Methods and apparatuses for adaptive beamforming in a satellite communications system

Abstract

According to disclosed methods and apparatuses, a satellite communications system (SCS) provides flexible and efficient adaptive beamforming with respect to service beams that carry traffic for user terminals distributed over a satellite-based service area, without requiring complex beamforming circuitry onboard the satellite.

Description

METHODS AND APPARATUSES FOR ADAPTIVE BEAMFORMING IN A SATELLITE COMMUNICATIONS SYSTEMTECHNICAL FIELD

[0001] Disclosed methods and apparatuses relate to adaptive beamforming in a satellite communications system.BACKGROUND

[0002] Satellite communication systems often employ phased-array-fed reflector (PAFR) antennas to generate multiple coverage beams that illuminate respective service regions on the Earth’s surface. In such systems, a two-dimensional array of feed elements is disposed in proximity to a reflector, and each feed element radiates a corresponding component beam toward the reflector. A beamforming network applies complex weights (e.g., amplitude and phase) to signals transmitted from, or received at, the feed elements such that, after reflection from the reflector, constructive and destructive interference among the component beams synthesizes a desired set of coverage beams.

[0003] Various challenges arise in such contexts, including the complexity of the required beamforming network (BFN), which scales in dependence upon the number of array elements used in beamforming. A typical feed array includes hundreds or even thousands of array elements, requiring significant beamforming complexity, even if the overall array is managed on a partitioned basis. With partitioning, each one of a small number of partitions has its own BFN, but the element count per partition remains large and the partitioning may result in irregularly shaped effective apertures and corresponding reduction of beam quality or beamforming efficiency.SUMMARY

[0004] According to disclosed methods and apparatuses, a satellite communications system (SCS) provides flexible and efficient adaptive beamforming with respect to service beams that carry traffic for user terminals distributed over a satellite-based service area, without requiring complex beamforming circuitry onboard the satellite. A user-link antenna system onboard the satellite provides a plurality of component beams via an array of component beam feeds, and whether or to what extent the component beams are defocused depends on a dynamically selectable focusing configuration of the antenna. Increased defocusing increases component beam overlap and a plurality of small beamforming circuits onboard the satellite operates synergistically with a dynamically configurable cluster size, such that the number of componentbeams used to form each service beam complements the focusing configuration of the user- link antenna system. Capping the configurable cluster size a defined maximum cluster size preserves simplicity of the beamforming circuits.

[0005] According to an example embodiment, a satellite is configured for adaptive beamforming in an SCS. The satellite includes a feeder-link interface system configured to transmit or receive one or more feeder link signals conveying service beam signals, each service beam signal carrying traffic to or from users in a corresponding service beam area associated with a corresponding service beam. A user-link antenna system of the satellite is configured to provide the service beams, wherein the user-link antenna system includes a plurality of component beam feeds, each component beam feed providing a corresponding component beam. The user-link antenna system is selectively operable in a plurality of defocused configurations in which the component beams are defocused, the plurality of defocused configurations including a first defocused configuration having less overlap of the plurality of component beams as compared to a second defocused configuration. A payload of the satellite comprises a plurality of beamforming circuits. Each beamforming circuit in the plurality has beam weight circuits corresponding to a subset (a cluster) of the plurality of component beam feeds. The subset is limited to a defined maximum cluster size.

[0006] For a first beamforming mode, a controller onboard the satellite controls the user-link antenna system to be configured into the first defocused configuration and controls the plurality of beamforming circuits to apply a first beamforming configuration. The first beamforming configuration is such that each service beam is formed as a composite of a first number of the component beams that is less than the maximum cluster size. For a second beamfomiing mode, the controller controls the user- link antenna system to be configured into the second defocused configuration and controls the plurality of beamforming circuits to apply a second beamforming configuration. The second beamforming configuration is such that each service beam is formed as a composite of a second number of the component beams, wherein the second number is greater than the first number and less than or equal to the maximum cluster size.

[0007] A related example embodiment comprises a method of operating a satellite with adaptive beamforming. The satellite is configured for operation in an SCS, and the method includes providing a plurality of service beams for serving users in respective ones among a plurality of service beam areas corresponding to the plurality of service beams. Each service beam associated with a respective service beam signal carrying user traffic to or from the users served by the service beam.

[0008] In this context, providing the plurality of service beams comprises forming each service beam using a respective cluster of component beam feeds in a feed array of a user-linkantenna system onboard the satellite. Here, each component beam feed provides a corresponding component beam and all respective clusters having a cluster size, with the method including selecting a beamforming mode dynamically from at least first and second beamforming modes, and reconfiguring beamforming circuits included in a payload of the satellite, to change the cluster size according to the selected beamfomring mode.

[0009] For operation in the first beamforming mode, the method includes configuring the user-link antenna system in a first defocused configuration corresponding to a first amount of defocusing of the component beams with a corresponding first amount of component beam overlap and configuring the beamforming circuits to perform beamforming according to a first cluster size corresponding to the first amount of component beam overlap. For operation in the second beamforming mode, the method includes configuring the user- link antenna system in a second defocused configuration corresponding to a greater second amount of defocusing of the component beams with a correspondingly greater second amount of component beam overlap and configuring the beamforming circuits to perform beamforming according to a larger second cluster size corresponding to the second amount of component beam overlap.

[0010] In another embodiments, an SCS is configured for adaptive beamforming. A satellite in a space segment of the SCS is configured to serve users via a plurality of service beams, each service beam illuminating a respective service beam area containing one or more users and each service beam associated with a respective service beam signal carrying traffic for the users served by the service beam. Each service beam is based on one or more ones among a plurality of component beams provided by a user- link antenna system of the satellite, with each component beam corresponding to a component beam feed in a feed array of the user- link antenna system.

