FR2783377A1 - Multiple beam satellite communications system, e.g. for digital TV, using receiver with signal combining and separating architecture to feed channel amplifiers providing ground stations with individual downlink power control facility - Google Patents

Abstract

The receiver section of the satellite repeater combines signals uplinked at e.g. 30 GHz via low noise amplifiers (30), and feeds them via hybrid input circuits (32) to a bank of receivers (34), where they are frequency translated to e.g. 20 GHz for subsequent transmission in the downlink. The signals are separated in input multiplexers (36) and applied to channel amplifiers (38) which preferably have individual gain control inputs, responding to a control signal received from the relevant ground station, to set the power level in that downlink. The amplified signals are fed to hybrid output circuits (40) before they are power-amplified (42, 44) and demultiplexed (46). An Independent claim is included for a space vehicle forming a number of beams covering regions on the earth incorporating a receiver according to the invention.

Description

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  IMPROVED SATELLITE COMMUNICATIONS SYSTEM

  USING HF INPUT MULTIPLEXERS FROM A

  MULTIPLE POINT BEAMS TO A RECEIVER

  This invention relates generally to spacecraft communications systems and, in particular, to spacecraft communications systems which include at least one spacecraft which receives uplink signals from a number transmitters from earth stations located within a particular beam, and which frequency shifts and retransmits the uplink signals received to receivers located within the same

particular beam.

  The use of a geosynchronous orbiting satellite to broadcast television signals to

  terrestrial receptors is well known in the art.

  For example, reference can be made to the following two publications: "Flight Hardware Test Results Obtained on High Power Equipment and on the Repeater Subsystem of 12 GHz DBS", by W. Liebisch et al., 86-0646 AIAA, pages 266 to 274 , 1986, and "The Thermal Control System of the German Direct Transmitting Communication Satellite TV-SAT", by Kreeb et al., AIAA 8th Conference on Satellite Communications Systems, 20-24

April, 1980.

  A number of problems arise in the design of a high performance satellite communications system which provides, for example, television service to terrestrial receivers dispersed over a large geographic area. In such a system, a number of different land stations, each associated with a different local and demographic market, can each transmit an uplink signal which. is intended to be received by a spacecraft, such as an orbiting satellite

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  geosynchronous, and then transmitted, via one or more repeater channels, from the spacecraft to television receivers within the locality served by the earth station. For example, a first land station may serve the New York City area, another may serve the St. Louis area, while another may serve the Salt Lake City area. Each earth station can provide one or more television channels, and is considered to be located within a particular beam of the spacecraft. More than one earth station can be served by a particular beam. As can be appreciated, in such a system, the size and therefore the power requirements of the downlink of each service area can differ significantly. That is, for a predetermined HF power value at ground level, more power from the spacecraft transmitter is required for a large beam than for a small beam. In addition, to be able to maximize the total number of earth stations that can be served, the spacecraft will require a significant number of uplink receivers, as well as a significant number of downlink power amplifiers, constructed so characteristic in the form of traveling wave tube amplifiers (TWTA). In addition, it is important to provide some possibility of controlling the transmission power so as to compensate for the localized annoyances for the signals, usually the attenuation due to rain, which can be encountered at any given time in a

  locality but not in others.

  It is known to provide HF gain and power control of the repeater channels on a downlink beam with a ground station, but not

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  not with HF gain and power control of different repeater channels with multiple earth stations in a downlink beam. In accordance with the prior art, and with reference to FIG. 1A, a spacecraft communications system may include a spacecraft 1 which uses separate TWTA amplifiers 2 which each receive a separate signal from the earth stations (GS) located at l inside the same bundle or different bundles. For example, a first beam (beam n l) can comprise four earth stations (GS1 to GS4) while a second beam (beam n 2) can comprise six different earth stations (GS1 to GS6). Each earth station signal is transmitted through a separate spacecraft repeater channel which includes a channel amplifier circuit, generally represented by an amplifier 4, and a TWTA amplifier 2. Each channel amplifier circuit 4 can be controlled separately in gain and / or in HF power by the associated earth station. The outputs of the TWTA 2 amplifiers for each beam are combined in an output multiplexer (OMUX) 3 before transmission on the downlink to the terrestrial receivers in each

regional or point beam.

