FR2751494A1 - GEOSYNCHRONOUS TELECOMMUNICATIONS SATELLITE SYSTEM WHOSE SERVICE AREA CAN BE RECONFIGURED - Google Patents

Abstract

A multi-beam phased array geosynchronous satellite system (20) transmits and receives radio frequency signals to and from Earth. The satellite system (20) has transmit (28) and receive (29) phase shift arrays, beam forming means (26 and 27), switch arrays (24 and 25), control (23) of switches and a telecommunications payload (22). The coverage provided by the satellite system (20) beams can be reconfigured while the satellite is in geosynchronous orbit. The satellite system provides a more cost and weight efficient means of providing telecommunications in geosynchronous satellite applications.

Description

The present invention relates generally to

  satellite communications and, more specifically, a satellite system

  telecommunications system with a so-called electro- scanning antenna

  multi-beam picnic that is able to reconfigure a service area.

  All satellites in geosynchronous Earth orbit (GSO) have

  with two important features. First, they remain approxima-

  tively fixed with respect to the Earth's surface; and, second, they have practically a whole hemisphere in their radio field of view. The first of these characteristics, the geostationary character, is what gives the geostationary orbit its name, and it has been fully exploited, since the first satellites were placed in GSO. However, the operation of the hemispherical field of view was hampered by what could be obtained using the systems

practical antennas.

  Conventional satellite communications systems use

  antennas that form each antenna beam using a feed structure

  special mention. These power supplies use a technique of passive microwave circuits (generally waveguides) and they are therefore relatively large and heavy, at least from the point of view of standards relating to satellites where size and weight are paramount. Traditionally, GSO satellites have been produced so as to form a small number of beams to exploit their immense field of view. Each beam covered a very large area of land, often approaching the coverage of an entire continent in a single beam. Since, by definition, a large beam provides a small antenna gain (namely directivity), these large beams required the presence of high power transmitters on the satellite and very large antennas in fixed land stations. The antennas of the terrestrial terminals go from 4 to meters for the Ka band up to several tens of meters for the lower frequencies. The current trend in satellite communications

  is at very small terrestrial terminals for satellites (VSAT) and at ter-

  remains for extremely small satellites (USAT). These terminals use small antennas and, therefore, relatively low gain. For various practical reasons (eg cost, security, balance of uplink and downlink), most of the lost gain from the antennas of the terrestrial terminals cannot be compensated using transmitters of a superior power. The satellite must compensate for the lost gain of the terrestrial terminal by an increase in the gain of the antenna of the satellite itself, which,

  naturally, reduces the area covered by each beam.

  Conventional antenna techniques are limited, due to the size and weight available, to a maximum of about 100 beams, but, however, a much smaller number of antennas is preferable. This is not only due to the size and weight of the antenna and the feed structures, but also to the size, weight and power of the transmitter power amplifiers. In a conventional antenna system, each beam has a specialized power amplifier and, to minimize the number of beams

  necessary, these amplifiers operate at a relatively high power.

  For these amplifiers, typically using progressive wave tube amplifiers (TWTA) are used despite their higher weight and lower reliability by

  comparison with solid state amplifiers.

  The Ka band (namely 20 GHz for downlinks and 30 GHz for uplinks) requires from 500 to 1000 beams approximately to cover the entire field of view of a GSO satellite, when the beams are sized to operate with low-power land terminals

  using "submetric" antennas (ie below the meter).

  Since a practical conventional satellite antenna system can form approximately

  100 beams, only about 10% of the field of view can be served.

  Thus, the commercial area which will be served must be predetermined, then the satellite antenna must be designed in a specific way according to the particular combination of the orbital position ("slice") and the area served. Such an approach has at least four disadvantages. First, in a dynamic and uncertain market, there is a risk that the location of the service area may have

  was chosen incorrectly, resulting in poor financial results.

  Second, even if the area was initially correct, there is a risk that the market will evolve so that the service demand area shifts relative to the chosen area before the satellite has reached the end of its duration. of useful life. Third, standby systems must be developed for each combination of orbital and antenna position (which is very costly), or standby systems cannot be implemented until a failure occurs (which leads to prolonged service interruptions). Finally, there is an increase in conceptual costs and a reduction in economies of scale, since each satellite must be adapted in a specific way to its orbital slice and to

  its particular service area.

  This is why there is a great demand for a geosynchronous satellite system making it possible to carry out communications from a geosynchronous orbit, which is more cost-effective and has less weight. In addition, what is needed is a multi-beam antenna which offers the possibility, while the satellite is in orbit, of configuring and reconfiguring the coverage provided by the antenna with respect to particular regions.

of the earth.