[0011] A ground segment of the SCS includes a control system that is configured to select a beamforming mode used for providing the plurality of service beams, from among two or more beamforming modes corresponding to different focusing configurations of the user-link antenna system. The two or more beamforming modes include a first beamforming mode associated with a first defocused configuration of the user-link antenna system in which there is a first amount of defocusing of the component beams and a corresponding first amount of component beam overlap, and further include a second bcamforming mode associated with a second defocused configuration of the user- link antenna system in which there is a greater second amount of defocusing of the component beams and a correspondingly greater second amount of component beam overlap.

[0012] The satellite includes a controller configured to control a plurality of beamforming circuits in a payload of the satellite to operate with a first beamforming configuration responsiveto selection of the first beamforming mode. Here, the plurality of beamforming circuits operates with a first cluster size in which each service beam is formed using a neighboring cluster of component beam feeds of the first cluster size. For operation in a second beamforming configuration responsive to selection of the second beamforming mode, the plurality of beamforming circuits operates with a larger second cluster size in which each service beam is formed using a neighboring cluster of component beam feeds of the second cluster size.

[0013] Of course, the present invention is not limited to the above features and advantages. Indeed, those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a diagram of an antenna feed array, according to an example embodiment.

[0015] Figure 2 is a diagram of a user-link antenna system for use onboard a satellite and configured for adaptive beamforming, according to an example embodiment.

[0016] Figures 3A, 3B, and 3C are diagrams illustrating component beams corresponding to different focusing configurations of a user-link antenna system for adaptive beamforming, according to an example embodiment.

[0017] Figures 4 and 5 are block diagrams of example beamforming circuits for inclusion in a satellite pay load for adaptive beamforming, according to example embodiments.

[0018] Figure 6 is a block diagram of a satellite communications system (SCS) configured for adaptive beamforming, according to an example embodiment.

[0019] Figure 7 is a block diagram of an example details for a satellite configured for adaptive beamforming, according to an example embodiment.

[0020] Figure 8 is a logic flow diagram illustrating a method of operating a satellite for adaptive beamforming, according to an example embodiment.

[0021] Figure 9 is a block diagram of further details for a satellite payload configured for adaptive beamforming, according to an example embodiment.

[0022] Figure 10 is a diagram of an example grid of component beam feeds and corresponding component beams.

[0023] Figure 11 is a diagram of an example grid of service beams formed using three-beam clusters of component beams.

[0024] Figure 12 is a diagram of example beamforming operations applied with respect selected service beam signals.

[0025] Figure 13 is a diagram of an example feeder uplink signal based on frequency division multiplexing.DETAILED DESCRIPTION

[0026] Figure 1 illustrates a feed array 10 comprising a plurality of component beam feeds 12, where each such component beam feed 12 launches and / or collects radio waves and has an associated component beam 14, as shown in Figure 2. As part of an antenna system 16, the feed array 10 cooperates with a reflector 18 to provide a set or plurality of component beams 14, where each component beam 14 can be understood as having a directional pattern of radiation emission or reception.

[0027] The feed array 10 is movable relative to a focus region of the reflector 18. For example, cither the reflector 18 or the feed array 10 moves along the focal axis of the reflector 18 under motorized control, to vary the offset of the feed array 10 relative to the focus region of the reflector 18. A particular offset can be understood as defining a corresponding “focusing configuration” of the antenna system 16, and the antenna system 16 is controllable for operation with different focusing configurations. For example, there may be two or more predefined offsets representing two or more selectable focusing configurations, including a first offset referred to as a first defocused configuration and a second offset referred to as a second defocused configuration. There may be multiple selectable offsets, going from a zero offset, referred to as a focused configuration, to increasingly larger offsets, each corresponding to a respective defocused configuration.

[0028] The amount of offset defines the extent to which the component beams 14 are defocused. With zero offset, the component beams 14 are at their sharpest or fullest focus. With increasing offset, the component beams 14 are increasingly defocused. There may be stepped or continuous defocusing, with stepped defocusing used in one or more embodiments.

[0029] The component beam feeds 12 of the feed array 10 are arranged as a grid and there is a corresponding grid or pattern of component beams 14 — a “component beam grid.” Figures 3A, 3B, and 3C offer examples of how the focusing configuration of the antenna system 16 affects the component beams 14 and, therefore, the component beam grid.

[0030] Figure 3 A corresponds to the focused configuration of the antenna system 16 and it depicts an example set of component beams 14 in cross-section. In the focused configuration, the component beams 14 have a minimum beam overlap, as measured according to 3dB beam width, for example, and each component beam 14 has a minimum beam coverage area or footprint. While Figure 3A depicts only three component beams 14, the antenna system 16 may providehundreds or thousands of component beams 14 in either or both the transmit and receive directions and using one or more signal polarizations.

[0031] Assuming a communications-system scenario involving providing communications service to user terminals, a “service beam” carries user traffic in the transmit and / or receive directions for terminals within the footprint or coverage area of the service beam 20. Different service beams have different coverage areas and serve different groups or subsets of terminals. Figure 3 A illustrates an example case where, with the antenna system 16 in its focused configuration, each component beam 14 functions as a respective service beam 20, which is denoted by the “14 / 20“ reference number labeling.

[0032] Figure 3B illustrates a set of three component beams 14, which are again shown in cross-section but this time with the antenna system 16 in a first defocused configuration.Defocusing makes the component beams 14 larger, meaning that beam overlap between adjacent or neighboring component beams 14 increases. Although not drawn to scale, the component beams 14 shown in Figure 3B may be understood as being defocused versions of the same three component beams 14 depicted in Figure 3 A. The service beam 20 depicted in Figure 3B is realized via beamforming interaction of three overlapping component beams 14.

[0033] Thus, in contrast to the one-to-one relationship between component beams 14 and service beams 20 that holds in the case the antenna system 16 is operated in its focused configuration, the defocused configuration associated with Figure 3B means that each service beam 20 is formed as a composite of three component beams 1 — a “cluster” of component beams 20. As such, it may be said that each service beam 20 is based on or corresponds to a cluster of component beam feeds 12.

