EP0707357B1 - Antenna system with multiple feeders integrated in a low noise converter (LNC) - Google Patents

Description

The invention relates to a reception device comprising a low noise frequency converter with multiple antennas source ("Feeds" in English terminology). The invention applies especially in the reception of signals transmitted by several satellites.

Reception of signals transmitted by satellites geostationary, for example satellites relaying emissions from television, is conventionally done using a parabola which concentrates the beam received at its focal point. We then place a source antenna in waveguide appropriately relative to the dish to couple the signal received by one or more probes which transmit it to a low noise frequency converter. The latter performs the signal conversion to intermediate frequency, the converted signal can be processed by satellite receiver and / or the decoder of the receiver.

If you want to target several satellites geostationary near, 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, is to use a single dish, but with two source antennas in waveguides and two frequency converters. The parable points either to one of the satellites, or to an intermediate position between both. The beams from the two satellites and reflected by the parabola then converge at two distinct points. Since in 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 as the parabola is small. Then appears the problem of positioning the guides side by side wave, whose dimensions are difficult to modify. Some products from market merge the ends of the waveguides, which degrades even more the quality of reception by increasing the coupling between beams. The presence of several other frequency converters strike share the price of the product.

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

The situation in which a 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.

Document US 4,712,111 describes a system comprising a reflector as well as two sources, intended respectively to receive signals from different polarizations and reflected in different directions by the reflector.

EP-A-682 383, cited under Article 54 (3) EPC describes a reception system comprising a focal point reflector linear for focusing signals to networks linear.

The subject of the invention is a device for receiving transmitted signals. by N (N> 1) satellites comprising means for focusing the beams corresponding to said signals as well as several source antennas independent, characterized in that said source antennas are antennas printed on a single substrate, the arrangement of said antennas on said substrate being determined by the location of the focal points of said beams.

The use of several slot antennas printed on a substrate eliminates problems related to the use of waveguides.

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

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

Such a lens allows optimal convergence of all the beams, unlike a parabola which has only one real focal point.

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

According to a particular embodiment, the means of focusing 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 ring slot antennas.

This form of antenna is particularly suitable for reception of orthogonally polarized waves having polarizations linear or circular.

According to a particular embodiment, said device includes at least one frequency converter made 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. It results in a significant saving of space and components.

According to a particular embodiment, said converter frequency is carried out 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 within the framework 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 convergence points optimal at the level of a parabolic reflector when the latter reflects the beams from two satellites angularly distant by an angle  . A parabola 1 of diameter ⊘ has a focal point F1. We assume that the dish 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 plane wave is tilted by the angle  relative to the axis of the parabola. Point of optimum convergence is on an inclined line of the angle - relative to the axis.

Figure 2 explains the position of the focal points in the case using a Luneburg type lens. For the clarity of the representation, lens 2 has the shape of a sphere, which allows represent the object points and the corresponding image points of a side and on the other of said sphere. The practical implementation will call on a half-sphere on a reflecting plane.

The Luneburg lens has a radius R. The focal points are are about 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 passing through the center of it. As mentioned earlier, the advantage of the lens compared to the parabola is to present as much of focal points that 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 allows to move these focal points to 1.5 times the radius. The separation between the focal points is thus improved.

Three satellites S3, S4, S5 are angularly distant of 1 and 2 respectively. These three satellites correspond focal points F3, F4 and F5 respectively. If we consider the angles 1 and 2 as small (less than 5 ° for example), the distances linear d34 and d45 separating F3 from F4 and F4 from F5 respectively substantially equal to 1.5R1 and 1.5R2 in meters, where 1 and 2 are given in radians.

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

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

An embodiment of the device according to the invention is illustrated in FIG. 3. The example illustrated relates to a device for reception of signals from three satellites, for example satellites S3, 54 and S5 of FIG. 2. Those skilled in the art will adapt the invention in other cases, such as that of Figure 1.

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

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

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

The metal layer is connected to earth. According to a mode of particular embodiment, the substrate is oriented so as to present the annular slots in 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 line at micro-tape penetrates at right angles into the enclosure formed by the slot annular 6, of a depth which is of the order of a quarter of the length guided wave. Penetration at right angles corresponds to coupling maximum. The dimensions of the micro-ribbon lines are optimized by so as to present a large bandwidth around the frequency of operation. They present 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 Figure 3, is to allow obtaining a wave belly at the level of the annular slot. The base is formed by a conductive cavity connected in the metallic plane of face 5 via a conductive line 9. An orifice 10 allows the microstrip line 4b to penetrate inside. of the base 8 while being electrically insulated from it. The depth H of the base is approximately a quarter of the wavelength Guided. The thickness of the substrate and the metallic planes has been exaggerated in Figure 4, so as to better highlight the characteristics described.

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

For greater clarity of the diagrams, the base 8 is not shown not on figure 3.

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

Note that the ends of the two micro-ribbon lines are curved inside the enclosure of the annular slot to avoid unwanted coupling between guided components.

Let ( o , i , j ) an orthonormal reference, o being the center of the annular slot 3a, i and j being vectors respectively parallel to the segments of the microstrip lines 4a and 4b penetrating perpendicularly into the enclosure formed by the slot.

A signal V = Acos (ωt) present at port 16 generates, at the ports connected to lines 4a and 4b, signals respectively of the form: Vx = AT 2 cos (ω t + ϕ) Vy = AT 2 cos (ω t + ϕ - π 2 )

The voltages Vx and Vy give rise by coupling to the slit to fields of the form: E x ≡ AT 2 cos (ω t + ϕ) i E there ≡ AT 2 sin (ω t + ϕ) j

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

By reciprocity, a wave with left circular polarization coupled to 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 focus of the different beams.

Finally, depending on the type of wave and polarization to be received, the Slot antennas can have other shapes than annular.

Claims (9)

1. Device for receiving signals transmitted by N (N>1) satellites (S1, S2, S3, S4, S5) comprising means (1, 2) for focusing the beams corresponding to the said signals, and several independent source antennas, characterized in that the said source antennas are printed antennas (3a, 3b, 3c) made on a single substrate (17), the arrangement of the said antennas (3a, 3b, 3c) on the said substrate (17) being determined by the location of the points of focusing (F1, F2, F3, F4, F5) of the said beams.
2. Device according to Claim 1 characterized in that the focusing means comprise an electromagnetic lens (2).
3. Device according to Claim 1, characterized in that the means for focusing the beams comprise a parabolic reflector (1).
4. Device according to Claim 3, characterized in that a first source antenna is placed at the focal point (F1) of the said reflector, the other antennas being placed on one side or on the other with respect to the said first antenna.
5. Device according to one of the preceeding claims, characterized in that the antennas are slot antennas (3a, 3b,3c).
6. Device according to one of the preceeding claims, characterized in that the antennas are annular slot antennas (3a, 3b, 3c).
7. Device according to one of the preceeding claims, characterized in that the device comprises multiplexing means (18, 19, 20, 21) which multiplex the signals received by the antennas (3a, 3b, 3c) towards a frequency converter (11,12, 13, f1, f2).
8. Device according to Claim 7, characterized in that the said frequency converter (11, 12, 13, f1, f2) is made on the same substrate (17) as the antennas (3a, 3b, 3c).
9. Device according to one of the Claims 1 to 7, characterized in that the said device comprises at least one frequency converter (11, 12, 13, f1, f2) made on the same substrate (17) as the said antennas (3a, 3b, 3c).

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