency.

An additional benefit can be obtained by designing a mesh fabric with a specific design. In particular, thicker or different sized wires and / or a portion of fabric with smaller mesh sizes can be placed in selected positions, where the current density or shielding effect require it. Smaller conductor wires and / or a web portion with larger meshs can be placed in selected positions that require less current density or shielding effect.

Compared with known techniques, this solution is more efficient for obtaining a low visual impact antenna system. It simultaneously improves the overall transparency of the antenna system, the RF performance, the mechanical robustness, the cost and the total weight of the antenna and simplifies the RF design of the antenna system. This solution allows the design of a new complete range of low visual impact antenna systems. It is particularly well suited to the installation of the antenna system on a vertical surface support. It also makes it possible to increase the usable frequency band.

• la figure 1 illustre, en vue partielle en perspective, un premier mode de réalisation d'un système d'antennes,
• les figures 2a et 2b illustrent, respectivement en vues de dessus et de côté, le premier mode de réalisation d'un système d'antennes,
• la figure 3 illustre, en vue partielle détaillée, un élément rayonnant d'antennes unitaire selon le premier mode de réalisation d'un système d'antennes,
• les figures 4a, 4b et 4c illustrent, respectivement en vues de côté et en perspective, la réalisation d'une surface conductrice,
• les figures 5a, 5b, 5c et 5d illustrent schématiquement des variantes de réalisation d'une surface conductrice en toile maillée,
• la figure 6 illustre, en vue partielle en perspective, un deuxième mode de réalisation d'un système d'antennes,
• les figures 7a et 7b illustrent, respectivement en vues de dessus et de côté, le deuxième mode de réalisation d'un système d'antennes,
• la figure 8 illustre en vue partielle détaillée le deuxième mode de réalisation d'un système d'antennes,
• la figure 9 illustre partiellement la vue qu'aurait un observateur placé face à un système d'antennes, selon le deuxième mode de réalisation, appliqué contre une surface verticale,
• les figures 10a et 10b illustrent l'adaptation en impédance du système d'antennes (VSWR et abaque de Smith),
• la figure 11 illustre l'ouverture à -3 dB du diagramme de rayonnement du système d'antennes dans le plan horizontal,
• la figure 12 illustre le rapport d'énergie entre la polarisation croisée et la copolarisation dans le plan horizontal et dans l'axe du système d'antennes,
• les figures 13a et 13b illustrent le diagramme de rayonnement du système d'antennes dans le plan horizontal selon les deux composantes de la polarisation croisée respectivement, pour un angle d'inclinaison de zéro degré,
• les figures 14a et 14b illustrent le diagramme de rayonnement du système d'antennes dans le plan vertical selon les deux composantes de la polarisation croisée respectivement pour un angle d'inclinaison de zéro degré,
• la figure 15 illustre le gain total du système d'antennes.

Other characteristics and advantages of the present invention will appear on reading the following description of an embodiment, given of course by way of illustration and not limitation, and in the accompanying drawing in which:

• the figure 1 illustrates, in partial perspective view, a first embodiment of an antenna system,
• the Figures 2a and 2b illustrate, respectively in top and side views, the first embodiment of an antenna system,
• the figure 3 illustrates, in a detailed partial view, a unitary antenna radiating element according to the first embodiment of an antenna system,
• the Figures 4a, 4b and 4c illustrate, respectively in side views and in perspective, the production of a conductive surface,
• the Figures 5a, 5b, 5c and 5d schematically illustrate alternative embodiments of a conductive mesh surface mesh,
• the figure 6 illustrates, in partial perspective view, a second embodiment of an antenna system,
• the Figures 7a and 7b illustrate, respectively in top and side views, the second embodiment of an antenna system,
• the figure 8 illustrates in partial detail the second embodiment of an antenna system,
• the figure 9 partially illustrates the view of an observer facing an antenna system, according to the second embodiment, applied against a vertical surface,
• the Figures 10a and 10b illustrate the impedance matching of the antenna system (VSWR and Smith chart),
• the figure 11 illustrates the -3 dB aperture of the radiation pattern of the antenna system in the horizontal plane,
• the figure 12 illustrates the energy ratio between the cross polarization and the co-polarization in the horizontal plane and in the axis of the antenna system,
• the Figures 13a and 13b illustrate the radiation pattern of the antenna system in the horizontal plane according to the two components of the cross polarization respectively, for an angle of inclination of zero degrees,
• the Figures 14a and 14b illustrate the radiation pattern of the antenna system in the vertical plane according to the two components of the cross polarization respectively for a tilt angle of zero degrees,
• the figure 15 illustrates the total gain of the antenna system.