[0034] Figure 3C illustrates a further defocusing of the component beams 14, in which the antenna system is operated in a second defocused configuration that, in the illustrated example, represents a greater extent of defocusing as compared to the first defocusing configuration corresponding to Figure 3B. As the defocusing increases, the cluster size grows, meaning that a greater number of component beams 14 / component beam feeds 12 contribute to the formation of a single service beam 20. Whereas the first defocused configuration shown in Figure 3B had a cluster size of three, the second defocused configuration depicted in Figure 3C has a cluster size of seven, meaning that the depicted service beam 20 is a composite of seven component beams 14. The “cluster size” may be understood as reducing to one in the focused configuration, with each component beam 14 being operated as a respective service beam 20.

[0035] Forming the desired service beams 20 from clusters of component beams 14 relies on applying appropriately calculated beamforming weights to the signals transmitted from or received by the component beam feeds 12 included in the cluster. Figures 5 and 6 illustrateexample beamforming circuits 34, which are adaptive in the sense that they support a range of beamforming cluster sizes. For example, there may be N beamforming circuits 34, for forming N service beams 20 as composites of the component beams 14 provided by a respective cluster of component beam feeds 12. Each such beamforming circuit 34 may be advantageously simplified by limiting its maximum cluster size, and each such circuit may be operated with cluster sizes ranging from one (focused) up to the maximum size, with intermediate cluster sizes corresponding to different amounts of antenna defocusing.

[0036] Figure 4 illustrates use of a beamforming circuit 34 in the forward or transmit direction (transmit beamforming), while Figure 5 illustrates use of a beamforming circuit 34 in the return or receive direction (receive beamforming). In one or more embodiments, beamforming applies in either or both the forward or return directions, and a plurality of beamforming circuits 34 onboard a satellite support both forward and return beamforming.

[0037] In Figure 4, a service beam signal 30 carries time-multiplexed or other multi-access traffic for a plurality of terminals 32 served by a given service beam 20. The service beam 20 is not shown explicitly but will be understood as resulting from the far-field interactions of a cluster of component beams 14, where the size of the cluster depends on the extent of antenna defocusing.

[0038] The beamforming circuit 34 includes a signal splitter 36 that splits the service beam signal 30 into a number of signal copies, and signal weighting circuitry 38 applies respective beam weights from a set of beam weights 40 to respective ones of the signal copies. While the signal splitting and combining may be configured to operate with a maximum number of signal copies, there are only as many signal copies of interest as there are component beam feeds 12 in the cluster. In other words, in the “adaptive” beamforming context germane in this disclosure, beamforming adapts to the size of the component beam clusters being used to form the respective service beams 20.

[0039] Limiting the maximum cluster size greatly limits the complexity of the beamforming circuits 34, and restricting clustering to two or more defined sizes offers additional simplifications, such as limiting the number of beamforming solutions required. Here, a “beamforming solution” refers to the overall set or sets of beam weights needed for concurrent formation of the service beams 20. For example, a “set” of beam weights 40 comprises a vector having a length equal to the cluster size and having vector elements computed to form a particular service beam 20. Each beam weight 40 comprises, for example, a complex value representing a defined signal attenuation and phase delay, and the set of beam weights 40 is calculated such that the far-field interactions of the respectively weighted signals transmittedfrom the cluster of component beam feeds 12 yields a pattern of destructive and constructive signal interference resulting in formation of the service beam 20.

[0040] The same cluster of component beam feeds 12 may be used for more than one service beam 20, such as for multiple service beams 20 at different radiofrequencies. There would be a set of weighted signals for each such service beam 20, with each weighted signal corresponding to a respective one of the component beam feeds 12 in the cluster. The weighted signals for each service beam 20 that correspond to the same component beam feed 12 are combined for transmission from the corresponding component beam feed 12.

[0041] Figure 5 use of the beamforming circuitry 34 in the return context. Return beamforming uses signal weighting circuitry 42 that applies respective beam weights 40 to the signals received on each component beam feed 12 included in the cluster. A signal combiner 44 combines the weighted signals to form a corresponding service beam signal 30. In the return context, the beam weights 40 are calculated to maximize the signal-to-interference-plus-noise ratio (SINR) of terminal transmissions originating from terminals 32 that are located within the footprint or beam coverage area of the involved service beam 20. It will be appreciated that the beam weights 40 in embodiments that perform both forward and return beamforming will have weights calculated for formation of forward service beams, and weights calculated for formation of return service beams.

[0042] Figure 6 illustrates a satellite communications system (SCS) 50 that uses adaptive beamforming in the forward direction or the return direction, or in both directions. Adaptive beamforming applies on a per-satellite basis, for example, with the SCS 50 including one or more satellites 52 that support adaptive beamforming. The illustrated satellite 52 is, for example, a geostationary or geosynchronous satellite.

[0043] Each satellite 52 includes an antenna system 16 as previously described. Because the antenna system 16 supports the user link between the satellite 52 and the terminals 32 served by it. the antenna system 16 is referred to as a user-link antenna system 16.

[0044] Each satellite 52 further includes a feeder link interface system 54, and a payload 56 that includes a plurality of beamforming circuits 34. In at least one embodiment, the payload 56 includes switches 58 — e.g., switch matrixes — that provide for configurable connectivity between the feeder link interface system 54 and the user link antenna system 16. The switches 58 allow for selectable or configurable mappings between individual service beam signals 30 and respective component beam feeds 12 or clusters thereof.

[0045] With respect to each satellite 52, the SCS 50 is operable in two or more adaptive beamforming modes, meaning that the SCS 50 performs adaptive beamforming by changing which adaptive beamforming mode is selected. Activating or applying a selected adaptivebeamforming mode means: (1) in the satellite 52, adopting a corresponding beamforming configuration of the payload 56, and (2) adopting a corresponding focusing configuration of the user- link antenna system 16. The corresponding beamforming configuration of the payload 56 refers to the cluster size setting.

[0046] Selecting different adaptive beamforming modes changes the cluster size — i.e., it changes how many individual component beams 14 are used to form each service beam 20. As seen in the diagram, each service beam 20 has a corresponding service beam coverage area 60 and the service beam 20 used to carry traffic for (serve) any particular terminal 32 among a population of terminals 32 within an overall satellite service area 62 depends on the location of the terminal 32 relative to the service beam coverage area boundaries. Adaptive beamforming modes thus may be used to change the service beams 20 in terms of pattern or number.

