EP2654126B1 - Directive mobile antenna with polarisation switching by moving radiant panels - Google Patents

Description

The present invention relates to a mobile directive plane antenna capable of switching its polarization by displacement of radiating panels. 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, coverage being provided by a set of adjacent spots in circular polarization right or left.

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 on two be 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 a different direction 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 European patent application published under the number EP1107019 discloses a radar having two antennas mounted back to back and powered by different emission sources. The power supply of each antenna is switched according to the scanning movement performed. This arrangement allows the radar to increase its scanning range. However, the proposed structure is not suitable for tracking.

An object of the invention is to provide a compact directional antenna capable of switching its polarization and whose manufacturing complexity is moderate. For this purpose, the subject of the invention is a polarization switching tracking antenna comprising a support having at least two faces each supporting a plurality of waveguides fed by radio frequency signals and perforated by openings arranged to illuminate elements radiators placed at a distance from said openings, characterized in that for at least one given antenna pointing, said support is able to switch between at least two different configurations, said support being configured to place, in the second configuration, the second face in a position identical to that taken by the first face in the first configuration, several radiating elements of the first face being, in said position, oriented differently from the radiating elements of the second face.

Pursuit antenna means an antenna able to maintain its pointing on a given target (for example a satellite), by compensating the movements of the mobile on which it is installed. The antenna according to the invention thus makes it possible to switch its polarization while keeping its pointing on the same target.

According to one embodiment of the antenna according to the invention, the support is fixed on a rotating axis adapted to switch between the two configurations by rotation.

The rotating axis can be configured so that the respective positions of the first and second faces of the support mutually substitute after rotation of the support by a half turn around said axis.

Advantageously, the rotating axis is parallel to each of the faces.

The rotating shaft, said first rotating axis, can be mounted on a second axis rotating orthogonal to said first rotating axis. According to a first embodiment, the first axis makes it possible to orient the antenna in elevation, the second axis making it possible to orient the antenna in azimuth. According to another embodiment, the first axis makes it possible to orient the antenna in azimuth, the second axis making it possible to orient the antenna in elevation.

Advantageously, the radiating elements are dipoles. In addition, the dipoles of the same face can all be oriented in the same direction.

According to one embodiment of the antenna according to the invention, the first face comprises a number of radiating elements equal to the number of radiating elements present on the second face, the radiating elements being arranged on each of the faces so that each radiating element of the first face corresponds to a radiating element of the second face whose centroid in the second configuration is identical to the barycentre of the corresponding radiating element of the first face when it is in the first configuration.

According to one embodiment of the antenna according to the invention, the waveguides are rectangular section guides, the openings being distributed, for each of the waveguides, on a face of said waveguide alternately on both sides of its longitudinal median axis.

According to one embodiment of the antenna according to the invention, for two adjacent openings of a waveguide, a radiating element is placed above each of the openings.

• les figures 1 a et 1 b, des schémas de principe illustrant l'antenne selon l'invention dans, respectivement, deux configurations différentes ;
• la figure 2, une vue d'un mode de réalisation d'une antenne selon l'invention ;
• la figure 3, une vue agrandie des supports de guides d'ondes utilisés par une antenne selon l'invention ;
• la figure 4, une illustration des configurations de dipôles comprises par un panneau multi-faces d'une antenne selon l'invention ;
• la figure 5, une représentation des circuits d'alimentation des guides d'ondes d'une antenne selon l'invention en signaux radiofréquence.

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 figures 1 a and 1b, schematic diagrams illustrating the antenna according to the invention in respectively two different configurations;
• the figure 2 a view of an embodiment of an antenna according to the invention;
• the figure 3 an enlarged view of the waveguide supports used by an antenna according to the invention;
• the figure 4 an illustration of the dipole configurations comprised by a multi-face panel of an antenna according to the invention;
• the figure 5 , a representation of the supply circuits of the waveguides of an antenna according to the invention in radiofrequency signals.

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. 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 figure 2 shows a view of an embodiment of an antenna according to the invention. The antenna 200 comprises two panels 202, 203 double-sided, the first panel 202 being intended for receiving radio frequency signals, the second panel 203 being intended for transmitting radio frequency signals. Each panel 202, 203 has a first face 202a, 203a facing forward and a second side 202b, 203b facing rearward.

Each panel 202, 203 is fixed around a first rotating axis 204 for adjusting the orientation of the panels according to the elevation angle. This first axis 204 is mounted on arms 206 movable about a second rotating axis 208, with a vertical pivot 209 for adjusting the orientation of the panels 202, 203 according to the azimuth angle. According to another embodiment, a third intermediate axis is mounted to avoid the blind zones in limit of movement of one of the two axes 204, 208 and thus allow the antenna to easily cover the celestial space.

The panels 202, 203 can be actuated in rotation from drive means included in the arms 206, and can be controlled to perform at least a full half-turn, so as to switch the positions of the two faces 202a, 202b , 203a, 203b of each of the panels 202, 203. The arms 206 are thus made sufficiently long to allow the panels 202, 203 to reverse their position without hitting the elements 207 making the junction between the arms 206 and the pivot 209.

