Patent Application
20060119504
The field of the invention is that of satellite communications, and more particularly that of controlling the coverage of multiple geographical areas (also known as “spots”) by communication satellites.
In the field of communications, in particular satellite communications, it is desirable for reception quality to be as good as possible. To this end, it is not only necessary that the reception area be covered, but also that the power of the received signals be sufficient.
Of the many types of multizone satellite coverage, there may in particular be cited that which the person skilled in the art knows as multibeam “beam hopping”. Broadly speaking, this type of coverage consists in providing continuous multizone (send and/or receive) coverage with passive antennas, the zones being grouped into cells within each of which only one, so-called “active”, zone is covered at any time and the various zones of the cells being active one after the other, periodically. In particular, this type of coverage enables the whole of the available frequency band to be allocated to an “active” portion of the set of zones during a given period.
Various arrangements provide this type of coverage. They are all based on the same technology whereby each coverage zone is associated with a sending source.
A first arrangement uses first, second, third and fourth send/receive (two-band) antennas containing sources respectively defining first, second, third and fourth zones, each cell then consisting of a first zone, a second zone, a third zone and a fourth zone. In this type of arrangement the mesh available at the level of the sources is sufficiently large to allow the use of wide-aperture (typically 4 to 6 λ) sources that are therefore highly directional. This yields very high illumination efficiencies, typically from 75% to 80%. However, the antennas being two-band antennas, the edge of coverage gain (GEOC) cannot be simultaneously optimized for sending and receiving. Moreover, beam hopping being effected by antenna switching, the losses generated at the level of the connecting guide between each source and the switch are high.
A second arrangement reproduces the preceding arrangement with the number of antennas doubled to four send antennas and four receive antennas. In this type of arrangement the mesh being substantially identical to that of the preceding arrangement it is therefore possible to obtain very high illumination efficiencies, typically from 75% to 80%. The antennas in this case being optimized in each frequency band, it is therefore possible to optimize the edge of coverage again (GEOC) simultaneously for sending and for receiving. However, using eight antennas introduces significant layout constraints. Moreover, beam hopping also being effected by antenna switching, the losses generated at the level of the connecting guides between each source and the switch are high.
A third arrangement is based on the first arrangement and reduces the number of antennas to three. Here the available mesh is slightly smaller than in the above two arrangements, so that the sources have an aperture of the order to 3 to 5 λ and are therefore slightly less directional. The illumination efficiency remains very acceptable and layout constraints are greatly reduced. However, beam hopping is still effected by antenna switching, so the losses generated at the level of the connecting guides between each source and the switch are high. Moreover, the mesh being tighter, the carrier/interference (C/I) ratio is degraded (the interfering signals “I” are generated by the other sources that are operating in the same frequency band and with the same polarization as the active zone).
A fourth arrangement consists in using only one send antenna and one receive antenna. Beam hopping now being effected by switching within the same antenna, the losses generated at the level of the connecting guides between each source and the switch are low. However, defining all the zones with a single antenna imposes a very tight mesh, so that the sources have an aperture of the order of 1.2 to 1.5 λ and are therefore only very slightly directional. The illumination efficiency is then very low (typically from 35% to 40%), which imposes oversizing of the antenna reflectors and the antennas, which can lead to technology problems, especially if the satellite is operating in the “Ka” frequency band. The edge of coverage gain (GEOC) is therefore reduced by 3 to 4 dB compared to the preceding arrangements, and the “roll-off” (the gain variation over the whole of the multizone coverage, and to be more precise the difference between the maximum gain in each zone and the EOC gain) is very high, typically of the order of 8 to 12 dB compared to the 4 to 6 dB of the preceding arrangements.
Thus no prior art arrangement gives entire satisfaction in terms of multizone coverage by “beam hopping”.
The situation is substantially the same in respect of the other types of multizone coverage and in particular multizone coverage by static deviation of multiple beams and multizone coverage by dynamic deviation of one beam.
One object of the invention is therefore to improve the situation in respect of multizone coverage.
To this end it proposes a multizone coverage telecommunication satellite including at least one send and/or receive antenna comprising at least one sender and/or receiver adapted to send and/or receive a beam in a chosen direction defined by a chosen phase and a chosen amplitude.
This satellite is characterized in that at least one of the senders and/or receivers is coupled to processing means for deviating its beam or its receive direction in at least one other chosen direction by variation of at least the amplitude.
