EP0707357A1 - Antenna system with multiple feeders integrated in a low noise converter (LNC) - Google Patents

Abstract

The receiver includes a focussing device which can be an electromagnetic lens e.g. Luneberg lens or parabolic reflector. A first feed (3b) is placed at the focus of the reflector and other feeds (3a,3c) are placed on either side of it. The feeds are slot antennae which are pref. in annular form. The receiver multiplexes (18-21) the incoming signals to a frequency converter (11-13,f1,f2) which is formed on the same substrate (17) as the feeds. The multiplexer can consist of voltage controlled blocking amplifiers and the frequency converter blocks can be an RF amplifier, mixer (12) and IF amplifier (13).

Description

The invention relates to a reception device comprising a low noise frequency converter integrating several source antennas ("Feeds" in English terminology). The invention is particularly applicable in the reception of signals transmitted by several satellites.

The reception of signals transmitted by geostationary satellites, for example satellites relaying television broadcasts, is conventionally done using a parabola which concentrates the received beam at its focal point. A source antenna is then placed as a waveguide in an appropriate manner with respect to the parabola to couple the received signal to one or more probes which transmit it to a low noise frequency converter. The latter performs the conversion of the signal to an intermediate frequency, the converted signal being able to be processed by satellite demodulator and / or the receiver decoder.

In the case where it is desired to target several close geostationary satellites, several solutions are currently used. The most obvious solution, if not the most economical, is to use as many satellite dishes as there are satellites. Another solution, suitable for receiving signals from two nearby satellites, consists in using a single dish, but with two source antennas in waveguides and two frequency converters. The parabola then points either to one of the satellites, or to an intermediate position between the two. The beams from the two satellites and reflected by the parabola then converge at two distinct points. Since in this case at least one of the signals is not optimally focused, this results in degraded reception. In addition, if the satellites are close, the points of convergence of the beams are also close, this proximity being all the greater the smaller the dish. Then appears the problem of positioning the guides side by side wave, whose dimensions are difficult to modify. Certain products on the market merge the ends of the waveguides, which further degrades the quality of reception by increasing the coupling between the beams. The presence of several frequency converters also strikes the price of the product.

There are also "paraboloid" reflectors whose role is to improve the convergence of beams coming from several more or less close satellites. The reflectors are then designed so as to present a substantially parabolic surface to each beam.

The situation in which a certain number of satellites are angularly very close is a situation which is far from exceptional and which will become more and more frequent as the congestion of the geostationary orbit. An example of a "bouquet" of satellites in Europe is the set of Eutelsat satellites.

The subject of the invention is a device for receiving signals transmitted by N (N> 1) satellites comprising means for focusing the beams corresponding to said signals characterized in that it comprises several source antennas, said antennas being printed source antennas produced on a single substrate.

The use of several slot antennas printed on a substrate makes it possible to overcome the problems associated with the use of waveguides.

According to a particular embodiment, the arrangement of said antennas on said substrate is determined by the location of the focal points of said beams.

In addition, the positioning of the antennas on the substrate is determined by the arrangement of the best available focal points for each beam. When installing the dish and antennas, it will suffice to correctly position these reception means with reference to a single satellite. Positioning for the other satellites is then performed automatically.

According to a particular embodiment, the focusing means comprise an electromagnetic lens, for example a Luneburg type lens (semi-sphere lens).

Such a lens makes it possible to obtain optimum convergence of all the beams, unlike a parabola which has only a true focal point.

According to another particular embodiment, the means for focusing the beams comprise a parabolic reflector. For relatively close satellites, a parabola can be considered sufficient to focus the different beams adequately. For larger angular distances, the Luneburg type lens is more suitable.

According to a particular embodiment, the focusing means being a parabolic reflector, a first antenna is placed at the focal point of the reflector, the other antennas being placed on one side or the other with respect to the first antenna.

According to a particular embodiment, the antennas are slot antennas.

According to a particular embodiment, the antennas are annular slot antennas.

This antenna shape is particularly suitable for receiving orthogonally polarized waves having linear or circular polarizations.