The figure 3 shows an enlarged view of the waveguide supports used by an antenna according to the invention. The panel 203 comprises a rigid frame 231, for example made of plastic or metal material, integral with the first rotating axis 204. This frame 231 makes it possible to form a double-face rotary panel by supporting on each face of the panel, a plurality of guide rails. 233 waves extending parallel to each other. The waveguides 233 may be powered with a circuit such as that shown and described below with reference to FIG. figure 5 .

In the example, these waveguides 233 are of rectangular section and are drilled in their upper part (that is to say the face located opposite the rigid frame 231), so as to form slots. Advantageously, the slots are oriented parallel to each other and in the longitudinal direction of the waveguides 233, as previously illustrated in FIG. figures 1 a and 1 b. In the example, the slots are placed identically from one waveguide to another. Moreover, in each waveguide 233, the slots are preferably placed alternately on either side of the longitudinal central axis of the waveguide 133 so that the slots radiate in phase, so as to form a regular grid of slots on the entire surface of a panel face 202, 203.

A layer 235 of radiofrequency-transparent material is placed above the waveguides 233 in order to support a plurality of dipoles 237. Advantageously, the dipoles 237 are placed facing the slots formed in the waveguides 233, FIG. in order to ensure good transmission to the waveguides of a signal received by the antenna or effective radiation by the dipoles 237 of a signal transmitted by these waveguides 233.

Such a structure is known to the artice Ide KS Min et al. "Single-layer dipole array for linear-to-circular polarization conversion of slotted waveguide array", IEE Proceedings: Microwaves, Antennas and Propagations, vol. 143, no. 3, June 13, 1996, pages 211-216 .

The figure 4 shows an example of dipole arrangement for a panel included by an antenna according to the invention. The left plane represents the first face 401 of an antenna panel according to the invention when this first face is turned towards the front of the antenna, and the right plane represents, from the same point of view, the second face 402 of this same panel (opposite side to the first face 401) when the second face 402 is in the same position as the first face, that is to say facing the front of the antenna (the first face then facing the back of the antenna). The dipoles 237 of the first face 401 are oriented in a first direction and the dipoles 238 of the second face 402 are oriented in a different position.

Thus, when the panel is rotated to perform a U-turn, the face that was in the inactive position (turned towards the rear of the antenna) replaces the face that was in the active position, that is, the one that was turned towards the front of the antenna. The antenna replaces a radiating face, which was oriented at a given elevation angle and azimuth angle, by a radiating face in the same position but with differently oriented dipoles. The polarization of the active face is thus modified by a simple rotation of the antenna panel.

The dipoles can be placed on the faces 401, 402 so that whatever the face is in active configuration, the locations of the centers of gravity of the dipoles on this active face are the same.

Depending on the configuration of the antenna panel support arms 206, the polarization change rotation is performed about the elevation angle adjusting axis 204, as shown in FIG. figure 2 . A dipole 237 of a face generally does not, when it undergoes a rotation of half a turn, end up in a configuration identical to that of the dipole of the opposite face which is at the same location in active configuration. This case should not occur at least for all dipoles, otherwise the two active antenna configurations would be identical and no change in polarization would be possible.

In the example shown in figure 4 , the dipoles of the same face are all oriented in the same direction and when the two faces 401, 402 are arranged one behind the other on a rotary panel, the dipoles 237 of the first face 401 are parallel to the dipoles 238 of the second face 402. According to another embodiment of the antenna according to the invention, the dipoles of the same face of a panel are not all oriented in the same direction.

The examples presented in this text include double-sided panels, but other embodiments including supports with three or more faces could be implemented. For example, a support having a triangular prism-shaped structure, the first rotating axis 204 of the antenna passing longitudinally at the center of the prism, makes it possible to place three radiating faces provided with dipoles oriented differently from one face to the other to the first two faces and a third non-dipole face and thus to propose three different polarization configurations.

The figure 5 presents a view of the waveguide supply circuits as radiofrequency signals. The architecture of the antenna with its rotating panels imposes particular constraints on its realization. Indeed, the signals received or transmitted by the antenna can pass only through the two junctions 261, 262 between the panels 202, 203 and the arms 206, at the axis of rotation 204. The antenna comprises therefore rotating joints at these junctions 261, 262. Waveguides for transporting the signals between the antenna panels 202, 203 and the filters and amplifiers of the radio processing chain (front-end) are passed through these junctions 261, 262. The antenna according to the invention comprises a supply circuit for each face of an antenna panel 202, 203. In the example, the antenna comprises a first supply circuit for the first face 202a of the receiving antenna panel 202 and a second supply circuit for the second side 202b of the receiving antenna panel 202. Each supply circuit comprises waveguides 251, 252 fixed to the core of the panel structure 202.

The first power supply circuit is described, the second being symmetrically identical in the embodiment. The first power supply circuit comprises power waveguides 251 configured to power slot guides 256a, 256b, 256c, 256d, which in the example are four slot guides orthogonal to the radiation waveguides 233. (cf. figure 3 ). The slot guides 256a, 256b, 256c, 256d are arranged to supply coupling all the radiation waveguides 233.