  You can see that this classic approach can waste energy and TWTA amplifiers, since each repeater channel will typically have different HF power requirements. If you wanted to use only one type of TWTA amplifier (for example, a 60 W TWTA amplifier) or only two types (for example 60 W and 120 W), then a repeater channel which requires only 10 W of HF power will use its TWTA amplifier much less

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  effectively than another repeater channel that requires

W of HF power.

  In addition, in accordance with the prior art, a spot beam of one size can be provided, which is contiguous over all of the continental United States (CONUS). Alternatively, as exemplified by U.S. Patent No. 4,819,227, "Satellite Communications System Employing Frequency Reuse" by H. A. Rosen, a bilateral satellite communications system can use spot beams in contiguous areas. In general, the prior art requires either more satellites, or a larger spot beam spacing, using a single spot beam size, in order to obtain the required performance. The prior art may also use more interleaved antennas on the CONUS area, with larger primary source spacings, and therefore require

  more surface on the satellite.

  It is also known from the prior art to provide as many receivers as the total number of repeater channels, or as many as the number of primary sources / beams, and to cause each receiver to translate its associated repeater channel or primary source / beam to appropriate downlink channel frequencies. Referring to Figure 1C, the prior art teaches a system which uses either a single receiver 7 for a repeater or a single receiver 7 for a primary source or a beam. As was also the case for FIG. 1A, each GS station signal can originate from a separate geographical area (for example from land stations located in different urban areas). As will be seen, and as was also the case for Figure 1A, the approaches to

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  prior art are not effective with regard to energy consumption, weight and / or

  the use of the spacecraft payload.

  It is a first object and advantage of this invention to provide an improved satellite communications system in which a plurality of channels of satellite repeaters are multiplexed on a single satellite receiver. It is another object and advantage of this invention to provide an improved satellite communications system in which a communications satellite payload is reduced in mass, complexity and power consumption by providing at least one input multiplexer to to combine together a plurality of uplink signals from one or more beams, and a single receiver or channel amplifier to transpose in frequency and

  amplify the combined uplink signals.

  Some of the above problems and others are overcome, and the aims and advantages are achieved by mode-conforming methods and devices

for carrying out this invention.

  In accordance with this invention, an HF power control system for satellite communications is provided to deliver digital data, such as digital television data, from multiple earth stations to a single point or regional beam. In the preferred embodiment of this invention, a single receiver serves multiple uplinks, an input multiplexer being used to first combine the uplink signals. The input multiplexer works to add n primary sources of different frequency with narrower bandwidth into an output signal at

wider bandwidth.

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  This aspect of the invention thus allows the use of input multiplexers which are considerably smaller and less expensive than the individual receivers of the prior art. Only one of the input multiplexers adds multiple beams and / or primary sources into the single receiver, thereby significantly reducing the number of receivers required for a given payload architecture. The single receiver is preferably designed to operate in the linear region so as to minimize interference from neighboring channels and products

  third order intermodulation.

  An example of the use of this invention is an original method of distributing digital data using multiple spot beams of different shapes and sizes to completely cover and serve the designated Nielsen commercial areas of the United States (DMA) using multiple spacecraft in geosynchronous orbit. Each spot beam has an assigned set of repeaters, and allocated repeaters of one or more spot beams can then be multiplexed and added into the same single receiver. This design of the communications payload system significantly reduces the number of receivers required, compared to the designed payload systems

  according to the prior art.