  The following description, intended to illustrate the invention, aims

  to give a better understanding of its characteristics and advantages; it is based on the appended drawings, among which: FIG. 1 shows antenna beams relating to a satellite covering part of the Earth within its field of view; Figure 2 is a block diagram showing the components of a satellite according to a preferred embodiment of the invention; FIG. 3 represents a small square grid section of the radiating face of the groupings; FIG. 4 represents a small triangular grid section of the radiating face of the groupings; FIG. 5 shows components of each active element of an emission group;

  Figure 6 shows components of each active element in a group.

  reception; Figure 7 shows part of an embodiment of a beam forming means for multiple beams;

  FIG. 8 represents a network of eight beam forming means

  column skids of 8 elements and eight means of forming beams in rows of 8 elements; FIG. 9 represents a network of eight combination means with columns of 8 elements and eight combination means with rows of 8 elements; Figure 10 shows an 8 x 8 set of contiguous beams which are formed by an array; and Figure 11 shows part of a second embodiment

  of a beam forming means for multiple beams.

  The invention finds its utility in the fact that a satellite system

  geosynchronous avoids the disadvantages listed above by combining the tech-

  nique phase shifting groups (or electronic scanning) with a

  on-board control and switching. The satellite system is characterized by a unique combination of three constituents: active electronically scanned transmit and receive antennas with means for forming multiple beams (eg Butler arrays); matrices of

  beam selection switches (one for transmission, one for reception)

  tion); and a device for controlling the selection of beams (controlled from the ground). Those skilled in the art will understand that beam forming means for multiple beams may include any beam forming means which forms multiple orthogonal beams, including for example Butler matrix beam forming means (as described herein ) and means for forming beams of Rotman lenses. In addition, the satellite includes a telecommunications payload and a conventional satellite bus. The telecommunications payload has a dynamic channel allocation capacity, so that this capacity can be moved from one beam to another. This further improves the capacity of the

  satellite to reconfigure the resources applied to the area served.

  FIG. 1 shows antenna beams 12 of a satellite covering part 10 of the Earth included within the field of view of the satellite. The antenna beams 12 can be selected while the satellite is in orbit, to provide active communications with terrestrial terminals. The terrestrial disc 10 as seen from a geosynchronous orbit is approximately + 8.7. Therefore, it takes about 500 beams each having a beam width of 0.7 to fully cover the Earth's disk as seen from a geosynchronous satellite. A geosynchronous satellite is a satellite which is in Earth orbit at a distance of 35,860 km and which remains directly above a

  assigned point on the Earth's equator.

  FIG. 2 represents a functional diagram of components 22 to 29 of a geosynchronous satellite system 20 according to a preferred embodiment of the invention. Components 22 to 29 are just some of the many components that make up a satellite. For example, there are navigation components for positioning the satellite and energy components for producing and maintaining the power required for the electronic components of the satellite.

satellite 20.

  As shown in Figure 2, the satellite system 20 is charac-

  terrified by a telecommunications payload 22, a switch control device 23, a matrix of transmit switches 24, a matrix of receive switches 25, means 26 and 27 for forming beams of Butler dies, a grouping with phase shift 28 of transmission and a group with phase shift 29 of reception. Telecommunications payload 22 receives L active beam signals to the transmit switch array

  24 and is responsible for the selection of beam instructions for use

  switch control sitive 23. The switching control device

  teurs 23 receives instructions of selected beams from the telecommunications payload 22 and selects N beam ports for the beam forming means 26 and 27 orthogonal (for example a Butler matrix). The transmit switch array 24 receives L active beam signals from the N beam ports (selected by the switch controller 23) from the beam forming means 26

  orthogonal (for example Butler matrix) and of the group with phase shift of emiss

  sion 28. The receive switch array 25 receives signals from

  N beam ports (selected by the switching controller

  teurs 23) coming from the beam forming means 27 orthogonal (for example Butler matrix) and transmits L active beam signals to the load

useful telecommunications 22.

  The emission phase shift group 28 and the phase shift group

  reception 29 are each characterized by a grouping of a certain number of elements. The emission phase shift group 28 is responsible for

  the transmission of radio frequency (RF) signals, while the phase shift

  reception 29 is responsible for receiving RF signals from the Earth. RF signals can be data or voice signals. A phased array with multiple emission beams 28 is characterized by a grouping of a number of active emission elements. A phased array with multiple reception beams 29 is characterized by an array

  of a number of active receiving elements.