• ▪ un joint tournant, un commutateur 254 et des guides d'ondes d'alimentation 251 ;
• ▪ des guides à fentes 256a, 256b ,256c, 256d alimentés par les guides d'onde d'alimentation 251 ;
• ▪ des guides d'ondes 233 pour rayonner sur les dipôles 237 ou recevoir les signaux captés par ces mêmes dipôles 237 (cf. figure 3) ;
• ▪ une couche de matériau transparent aux ondes radioélectriques 235 pour supporter à une distance prédéterminée les dipôles 237 au-dessus des guides d'ondes 233.

In summary, a face of a panel thus comprises successively starting from the heart of the panel towards the outside of this panel:

• ▪ a rotary joint, a switch 254 and supply waveguides 251;
• Slot guides 256a, 256b, 256c, 256d powered by the supply waveguides 251;
• ▪ waveguides 233 for radiating on the dipoles 237 or receiving the signals picked up by these same dipoles 237 (cf. figure 3 );
• A layer of radio-wave-transparent material 235 for supporting at a predetermined distance the dipoles 237 above the waveguides 233.

The antenna according to the invention further comprises a switch 254 making it possible to link the signal transmission waveguides to the front-end and the supply waveguides 251, 252 of the panel 202. When of the polarization switching, the switch 254 fixed for example in the rigid frame 231 makes it possible to select one or the other of the supply circuits 251, 252. Thus, for example, if the first face 202a is in the active position and the second face in the inactive position 202b, the switch 254 is configured to transmit to the front-end the signals picked up on the first face 202a. When a polarization switching is triggered, the panel 202 is rotated half a turn, which takes, for example a second or a few seconds. Concomitantly, the switch 254 connects the front-end circuit of the antenna to the new active face, that is to say the second face 202b.

An advantage of the antenna according to the invention is that it does not impose a distance between the slots formed in the waveguides, which makes it possible to densify the array of radiating elements and thus to obtain a diagram of directional radiation. Moreover, its manufacturing principle is simple and makes it possible to modify the orientation of all the dipoles by means of a common movement (in the example, a rotation of the panel), which avoids the differences of orientation adjustment. between the dipoles. It makes it possible to perform polarization switching at a lower cost, avoiding complex mechanisms operating distinct switching by dipoles or groups of dipoles.

Claims (11)

1. A tracking antenna with polarisation switching, comprising a support (231) that comprises at least two faces (202a, 202b, 203a, 203b), wherein, for at least one given antenna pointing operation, said support (231) is able to switch between at least two different configurations, said support (231) being configured, in the second configuration, to place said second face (202b, 203b) in an identical position to that assumed by said first face (202a, 203a) in the first configuration, said antenna being characterised in that each of said faces supports a plurality of waveguides (233) fed by radiofrequency signals and perforated with openings (110) arranged to illuminate radiating elements (120, 237) placed at a distance from said openings (110), a plurality of radiating elements (237) of said first face (202a, 203a) being, in said position, oriented differently to radiating elements (238) of said second face (202b, 203b).
2. The antenna with polarisation switching according to claim 1, wherein said support (231) is fixed on a rotary axis (204) designed to switch between said two configurations per rotation.
3. The antenna with polarisation switching according to claim 2, wherein said rotary axis (204) is configured so that the respective positions of said first face (202a, 203a) and of said second face (202b, 203b) of said support (231) are mutually substituted after said support (231) is rotated by a half-turn about said axis (204).
4. The antenna with polarisation switching according to claim 2 or 3, wherein said rotary axis (204) is parallel to each of said faces (202a, 203a, 202b, 203b).
5. The antenna with polarisation switching according to any one of claims 2 to 4, wherein said rotary axis (204), called first rotary axis, is mounted on a second rotary axis (208) orthogonal to said first rotary axis (204).
6. The antenna with polarisation switching according to any one of the preceding claims, wherein said radiating elements are dipoles (237).
7. The antenna with polarisation switching according to claim 6, wherein the dipoles (237, 238) of the same face (202a, 202b, 203a, 203b) are all oriented in the same direction.
8. The antenna with polarisation switching according to any one of the preceding claims, wherein said first face (202a, 203a) comprises a number of radiating elements (237) equal to the number of radiating elements present on said second face (202b, 203b), said radiating elements being disposed on each of said faces so that for each radiating element of said first face there is a corresponding radiating element of said second face, the barycentre of which in said second configuration is identical to the barycentre of the corresponding radiating element of said first face when it is in said first configuration.
9. The antenna with polarisation switching according to any one of the preceding claims, wherein said waveguides (233) are rectangular-section guides, said openings (110) being distributed, for each of said waveguides (233), on one face of said waveguides alternately on either side of its longitudinal median axis.
10. The antenna with polarisation switching according to any one of the preceding claims, wherein, for two adjacent openings of a waveguide (233), a radiating element (237) is placed above each of said openings.
11. A method for using an antenna with polarisation switching according to any one of the preceding claims, comprising the following steps:

    - pointing a face of said antenna, called first face, towards a target and tracking said target; and

    - rotating said support, whilst tracking said target, so that another face of said antenna, called second face, assumes the place of said first face.

Images