  In accordance with this aspect of the invention, a communication system is taught which includes a plurality of spacecraft in geosynchronous orbit, each spacecraft providing a plurality of beams on the surface of the Earth, and a plurality of earth stations, individual stations of which are located in one of the beams to transmit uplink signals to one of the spacecraft. Each spacecraft has a plurality of

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  repeater receivers for receiving a plurality of uplink signals from earth stations, channel amplifiers, and a plurality of transmitters for transmitting a plurality of downlink signals within the same beams as the signals corresponding uplink. Each repeater receiver includes a combination module for combining together a plurality of uplink signals and a single receiver having an input connected to an output of the combination module. The single receiver includes a frequency transposer for transposing the received uplink signals to a transmission frequency of the plurality of the downlink signals. The combination module is designed to have a plurality of resonant filters, one for each uplink signal that is received as an input to the combination module, and a hybrid combination module connected to an output of each of the resonant filters. The hybrid combination module has a bandwidth which is wide enough to encompass a bandwidth of

  each filter of the plurality of resonant filters.

  Each of the amplifiers in the plurality of channel amplifiers can be gain controlled by

  a corresponding station among the earth stations.

  In the preferred embodiment, the uplink beams to a first of the satellites have a first polarization and the downlink beams have a second opposite polarization, and the uplink beams to a second of the satellites have the second polarization and the downlink beams present the

first polarization.

  In the presently preferred embodiment, the uplink and downlink signals carry digital television signals, the

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  beams are spot beams having non-uniform sizes and shapes, and the individual beams among the spot beams cover a predetermined area of a designated commercial television area.

  The characteristics of the invention presented below

  above and others are made more evident in the

  detailed description which follows of the invention, read in

  conjunction with the accompanying drawings in which: FIG. 1A is a simplified block diagram showing part of a payload of communications of conventional spacecraft, and more particularly the use of TWTA amplifiers

  individual for individual repeater channels.

  Figure 1B is a simplified block diagram of a portion of a spacecraft communications payload in accordance with one aspect of this invention, in which a plurality of repeater channels are

  combined and applied to a single TWTA amplifier.

  Figure 1C is a simplified block diagram showing another part of a conventional spacecraft communications payload, more particularly the use of individual receivers

  for individual repeater channels.

  Figure 1D is a simplified block diagram of the portion of a spacecraft communications payload according to another aspect of this invention, in which a plurality of repeater channels are, instead, combined in a multiplexer input (IMUX) and are applied to a single receiver, Figure 1E illustrates the IMUX multiplexer of Figure 1D in more detail for configuration

example 4: 1,

  FIG. 2A is an elevation view of a communications spacecraft which is suitable for practicing this invention,

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  FIG. 2B describes a part of the spacecraft of FIG. 2A, and shows in more detail three antenna reflectors intended to generate spot beams of different sizes, FIG. 2C describes a communications system with two spacecraft in accordance with one aspect of this invention, FIG. 3A is a diagram illustrating a generalized spacecraft payload for an example of uplink and downlink with 37 beams, FIG. 3B is a block diagram of the load circuit useful spacecraft for the example case of uplink and downlink 37 beams shown in Figure 3A, and Figures 4A and 4B illustrate various sizes and shapes of example spot beams for a first spacecraft of communications (Figure 4A) and a second communications spacecraft (Figure 4B) which cooperate, as in Figure 2C, to provide direct television coverage by r spacecraft on

the continental United States.

  Reference will be made to FIGS. 2A and 2B to illustrate a satellite or spacecraft in geosynchronous orbit 10 which is suitable for putting into practice

  this invention. In the following description, we

  assume that two such spacecraft are used together to provide direct digital spacecraft television coverage over localized regions of the continental United States (see also Figures 4A and 4B), as well as for Hawaii and Alaska . It will be appreciated, however, from the outset that the teachings of this invention are not limited to providing only digital television signals, but can be used to provide any type of digital data, including, but

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  but not limited to digital voice, facsimile, paging, and network data

  computing, including Internet data packets.

  The teaching of this invention is also not limited to the use of two spacecraft, to the extent that a number less than or greater than this can be used, nor is teaching limited, for example. example, only at frequencies and / or numbers, sizes and / or shapes of particular beams which will be described below. The teachings of this invention are further not intended to be limited by particular numbers of repeaters or channel amplifiers or else by the particular types of antennas, polarizations, high power amplifiers (HPA), such as

TWTA amplifiers, etc ...