  FIG. 3 shows individual antenna elements in a square grid 30. For a transmission phase shift array 28, the individual transmission antenna elements 32 are used. For a reception phase shift array 29, use is made individual reception elements. The emitting phase shifting group 28 or the receiving phase shifting grouping 29 can be positioned inside an opening of the grouping located inside the square grid.

  shown in Figure 3 or in a triangular grid 40 as shown

shown in Figure 4.

  FIG. 3 shows a small square grid section 30 of one face of a group, the arrangement of the individual radiating elements being according to a square grid of columns and rows where each element 32 occupies a square section 34 of the area of the total grouping. FIG. 4 shows a small triangular grid section 40 of an emission face of a grouping, the arrangement of the individual radiating elements being according to a triangular grid of columns and rows where each element occupies a hexagonal section of the area of the total group. (In FIGS. 3 and 4, only a subset 30, 40 of 64 elements of the total grouping 22 with N elements is shown). The choice of a grid of elements depends on considerations relating to the encapsulation, the management of thermal problems and the angular field of view, as is well

understood by those skilled in the art.

  In the configuration of grouping 30 (FIG. 3) or in that of grouping 40 (FIG. 4), the directivity of the opening of the grouping is defined as being N times the directivity of a single element 32 or 42 of the grouping, o N is the number of elements 32 or 42 and the directivity of a single element is 4rA, / X2. Here, the area A & of the element 34 or 44 is the area of an individual square 34 in FIG. 3 or of an individual hexagon 44 in FIG. 4. X denotes the wavelength of the frequency of carrier for which the grouping is designed (for example 20 GHz for a transmission grouping and 30 GHz for a grouping

reception).

  For substantially circular grouping openings, the width

  angular, at the border at - 4 dB, of each of the beams formed by the group -

  ment is worth approximately 67 X / D degrees and the contiguous beams are placed on centers distant from 57 k / D degrees. Since transmission and reception take place on different frequencies or wavelengths, the transmission and reception groups must have different diameters so that the pairs of beams

  transmission / reception have the same service area.

  FIG. 5 represents one of the individual emission elements 50 of the

  emission phase shift group 28, which is characterized by a radius element

  nant 51 and an active emission module 54. The radiating element 51 is characterized by a passive radiator 52, which is coupled to a polarization network controlled by computer 53 placed in the active emission module 54 offering the possibility of reconfiguring the polarization of the beam in orbit. The radiating element 51 and the polarization network 53 are supplied to the commercial market by various

  sellers and are well known to those skilled in the art.

  The transmission module 54 is characterized by a network 53 of switching

  computer-controlled polarization, an isolator 56, a linear power amplifier 57 with a monolithic microwave integrated circuit (MMIC), a computer-controlled phase shifter 58 and a computer-controlled attenuator 59. As shown in FIG. 5, the network of polarization 53 is coupled to the isolator 56, itself being coupled to the solid state power amplifier 57. The amplifier 57 is coupled to the active phase shifter 58, which is coupled to the active attenuator 59. The attenuator 59 is coupled to the RF input. The phase shifter 58 and

  the attenuator 59 (which are also MMICs) are provided to ensure the com

  phase and amplitude command for compensation and calibration of each

  RF path in the multibeam electronic scanning antenna. A computer

  tor placed somewhere on the geosynchronous satellite sends instructions to excitation circuits arranged inside components of the network 53, of the phase shifter 58 and of the attenuator 59 so as to cause modifications of the polarization, of the phase or attenuation as determined as necessary by the on-board control equipment. The components of the active emission module 54 are offered on the commercial market by companies

  Raytheon, Texas Instruments, and others, and are well known to those of skill in the art.

  FIG. 6 represents one of the individual reception elements 60 of a reception phase shifting group 29, which is characterized by a reception element 61 and an active reception module 64. The reception element 61 comprises a passive radiator 62 which is coupled to a polarization network, controlled by computer, 63, placed in the active reception module 64 which ensures, in orbit, the reconfiguration of the polarization of the beams. The receiving element 61 is offered on the commercial market by various sellers and is well

known to those skilled in the art.