[0047] The SCS 50 in one or more embodiments is operable in either a first adaptive beamforming mode or a second adaptive beamforming mode. The first adaptive beamforming mode entails a first beamforming configuration of the payload 56 onboard the involved satellite 52, and a first focusing configuration of the user- link antenna system 16. This first focusing configuration may be referred to as a first defocused configuration of the user- link antenna system 16 and it corresponds to a first amount or extent of defocusing and, hence, a first cluster size. The second adaptive beamforming mode entails a second beamforming configuration of the payload 56 onboard the involved satellite 52, and a second focusing configuration of the userlink antenna system 16. This second focusing configuration may be referred to as a second defocused configuration of the user- link antenna system 16 and it corresponds to a second amount or extent of defocusing and, hence, a second cluster size. For example, the second defocused configuration uses a greater defocusing as compared to the first defocused configuration and the second cluster size is larger than the first cluster size.

[0048] Consider an example case where the first beamforming mode entails a first cluster size is N, meaning that an A-sized cluster of component beam feeds 12 is involved in the formation of each service beam 20. N is three, for example, or some other integer. Continuing the same example case, the second beamforming mode entails a second cluster size of M, meaning that an M- sized cluster of component beam feeds 12 is involved in the formation of each service beam 20. M is seven, for example, or some other integer, and M is greater than N.

[0049] The SCS 50 in at least one embodiment is operable in a third adaptive beamfomiing mode, which entails a third beamforming configuration of the payload 56 and a third focusing configuration of the user-link antenna system 16. In this third adaptive beamforming mode, the component beams 14 are focused, hence the third beamforming configuration configures the beamforming circuits 34 for straight-through or bypass connectivity, allowing a one-to-onecoupling of service beam signals 30 to component beam feeds 12. Of course, there may still be filtering, amplification, frequency translation, etc., as applied by corresponding circuitry in the payload. In this third beamforming mode, the third focusing configuration of the user-link antenna system 16 is a focused configuration in which the feed array 10 resides in the focus region of the reflector 18, and the component beams 14 have minimum inter-beam overlap.

[0050] Broadly, the SCS 50 supports a plurality of adaptive beamforming modes with respect to a particular satellite 52, and a ground segment 64 of the SCS 50 operates with respect to that satellite 52 in accordance with the currently selected adaptive beamforming mode. Thus, adaptive beamforming affects both the ground segment 64 of the SCS 50 and a space segment 66 of the SCS 50.

[0051] Operating the ground segment 64 according to the selected adaptive beamforming mode means controlling how user traffic is mapped to or from the service beam signals 30. As the coverage areas or directionality of the service beams 20 change with changing adaptive beamforming modes, the SCS 50 accounts for the changes in terms of managing which terminals 32 are associated with which service beam signals 30 and / or service beams 20.

[0052] For example, the ground segment 64 includes a communications processing system (CPS) 68, such as one or more programmatically configured computer servers. The CPS 68 routes user traffic flowing into the SCS 50 from one or more external networks 70, such as the Internet, and routes user traffic flowing from the SCS 50 into the one or more external networks 70. The CPS 68 in this example controls how service beam signals 30 are defined, based on controlling how user traffic to / from different user terminals 32 is managed. In a forward link example, the CPS 68 aggregates forward user traffic and multiplexes it to form service beam signals 30 according to the currently selected adaptive beamforming mode, and it transmits the service beam signals 30 to a gateway station 72. The gateway station 72 transmits the service beam signals 30 via one or more a feeder uplink signals 74 in a feeder link 76 established between gateway station 72 and the satellite 52. In one or more embodiments, the satellite 52 may be in communication with more than one gateway station 72.

[0053] In a return link example, the satellite 52 transmits service beam signals 30 via one or more feeder downlink signals 78 of the feeder link 76, and the gateway station 72 transmits the service beam signals 30 to the CPS 68. Of course, the satellite 52 in one or more embodiments may support multiple feeder links 76 with multiple gateway stations 72. In either case, the CPS 68 demultiplexes the respective user traffic from them and, for example, forwards it towards the external network(s) 70.

[0054] With the foregoing example details in mind, one embodiment disclosed herein is a satellite 52 that is configured for adaptive beamforming in an SCS 50. The satellite includesfeeder-link interface system 54 configured to transmit or receive one or more feeder link signals conveying service beam signals 30. Each service beam signal 30 carries traffic to or from users (e.g., terminals 32) in a corresponding service beam area 60 associated with a corresponding service beam 20.

[0055] A user-link antenna system 16 of the satellite 52 is configured to provide the service beams 20, and it includes a plurality of component beam feeds 12. Each component beam feed 12 provides a corresponding component beam 14. Advantageously, the user-link antenna system 16 is selectively operable in a plurality of defocused configurations in which the component beams 14 are defocused. The plurality of defocused configurations includes a first defocused configuration having less overlap of the plurality of component beams 14 as compared to a second defocused configuration.

[0056] A payload 56 of the satellite 52 comprises a plurality of beamforming circuits 34, wherein each of the plurality of beamforming circuits 34 have beam weight circuits (38 or 42) corresponding to a subset of the plurality of component beam feeds 12. For a first beamforming mode, a controller 82 onboard the satellite 52 controls the user- link antenna system 16 to be configured into the first defocused configuration and controls the plurality of beamforming circuits 34 to apply a first beamforming configuration. The first beamforming configuration is such that each service beam 20 is formed as a composite of a first number of the component beams 14. That is, each service beam 20 is based on a cluster of component beam feeds 12, with the cluster size being the first number.