Directional terminology such as "left", "right", "up", "down", "forward", "backward", "vertical", horizontal ", etc. is used with reference to the orientation of the figures here described. Because the elements composing the embodiments of the present invention can be placed in different orientations, the directional terminology is only used here for purposes of illustration and is in no way limiting.

In the first embodiment illustrated on the figure 1 and the Figures 2a and 2b , a phased array antenna system 1 with a low visual impact includes a first VET 2A variable tilt unit panel antenna and a second VET 2B variable tilt unit panel antenna . In telecommunications, a phased array antenna system is a group of unitary antennas powered with signals whose phase is adjusted to obtain the desired radiation pattern.

Here unitary panel antenna 2A, 2B is understood to mean an alignment of radiating elements 3 operating in a given frequency range and having its own power supply system. The antenna system 1 groups unit antennas 2A, 2B operating with different polarizations inside a single mechanical structure 4, or chassis, having a fixed and limited volume, each unit antenna 2A, 2B having its adapted power supply. at its operating frequency band. Antenna system 1 for use in a base station of a mobile telecommunication network has a plurality of transmit / receive ports 5 . The ports 5 are RF connectors, for example type 7/16, N type connectors, etc.

In this embodiment, the + 45 ° inclined polarization VET 2A panel antenna is separated from the polarized VET 2B panel antenna inclined at -45 ° to enhance the natural isolation of the +45 and -45 polarizations. ° antennas, and reduce the length of power lines to reduce their losses. The radiating elements 3 are arranged on a reflector 6, common to the two unitary antennas 2A and 2B, belonging to the mechanical structure 4 of the antenna system 1.

Longitudinal partitions 7 and transverse 8 are used to physically separate the radiating elements 3 of each antenna unit 2A, 2B, and separating the rows of radiating elements 3 of each of the unit antennas 2A and 2B. The presence of the longitudinal partitions 7 contributes to the formation of the horizontal beam -3 dB of the antenna pattern. The transverse partitions 8 make it possible to improve the insulation between the radiating elements 3 and to participate in the formation of the overall diagram of the antenna system. These partitions 7, 8 can be supported by any type of transparent material such as glass, but preferably a light transparent material such as polycarbonate PC is used for example, in order to reduce the overall weight of the antenna system 1 . as the reflector 6, the radiating elements 3 and their feed lines, the partitions 7, 8 have conductive surfaces which may be a conductive film, such as an optically transparent oxide film said OTC (for "transparent Oxides and Conductors "), such as an indium oxide doped with tin ITO, or a wire mesh made of conducting wires, such as copper wires for example, or else an optically transparent conductive film associated with a mesh fabric in conducting wires. The partitions 7, 8 contribute to the overall robustness of the mechanical structure 4 of the system of antennas 1. If necessary, the partitions 7, 8 may include orifices to allow the passage of the supply lines.

The antenna system 1 is intended to be placed on a substantially vertical plane support so that its axis X-X ' makes an angle which is as close as possible to 90 ° with respect to the most probable direction of vision V d an observer. In the best case, the axis Y-Y ' of the radiating element 3 is thus substantially collinear with the viewing direction V of the observer.