  The reception module 64 is characterized by a communication network 63

  computer controlled polarization, limiter / protector circuit 66

  providing protection against high level interference signals, an amplifier

  low noise reception ficator 67 of the MMIC type, a computer controlled phase shifter 68 and a computer controlled attenuator 69. As can be seen in FIG. 6, the bias network 63 is coupled to the limiter / protector circuit 66, which is coupled to the low noise solid state reception amplifier 67. The amplifier 67 is coupled to the phase shifter active 68, itself coupled to the active attenuator 69. The attenuator 69 is coupled to an RF output. The phase shifter 68 and the attenuator 69 (which are also MMIC type devices) are provided to ensure phase and amplitude control in connection with the compensation and calibration of each RF path using the electronic scanning antenna with multiple beams. A computer located somewhere on the geosynchronous satellite sends instructions to excitation circuits comprised within components of the network 63, of the phase shifter 68 and of the attenuator 69 so as to cause changes in the polarization, the phase or attenuation as determined as necessary by the on-board control equipment. The components of the active reception module 64 are supplied to the commercial market by the companies Raytheon, Texas Instruments, and others,

  and are well known to those skilled in the art.

  Figure 7 shows part of an embodiment of the multi-beam beam forming means 26 or 27 (Figure 2). As can be seen in Figure 7, part of each beam transformation means 26 or 27 is a Butler matrix power supply (which is well known to those skilled in the art) forming 8 beams using of 8 radiating elements. The inputs of the network 70 of FIG. 7 consist of all the outputs of the elements

  transmitting or receiving elements in a column of the group-

  emitting phase shift 28 or receiving phase shifting group 29

  (figure 2). The beam available on each output beam port is a bundle

  fan-shaped skin which is narrow along the dimension associated with the length of the column of elements and which is wide according to the dimension associated with the width of a

  single element. An example with 8 inputs of network 70 is presented in detail.

  lée in Figure 8. As can be seen in Figure 8, each means of form

  Butler matrix beams 26 or 27 are characterized by a number of hybrid couplers 82 and fixed phase shifters 84. The configuration of the

  Butler matrix 70 shown in Figure 8 is well known to those skilled in the art.

  When a network 70 as shown in FIG. 7 is connected to each column of elements of a transmission phase shift group 28 or of a reception phase shift group 29 and a similar network is connected to each row of column beam ports, very narrow beams (brushes) are formed. These brushes are contiguous, in contact with each other at the level

  points at - 4 dB and, if the transmission phase shift grouping 28 or the group -

  ment to phase shift reception 29 was directed towards the Earth, it would cover the part of

the Earth shown in Figure 1.

  In FIG. 9, a network 90 is presented, used to combine a group.

  pement of 64 elements with 8 columns and 8 rows. This network forms the whole

  8 x 8 of beams shown in Figure 10.

  A variant of the beam forming operation which consists in forming all the beams necessary for covering the Earth, then in selecting M of these beams to activate them, consists in calling upon an implementation.

  in which only M beams are formed, each of them however being individual

  dual orientable to any position on the Earth's surface. The network intended to take the place of the beam forming network described in FIGS. 7, 8 and 9 is partially represented in FIG. 11. Here, the active modules (FIGS. 5 and 6) of each element of the group with phase shift of transmission 28 or of the reception phase shifting group 29 are followed by a separator / combiner network "1 to M",

  designated by the reference 100, where M is the number of beams to be used.

  At each of the M outputs of the separator / combiner network 100, there is a dephlia-

  seur 102 controlled by computer. One of the M phase shifters 102 of each of the N elements of the grouping is then connected to a combiner / separator "N to 1" in order to form an individually orientable beam. So, M x N phase shifters

  are necessary in this form of implementation.

  In either form of implementation of the beamforming network, microwave circuits are inherently low power and can be manufactured using very large scale integration techniques to

  minimize weight and cost. The overall cost of the telecommunication antenna

  solid state type multibeam electron cations and low power type transmit power amplifiers that are distributed across the face of the antenna will be less than that of the traditional approach using a radiating horn reflector and a high power TWTA transmitter. Moreover,

  the device described according to the invention will have a lower weight and will allow the recon-

figuration of beams in orbit.

  One of the important points of the satellite system 20 is that the groups-

  phase shift elements 28 and 29 and the Butler matrices 26 and 27 form a group-

  regularly of potential antenna beams which cover the entire hemispherical field of view of satellite 20. The matrixes of switches 24 and 25 select which of these beams will be active at a particular time. Of this

  way, only one conceptual type of satellite can be used for all posi-

  orbital slice / service area, so the above disadvantages

listed are all avoided.