[0057] For a second beamforming mode, the controller 82 controls the user-link antenna system 16 to be configured into the second defocused configuration and controls the plurality of beamforming circuits 34 to apply a second beamforming configuration. The second beamforming configuration is such that each service beam 20 is formed as a composite of a second number of the component beams 14, wherein the second number is greater than the first number. Here, each service beam 20 is based on a cluster of component beam feeds 12, with the cluster size being the second number, such that second beamforming configuration can be understood as involving a larger cluster size that reflects or accounts for the fact that the greater defocusing associated with the second defocused configuration of the user- link antenna system 16 results in greater component beam overlap as compared to the first defocused configuration. Increasing or decreasing the component beam overlap changes the number of component beams 14 that contribute to the formation of any given service beam 20.

[0058] The first and second beamforming modes are respective ones among a plurality of beamforming modes, in at least one embodiment. Each beamforming mode among the plurality of beamforming modes is individually selectable by the controller 82, based on the controller 82being responsive to ground commands incoming to the satellite 52 from a ground segment 64 of the SCS 50. Additionally, or alternatively, the controller 82 in one or more embodiments is configured to select a particular beamforming mode based on onboard processing, such as detection that one or more component beam feeds 12 are inoperative.

[0059] The plurality of beamforming modes comprises the first and second beamforming modes and at least a third beamforming mode, in one or more embodiments. For the third beamforming mode, the controller 82 controls the user-link antenna system 16 to be configured into a focused configuration and controls the plurality of beamforming circuits 34 to apply a third beamforming configuration comprising a pass-through configuration such that each component beam 14 operates as a respective one of the service beams 20 and there is a one-to- one mapping of service beam signals 30 to component beams 14.

[0060] Payload complexity is advantageously reduced by defining a limited number of focusing configurations of the user-link antenna system 16 and by hardwiring or hardcoding the beamforming circuits 34 to accommodate a modest maximum cluster size corresponding to a maximum amount of antenna defocusing. In one embodiment, there are three beamforming configurations, one of them corresponding to a cluster size of one — i.e., no clustering — in which the user- link antenna system 16 is focused and each service beam 20 is a respective single component beam 14. Another one of the three beamforming configurations corresponds to a cluster size of three, in which the user- link antenna system 16 is defocused by a first amount and each service beam 20 is based on three overlapping ones among the component beams 14. A further and final one of the three beamforming configurations corresponds to a cluster size of seven, in which the user- link antenna system 16 is defocused by a greater second amount, and each service beam is based on seven overlapping ones among the component beams 14.

[0061] In this regard, it will be understood that component beams 14 included in any cluster are neighboring component beams in the sense that they overlap for formation of the service beam 20 associated with the cluster. Of course, any given component beam feed 12 may be included in more than one cluster, such as where the component beam feed 12 is involved in the formation of two or more service beams 20 at different carrier frequencies. In this context, the component beam feed 12 may be regarded as providing two component beams 14, with each such component beam 14 corresponding to a different carrier frequency.

[0062] The user-link antenna system 16 comprises, for example, a multi-feed reflector assembly comprising a feed array 10 that contains a plurality of component beam feeds 12, along with a reflector 18. First and second defocused configurations of the user- link antenna system 16 in this case comprise first and second defocused positions of the feed array 10. Here, “defocusedposition” refers to the offset of the feed array 10 along a focal axis of the reflector 18 in relation to the focus region of the reflector 18.

[0063] The feeder-link interface system 54 in one or more embodiments comprises an optical transceiver system configured to transmit or receive the one or more feeder link signals 74, 78 as one or more optical signals conveying the one or more feeder link signals. For example, the feeder-link interface system 54 includes an optical receiver configured to receive and demultiplex a feeder uplink signal 74 comprising a multiplexed optical signal in which different service beam signals 30 are modulated onto different optical earners at different optical wavelengths. Or, similarly, the feeder-link interface system 54 comprises an optical transmitter configured to transmit a feeder downlink signal 78 comprising a multiplexed optical signal in which different service beam signals 30 are modulated onto different optical carriers at different optical wavelengths.

[0064] In one or more other embodiments, the feeder-link interface system 54 is a feederlink antenna system, such as a phased array antenna. In such embodiments, the feeder link(s) 76 that communicatively couple the satellite 52 to a ground segment 64 of the SCS 50 are radiofrequency (RF) links. Such RF links may be in a different portion of the RF spectrum than is occupied for the user link.

[0065] The controller 82 onboard the satellite 52 is configured to control the plurality of beamforming circuits 34 to apply the first beamforming configuration by configuring the plurality of beamforming circuits 34 to operate with a first cluster size, the first cluster size being the number of neighboring component beam feeds 12 in the feed array 10 used for formation of each service beam 20 in the first beamforming configuration. The controller 82 is further configured to control the plurality of beamforming circuits 34 to apply the second beamforming configuration by configuring the plurality of beamforming circuits 34 to operate with a second cluster size that is larger than the first cluster size, the second cluster size being the number of neighboring component beam feeds 12 in the feed array 10 used for formation of each service beam 20 in the second beamforming configuration.

[0066] Each beamforming circuit 34 performs beamforming using a corresponding cluster of component beam feeds 12 from the feed array 10. The cluster size of the corresponding cluster is configurable and changes between the first and second bcamforming configurations.

[0067] For example, the controller 82 is configured to control the cluster size used by the plurality of beamforming circuits 34 in dependence upon the extent to which the user- link antenna system 16 is defocused. The first and second defocused configurations of the user-link antenna system 16 are respective ones among a plurality of focusing configurations of the userlink antenna system 16, in one or more embodiments. The plurality ranges stepwise from zero(no defocusing) or a minimum amount of defocusing to a maximum amount of defocusing. The maximum amount of defocusing defines the maximum cluster size to be accommodated by each one of the beamforming circuits 34

[0068] With respect to Figure 7, the payload 56 in one or more embodiments includes channelizers and / or switch arrangements configurable to control the mapping (connectivity) between feeds in the feeder-link interface system 54 and feeds in the user link antenna system 16. Connectivity may be frequency selective. The payload 56 further includes or is associated with a controller 82 that is configured to control the aforementioned connectivity, along with controlling the beamforming configuration of the beamforming circuits 34 in the payload 56. Such control is based on control commands, generated in the ground segment 64 of the SCS 50 or onboard the satellite 52.