  In FIGS. 2A and 2B, the spacecraft 10 comprises a bus 12 and arrays of solar cells 14. A plurality of direct radiation TWTA amplifiers 16 are mounted on the bus 12, for example Ka-band TWTA amplifiers, or Ku band or C band. For the Ka band, three antennas are used per spacecraft to generate the spot beams: an antenna 18 of Gregorian type of 3 meters, transmitter / receiver antenna intended to generate a spot beam of 0.35, an antenna 20 of transmitter / receiver with primary source offset by 2.1 meters intended to generate a spot beam of 0.5, and an antenna 22 of transmitter / receiver with primary source offset by 1 , 5 meter intended to generate a point beam of 0.70. Antenna pointing mechanisms 24 are provided, as well as an adjustable sub-reflector 18A which allows automatic monitoring for the antenna 18 of 3 meters. Other antennas include two Gregorian type antennas formed 26A and 26B for high definition television (HDTV), as well as an 11i 2783377 Gregorian type antenna formed 26C to allow conditional access to a ground controller. The antennas 26A to 26C do not relate to the teachings of this invention, nor are they described with any degree of specificity. Each antenna is preferably with automatic tracking to allow a very small pointing error. Although they are described in the context of Gregorian type antennas, the antennas could also be made with Cassegrain type antennas. In general, the use of Gregorian or Cassegrain type antennas is preferred to allow large scanning possibilities with high side lobe isolation. The ratio of focal length to diameter (F / D) is preferably in the range of about two to about three. Furthermore, and although they are illustrated in the form of circular antennas, it will be appreciated that one or more of the antennas 18, 20 or 22 could have a non-circular shape, for example an elliptical shape, in order to provide non-circular beams at the

surface of the earth.

  The antenna 3 of 0.35 Ka band 3 meters is

  located on the east side of spacecraft 10, and the

  18A reflector is used for this large antenna because it is much lighter and easier to orient than the main reflector. The 18A sub-reflector gives additional benefits. For example, the transmit and receive beams have the same collimation, while there is a small offset when single offset reflectors are used. this is

  particularly important for this small beam.

  Eleven beams are generated from the 3 meter antenna 18 of the LHCP polarized spacecraft, while the 3 meter antenna on the RHCP polarized spacecraft generates twelve beams. The antenna 18

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  is preferably pointed in the south-eastern part of the CONUS area in order to minimize sweep losses in areas with heavy rain. The spacing of the beams allows the use of primary sources of 2X or larger. This primary source diameter reduces the levels of dispersal loss of the secondary lobes and

the side lobe levels.

  The 2.1 and 0.5 meter 1.5 and 0.7 meter Ka band antennas 20 and 22 are located side by side on the west side of spacecraft 10. These antennas use two mechanisms articulated to the Cardan in two axes for their deployment. The sub-reflectors 20A and

  22A are arranged as described above.

  In the illustrated but nonlimiting embodiment, the LHCP polarization spacecraft comprises ten beams of 0.5 and the RHCP polarization spacecraft comprises eleven beams. The 1.5 meter, 0.7 antenna generates 9 CONUS beams and the Hawaii beam on the LHCP polarization spacecraft. The 0.7 antenna of the RHCP polarization spacecraft generates 8 CONUS beams. The Alaska beam can also be generated from this antenna using two primary sources to create an elliptical pattern. In a first embodiment, the system uses a frequency band of 700 MHz to the Ka band with an uplink from 29.3 to 30 GHz and a downlink from 19.5 to 20.2 GHz. The frequency plan provides for 46 transponders at 26 MHz, 23 on each polarization. The HDTV television system uses 12 repeaters, while the SDTV system uses 34. The spot beams are divided between the two spacecraft by polarization. Spacecraft 1 processes 149 repeaters in 31 beams with left circular polarization (LHCP), while spacecraft 2 processes 145

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  repeaters in 32 circularly polarized beams

right (RHCP).