The reflector 6 serving as ground plane ("ground plane" in English), consists of a conductive surface carried by the rear face of the antenna system 1. It is made of a visually transparent material such as glass , laminated glass, smoked glass, tinted glass, shatterproof glass, safety glass, etc., but also a transparent plastic such as acrylic, for example polymethyl methacrylate PMMA, polyethylene terephthalate PET, polycarbonate PC, a composite material based on glass fibers, for example linked by a polyester resin, etc. This material is then coated with a conductive surface which may be constituted by an optically transparent conductive film, such as an OTC optically transparent conductive oxide film, such as tin-doped indium oxide ITO, or by a wire mesh consisting of conducting wires, for example made of copper, or else by n optically transparent conductive film associated with a wire mesh of conductive wires. The front face of the antenna system 1, here forming the radome 9 is also made of a visually transparent material which may be one of the aforementioned materials.

In order to reinforce the mechanical strength of the antenna system 1, a bottom and a cover (not shown) belonging to the mechanical structure of the antenna system can be added. The bottom and the cover may also be made of a visually transparent material to improve the overall transparency of the antenna system. However part of the bottom and / or the cover could be made of a non-transparent material, for example a metal, in the case where additional mechanical protection is necessary (for example a protection against falling objects on these surfaces) or to improve the overall mechanical strength of the antenna system.

As illustrated on the figure 3 , The radiating element 3 is a 10 half-wave dipole, the conductive arms are carried by a foot 11 place perpendicularly to the reflector plane 6. The reflector 6 plane conductive surface is provided with lateral flanges 12 parallel to the longitudinal partitions 7 . The lateral flanges 12 of the reflector 6 are formed by folding the longitudinal edges of the reflector 6 towards the radiating elements 3. The radiating elements 3 may be quasi-yagi dipoles or any other type of dipole placed at a distance from the reflector 6 of the reflector 6. preferably of the order of λ / 4, where λ is the central operating frequency of the unit antenna.

The dipole 10 is printed on one of the faces of a transparent substrate 14 having a high dielectric constant ε _r (1 <ε _r <5), for example a PC polycarbonate substrate, polyethylene terephthalate PET, polychlorinated biphenyl PCB or in any other optically transparent material. It should be noted that the radiating elements 3 are placed inside the mechanical structure 4 of the antenna system 1, so that they will not have to cope with a direct mechanical external stress or an impact. The conductive surface of the arms of the dipole 10 may be made either by the deposition on a transparent substrate of an optically transparent conductive film, such as an OTC optically transparent oxide conductive film such as a tin doped indium oxide. ITO, or by a mesh fabric consisting of conductive son, for example copper, or even by an optically transparent conductive film associated with a wire mesh conductive son.

At least one conductive portion 13 feeding the dipole 10, which ensures the transition between the supply lines and the radiating element 3, is printed on the same substrate 14 as the dipole 10, on the opposite side to the dipole 10, and on the reflector 6 . Preferably, these portions 13 of the feed lines are microstrip lines or stripline lines in order to improve the overall transparency of the antenna system. The portion 13 of the feed line may be constituted by an optically transparent conductive film, such as an optically transparent conductive oxide film OTC such as an indium oxide doped with tin ITO, or by a mesh fabric consisting of conductive son, for example copper, or even by an OTC optically transparent oxide conductive film associated with a mesh of conductive son, similar to the dipoles. The portion of the power line located outside the printed portion may be a coaxial cable that is connected to the RF connectors of the transmit / receive ports.

The antenna system includes FET (fixed tilt) or VET (variable tilt) power supply networks. There is a power supply for the unit antenna 2B polarized at + 45 °, a power supply for the unit antenna 2A polarized at -45 °. The supply networks (not visible in the figure) can be placed, as here, inside the lateral flanges 12 of the reflector 6. In this case the lateral flanges 12 are made of metal in order to ensure the mechanical rigidity of the antenna system. Although non-transparent, their visual impact remains minimal. They make it possible to house not only the power supply networks but also the electronic control devices for the variable electrical inclination of the antenna system 1. The lateral flanges 12 containing the supply networks thus participate in the overall mechanical structure of the system. antennas. These lateral flanges 12 are formed by metal portions, but it is also possible to use a transparent conductive material, for example having undergone a metallization treatment so as to leave visible the various elements placed inside.