According to a particular embodiment, said device comprises at least one frequency converter produced on the same substrate as said antennas.

According to a particular embodiment, the device comprises multiplexing means which multiplex the signals received by the antennas to a frequency converter.

Thus, only one frequency converter is necessary. This results in a very significant saving of space and components.

According to a particular embodiment, said frequency converter is produced on the same substrate as the antennas.

• la figure 1 représente schématiquement les points de convergence au niveau d'un réflecteur parabolique pour des faisceaux issus de deux satellites angulairement proches,
• la figure 2 représente schématiquement les points focaux au niveau d'une lentille de type Luneburg pour des faisceaux issus de trois satellites,
• la figure 3 représente schématiquement un exemple de réalisation de dispositif conforme à l'invention pour la réception dans le cadre de la configuration de la figure 2,
• la figure 4 représente une variante de réalisation reprenant une coupe de la figure 3,
• la figure 5 représente schématiquement un coupleur hybride utilisé pour le couplage d'ondes polarisées circulairement.

Other characteristics and advantages of the invention will appear through the description of two particular non-limiting embodiments and illustrated by the attached figures, among which:

• FIG. 1 schematically represents the points of convergence at the level of a parabolic reflector for beams coming from two angularly close satellites,
• FIG. 2 schematically represents the focal points at the level of a Luneburg type lens for beams coming from three satellites,
• FIG. 3 schematically represents an exemplary embodiment of a device according to the invention for reception in the context of the configuration of FIG. 2,
• FIG. 4 represents an alternative embodiment using a section from FIG. 3,
• FIG. 5 schematically represents a hybrid coupler used for the coupling of circularly polarized waves.

Figure 1 explains the position of the optimal convergence points at the level of a parabolic reflector when the latter reflects the beams from two satellites angularly distant by an angle θ. A parabola 1 of diameter Ø has a focal point F1. It is assumed that the parabola is oriented so that, ideally, a satellite S1 is on the axis of the parabola and that the wave plane of this beam is perpendicular to this axis. The reflected beam converges in F1, located on the axis of the parabola.

A second satellite S2 emits a second beam whose wave plane is inclined by the angle θ relative to the axis of the parabola. The optimum point of convergence is on a line inclined by the angle -θ relative to the axis.

FIG. 2 explains the position of the focal points when using a Luneburg type lens. For clarity of representation, the lens 2 has the shape of a sphere, which makes it possible to represent the object points and the corresponding image points on one side and the other of said sphere. The practical implementation will use a half-sphere on a reflective plane.

The Luneburg lens has a radius R. The focal points are located approximately 1.5xR from the center of the lens. A focal point is located on the right parallel to the beam which illuminates the lens and passes through the center of it. As mentioned earlier, the advantage of the lens over the dish is that it has as many focal points as there are signal sources. There is no defocus given the spherical symmetry of the lens.

Strictly speaking, a Luneburg lens has its focal points at the surface of the lens. An approximation used here makes it possible to move these focal points towards 1.5 times the radius. The separation between the focal points is thus improved.

Three satellites S3, S4, S5 are angularly distant from θ1 and θ2 respectively. These three satellites correspond respectively to focal points F3, F4 and F5. If we consider the angles θ1 and θ2 as small (less than 5 ° for example), the linear distances d34 and d45 separating respectively F3 from F4 and F4 from F5 are substantially equal to 1.5Rθ1 and 1.5Rθ2 in meters, where θ1 and θ2 are given in radians.

For a lens with a radius of 30 cm and angles of 3 °, the linear distances are approximately 2.4 cm.

For the sake of clarity in FIG. 2, the distance between the focal points and the center of the lens is not to scale with respect to the radius R of this same lens.

An exemplary embodiment of the device according to the invention is illustrated in FIG. 3. The illustrated example relates to a device for receiving signals from three satellites, for example the satellites S3, S4 and S5 in FIG. 2. L he skilled in the art will adapt the invention to other scenarios, such as that of FIG. 1.

The device comprises a dielectric substrate 17 which supports three antennas with annular slots 3a, 3b, 3c etched directly on the substrate. These antennas are excited by microstrip lines 4a to 4f in a manner described later. The centers of the slits are positioned on the substrate so that the distances which separate them are equal to the distances which separate the focal points F3, F4 and F5.