If multiple deviation is required, the processing means deviate the beam in a plurality of chosen directions as a function of a variation law in respect of the amplitude.
Using a small number of senders and/or receivers simplifies in particular the architecture of the antennas and the satellites that carry them, improves the directionality and the C/I ratio thereof and controls the roll-off thereof.
In an embodiment adapted to arrangements in which the sender and/or receiver comprises a main line connecting a feeder module to a send module and/or receive module, the processing means preferably comprise a first coupler installed on the main line and coupled to a first end of an auxiliary line comprising amplitude variation means and a second coupler installed on the main line between the first coupler and the send or receive module and connected to a second end of the auxiliary line. In this case, the second coupler may be a mode extractor coupler, for example a mode extractor comprising a circular waveguide coupled to at least one rectangular waveguide via a row of slots.
Alternatively, the processing means may comprise a single coupler installed on the main line and coupled to at least one resonant cavity defining the amplitude. In this case the processing means may comprise at least two resonant cavities each controlled by a PIN diode and having selected electromagnetic couplings between them that define the amplitude.
According to another feature of the invention, the processing means may deviate the beam or the receive direction in at least one of the chosen directions by varying the amplitude and the phase. If multiple deviation is required, the deviation is preferably a function of a law of variation of the amplitude and a law of variation of the phase. The embodiment with auxiliary line described above then comprises phase variation means installed on said auxiliary line. Similarly, in the embodiment with resonant cavities, the single coupler is coupled to at least three resonant cavities each controlled by a PIN diode and having chosen electromagnetic couplings between them defining the amplitude and the respective positions whereof relative to the coupler define the phase.
If this proves necessary, the send and/or receive antenna comprises a multiplicity of senders and/or receivers each sending or receiving a beam in a chosen direction and first control means intended to control the processing means (which are coupled to the senders and/or receivers) as a function of a chosen spatial-temporal scheme.
In this case, the processing means of each sender and/or receiver may deviate their beam (or their receive direction) cyclically in N (for example N=4) different directions corresponding to N coverage areas, each beam (or receive direction) being deviated in one of the N directions for a chosen duration equal to the Nth part of the cycle duration. The first control means may then instruct the processing means to function simultaneously and in cycles of equal duration so that the satellite assures multizone coverage by beam hopping.
The invention finds a particularly beneficial application to sending and/or receiving beams in the “Ku” and/or “Ka” frequency band(s), although this application is not limiting on the invention.
Other features and advantages of the invention will become apparent on reading the following detailed description and examining the appended drawings, in which:
The appended drawings constitute part of the description of the invention as well as contributing to the definition of the invention, if necessary.
The invention relates to telecommunication satellites that provide multizone send and/or receive coverage, and in particular to satellites of this kind comprising at least one passive send antenna and/or at least one passive receive antenna.
An application of the invention to a send and/or receive antenna A of a satellite ST is described first with reference to FIGS. 1 to 5. The satellite ST is not shown in these figures to avoid overcomplicating the diagrams.
As shown in
The function of the processing module MTi is to deviate the beam (or the receive direction) that the associated horn Ci must send (and/or receive) in at least one chosen direction that differs from the direction associated with the standard propagation mode of the send and/or receive channel i (or source Si), which is defined by an amplitude A and a phase Φ.
The deviation is obtained at least by a variation p of the value of the amplitude A of the beam sent or received by a send and/or receive module R. However, as shown on
It is clear that by varying the amplitude and where applicable the phase of a send or receive beam it is possible to choose the plane in which said beam must be deviated.
The maximum deviation is limited to the value of θ, which corresponds to the 3 dB width of the lobe.
The processing module TMi may be adapted in various ways to provide this deviation.
For example, a first way consists in installing on the main line LP of a send and/or receive channel one or more resonant cavities adapted to vary the amplitude and where applicable the phase of the signals.
In the example shown in
This embodiment allowing only one deviation is particularly suitable for situations in which beam deviation is static.
This is the case, for example, when it is required to use large sources to generate overlapping zones (or spots); the sources are prepositioned since the respective positions of the spots to be generated are known in advance. In this case, the invention can replace one or more spots whilst additionally offering more directional sources, as shown in
This embodiment also corresponds to situations requiring the coverage of overlapping adjacent zones. This kind of situation corresponds in particular to satellites using four antennas, one of which provides coverage by means of Ku and Ka spots.