The Figures 4a, 4b and 4c illustrate the method of producing the reflector, a radiating element or a portion of its feed line. An OTC optically transparent oxide conductive film 40 is deposited on a substrate 41.

The substrate 41 is made of a flexible or rigid visually transparent material such as for example glass, laminated glass, smoked glass, tinted glass, unbreakable glass, safety glass, etc., but also a material transparent plastic such as acrylic, for example polymethyl methacrylate PMMA, polyethylene terephthalate PET, polycarbonate PC, polychlorinated biphenyl PCB, a composite material based on glass fibers, for example linked by a polyester resin, etc. .

The optically transparent conductive film 40 is, for example, an OTC optically transparent conductive oxide film consisting of indium tin-doped indium oxide ("Indium Tin Oxide"), tin oxide doped with AgHT silver, zinc oxide doped with aluminum AZO (for "Aluminum Zinc Oxide" in English), oxide of zinc indium-doped IZO (for "Indium Zinc Oxide" in English), or gallium-doped zinc oxide GZO (for "Gallium Zinc Oxide" in English), etc ... The optically transparent conductive film 40 can still be an optically transparent conductive polymer film containing in particular a polyaniline or poly (3,4-ethylenedioxythiophene) PEDOT, for example a PEDOT-PSS mixture of sodium polystyrene sulfonate PSS and poly (3,4 -ethylenedioxythiophene) PEDOT or a derivative of poly (3,4-ethylenedioxythiophene) and tetramethylacrylate PEDOT-TMA. Finally, the optically transparent conductive film 40 may be a film of an optically transparent conductive nanomaterial chosen from a fullerene, a graphene, a carbon nanotube CNT (for "Carbon NanoTube" in English) and a nanometal such as in particular a nanowire or a nanoparticle metal, for example silver, gold, copper or aluminum.

The conductive film 40 may be deposited on the substrate 41 made of transparent material by any suitable known method such as a mechanical, physical or chemical process. For example, the deposition can be carried out physically by vapor phase (PVD), by sputtering, evaporation under vacuum, laser ablation, etc., by chemical vapor phase (CVD, PECVD, OMCVD, etc.). by electrolytic deposition (silver plating, copper plating, gilding, aluminide, tin plating, nickel plating, etc ...), by screen printing or painting, etc. The conductive film 40 could also be placed on a thin transparent intermediate layer (for example of 0 , 1 to 0.5 mm), itself being bonded to the substrate 41 of transparent material or held in place by electrostatic effect for example. At high frequencies, electromagnetic currents circulate mainly in the "skin" of the conductive material, i.e. within a small thickness near the surface of the conductive material.

If ITO tin-doped indium oxide is transparent and colorless for very thin thicknesses, for thicker layers it turns yellowish to gray in color. So that a compromise must be made between the conductivity and the transparency, since the increase in the thickness of the conductive oxide film and the increase in the concentration of charge carriers makes it possible to increase the conductivity of the material but decreases it. correlatively its transparency. For frequencies ranging from 1 to 10 GHz, the "skin" thicknesses for copper or gold conductors range from less than a micrometer to a few micrometers. By way of example, the "skin" thickness for a coppered surface is 0.65 μm at 10 GHz and 2.1 μm at 1 GHz.

However, the performance of the antenna system also depends on the conductivity of its various components, due to the presence of losses and the influence of the shielding efficiency on the antenna pattern, for example; it is therefore necessary to increase the conductivity (inverse of the resistivity). Compared to copper (resistivity of copper about 1.68 × 10 ^-8 Ω · m) or gold (gold resistivity about 2.44 × 10 ^-8 Ω · m), indium oxide doped with Tin ITO has a resistivity of about 10 ^-4 Ω • cm which is much higher.