  Referring to Figures 3A and 3B, the repeater is of a simple conversion design. The uplinks at 30 GHz (37 beams of different sizes) are amplified by low noise amplifiers (LNA) 30 and are applied via hybrid input circuits 32 to receivers 34. The uplinks are amplified and transposed in frequency by a local oscillator (LO) at 9.8 GHz in the downlink band at 20 GHz. The signals from each beam are then separated in input multiplexers 36 and are applied to channel amplifiers 38, and then to hybrid output circuits 40. Each of the beam repeaters are amplified as a group in a high power linearized TWTA 42 amplifier

  operating at an output tolerance of 2.5 dB to 3 dB.

  In some cases where beams have only a few repeaters and also require low power, the signals from two beams are amplified in the same TWTA amplifier, then separated in an output multiplexer 46. Simple TWTA amplifiers of 120 W and 120 W 42 double (in parallel) and

44 are planned.

  This design approach minimizes the mass of the payload and its complexity. Input multiplexers allow uplinks to be received using only 11 active receivers instead of 30 or 31 if individual receivers were used for each beam. By processing the signals from each beam as a group, much less

  filters and channel amplifiers are required.

  The use of a TWTA amplifier of a single rating (for example 120 W) allows the use of large

  redundancy circuits to improve reliability.

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  The TWTA amplifier is a direct radiation collector (DRC) design that radiates more than half of the heat dissipation in space rather than inside the spacecraft structure, which greatly simplifies the thermal design of the spacecraft. Each channel amplifier 38 preferably provides a nominal gain of 50 dB. The output level can be controlled in 0.5 dB steps over, for example, a 6 dB range so that the drive of the TWTA amplifiers 42, 44 can be fine-tuned. The output linearization modules 41 are preferably optimized for output tolerances of the TWTA amplifiers from approximately 2 dB to approximately 3 dB. The

  TWTA amplifiers use one EPC for two TWT tubes.

  This produces excellent phase tracking when two or more TWTA amplifiers are used in the combined high power mode (in parallel). Reference may be made in this connection to the United States patent assigned jointly 5,649,310 "Signal Translation and Amplification System Including a Thermal Radiation Panel Coupled Thereto", by Randall D. Tyner et al., Whose

  description is incorporated by reference here in its

whole.

  In accordance with one aspect of this invention, and with reference to FIG. 1B, there is provided an HF power control system for satellite communications for supplying digital data, such as digital television data, from stations multiple terrestrial towards a single point or regional beam. Each earth station in the point or regional beam has a separate and individual control of the HF power for its channel or its repeater channels. The HF power control for each individual earth station allows the

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  downlink power adjustment due to rain attenuation inside the point or regional beam. That is, power adjustments are made in a particular repeater channel before combination with other repeater channels and amplification by a single common TWTA amplifier or multiple TWTA amplifiers in parallel. The power control commands can be sent to the spacecraft on a particular control channel reserved for this purpose using, for example, the Gregorian type antenna formed 26C which has

was shown in Figure 2A.

  In FIG. 1B, the example configuration of the prior art of FIG. 1A is modified to insert hybrid combination modules 5 in order to combine the outputs of the gain-amplified channel amplifier circuits 4 for the beam n1 and the circuits of gain-controlled channel amplifiers 4 for beam n 2. The combined outputs then pass through a buffer circuit and are linearized with the linearization module 6 before being applied to the TWTA amplifiers 2. The earth stations assigned to each circuit hybrid 5 and amplifier TWTA 2 will be selected so that the maximum power of the worst case does not exceed the power which can be taken into account by the point beam channeled. For just one example, for the nl beam, earth stations 1 to 4 can be at frequencies of 30.3,, 2, 29.9 and 29.8 GHz, and the signals transposed in frequency applied to the TWTA 2 amplifier can be at 20.3, 20.2, 19.9 and 19.8 GHz. The bandwidth of

  the TWTA amplifier can be at least 500 MHz.

