EP2595245B1 - Directional mobile antenna with polarisation switching - Google Patents

Description

The present invention relates to a mobile directive plane antenna with polarization switching. It applies in particular to the switching of embedded antennas on ground mobiles to operate high-speed communications with a satellite, in particular a geostationary satellite.

In order to ensure communications between a fixed point, for example a geostationary satellite, and a moving point, for example a vehicle on the ground, an antenna for tracking the fixed point is disposed at the mobile. The constraints to be respected by this antenna are severe. In particular, it must be configured not to emit in other directions signals with a power density greater than a regulated level, so as not to disturb the service provided by adjacent satellites. Relatively high accuracy in tracking the satellite must therefore be guaranteed with this type of antenna. For example, for a coverage of the European continent, the reflector of an antenna on the ground (or air carrier) must be oriented at an angle range of between approximately 10 ° in elevation for Spain and 60 ° for Northern Europe, the reflector being orientable at 360 ° according to the azimuth angle. The reflector, with a diameter of approximately 60 to 70 cm must thus enjoy a great freedom of movement and a reliable and precise control system, which leads to bulky and expensive antennas. In addition, when the polarization of the signals is linear - if, for example, the satellite comprises a single-source antenna of signals - the ground antenna must be constantly aligned with the polarization direction.

In order to reduce the constraints to be satisfied by the antennas on the ground and thus simplify their realization, a circular polarization can be used instead of the linear polarization mentioned above, for example in the Ka band. By way of illustration, the frequency band between 19.7 GHz and 20.2 GHz can be used for reception at the satellite, while the band between 29.5 GHz and 30 GHz can be used in transmission, the coverage being provided by a set of adjacent spots in right or left circular traffic.

Multibeam satellites cover a territory with a plurality of spots configured so that the signals transmitted on two neighboring spots are not interfering. Also, the coverage of a satellite comprises spots having different transmission frequencies and / or different polarizations, two neighboring spots being configured so as not to have, at the same time, the same polarization and the same transmission frequency. The frequency and polarization characteristics of the signals transmitted on a spot are generally designated by the expression "spot color", two neighboring spots thus having distinct colors. As an illustration, with two different polarizations and two different transmission frequencies, four spot colors can be created.

Antennas embedded on mobile gear to ensure communication with a satellite sometimes cross a border between two spots. This is the case, for example, antennas for providing an internet connection from an aircraft or a train. When the antenna leaves the area covered by a first spot configured with a first polarization (for example circular right) to enter the area covered by a second spot configured with a second polarization (left circular), the antenna must switch quickly to modify its transmission and / or reception polarization. In addition, the radiating elements of a beam-forming antenna must be sufficiently close to one another to avoid the formation of lateral radiation lobes, which may interfere with adjacent communication systems.

A publication of Kwang-Seop Son et al, published in 2006 in "Proceedings of Asia-Pacific Microwave Conference" under the title "Waveguide Slot Array In-Motion Antenna for Receiving both RHCP and LHCP using Single Layer Polarizer", discloses a structure of An antenna comprising signal sources exciting polarizers aligned on a film. The polarizers are arranged alternately in opposite directions and the sources are separated from the polarizer film by an RF insulating layer and provided with a series of cavities placed opposite the polarizers so that at a given moment a polarizer out of two is lit by a source. The film can be actuated in translation so that the cavities are placed opposite the polarizers which were not previously lit. These polarizers being oriented in one direction different from the first polarizers, the polarization of the signals emitted by the antenna is reversed. This antenna thus makes it possible to switch between two different polarizations. However, it has disadvantages. Indeed, its structure imposes a relatively high distance between the radiating elements, which generates sidelobes too important in the radiation pattern.

The article of Min K.-S. et al Single-layer dipole array for linear-to-circular polarization conversion of a slotted waveguide array, IEE Proceedings: Microwave Antennas and Propagation, Vol. 143, No. 3, June 13, 1996 describes an antenna according to the preamble of claim 1.