[0069] A third beamforming mode that is used selectively by the SCS 50 in one or more embodiments corresponds to the user- link antenna system 16 being configured in a focused mode. For this mode, the plurality of beamforming circuits 34 is configured by the controller 82 for pass-through (or bypass) operation in which there is a one-to-one association between service beam signals 30 and component beam feeds 12. As such, each component beam 14 correspondingly operates as a respective one of the service beams 20. The controller 82 is configured to change from the third beamforming mode to the first or second beamforming mode responsive to onboard or ground-segment determination that one or more of the component beam feeds are inoperative. Or, vice versa, the controller 82 changes from the third beamforming mode to a selected one of the first or second beamforming modes, which can be understood as dynamically changing from operating with the user- link antenna system 16 in a focused configuration to operating with the user- link antenna system 16 with a selected amount of defocusing.

[0070] Figure 8 illustrates a method 800 of operation by a satellite 52 according to one embodiment. As before, the satellite 52 is configured for adaptive beamforming in an SCS 50, with the method comprising providing (Block 802) a plurality of service beams 20 for serving users in respective ones among a plurality of service beam areas 60 corresponding to the plurality of service beams 20. Each service beam 20 is associated with a respective service beam signal 30 carrying user traffic to or from the users served by the service beam 20.

[0071] In this context, the providing operation comprises forming (Block 804) each service beam 20 using a respective cluster of component beam feeds 12 in a feed array 10 of a user- link antenna system 16. Each component beam feed 12 provides a corresponding component beam 14 and all respective clusters have a defined cluster size. “Cluster size” refers to the number or count of component beam feeds 12 used for each service beam 20. Service beams 20 at the sameearner frequency use distinct clusters, while two or more service beams 20 at different carrier frequencies may share some or all of the same component beam feeds 12 in their respective clusters.

[0072] The method 900 further includes selecting (Block 806) a beamforming mode dynamically from at least first and second beamforming modes, and reconfiguring (Block 808) beamforming circuits 34 included in a payload 56 of the satellite 52, to change the cluster size according to the selected beamforming mode. For operation in the first beamforming mode, the method 900 includes configuring the user-link antenna system 16 in a first defocused configuration corresponding to a first amount of defocusing of the component beams 14 with a corresponding first amount of component beam overlap and configuring the beamforming circuits 34 to perform beamforming according to a first cluster size corresponding to the first amount of component beam overlap.

[0073] Similarly, for operation in the second beamforming mode, the method 900 includes configuring the user- link antenna system 16 in a second defocused configuration cones ponding to a greater second amount of defocusing of the component beams 14 with a correspondingly greater second amount of component beam overlap and configuring the beamforming circuits 34 to perform beamforming according to a larger second cluster size corresponding to the second amount of component beam overlap. For example, the first cluster size is three and the second cluster size is seven.

[0074] Of course, the first and second clusters sizes need not be three and seven and there may be multiple selectable cluster sizes. A nice aspect, however, is that limiting the maximum cluster size limits the signal splitting and signal combining requirements in the beamforming circuits 34. Thus, limiting the maximum selectable cluster size to a relatively small number of neighboring component beam feeds 12 in the feed array 10 yields beamforming circuit simplifications that translate into any one or more of lower cost, lower power consumption, lower size, or lower weight for the payload 56.

[0075] There may be a plurality of beamforming modes, with the method 900 including changing from a currently selected beamforming mode to a newly selected beamforming mode responsive to at least one of: ground commands incoming to the satellite 52 from a ground segment 64 of the SCS 50, or onboard control processing, such as by a controller 82 onboard the satellite 52. Here, the controller 82 comprises, for example, a microprocessor and supporting memory and other circuitry, wherein the microprocessor is specially adapted for operation as the controller 82 based on executing computer program instructions stored in the memory. In at least one example, the onboard control processing comprises determining that one or more of thecomponent beam feeds 12 is inoperative, or ground commands are received responsive to one or more component beam feeds 12 being inoperative.

[0076] Consider, for example, a case where each service beam 20 is based on one component beam 14 — i.e., a “focused” scenario. Loss of a component beam 14 means loss of the corresponding service beam 20, so changing to a beamforming configuration in which multiple component beam feeds 12 contribute to each service beam 20 is a form of compensation for or adapting to the loss of the component beam 14. Of course, adapting whether or to what extent the component beams 14 are defocused may be done responsive to changing service needs or for other reasons.

[0077] In another example embodiment, an SCS 50 is configured for adaptive beamforming, and it includes a satellite 52 that is configured to serve users via a plurality of service beams 20. Each service beam 20 illuminating a respective service beam area 60 containing one or more users and each service beam 20 is associated with a respective service beam signal 30 carrying traffic for the users served by the service beam 20. Further, each service beam 20 is based on one or more ones among a plurality of component beams 14 provided by a user-link antenna system 16 of the satellite 52. Each component beam corresponds to a component beam feed 12 in a feed array 10 of the user-link antenna system 16.

[0078] The SCS 50 further includes a ground segment 64 (or ground network) that includes a control system 80 that is configured to select a beamforming mode used for providing the plurality of service beams 20, from among two or more beamforming modes corresponding to different focusing configurations of the user- link antenna system 16. The two or more beamforming modes include a first beamforming mode associated with a first defocused configuration of the user- link antenna system 16. This first defocused configuration involves a first amount of defocusing of the component beams 14 and a corresponding first amount of component beam overlap. The two or more beamforming modes further include a second beamforming mode associated with a second defocused configuration of the user- link antenna system 16 in which there is a greater second amount of defocusing of the component beams 14 and a correspondingly greater second amount of component beam overlap.