A radio frequency amplifier 11 amplifies one of the signals from the microstrip lines. This signal is transmitted to a mixer 12, receiving one of the frequencies F1 or F2 from appropriate oscillators. The signal at the output of the mixer is amplified by an amplifier for intermediate frequencies 13, before being transmitted, for example by coaxial cable (not illustrated) to an indoor unit (demodulator, decoder, TV receiver).

Figure 4 illustrates a section of Figure 3 through the center of the annular slot 3a. This figure illustrates a variant embodiment, certain elements of which are not shown in FIG. 3. The side 5 of the dielectric substrate is covered with a metal layer in which a ring 6 is engraved. As a first approximation, the resonant modes of the slot are occur at frequencies for which the circumference of the slit is equal to an integer multiple of the guided wavelength.

The metal layer is connected to earth. According to a particular embodiment, the substrate is oriented so as to present the annular slots to the reflector.

The side 7 of the substrate comprises the means for exciting the slot. In FIG. 4, the microstrip line 4b is visible. This microstrip line enters at a right angle into the enclosure formed by the annular slot 6, of a depth which is of the order of a quarter of the guided wavelength. Penetration at right angles corresponds to maximum coupling. The dimensions of the microstrip lines are optimized so as to have a large bandwidth around the operating frequency. They have in particular a narrowing (not illustrated) before entering the enclosure formed by the annular slot.

According to a particular embodiment, a base 8 is arranged on the face 7 of the substrate. The function of this base, which is not illustrated in FIG. 3, is to allow obtaining a wave belly at the level of the annular slot. The base is formed by a conductive cavity connected to the metal plane of the face 5 by means of a conductive line 9. An orifice 10 allows the microstrip line 4b to penetrate inside the base 8 while being electrically isolated from it. The depth H of the base is equal to approximately a quarter of the guided wavelength. The thickness of the substrate and of the metal planes has been exaggerated in FIG. 4, so as to better bring out the characteristics described.

According to the present exemplary embodiment and returning to FIG. 3, each annular slot is provided with two microstrip lines arranged at right angles, thus allowing the reception of waves linearly polarized horizontally and vertically. There are thus six signals available respectively at the end of each microstrip line 4a to 4f. Multiplexing means (represented schematically by switches 18 to 21 and by dotted lines indicating the possible connections) allow the selection of one of these signals for transmission to the amplifier 11. These multiplexing means are, for example, blocking amplifiers whose passing or blocking state is controlled by a DC voltage.

For greater clarity of the diagrams, the base 8 does not appear in FIG. 3.

For the reception of circularly polarized waves in the trigonometric direction or in the opposite direction, a hybrid coupler is interposed between each annular slot and the multiplexing means. The coupler 14 is illustrated in FIG. 5. This hybrid coupler is supplied via the two microstrip lines 4a and 4b. The length of each side of the coupler is about a quarter of the wavelength of the guided wave.

It will be noted that the ends of the two microstrip lines are curved inside the enclosure of the annular slot to avoid unwanted coupling between the guided components.

, $\overrightarrow{\mathit{\text{j}}}$

) un repère orthonormé, o étant le centre de la fente annulaire 3a, $\overrightarrow{\mathit{\text{i}}}$

et $\overrightarrow{\mathit{\text{j}}}$

étant des vecteurs respectivement parallèles aux segments des lignes micro-ruban 4a et 4b pénétrant perpendiculairement dans l'enceinte formée par la fente.Let ( o , $\overrightarrow{\mathit{\text{i}}}$

, $\overrightarrow{\mathit{\text{j}}}$

) an orthonormal reference, o being the center of the annular slot 3a, $\overrightarrow{\mathit{\text{i}}}$

and $\overrightarrow{\mathit{\text{j}}}$

being vectors respectively parallel to the segments of the microstrip lines 4a and 4b penetrating perpendicularly into the enclosure formed by the slot.