The document WO 2012/048174 discloses a slit antenna array for polarization switching by means of movable panels that can be configured in two distinct configurations and adapted to orient irradiated radiating elements in a first configuration in a different direction of the illuminated radiating elements in a second configuration.

An object of the invention is to provide a directional and compact electron beam forming antenna capable of switching its polarization. For this purpose, the subject of the invention is a polarization-switching antenna as defined in claim 1. The antenna comprises inter alia a plurality of waveguides fed by radiofrequency signals and perforated by apertures arranged to illuminate radiating elements placed on mobile support means in a plane remote from said openings, said support means being configurable according to at least two distinct configurations, said antenna being characterized in that the radiating elements illuminated in the same configuration are adjacent, the means with support being adapted to orient the illuminated radiating elements in a first configuration in a different direction of the radiating elements illuminated in a second configuration. The radiating elements can have a linear shape. The antenna according to the invention does not impose a distance between the radiating slots, which makes it possible to respect the rejection criterion of the grating lobes outside a scanning zone, even for a scan of +/- 40 ° .

According to one embodiment of the antenna according to the invention, the radiating elements illuminated according to the first configuration and the radiating elements illuminated according to the second configuration are the same, the support means being adapted to modify their orientation relative to the openings. Thus, only one radiating element per aperture is needed and each of the radiating elements is illuminated via the same aperture irrespective of the polarization configuration.

According to one embodiment of the polarization switching antenna according to the invention, the waveguides are rectangular section guides, the openings being distributed, for each of the guides. of waves, on one side of said waveguide alternately on either side of its longitudinal median axis. Through the use of hollow waveguides, losses are reduced; the ohmic efficiency is maximum.

According to one embodiment of the polarization switching antenna according to the invention, the openings are slots. This antenna is more robust than other planar antennas, such as microstrip patch antennas.

According to one embodiment of the polarization switching antenna according to the invention, the slots are parallel to the longitudinal axis of the waveguides This embodiment allows a saving of space.

According to one embodiment of the polarization switching antenna according to the invention, the radiating elements are dipoles. The dipoles may for example be formed of a rectilinear metal piece.

According to one embodiment of the polarization switching antenna according to the invention, the radiating elements are placed above the openings at a height of approximately between one-fifth and one-quarter of the wavelength of the radio-frequency signals transiting through the waveguides.

According to one embodiment of the polarization switching antenna according to the invention, the means for supporting the radiating elements consist of a material that is transparent to radiofrequency waves.

According to the polarization switching antenna according to the invention, the means for supporting the radiating elements comprise a plurality of parallel ribbons held above the openings, said ribbons being able to be arranged in two configurations, said ribbons being able to turn over so as to placing a first face of the ribbons opposite the openings in the first configuration, and the opposite face of said ribbons facing the openings in the second configuration.

According to one embodiment of the polarization switching antenna according to the invention, the radiating elements form a non-zero angle and non-orthogonal with the longitudinal axis of the ribbons, the ribbons being able to rotate about said longitudinal axis for to turn around.

According to an example of the polarization switching antenna, the support means of the radiating elements comprise pivoting elements aligned in several rows, said support means comprising, for each of said rows, a rod adjoining the pivoting elements of said row, said rod and said pivoting elements being configured so that a translation movement of said rod causes said rotating elements to rotate. The rod may for example be a rack, the pivoting elements being cylinders having streaks on their edge to be driven by said rack. Thus, only one radiating element per aperture is needed and each of the radiating elements is illuminated via the same aperture irrespective of the polarization configuration.

According to an example of the polarization switching antenna, the means for supporting the radiating elements comprise rollers and a flexible band arranged to be able to wind around said rollers, the flexible band comprising a first part on which radiating elements are fixed. adjacent ones oriented in a first direction, and a second portion on which are attached adjacent radiating elements oriented in a direction different from said first direction.