[0079] As noted, in one or more embodiments, a controller 82 onboard the satellite 52 is configured to control a plurality of beamforming circuits 34 in a payload 56 of the satellite 52 to operate with a first beamforming configuration responsive to selection of the first beamfomiing mode. Here, the plurality of beamforming circuits 34 operates with a first cluster size in which each service beam 20 is formed using a neighboring cluster of component beam feeds 12 of the first cluster size. The controller 82 is further configured to control the beamforming circuits 34 to operate with a second beamforming configuration responsive to selection of the secondbeamforming mode. In this case, the plurality of beamforming circuits 34 operates with a larger second cluster size in which each service beam 20 is formed using a neighboring cluster of component beam feeds 12 of the second cluster size.

[0080] In one or more embodiments, a satellite configured for adaptive beamforming includes beamforming circuitry onboard the satellite that is coupled to a user-link antenna system. The beamforming circuitry is configured to: (i) group the component beam feeds of the user link antenna system a plurality of clusters (feed clusters), each feed cluster comprising a proper subset among the plurality of component beam feeds included in a feed array of the userlink antenna system; (ii) form, for each feed cluster, a corresponding service beam by combining signals associated with the component beams of that feed cluster; and (iii) serve user terminals within respective service beam coverage areas defined by the corresponding service beams. A controller adapts the beamforming circuitry to control the number of component beam feeds included in each feed cluster (control the feed cluster size) as a function of the extent of defocusing applied to the component beams, of the user-link antenna system.

[0081] Figure 9 illustrates an example configuration for the payload 56 of a satellite 52 configured for adaptive beamforming. A plurality of gateway (GW) feeds 100 and a plurality of user feeds 102 couple to a channelizer / s witch matrix 104 of the payload 56. Each feed (gateway or user) supports transmit and receive and may support multiple signal polarities. Although not shown in Figure 9, the GW feeds 100 may be associated with respective reflectors, such as steerable reflectors, and the user feeds 102 may be associated with a reflector in the user link antenna system 16.

[0082] The channelizer / switch matrix 104 determines the coupling or mapping between GW feeds 100 and user feeds 102. More particularly, the channelizer / switch matrix 104 maps input signals to respective ones of the beamforming circuits 34 and maps output signals from the beamforming circuits 34 to respective feeds. Here, an “input signal” refers to a signal incoming on one of the feeds (either GW or user), or frequency-filtered from a composite input signal incoming on one of the feeds (either GW or user). Further, “output signal” refers to a signal targeted for transmission from one of the feeds (either GW or user), as provided from a respective one of the beamforming circuits 34.

[0083] The plurality of bcamforming circuits 34 includes a plurality of divider circuits 106, routing circuitry 108, a plurality of beam weighting circuits 110 and an associated plurality of summing / combining circuits 112. The controller 82 or other control circuit provides control / configuration signaling to select or fix the configuration of the channelizer / switch matrix 104 and the beamforming circuits 34 — e.g., controlling GW-feed-to-user-feed mapping and controlling the cluster size used by the plurality of beamforming circuits 34. The routingcircuitry 108 allows any given user feed to participate in the formation of more than one service beam 20, e.g., a given user feed may participate in the formation of multiple service beams 20 at different frequencies. Note that the example details in Figure 9 assume a maximum cluster size of seven (7). Here, each “user feed” provides or is associated with a corresponding component beam used for beamforming towards or from a population of users, shown earlier as terminals 32.

[0084] In an example forward beamforming case with respect to the arrangement shown in Figure 9, assume a service beam signal 30 is received via a GW feed 100. That service beam signal 30 is coupled / switched via the channelizer / switch matrix 104 into a divider circuit 106, where it is divided into a number of signal copies, each copy to be transmitted from a respective user feed 102, after routing, weighting, and summing with other signal copies associated with other service beams 20 that use that same respective user feed 102.

[0085] In an example return beamforming case, assume that each one among a cluster of three user feeds 102 receives an uplink signal (which may be a composite of uplink signals from multiple UTs 32). Each such user-feed signal is coupled through the channelizer / switch matrix 104 through a respective divider circuit 106, e.g., for pass through into one of the weighting circuits 110, which applies respective beam weights to the user-feed signals from a set of beam weights computed for formation of a service beam 20. Summation of these respectively weighted user-feed signals by the weighting circuit 110 yields a service beam signal 30 (in the return direction) in which the SINR of uplink signals from UTs 32 that are within the beam coverage area of the service beam 20 is increased relative to UTs 32 outside the beam coverage area.

[0086] Figure 10 illustrates an example grid of component beam feeds / component beams, based on example arrangement of thirty-seven (37) component beams, numbered 1 through 37 in the diagram. Figure 11 corresponds to Figure 10 in the sense that it depicts an example set of fifty-four (54) service beams numbered “1” through “54,” each service beam formed from a respective cluster of three (3) component beams. Figure 11 also illustrates an example color map for reuse of a plurality of beam frequencies and polarizations over an overall service area encompassed by the set of service beams.

[0087] Figure 12 relates to Figures 10 and 11, illustrating that the signal to be conveyed by the service beam “53” is split into three copies (again assuming a cluster size of three) and applied to user feeds “33”, “34”, and “37”, with those numbers referring back to the user feed numbering seen in Figure 11. The signal to be conveyed by the service beam “54” is split into three copies (again assuming a cluster size of three) and applied to user feeds “34”, “35”, and “37”. One sees that user feeds “33” and “34” are shared between the two beams, which may be at different frequencies. Thus, in this limited example, the user feed “34” can be understood astransmitting a component beam at the carrier frequency associated with the service beam “53” and a component beam at the carrier frequency associated with the service beam “54.” The same holds for the user feed “37”.

[0088] With respect to the use of different frequencies, Figure 13 illustrates an example case where a feeder uplink signal incoming on a given gateway feed 100 comprises a plurality of RF chunks or segments, with each such segment being a respective service beam signal. Merely by way of example, the figure illustrates five RF chunks corresponding to five service beam signals. With example reference to Figure 9, the incoming feeder uplink signal flows into the channelizer / switch matrix 104, which filters it into its constituent parts — i.e., the five service beam signals at respective frequencies, with those respective service beam signals output from the channelizer / switch matrix 104 into the plurality of beamforming circuits 34, for weighting / combining. The channelizer / switch matrix 104 receives the output signals from the beamforming circuits 34 and map them onto the selected / configured user feeds 102. Like mapping and connectivity applies in the case of return- link beamforming. The channelizer / switch matrix 104 comprises digital circuitry in one or more embodiments and comprises analog circuitry in one or more other embodiments.