$$\mathit{\text{Vy}}\text{=}\frac{\mathit{\text{A}}}{\sqrt{\text{2}}}\text{cos(ω}\mathit{\text{t}}\text{+ ϕ-}\frac{\text{π}}{\text{2}}\text{)}$$

A signal V = Acos (ωt) present at port 16 generates, at the ports connected to lines 4a and 4b, signals respectively of the form: $$\mathit{\text{Vx}}\text{=}\frac{\mathit{\text{AT}}}{\sqrt{\text{2}}}\text{cos}\left(\text{ω}\mathit{\text{t}}\text{+ ϕ}\right)$$

$$\mathit{\text{Vy}}\text{=}\frac{\mathit{\text{AT}}}{\sqrt{\text{2}}}\text{cos (ω}\mathit{\text{t}}\text{+ ϕ-}\frac{\text{π}}{\text{2}}\text{)}$$

$$\overrightarrow{\mathit{\text{E}}}\mathit{\text{y}}\text{≡}\frac{\mathit{\text{A}}}{\sqrt{\text{2}}}\text{sin}\left(\text{ω}\mathit{\text{t}}\text{+ ϕ}\right)\overrightarrow{\mathit{\text{j}}}$$

The voltages Vx and Vy give rise by coupling to the slit to fields of the form: $$\overrightarrow{\mathit{\text{E}}}\mathit{\text{x}}\text{≡}\frac{\mathit{\text{AT}}}{\sqrt{\text{2}}}\text{cos}\left(\text{ω}\mathit{\text{t}}\text{+ ϕ}\right)\overrightarrow{\mathit{\text{i}}}$$

$$\overrightarrow{\mathit{\text{E}}}\mathit{\text{y}}\text{≡}\frac{\mathit{\text{AT}}}{\sqrt{\text{2}}}\text{sin}\left(\text{ω}\mathit{\text{t}}\text{+ ϕ}\right)\overrightarrow{\mathit{\text{j}}}$$

The total radiated field corresponds to the sum of these two fields. We can verify that the sum vector rotates in a trigonometric direction and that the end of this vector describes a circle.

By reciprocity, a wave with left circular polarization coupled to the slot 3a will give rise to a voltage V = Acos (ωt) at port 16.

According to a particular embodiment, the reflector used in conjunction with the invention is a paraboloid reflector intended to improve the focusing of the different beams.

Finally, depending on the type of wave and polarization to receive, the slot antennas can have other shapes than annular.

Those skilled in the art can easily adapt the invention to the various configurations that may arise.

Claims (10)

Device for receiving signals transmitted by N (N> 1) satellites (S1, S2, S3, S4, S5) comprising means for focusing (1, 2) the beams corresponding to said signals characterized in that it comprises several source antennas , said source antennas being printed antennas (3a, 3b, 3c) produced on a single substrate (17). Device according to claim 1, characterized in that the arrangement of said antennas (3a, 3b, 3c) on said substrate (17) is determined by the location of the focal points (F1, F2, F3, F4, F5) of said beams. Device according to one of claims 1 or 2, characterized in that the focusing means comprise an electromagnetic lens (2). Device according to one of claims 1 or 2, characterized in that the beam focusing means comprise a parabolic reflector (1). Device according to claim 4, characterized in that a first source antenna is placed at the focal point (F1) of said reflector, the other antennas being placed on one side or the other with respect to said first antenna. Device according to one of the preceding claims, characterized in that the antennas are slot antennas (3a, 3b, 3c). Device according to one of the preceding claims, characterized in that the antennas are annular slot antennas (3a, 3b, 3c). Device according to one of the preceding claims, characterized in that the device comprises multiplexing means (18, 19, 20, 21) which multiplex the signals received by the antennas (3a, 3b, 3c) to a frequency converter ( 11, 12, 13, f1, f2). Device according to claim 8, characterized in that said frequency converter (11, 12, 13, f1, f2) is produced on the same substrate (17) as the antennas (3a, 3b, 3c). Device according to one of Claims 1 to 8, characterized in that the said device comprises at least one frequency converter (11, 12, 13, f1, f2) produced on the same substrate (17) as the said antennas (3a, 3b , 3c).

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