• la figure 1, un schéma de principe illustrant l'antenne selon l'invention ;
• la figure 2a, un premier mode de réalisation de l'antenne selon l'invention vu en perspective;
• la figure 2b, le premier mode de réalisation de l'antenne selon l'invention vu de côté ;
• la figure 2c, le premier mode de réalisation de l'antenne selon l'invention vu de dessus ;
• les figures 2d, 2e, et 2f, des illustrations de la phase de commutation du premier mode de réalisation de l'antenne selon l'invention, vu en perspective ;
• les figures 3a, 3b et 3c, un exemple de l'antenne
• les figures 4a, 4b et 4c, un autre exemple de l'antenne.

Other characteristics will become apparent on reading the detailed description given by way of nonlimiting example, which follows, with reference to appended drawings which represent:

• the figure 1 a schematic diagram illustrating the antenna according to the invention;
• the figure 2a , a first embodiment of the antenna according to the invention seen in perspective;
• the figure 2b , the first embodiment of the antenna according to the invention seen from the side;
• the Figure 2c , the first embodiment of the antenna according to the invention seen from above;
• the Figures 2d , 2nd , and 2 F , illustrations of the switching phase of the first embodiment of the antenna according to the invention, seen in perspective;
• the Figures 3a, 3b and 3c , an example of the antenna
• the Figures 4a, 4b and 4c , another example of the antenna.

The figures 1a and 1b illustrate by diagrams of principle the antenna according to the invention. The antenna 100 is seen from above. Each of the waveguides 101, 102, 103 is supplied with radiofrequency signals 101a, 102a 103a and extends parallel to the Y axis. The waveguides may be rectangular section guides. Each waveguide 101, 102, 103 is pierced regularly by openings 110 in the form of rectangular slots preferably parallel to the waveguide, so as to reduce the dimensions of the antenna. For example, the antenna occupies an area of about 6 cm x 6 cm.

A radiating element 120 in the form of a dipole is placed above each opening 110, in a plane parallel to the plane in which the openings 110 are written. The plane in which the dipoles are placed is advantageously located at a distance of between and a quarter of the wavelength of the signals transmitted in the waveguides so as to produce a field emerging from the aperture such as two orthogonal components of the same amplitude and phase shifted by 90 ° - that is, say a circularly polarized field - be obtained. The choice of distance results in a phase difference of 90 °. The dipoles 120 form, in top view, a non-zero angle and not perpendicular with the openings 110 formed in the waveguide 101, 102, 103.

The antenna according to the invention can take at least two configurations. The figure 1a illustrates a first configuration of the antenna in which a first angle is formed between each of the openings 110 and the dipoles 120, this angle being equal, for example to 45 °. This first angle can theoretically take any value between 0 ° and 90 °, values 0 ° and 90 ° being excluded. The angle chosen may result from an analysis involving the lengths and widths of the slots and dipoles, as well as the distance between them and the permittivity of the surrounding medium. The figure 1 b illustrates a second configuration of the antenna in which the angle formed between the openings 110 and the dipoles 120 is equal to the opposite of the first angle. In other words, the dipoles 120 placed above the openings 110 in the second configuration of the antenna 100 ( Figure 1 (b) form, with the dipoles 120 placed above the openings 110 in the first configuration ( figure 1a ), an angle equal to twice the angle formed between the dipoles 120 of the first configuration and the openings 110.

The Figures 2a , 2b and 2c show a first embodiment of the antenna according to the invention, seen respectively in perspective, from side and from above. The antenna 200 comprises support means 201 on which waveguides 203a, 203b and two brackets 205a, 205b are disposed supporting a plurality of rigid ribbons 251a, 251b above the waveguides 203a, 203b.

The waveguides 203a, 203b extend parallel to each other. They can be supplied with signals from one end. In the example, these waveguides 203a, 203b are of rectangular section. They are drilled in their upper part, so as to form slots 231. Advantageously, the slots are oriented parallel to each other and in the longitudinal direction of the waveguides 203a, 203b. In the example, the slots are placed identically from one waveguide 203a to the other 203b. In addition, in each waveguide 203a, 203b, the slots 231 are preferably placed alternately on either side of the longitudinal central axis of the waveguide so that the slots radiate in phase, so as to forming a regular grid of slots 231 over the entire surface of the antenna 200.