  Beams are switched and channels are reassigned between the beams whenever the service area of a satellite needs to be changed. This can happen for the following reasons. (1) Initial configuration in orbit; (2) modification of the area served by a particular satellite in a given band, for example to serve a new market; (3) scheduled daily changes to keep up with peak market demand, mainly concerning changes in channel assignments, although for some systems (eg educational programs) complete changes may take place which concerns the beams; (4) configuration of a standby system when it is intended to replace a failed satellite (note that the standby system can be set up in orbit in the absence of any knowledge of the section in which it will ultimately be necessary); (5) temporary reconfiguration of the service area of a satellite in order to replace the service provided by a broken satellite; and (6) passage of a satellite from one section to another in order to modify its area

service.

  Those skilled in the art will have understood that the invention offers a more

  cost-effective to provide telecommunications in applications

  geosynchronous satellites. The phase shift array carried by satellite 20 is more flexible to use than a reflector type antenna system

  parabolic excited by radiant horn.

  In addition to the advantages listed above, the ability to reconfigure

  System 20 offers the unique possibility of dynamically allocating peak capacity from GSO using multiple coverage of the service area from different tranches. In this operating configuration, a certain satellite covers a region "A" and a second satellite covers a region "B" from the same or a different slot. A third satellite covers the congested parts of region "A" and the congested parts of the

  region "B" from a slice different from those of the first two satellites.

  This "cutting-edge" satellite could reconfigure in a very dynamic manner.

  mique in order to serve peak areas while the other satellites provide the

basic cover.

  The GSO 20 electronic scanning satellite system has at least two additional advantages. First of all, the phase shifting group is, by nature, more reliable than a TWTA approach based on the capacity it offers to withstand a "partial failure". Second, the phase shift grouping approach allows for smaller beams, which themselves require less transmission power. This power saving is used to compensate for the lower efficiency of the phase shifting group and to allow a larger payload or the incorporation of a larger number of beams if necessary. The use of smaller beams also allows a land terminal to use smaller antennas and lower transmission power, which improves the commercial viability of the system. Of course, those skilled in the art will be able to imagine, from the

  systems whose description has just been given for illustrative purposes only and

  in no way limiting, various variants and modifications not departing from the scope of the invention.

Claims (10)

  1. satellite system (20), characterized by: a grouping of elements (28), o each element is able to transmit signals from the satellite system (20) in geosynchronous orbit; beam forming means (26) coupled to the array of elements (28); a transmit switch array (24) coupled to the beam forming means (26) via a plurality of beam ports; and a switch controller (23) coupled to the transmit switch array (24), which is able to select certain ports of beams.   2. System according to claim 1, characterized in that each element   element grouping (28) occupies a square section in a grid   square of one of several columns and rows.   3. System according to claim 1, characterized in that each element   ment of the grouping of elements (28) occupies a hexagonal section in a   triangular grid of one of several columns and rows.   4. System according to claim 1, characterized in that each element   ment of the group of elements (28) comprises: a radiating element (51); and   an active emission module (54) coupled to the radiating element (51).   5. System according to claim 4, characterized in that the element   radiant (51) includes a passive radiator (52).   6. System according to claim 5, characterized in that the active transmission module (54) comprises: a polarization switching network (53) which is able to reconfigure the polarization of the beams while the satellite (20) is in geostationary orbit; an isolator (56) coupled to the polarization switching network (53); a linear power amplifier (57) coupled to the isolator (56); a phase shifter (58) coupled to the linear power amplifier (57); and   an attenuator (59) coupled to the phase shifter (58).   7. System according to claim 1, characterized in that the means of   beam formation (26) includes a Butler matrix (70).   8. System according to claim 7, characterized in that the Butler matrix (70) comprises: a plurality of hybrid couplers (82); and a plurality of phase shifters (84) coupled to some of the couplers hybrids (82).   9. satellite system (20), characterized by: a grouping of elements (29), where each element is able to receive signals in the satellite system (20) in geosynchronous orbit;   a beam forming means (27) coupled to the group of elements   elements (29); a receive switch array (25) coupled to the beam forming means (27) via a plurality of beam ports; and a switch controller (23) coupled to the receive switch array (25), which is able to select some of the beam ports.   10. Satellite (20), characterized by: a transmission phase shift grouping (28) formed by transmission elements (51), o each transmission element (51) is able to transmit signals from the satellite (20) in geosynchronous orbit; a reception phase shift group (29) formed of reception elements (61), o each reception element (61) is able to receive signals in the satellite (20) in geosynchronous orbit; and   a switch control device (23) coupled to the group   with phase shift of transmission (28) and with grouping with phase shift of reception (29),   and being able to select some of the emission elements (51) and some of the elements receiving elements (61).