  The linearization module 6 can be of conventional design, and is preferably chosen to maximize the noise power ratio (NPR) of the TWTA amplifier. As the NPR ratio increases, the linearity

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  of the TWTA amplifier increases, and unwanted intermodulation products decrease. Each earth station can monitor the resulting downlink beam and thereby compensate for signal disturbance, such as rain fading. Because the uplink is at a higher frequency than that of the downlink, the effect of rain will be more marked on the uplink than on the downlink. However, each earth station is designed to separately control its own beam gain before combining and amplifying power, so as not to influence the power of the other beams which

  are also amplified by the TWTA 2 amplifier.

  It can also be noted that the OMUX 3 multiplexers of FIG. 1A can be omitted, thereby eliminating the losses of DC power in these usually ineffective components. The use of this aspect of the invention thus allows multiple ground stations with assigned repeater channels to present HF power and gain control in an affected point or regional beam, with minimal effects on the signal or signals from neighboring land stations. In the innovative satellite communications system, there is a sharing of the gain and power control ratio between the earth station and the spacecraft. For a given point or regional beam, a certain number of earth stations is determined which can share a common TWTA amplifier, without exceeding the possibilities of the TWTA amplifier in the worst case conditions, and then an allocation is made of amplifiers of separate channels for each earth station. An addition of the outputs of the channel amplifiers is applied to a

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  common linearization which attacks a TWTA amplifier

  common or multiple TWTA amplifiers in parallel.

  This technique makes it possible to use a single type and a single size of TWTA amplifier on a given spacecraft, thereby reducing the cost and complexity of

  same as energy consumption.

  In this embodiment, a multiple repeater channel analysis in a nonlinear system is performed to determine the number of repeaters that can be used for each of the multiple ground stations, each with their own spacecraft channel amplifiers, in order to attack a linearized TWTA amplifier or multiple TWTA amplifiers in parallel in a beam. This technique thus also eliminates losses from the output multiplexers which can directly influence the energy and thermal efficiency of the spacecraft. An example of this invention is a method of distributing digital data, such as digital television data, using multiple spot beams of different shapes and sizes to completely cover and serve designated commercial areas (DMA) using a device multiple space in geosynchronous orbit. Each beam

  point can contain multiple earth stations.

  Each earth station can be assigned multiple repeater channels and has the ability to adjust the power or gain of the repeater channels. By assigning a channel amplifier for each ground station, multiple ground stations can share a TWTA amplifier or TWTA amplifiers

in parallel multiple.

  In another aspect, this invention teaches a spacecraft communications payload design to reduce the number of receivers and the

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  DC power consumption of the payload system. This is achieved by using input multiplexers to add the signals arriving from multiple point or regional beams, while being selective during this addition to avoid using the same repeater channels in the same input multiplexer. The added output

  is then taken to a single receiver.

  With reference to FIG. 1D, the embodiment of FIG. 3B can be modified so as to provide a single receiver 7 which serves multiple uplinks, an input multiplexer (IMUX) 8 being used to combine all of first the uplink signals. Figure 1E illustrates the IMUX multiplexer 8 of Figure 1D in more detail. It can be seen that each IMUX multiplexer 8 is made up of a plurality of n resonant filters, represented in the form of four bandpass filters 8A to 8D, the output nodes of which are connected to a hybrid combination module n: l. The effect consists in adding n primary sources of different frequencies with narrower bandwidths in a single output signal with wider bandwidth. The characteristics of the bandpass filters 8A to 8D are selected so as to obtain a band rejection of the adjacent channels, and the hybrid module 8E is selected so as to have a sufficient bandwidth to take into account the band

  the primary input sources.

  For just one example, in the case of the Ka band, the total spectrum of 500 MHz is separated into 27 MHz channels, each bandpass filter of the IMUX 8 multiplexer is optimized to work with one 27 MHz channels, and receiver / transposer 7

  has a bandwidth of 500 MHz.