The brackets 205a, 205b are placed opposite one another on two opposite edges of the support means 201, parallel to the waveguides 203a, 203b. Ribbon holding members 253a, 253b are mounted in pairs on each of the brackets, a first holding member being mounted on the first bracket 205a, a second holding member being mounted on the second bracket 205b, the two members facing each other. to each other so as to maintain the ribbons 251a, 251b at a predetermined distance above the waveguides 203a, 203b, the ribbons extending in a direction perpendicular to the waveguides. The holding elements 253a, 253b are mounted so that they are able to rotate about an axis connecting two holding elements 253a, 253b of the same pair, that is to say by two holding elements supporting a same ribbon 251 a. The holding members 253a, 253b of the same pair can thus rotate in a coordinated manner to drive the ribbon they maintain in rotation about the longitudinal axis of the ribbon 251a. In the example, the first holding member 253a of a pair is driven by controlled rotation means, the second holding member 253b is simply freely rotatable about an axis and driven under the effect of a rotation. ribbon 251 a. The controlled rotation means may comprise a set of two conical gears 255, 256 making it possible to transform a rotational movement about an orthogonal axis to the plane of the antenna 200 in a rotational movement about an axis parallel to the brackets 205a. . The first pinion 255 is for example integral with a rod 254 rotated by a motor (not shown in the figure). The second pinion 256 drives a worm 257 adjacent the holding members 253a, 253b, thus allowing them to transmit the rotational movement, these holding elements having a prominent striated portion 258 protruding from the rear of the bracket 205b.

Dipoles 252a, 252b are arranged on the tapes 251a, 251b so as to be positioned above the slots 231 formed in the waveguides 203a, 203b. The ribbons 251a, 251b are transparent to the radio frequency signals so as not to disturb the radiating effect of the dipoles 252a, 252b.

The support means 201 comprise a lower part 211 and an upper part 212, which is mounted so as to move along an axis orthogonal to the plane formed by the support means 201. In the example, the lower part 211 and the part upper 212 are material plates adapted to move away from or toward each other by means of sliding means, comprising for example rods 254, cylinders, worm, or any other means to make vary the distance between the two parts 211, 212. The upper portion 212 maintains a constant distance with the brackets 205a, 205b and the tapes 251a, 251b, the brackets 205a, 205b being fixed on this upper part 212. The lower part 211 retains a constant distance with the waveguides 203a, 203b, the waveguides 203a, 203b being fixed on integral amounts of this lower part 211. Thus when both portions 211, 212 move away, the brackets 205a, 205b and the ribbons 251a, 251b away from the waveguides 203a, 203b.

In normal operation of the antenna 200, the lower portion 211 and the upper portion 212 are contiguous. The distance between the slots 231 and the ribbons 251a, 251b is chosen so that the radio frequency signals passing through the slots 231 excite the dipoles and thus make it possible to create an array of radiating elements in a given polarization.

When a rotation of the ribbons 251a, 251b must be performed, the upper portion 212 is remote from the lower portion 211, so as not to damage the ribbons 251a, 251b and / or the holding members 253a, 253b during rotation, avoiding a collision of these elements with the waveguides 203a, 203b. Also, when the polarization of the antenna is to switch, the upper portion 212 is detached from the lower portion 211 to allow the rotation of the ribbons 251a, 251b unfold without damage, before bringing the two parts 211, 212 again once the rotation has been made - the reconciliation can occur gradually after the rotation of a quarter of a turn has been made.

The Figures 2d , 2nd , and 2 F illustrate the switching phase of the first embodiment of the antenna according to the invention, seen in perspective. According to a first configuration of the antenna 200, illustrated in figure 2d the ribbons 251a, 251b are held in a horizontal position, all the dipoles 252a, 252b being oriented in a given direction.