Increasing the thickness of tin-doped indium oxide film so as to have a thickness greater than the "skin" depth is a first avenue of improvement. But this solution alone will quickly lead to a loss of transparency while having a limited effect on conductivity.

Another way of improvement is to replace the conductive surfaces in optically transparent conductive films, for example an indium oxide film doped with tin ITO, with a mesh, or mesh, made by means of metal conductive wires. , such as copper or other good conductor wires (aluminum, silver, gold), or conductive traces printed on an optically transparent substrate. If the pitch of the fabric (surface of the mesh) is sufficiently small compared to the operating frequency of the antenna (typically less than λ / 10 where λ is the wavelength) and if the conducting wires are sufficiently thick (typically 10 ^-4 mm to 1 mm), a very good shielding effect can be obtained. Nevertheless, for areas with a high current density, such a fabric could be insufficient with respect to losses.

A fabric 42, or lattice, made of conductive wire mesh can then be deposited on the optically transparent conductive film 40 . The term "fabric" means a set of vertical and horizontal son forming approximately parallelepiped mesh, and "lattice" means a set of vertical son, horizontal and diagonal which form meshes approximately triangular. Throughout the present description the word "canvas" means both a canvas and a lattice.

The presence of a fabric or mesh also greatly improves the overall mechanical behavior of the antenna system vis-à-vis external aggression, such as vibration and shock for example. It should be noted that a wire mesh Conductors can be added to the optically transparent conductive film only in areas of higher current density for example.

The Figures 5a and 5b illustrate several examples of conductive surfaces made of a wire mesh fabric. The Figures 5c and 5d illustrates a detailed view of a web of conductive threads or conductive tracks printed respectively.

On the figure 5a is shown an example of conductive surface which is a web 50 made of metal conductive son 51, copper or gold for example, the same thickness e forming parallelepipedal meshes 52 . Meshes 52 have a vertical height h and a horizontal width l. In the embodiment shown here these dimensions h and l are substantially equal, and the mesh 52 is substantially square. However one could equally well have rectangular or trapezoidal meshes for example. The dimensioning of the mesh of a conductive surface is defined by the ratio between its pitch (surface of a mesh) and the dimension of the conducting wires which compose it. The higher this ratio, the more difficult the meshed driver plane will be to discern.

On the figure 5b is another example of a conductive surface which is a mesh fabric 54 made of metal conductors 55 , for example of copper, of thickness E forming meshes 56 of vertical height H and of horizontal width L. These meshes 56 are divided into sub-meshes 57 of smaller dimension. Sub-meshes 57 consist of conductive son 58 of e lesser thickness for example. Sub-meshes 57 have for example a vertical height h and horizontal width l . In the embodiment shown here, the meshes 56 and the sub-meshes 57 are substantially square. A fabric of this type is preferably used in areas of high current densities.

The conductive son may have a section of different geometric shape, including circular or parallelepiped. In the case of a parallelepiped-shaped conductor wire as shown in FIG. figure 5c by thickness e is the dimension of the conductive wire 58 in the plane of the wire 54. The thickness e of the conductive wire 58 may be equal to or different from its dimension d in the direction perpendicular to the plane of the wire 54. thickness E means the dimension of the conducting wire 55 in the plane of the wire 54. The thickness E of the conducting wire 55 may it is equal to or different from its dimension D in the direction perpendicular to the plane of the fabric 54. In this description, the term "dimension" is used to designate both the thickness e, E of the conductive wire in the plane of the fabric, the dimension d, D of the conductive wire in the direction perpendicular to the plane of the fabric, or the diameter of a conductive wire of circular section.