  This aspect of the invention thus allows the use of input multiplexers 8 which are considerably

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  smaller and less expensive than the individual receivers of Figure 1C. Only one of the input multiplexers 8 adds multiple beams and / or primary sources into the single receiver 7, and therefore significantly reduces the number of receivers required for a given architecture of the payload. The single receiver 7 is preferably designed to operate in the linear region in order to minimize interference from adjacent channels and third order intermodulation products. The single receiver 7 is assumed, for the purposes of this invention, to include a low noise amplifier (LNA) which feeds a frequency transposition mixer circuit operating with a generated local oscillator signal. The receiver 7 is further assumed to have sufficient bandwidth to take into account the bandwidth requirements of the multiple combined inputs. An example of the use of this invention is a unique method of distributing digital data using multiple spot beams of different shapes and sizes to completely cover and service the designated Nielsen commercial areas of the United States (DMA) using multiple spacecraft in geosynchronous orbit. Each spot beam has an assigned set of repeaters, and allocated repeaters of one or more spot beams can then be multiplexed and added into the same single receiver 7. This design of the communications payload system significantly reduces the number of receivers required 7 compared to designed payload systems

  according to the prior art.

  Referring now to Figures 4A and 4B, another aspect of this invention is the ability to use the communications system of the craft.

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  space to deliver digital data from a land station within a point beam to the same point beam, in one direction, through various configurations of point beam antennas. The configurations use a variant of the spot beams of different sizes, each having either a non-circular shape such as an elliptical shape, or a circular shape, or a combination of the two shapes to cover an entire geographical area which must be served. This type of service can therefore take into account differences

  commercial, demographic, languages, etc ...

  A combination of non-circular and circular spot beams of different sizes is used in the preferred embodiment of this invention to form a non-contiguous configuration of non-contiguous areas, thereby allowing improved inter-beam isolation. An example of the utility of this invention is its ability to allow coverage of all DMA Nielsen CONUS areas with two spacecraft in a single geosynchronous orbit orbit

  multiple geosynchronous, as shown in Figure 2C.

  This technique improves the reuse of frequencies in a given bandwidth, with a minimum set of antennas and spacecraft, compared to a conventional contiguous approach for the locations of

spot beams.

  In the preferred, but nonlimiting, embodiment shown in Figure 2C, there are two spacecraft on a single location of geosynchronous orbit, for example within about 0.2, which are used to cover all areas DMA using different point beam locations between the two spacecraft. Each spacecraft performs the uplink with a single

  polarity, but opposite to that of the other spacecraft.

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  More particularly, the spacecraft nl performs the uplink either with an RHCP polarization or with an LHCP polarization and the spacecraft n 2 performs the uplink either with an LHCP polarization or with an RHCP polarization (with an opposite polarity), or the spacecraft nl performs the uplink with a vertical linear polarization and the spacecraft n 2 performs the uplink with a

  horizontal linear polarization, or vice versa.

  The downlink for each spacecraft is

  of opposite polarity to its uplink polarity.

  For example, the spacecraft nl performs the uplink with an RHCP polarization and the downlink with an LHCP polarization, while the spacecraft n 2 performs the uplink with an LHCP polarization and the downlink with an RHCP polarization, or the spacecraft nl performs the uplink with vertical linear polarization and the downlink with horizontal linear polarization, while spacecraft n 2 performs the uplink with horizontal linear polarization and the downlink with a

vertical linear polarization.

  The two spacecraft system design can either use all non-circular spot beams of different sizes, all circular spot beams of different sizes, or a combination of non-circular and circular spot beams of different sizes to cover all of the DMA areas . General techniques for making spot beams of different sizes with reflector antennas of the type described above, as well as for making spot beams either circular or non-circular, are known to those skilled in the art, but not the combination of spot beams of different sizes and shapes to cover various

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  terrestrial regions, allowing improved frequency reuse and reduced interference

inter-beam, as described here.

  For what is only an example, the circular antenna 18 of 3 meters could be instead an elliptical antenna having dimensions of 3.2 meters by 2.5 meters in order to develop beams

ellipticals instead of circulars.