When switching of the antenna 200 is performed, the upper portion 212 of the support means is moved away from the lower portion 211. Once the tapes 251a, 251b are sufficiently distant from the waveguides 203a, 203b, the rod 254 is rotated. This rod 254 causes rotation of the first bevel gear 255, which transmits the rotational movement to the second bevel gear 256, which rotates the worm 257 to rotate the holding members 253a fixed to the bracket 205a, and accordingly the ribbons 251a, and the holding members 253b fixed on the opposite square 205b. The figure 2e illustrates the first embodiment of the antenna when the rotation of the ribbons 251a, 251b is in progress. The ribbons 251a, 251b are turning over. Rotation is activated until the face upper ribbons 251 a, 251 b come to replace the underside. Advantageously, the dipoles 252a, 252b are centered on the axis of rotation of the ribbon on which they are fixed, so that their position in the first configuration is symmetrical with their position in the second configuration. Once the rotation is completed, the antenna 200 is in the second configuration, illustrated by the figure 2f . The orientation of the dipoles 252a, 252b is then modified since their position undergoes a transformation with respect to the axis of symmetry formed by the axis of rotation of the ribbon 251a, 251b. Because of the change of position of the dipoles relative to the slots above which they are located, the polarization of the signals transmitted by the antenna is reversed. Thus, in the case of circularly polarized signals, the passage from one configuration to another of the antenna makes it possible to go from a left circular circulation to a right circular circulation.

Unlike some antennas known in the prior art, no element is interposed between the dipoles, regardless of the configuration of the antenna, which reduces the spacing between the dipoles. The arrangement of slots and dipoles thus provides an antenna having a high density of radiating elements, while having the ability to switch its polarization.

The Figures 3a, 3b and 3c present an example of the antenna. The antenna 300 has waveguides 303 parallel to each other. Slots 331 are formed in the upper portion of the waveguides, similarly to those of the first embodiment shown in FIG. figure 2a . A pivoting support 310, for example as illustrated by the detail of the figure 3a , rotatable about an axis orthogonal to the plane of the antenna 300 is disposed on each slot 331. A dipole 320 is fixed on each of the pivoting supports 310, so as to be illuminated by the radio frequency signals passing through the slots 331. The pivoting support 310 may be cylindrical and formed of a material transparent to radio frequency signals.

The antenna 300 takes at least two configurations, a first configuration, illustrated in FIG. figure 3a , in which the dipoles are oriented in a first direction, and a second configuration, illustrated in figure 3b , in which the dipoles are oriented in a second direction. The two configurations of the antenna 300 correspond to different polarizations.

The orientation of dipoles arranged in a row is controlled by a rack 340 placed along this row. For example, a row 350 having pivoting supports 310 placed above different waveguides 303a, 303b, 303c is controlled by a rack adjacent to the pivoting supports and having notches at least at the pivoting supports 310. The supports pivoting member 310, in the cylindrical example, have striations on their wall, so that when the rack 340 is moved in translation movement along the row 350, it drives the pivoting supports 310 in rotation, and consequently the 320 dipoles attached thereto. A different rack can be assigned to each row of dipoles, so that drive means cause the translation of all of said racks, to rotate all the pivoting supports and thus change the polarization configuration of the antenna . Advantageously, the antenna 300 is configured so that the translations of the racks 340 correspond to a rotation of a half-turn of the pivoting supports 310.

According to another example of the antenna, the rack 340 is replaced by a rod held in pressure against the pivoting supports 310, said rod having adhesion capabilities to the pivoting supports 310, said rod and said pivoting supports being for example formed of a rubbery material.

The Figures 4a, 4b and 4c present another example of the antenna. The antenna comprises a flexible band 401 having two separate parts 411, 412. The first part 411 and the second part comprise dipoles 420 in equal numbers in the two parts 411, 412. The dipoles 420 of the second part 412 are placed in such that their respective centers of gravity could be superimposed on the centers of gravity of the dipoles 420 of the first part 411. The orientations of the dipoles are identical within the same part 411, 412, but are different from one part to the other. 'other.