In the case of a fabric made of conductive tracks 60 printed on a substrate 61, as shown in FIG. figure 5d , the deposit is for example made by lithography techniques, screen printing, gravure etc ... For example, for a deposit of a conductive track 60 silver made by lithography, using an ink with which conductive tracks 60 obtained are more or less wide e 'according to the size of the slots in the mask. One can also vary the thickness of some of these conductor tracks 60 by renewing the inking operation on the desired tracks as many times as necessary until the desired thickness.

The current density on the conductive surfaces of the antenna system has been modeled using 3D electromagnetic simulation software (for example the "HFSS" software from ANSYS). Advantageously, at least a portion of the wires have a thickness e, E or a greater perpendicular dimension d, D in the zones of high current density, alternatively the width l, L and / or the height h, H of at least one Part of the mesh is reduced in areas of high current density.

Given their small size relative to the entire antenna system, it is even possible to envisage the use of a solid metal, such as copper or gold, for conductive surfaces of very small size, typically less than 0.5 mm wide, like a microstrip or triplate line. For conductive surfaces of medium size, such as radiating elements, for example, it is advantageous to use a mesh of the non-homogeneous fabric, ie a fabric whose mesh pitch and / or the size of the conductive wires vary according to the zones depending on the current density. In addition, the overall conductivity of the conductive surfaces can be enhanced by arranging the fabric directly against the surface of the transparent conductive oxide. This effect can be obtained in particular by superimposing several thin conductive surfaces.

We will now consider the figure 6 and the Figures 7a and 7b which illustrate a second embodiment of a system 100 of phased array antennas in cross-polarization (+ 45 ° and -45 °) and variable electrical tilt VET, which comprises a first antenna unit 101A panel and a second panel antenna unitary 101B. This is in particular unitary antennas 101A, 101B called "panel antennas"("PanelAntenna" in English). Each unit antenna 101A and 101B respectively comprises a network of supply lines 102A and 102B connected to a TX / RX transmission / reception port 103A and 103B . The unitary antennas 101A, 101B are grouped to reduce the area they occupy on the common reflector 104 .

A radiating element 105, common to the two unitary antennas 101A and 101B, is formed of a first half-wave dipole 106A belonging to the unit antenna 101A and a second half-wave dipole 106B belonging to the unit antenna 101B. The two dipoles 106A and 106B are crossed with orthogonal polarization, obtained by duplication of the same dipole by a rotation of 90 °. The aligned radiating elements 105 are separated by transverse partitions 107 which improve the insulation between the radiating elements and framed by longitudinal partitions 108. These partitions 107, 108 contribute to the formation of the overall diagram of the antenna system. Side flanges 109 make it possible to house the supply networks of the radiating elements and / or the electronic devices for controlling the variable electrical inclination of the antenna system and also to ensure the mechanical rigidity of the antenna system 100 if necessary. . In the latter case, they are preferably formed by massive metal portions.

As illustrated in detail on the figure 8 the dipoles 106A, 106B are printed respectively on the two orthogonal planes of a substrate 110. The substrate 110 is made of a high dielectric constant material εr (1 <εr <5), such as, for example, PC polycarbonate, polyethylene terephthalate PET or any other optically transparent material.

Spurious elements 111 may also be disposed above the dipoles, parallel to the plane of the reflector 104. By parasitic element is meant a conductive element disposed above a dipole, which is not powered, nor directly or indirectly via the dipole; he is also often referred to as the "director". The parasitic elements 111 are used to form the antenna pattern and for the impedance matching of the radiating element 105 for example. These parasitic elements 111 have a conductive surface made in the manner previously described.

In addition, conductive areas 112, which may take the form of son or pieces of geometric shape such as a rectangle for example, may be preferably placed directly against the inner surface of the front face 113 of the antenna system 100 . These conductive regions 112 has a function to improve the isolation level of the unit cells with each other, i.e. the zones delimited by the partitions 107 and 108 and containing a radiating element 105.