  It will also be appreciated that the teaching of this invention is not limited to use with two spacecraft operating with different polarizations. For example, there could be three or more spacecraft each operating with one

double polarization.

  Thus, although the invention has been particularly presented and described according to the preferred embodiments thereof, the person skilled in the art will understand that variants of form and details can be made thereto without s deviate from the scope and spirit of

the invention.

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Claims (14)

  A communications system comprising: a plurality of spacecraft (10) in geosynchronous orbit, each spacecraft (10) cooperating to provide a plurality of beams on the surface of the Earth, and a plurality of earth stations including individual stations are located in one of said beams to transmit uplink signals to one of said spacecraft (10), wherein each spacecraft (10) is made up of a plurality of repeater receivers (34) for receiving a plurality of uplink signals from earth stations, a plurality of channel amplifiers and a plurality of transmitters for transmitting a plurality of downlink signals within the same beams as the signals corresponding uplink, and in which each said repeater receiver consists of a combination module intended to combine a plurality of of uplink transmitted signals and a single receiver having an input connected to an output of said combination module, said single receiver comprising a frequency transposer for transposing the uplink signals received to a plurality of transmission frequencies signals from downlink.   2. The system of claim 1, wherein each amplifier of said plurality of channel amplifiers is gain controlled by a station   corresponding among said earth stations. 24 2783377   3. The system of claim 1, wherein said beams have different sizes and shapes, and are not contiguous on at least a portion from the surface of the Earth.   4. The system of claim 1, wherein the uplink beams to a first of said satellites have a first polarization and downlink beams have a second opposite polarization, and wherein the uplink beams to a second of said satellites have said second polarization and the downlink beams have said first polarization. 5. The system of claim 1, wherein the uplink and downlink signals   include digital data signals.   The system of claim 1, wherein the uplink and downlink signals   include digital television signals.   7. The system of claim 6, wherein said beams are spot beams having non-uniform sizes and shapes, and wherein individual beams among said point beams cover a predetermined area of an area   designated television commercial.   8. The system of claim 1, wherein said combination module consists of a plurality of resonant filters, one for each uplink signal that is received as input to said combination module, and a connected hybrid combination module. at an output of each of said resonant filters, in 2783377   wherein said hybrid combination module has a bandwidth which is wide enough to encompass a bandwidth of each filter of said plurality resonant filters.   9. The system of claim 1, wherein each spacecraft comprises a plurality of reflector antennas of different sizes, for both transmitting and receiving said beams.   The system of claim 1, wherein each spacecraft includes a plurality of reflector antennas for both transmitting and receiving said beams, wherein at least two of said antennas are   reflector have different shapes.   The system of claim 1, wherein each spacecraft comprises a plurality of reflector antennas for both transmitting and receiving said beams, wherein the antennas of said plurality of reflector antennas each consist of a Gregorian type antenna.   The system of claim 1, wherein each spacecraft comprises a plurality of reflector antennas for both transmitting and receiving said beams, wherein the antennas of said plurality of reflector antennas each consist of a Cassegrain type antenna.   13. The system of claim 1, wherein the uplink beams to a first of said satellites have right circular polarization (RHCP) and the downlink beams have left circular polarization (LHCP), and wherein the link beams rising towards a second of said 26 2783377   satellites have LHCP polarization and the downlink beams have RHCP polarization.   14. A spacecraft intended to provide a plurality of beams to the surface of the Earth and to receive uplink signals from a plurality of earth stations, the individual stations of which are located in one of said beams, said spacecraft space comprising a plurality of repeater receivers for receiving a plurality of uplink signals from earth stations, and a plurality of transmitters for transmitting a plurality of downlink signals, within the same beams as the corresponding uplink signals, wherein each said repeater receiver includes a combining module for combining together a plurality of uplink signals from a plurality of indoor ground stations within a beam and a single receiver having an input connected to an output of said combination module, ledi t single receiver comprising a frequency transposer for converting the plurality of uplink signals received into transmission frequencies of the plurality of downlink signals.