The antenna 400 also comprises a set of waveguides comprising slot-shaped openings 431, as well as drive means of the flexible band 401 in order to place this flexible band 401 over the slots 431 by matching the positions of the dipoles 420 and the positions of the slots 431. The drive means may comprise two rollers 440 (the figure 4c has the antenna viewed from the top) placed opposite one another to wind or unroll the flexible band 401 above the waveguides. The two rollers 440 can be placed on the edges of the antenna 400, similarly to the arrangement of the brackets (cf. figure 2a ) in the first embodiment described above.

In a first configuration of the antenna 400, the rollers 440 are activated to place the first portion 411 above the slots 431, to generate a first antenna bias. In a second configuration of the antenna 400, the rollers 440 are activated to place the second portion 412 above the slots 431, to generate a second antenna bias.

The antenna switching can thus be triggered by the motorized activation of the rollers in one direction or the other, in order to modify the orientation of the dipoles illuminated by the radio frequency signals passing through the slots of the waveguides.

An advantage of the antenna according to the invention is that it does not impose a distance between the slots, which makes it possible to densify the array of radiating elements and thus to obtain a directional radiation pattern.

Claims (9)

1. A polarisation switching antenna comprising a plurality of waveguides (203a, 203b, 303) fed with radiofrequency signals and perforated with openings (231, 331, 431) that are disposed so as to illuminate radiating elements (252a, 252b, 320, 420) placed on support means (251a, 251b, 310, 401) in a plane remote from said openings,
   said support means can be configured in at least two distinct configurations, the radiating elements illuminated in the same configuration being adjacent, said support means (251a, 251b, 310, 401) are movable and are adapted to orient the radiating elements illuminated in a first configuration in a direction that is different to the radiating elements illuminated in a second configuration, and characterised in that
   said means for supporting said radiating elements (252a, 252b, 320, 420) comprise a plurality of parallel strips (251a, 251b) held above openings (231), said strips being able to be arranged in two configurations, said strips (251a, 251b) being capable of upturning so as to place a first face of said strips (251a, 251b) opposite openings (231) in the first configuration and the opposite face of said strips opposite openings in the second configuration.
2. The polarisation switching antenna according to claim 1, wherein said radiating elements (252a, 252b, 320) that are illuminated according to the first configuration and said radiating elements (252a, 252b, 320) that are illuminated according to the second configuration are the same, said support means (251a, 251b, 310) being adapted to modify their orientation relative to said openings (231, 331).
3. The polarisation switching antenna according to claim 1 or 2, wherein said waveguides (203a, 203b, 303) are rectangular-section guides, said openings (231, 331, 431) being alternately distributed, for each of the waveguides, on a face of said waveguides on either side of its longitudinal median axis (233).
4. The polarisation switching antenna according to any one of the preceding claims, wherein said openings (231, 331, 431) are slots.
5. The polarisation switching antenna according to claim 4, wherein said slots are parallel to said longitudinal axis (233) of said waveguides.
6. The polarisation switching antenna according to any one of the preceding claims, wherein said radiating elements are dipoles.
7. The polarisation switching antenna according to any one of the preceding claims, wherein said radiating elements are placed above said openings (231, 331, 431) at a height that is between a fifth and a quarter of the wavelength of the radiofrequency signals passing through said waveguides (203a, 203b, 303).
8. The polarisation switching antenna according to any one of the preceding claims, wherein said means (251a, 251b, 310, 401) for supporting said radiating elements are made up of a material that is transparent to the radiofrequency waves.
9. The polarisation switching antenna according to any one of the preceding claims, wherein said radiating elements (252a, 252b) form a non-zero and non-orthogonal angle with the longitudinal axis of said strips (251a, 251b), said strips (251a, 251b) being capable of rotating about said longitudinal axis (251a, 251b) so as to upturn.

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