The antenna system 100 is intended to be fixed on a support 200, for example by means of fastening tabs 201 as illustrated in FIGS. Figures 9a and 9b so that its X-X ' axis makes an angle as close as possible to 90 ° with respect to the most likely viewing direction V of an observer. The rear face of the antenna carrying the reflector function 104 is applied against the support 120, for example a vertical wall, facing the observer. Consisting of an optically transparent substrate coated with one or more conductive surfaces chosen for example from an optically transparent conductive film and a wire mesh of conducting wires, the rear face serving as a reflector 104 and the front face 113 of the antenna system 100 are not visible and are confused with the support 120. Only the side edges 109 are visible here, but their presence is discreet. By way of example, the dimensions of the antenna system are a height of about 500 mm, a width of about 400 mm and a thickness of about 60 mm.

The Y-Y ' axis of the radiating elements 105 is then more or less parallel to this direction of vision V so that the observer sees only the edge of the transparent substrate 110 carrying the conductive surfaces of the element's dipoles 106A, 106B radiating 105. Thus only the film thickness conducteuroptiquement trtansparent and / or the mesh fabric is visible which leads to an overall visual impact very reduced.

Since the design of the antenna system is simplified, it has fewer parts and the amount of material needed is reduced, weight and cost The overall values of such an antenna system are reduced. The use of voluminal radiators, dipole type or equivalent, allows easy access to antenna systems operating in very wide frequency bands, such as ultra-wideband antenna systems 1 , 7-2.7 GHz.

The Figures 10a and 10b illustrate the standing wave ratio of an antenna system, obtained by impedance matching of the connection ports.

The figure 10a shows the standing wave ratio VSWR (for "Voltage Standing Wave Ratio" in English) given in ordinate according to the frequency F in GHz given in abscissa. The stationary wave ratio is represented here by the curve 200 for the port at + 45 ° and by the curve 201 for the port at -45 °. It is found that values of the VSWR stationary wave ratio of less than 2 are easily obtained in the frequency band between 1.7 GHz and 2.7 GHz. This demonstrates the ability of the antenna system to operate satisfactorily in a very wide range of frequencies.

The figure 10b shows the result of the impedance matching carried on a Smith chart (with respect to a characteristic impedance of 50 Ohms), respectively represented by the curves 202 and 203 for the two polarizations at + 45 ° and -45 °. It is recalled that the Smith chart allows to find the impedance at the end of a transmission line of given length, loaded at the other end by any given impedance.

The figure 11 illustrates the -3 dB aperture of the radiation pattern of the antenna system in the horizontal plane (ports at + 45 ° and -45 °), the opening HBW (for "Horizontal BeamWidth" in English) in degrees is given in ordinate according to the frequency F in GHz given on the abscissa. A satisfactory result of between 50 ° and 75 °, represented by the curve 210 for the port at + 45 ° and by the curve 211 for the port at -45 °, is observed, despite the constraints which the construction of such an antenna system which has the desired optical transparency and an extreme width of the 1 GHz frequency band, centered around 2.2 GHz.

The figure 12 illustrates the energy ratio between a cross polarization and its co-polarization in the horizontal plane (ports at + 45 ° and -45 °) and in the axis of the antenna system. The energy ratio XP in dB is given in ordinate according to the frequency F in GHz given in abscissa. It is observed that the energy ratio XP, represented by curve 220 for the port at + 45 ° and curve 221 for the port at -45 °, remains below 20 dB in the frequency band between 1, 7 GHz and 2.7 GHz, which is a very good result.

On the Figures 13a and 13b the radiation diagram of the antenna system in the horizontal plane is illustrated according to the two components of the cross polarization respectively (ports at + 45 ° and -45 °) for a tilt angle of zero degrees, the intensity radiation in dB is given on the ordinate and on the abscissa the angle of reflection θ in degrees.

On the Figures 14a and 14b the radiation diagram of the antenna system in the vertical plane is illustrated according to the two components of the cross polarization respectively (ports at + 45 ° and -45 °) for a tilt angle of zero degrees, the intensity radiation in dB is given on the ordinate and on the abscissa the angle of reflection θ in degrees. It should be noted, however, that the radiation pattern in the vertical plane would not be as grouped in the case of a longer antenna system with a higher number of radiating elements.