Satellites of the above kind generally cover nine zones in the Ka band and four zones in the Ku band. The Ku receive band corresponds substantially to the range (13.7 GHz, 15.6 GHz) and the Ku send band corresponds substantially to the range (10.7 GHz, 12.8 GHz). The Ka receive band corresponds substantially to the range (27.5 GHz, 30 GHz) and the Ka send band corresponds substantially to the range (18.2 GHz, 20.2 GHz). In this case, the invention allows the use of highly directional Ka and Ku sources, and consequently significantly improves the gain and the C/I ratio, optimizes roll-off and significantly reduces power consumption.
This embodiment also corresponds to situations requiring dynamic deviation of a beam (also known as “theater displacement”). This situation may arise if a beam is used having an angular dispersion from about 1.6° to about 3.2°, providing coverage of a zone of 1000 to 2000 kilometers. This is the case during certain events in particular, such as the Olympic Games. Here the invention enables a beam to be repositioned at will, electronically and quickly, without having to move the satellite, as is the case at present, and this reduces energy consumption and significantly improves the accuracy and speed of positioning.
A variant of this embodiment using a single resonant cavity active at all times consists, as shown in
Here the number of deviations is set by the number of combinations of activation of the various resonant cavities CR via the associated control PIN diodes DP, which obviously depends on the number of resonant cavities used (for example four or eight cavities).
In this embodiment, and in the nonlimiting case of sending a telecommunication signal, the first coupler CP1 is adapted to sample from the main line LP a portion of the telecommunication signal to be sent in beam form, so as to inject it into the auxiliary line LA, where it is subjected to amplitude variation in the amplitude attenuator AA and where applicable to phase variation in the phase shifter DP, before being reinjected into the main line LP by the second coupler CP2.
The second coupler CP2 generates at the input of the horn C one or two modes (for example the modes TM0 and TE21 that generate antisymmetrical radiation diagrams with no signal on the axis) of higher order than the fundamental mode of the telecommunication signal to be sent, as coming from the send module R, which induces the deviation of the beam. In other words, injecting one or two higher order modes at the input of the horn C leads to deviation of its main send lobe. By virtue of the theorem of reciprocity, which applies when the elements are passive, this applies equally to reception.
The amplitude attenuator M and/or the phase shifter DP may be of the variable type if necessary.
For example, a beam may be deviated in four directions by varying the amplitude by a fixed amount in the attenuator AA and varying the phase in steps ΔΦ of 90° in the phase shifter DP. As a general rule, a beam can be deviated in N directions by varying the amplitude by a fixed amount and varying the phase by steps ΔΦ of 360°/N. In these situations, the processing module TM is therefore configured to vary the amplitude in accordance with a chosen amplitude law and/or the phase in accordance with a chosen phase law.
Of course, an embodiment may be envisaged in which the phase shift DP is omitted. In this case, the deviation results exclusively from an amplitude variation.
This embodiment, just like that described above with reference to
As indicated in the introduction, multizone (or multispot) coverage by beam hopping consists in forming a “cluster” or “mosaic” G of adjacent coverage zones (or spots) Z which preferably overlap partially.
Each cluster G is divided into cells Cel including the same number j of zones Zj. In the example shown in
Accordingly, the whole of the available frequency band can be allocated to an (active) portion of the set of zones during a given period. This situation corresponds, in particular, to satellites that define at any given time around 100 active zones ZA in the Ka band with an angular dispersion (or extent) of about 0.36°.
Thanks to the invention, the same source Si can now cover the four (or N) zones Zj of the same cell Cel using the beam deviation principle described above.
For example, in the situation shown in
In this example, the first zone (or spot) Z1 corresponds to a beam deviated in a first direction defined by an amplitude A0 and a phase Φ0, the second zone Z2 corresponds to a beam deviated in a second direction defined by an amplitude A0/3 and a phase Φ0+90°, the third zone Z3 corresponds to a beam deviated in a third direction defined by an amplitude A0 and a phase Φ0+180°, and the fourth zone Z4 corresponds to a beam deviated in a fourth direction defined by an amplitude A0/√3 and a phase Φ0+270°. Moreover, if the angle θ subtended by the beam sent (or received) by the horn C is made similar to the diameter of a zone Zj, then the amplitude of deviation ρ1 of the center of the beam corresponding to the first zone Z1 relative to the reference direction defined by the center of the undeviated beam Fnd is substantially equal to 3Φ/4 and the deviation amplitude ρ2 of the center of the beam corresponding to the second zone Z2 relative to the reference direction is substantially equal to θ√3/4.