The figure 15 shows the total gain of the antenna system for a tilt of 0 °, the gain G in dB given in ordinate according to the frequency F in GHz given in abscissa.

Thus these results thus demonstrate that the optically quasi-transparent antenna system described above can advantageously replace the known non-transparent antenna systems without decreasing their radiofrequency performance.

Of course, the present invention is not limited to the described embodiments, but it is capable of many variants accessible to those skilled in the art without departing from the spirit of the invention. Although a VET variable tilt antenna system with dual polarization inclined + 45 ° / -45 ° and wide As described above, those skilled in the art will understand that the previously described solution is equally applicable to other devices, for example such as antenna systems having unitary panel antennas in "side-by-side" configuration. duplex antenna systems, etc.

Claims (16)

An optically transparent antenna system comprising at least one unitary antenna comprising at least one radiating element formed by at least one dipole carried by a foot placed on a reflector, the radiating element being surrounded by longitudinal and transverse partitions and connected to a line in which the dipole, the reflector, the partitions and the supply line consist of an optically transparent substrate covered with at least one optically transparent conductive surface, the conductive surface being selected from an optically transparent conductive film , a conductive mesh, and a combination of an optically transparent conductive film and a conductive mesh. Antenna system according to claim 1, wherein the mesh is formed of a set of vertical and horizontal conductive wires forming approximately parallelepipedic meshes, or a set of vertical, horizontal and diagonal conductor wires forming approximately triangular meshes . Antenna system according to claim 1, wherein the mesh is formed of a set of conductive traces printed on an optically transparent substrate. Antenna system according to one of claims 1 to 3, wherein the dimensions of the conductive wires or conductive tracks vary according to the zones as a function of the current density in these zones. Antenna system according to one of the preceding claims, wherein the pitch of the mesh of the mesh varies according to the zones as a function of the current density in these zones. Antenna system according to one of the preceding claims, wherein the feed line is disposed on the opposite side of the substrate to the dipole. Antenna system according to one of the preceding claims, in which the dipole, the reflector, the partitions and the feed line consist of a an optically transparent substrate covered with an optically transparent conductive film, the conductive film being covered with a conductive mesh. Antenna system according to one of claims 1 to 7, wherein the optically transparent conductive film is a film of an optically transparent conductive oxide selected from tin-doped indium, silver-doped tin , aluminum-doped zinc, indium-doped zinc oxide and gallium-doped zinc oxide. Antenna system according to one of claims 1 to 7, wherein the optically transparent conductive film is an optically transparent conductive polymer film containing polyaniline or poly (3,4-ethylenedioxythiophene). Antenna system according to one of claims 1 to 7, wherein the optically transparent conductive film is a film of an optically transparent conductive nanomaterial selected from fullerene, graphene, carbon nanotube and nanometal. Antenna system according to one of the preceding claims, wherein the optically transparent conductive film is deposited on the substrate by a mechanical, physical or chemical process. Antenna system according to one of the preceding claims, wherein the conductive wires are made of a metal selected from copper, aluminum, silver and gold. Antenna system according to one of the preceding claims, wherein the optically transparent substrate is selected from glass, acrylic polymer, polyethylene terephthalate PET, polycarbonate PC, resin-bonded glass fiber composite material polyester. Antenna system according to one of the preceding claims, comprising two unitary antennas whose radiating elements are aligned in parallel rows separated by a longitudinal partition. Antenna system according to one of claims 1 to 14, comprising two unitary antennas whose radiating elements are formed of a first dipole belonging to the first unitary antenna and a second dipole belonging to the second unitary antenna, both dipoles being crossed with orthogonal polarization. Antenna system according to one of claims 14 and 15, comprising at least two unitary antennas, each operating in a different frequency band.

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