The processing module MTi of a send and/or receive channel i (or source Si) is therefore adapted to“switch” the beam sent by (or the receive direction of the beam received by) its horn Ci from one zone to another. In the case of sending, for example, during the first quarter of the period the beam is deviated in the first direction, so that only the first zone Z1 of the cell Ci is covered (or active). This situation corresponds to the upper right-hand portion of
The control module MC of the send antenna A causes the processing modules MTi of each send channel i (or source Si) to operate in accordance with a spatial-temporal law. The control module MC preferably controls the processing modules MTi so that they function synchronously, simultaneously and periodically and so that during each period fraction δT the same zone Zj of each cell Cel is activated (or covered).
The invention therefore enables the use of j times fewer Ka sources than the prior art (j=2, 3, 4, . . . ), which significantly reduces the overall size of the satellite (for example there is only one send antenna instead of four). Moreover, these sources can be highly directional, optimizing illumination efficiency. Also, this optimizes the edge of coverage gain GEOC. Finally, the beam hopping type switching being effected within the same antenna, waveguide losses are greatly reduced.
By virtue of the theorem of reciprocity, which applies if the elements are passive, this also applies to reception.
One embodiment of a second coupler CP2 that can be used on a send and/or receive channel of the type of cells shown in
In this embodiment, the second coupler CP2 is preferably a “mode extractor” coupler adapted to sample from the main line LP, at the output of the receive horn C, the tracked mode(s) to inject it (or them) into the first auxiliary line LA. The mode extractor coupler CP2 is designed to define a short circuit plane for the tracking mode(s) that will constrain it (or them) to rejoin the first auxiliary line LA (the lower order standard (or fundamental) propagation mode, as well as the other non-tracked modes therefore continuing along their path within the main line LP).
For example, the mode extractor coupler CP2 is adapted to extract and/or to generate the TMO1 and TE21 modes from the main line LP and inject them into the first auxiliary line LA.
This extraction and/or generation of mode(s) may be effected in various ways. However, it is advantageous to use for this purpose one or more rows of coupling slots, as shown in
The send and/or receive element is here of the monoblock type. It comprises an upstream portion defining a horn C and a downstream portion extending the upstream portion and defining a mode extractor coupler CP2. In fact, the downstream portion CP2 here consists of: i) a central waveguide LP of circular section defining the main line in which are extracted and/or generated the tracked modes, ii) four peripheral waveguides LAa to LAd of rectangular section defining four portions of the first auxiliary line, and iii) four rows of coupling slots FEa to FEd, preferably of rectangular shape, providing the coupling between the central waveguide LP and the four peripheral waveguides LAa to LAd.
Of course, other types of coupling slots may be used, for example slots of circular, elliptical or cruciform shape, etc.
In this embodiment, the tracked higher order modes are therefore extracted and/or generated from the main waveguide LP by the coupling slots FEa to FEd and then injected into peripheral waveguides LAa to LAd.
Of course, the number of rows of slots, and consequently the number of peripheral waveguides, of the embodiment shown in
Generally speaking, it is preferable to extract at most two higher order modes.
Only one higher order mode (generally the TMO1 mode) is used if the polarization of the incident or transmitted wave is circular. Knowing the values of the amplitude and the phase, a single mode then suffices each time for determining the parameters ρ and Φ described above with reference to
On the other hand, two higher order modes (generally the orthogonal pairs (TMO1 and TE21) or (TE21 and TE21)) are used if the polarization of the incident or transmitted wave is linear. Knowing the values of the amplitude and the phase of these two modes, it is possible each time to determine the parameters ρ and φ described above with reference to
It is equally important to note that, in this latter embodiment, the coupling cannot be modified dynamically because a mode extractor is a mechanical part that has to be carved out. Consequently, once the polarization of the wave has been chosen, it remains only to determine whether one or two higher order modes will be extracted, and then to design the mode extractor accordingly.
The invention is not limited to the telecommunication satellite embodiments described hereinabove by way of example only, and encompasses all variants that the person skilled in the art might envisage that fall within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03/05300 | Apr 2003 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR04/01043 | 4/29/2004 | WO | 12/19/2005 |