[0089] Broadly, disclosed methods and apparatuses embody an advantageous synergy between dynamic antenna focusing control and corresponding, complementary control of beamforming cluster sizes. In one or more embodiments, a satellite is equipped with a user-link antenna system that includes an array of component beam feeds, each configured to generate a corresponding component beam.

[0090] The user-link antenna system 16 of the example satellite 52 has a dynamically adjustable focusing configuration, which determines whether, and to what degree, the component beams are defocused. Increasing the defocus enlarges the beams and thus increases the overlap between neighboring component beams. The satellite 52 further carries multiple beamforming circuits, each simplified by being constrained to a maximum cluster size, where the cluster size is the number of component beam feeds that the circuit can jointly process to form a corresponding service beam. Each service beam carries user traffic within an associated service beam area on the ground. In certain embodiments, a channelizer / switch matrix assigns to each beamforming circuit a selectable cluster of component beam feeds and / or controls the association between beamforming circuits and feeder links, to the associations between service beams and gateway stations in a ground segment of the SCS. As noted, in one or more embodiments, the channelizer / switch matrix is an RF switch matrix that is in essence an analog channelizer that breaks up a given full spectrum into smaller chunks of spectrum and routes those spectrumchunks to different feeds. For example, the RF switch matrix breaks a 3.5 GHz spectrum into respective 500 MHz chunks.

[0091] Regardless of such details, the adaptive beamforming disclosed herein represents an advantageous synergy between the adjustable focusing of the user-link antenna and dynamic control of the beamforming cluster sizes. By coordinating these two mechanisms, the satellite communications system adapts the beamforming configuration to different amounts of component beam overlap, up to a maximum overlap that is compatible with the capped cluster size of the beamforming circuits.

[0092] Notably, modifications and other embodiments of the disclosed invention(s) will come to mind to one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention(s) is / are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of this disclosure. Although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

CLAIMSWhat is claimed is:

1. A satellite configured for adaptive beamforming in a satellite communications system, the satellite comprising: a feeder-link interface system configured to transmit or receive one or more feeder link signals conveying service beam signals, each service beam signal carrying traffic to or from users in a corresponding service beam area associated with a corresponding service beam; a user-link antenna system configured to provide the service beams, wherein the user-link antenna system includes a plurality of component beam feeds, each component beam feed providing a corresponding component beam, and wherein the user-link antenna system is selectively operable in a plurality of defocused configurations in which the component beams are defocused, the plurality of defocused configurations including a first defocused configuration having less overlap of the plurality of component beams as compared to a second defocused configuration; and a payload comprising a plurality of beamforming circuits, wherein each of the plurality of beamforming circuits have beam weight circuits c rresponding to a subset of the plurality of component beam feeds, the subset being limited to a defined maximum cluster size; and wherein: for a first beamforming mode, a controller onboard the satellite controls the userlink antenna system to be configured into the first defocused configuration and controls the plurality of beamforming circuits to apply a first beamforming configuration, the first beamforming configuration such that each service beam is formed as a composite of a first number of the component beams that is less than the maximum cluster size; for a second beamforming mode, the controller controls the user- link antenna system to be configured into the second defocused configuration and controls the plurality of beamforming circuits to apply a second beamforming configuration, the second beamforming configuration such that each service beam is formed as a composite of a second number of the component beams, wherein the second number is greater than the first number and less than or equal to the maximum cluster size.

2. 1'he satellite according to claim 1, wherein the first and second beamforming modes are respective ones among a plurality of beamforming modes that are individually selectable by the controller, based on the controller being responsive to ground commands incoming to the satellite from a ground segment of the satellite communications system.

3. The satellite according to claim 2, wherein the plurality of beamforming modes comprises the first and second beamforming modes and at least a third beamforming mode, and wherein, for the third beamforming mode, the controller controls the user-link antenna system to be configured into a focused configuration and controls the plurality of beamforming circuits to apply a third beamforming configuration comprising a pass-through configuration such that each component beam operates as a respective one of the service beams and there is a one-to-one mapping of service beam signals to component beams.

4. The satellite according to any one of claims 1-3, wherein the user- link antenna system comprises a multi-feed reflector assembly, and wherein the first and second defocused configurations comprise first and second defocused positions of a feed array comprising the plurality of component beam feeds.

5. The satellite according to any one of claims 1-4, wherein the feeder-link interface system comprises an optical transceiver system configured to transmit or receive the one or more feeder link signals as one or more optical signals conveying the one or more feeder link signals.

6. The satellite according to any one of claims 1-5, wherein the controller is configured to control the plurality of beamforming circuits to apply the first beamforming configuration by configuring the plurality of beamforming circuits to operate with a first cluster size, the first cluster size being the number of neighboring component beam feeds in a feed array used for formation of each service beam in the first beamforming configuration, and wherein the controller is configured to control the plurality of beamforming circuits to apply the second beamforming configuration by configuring the plurality of beamforming circuits to operate with a second cluster size that is larger than the first cluster size, the second cluster size being the number of neighboring component beam feeds in the feed array used for formation of each service beam in the second beamforming configuration.

7. The satellite according to any one of claims 1-6, wherein each beamforming circuit performs beamforming using a corresponding cluster of component beam feeds from the feedarray, and wherein a cluster size of the corresponding cluster is configurable up to the maximum cluster size and changes between the first and second beamforming configurations.

8. The satellite according to claim 7, wherein the controller is configured to control the cluster size used by the plurality of beamforming circuits in dependence upon an extent to which the user- link antenna system is defocused, and wherein the first and second defocused configurations of the user- link antenna system are respective ones among a plurality of focusing configurations of the user- link antenna system that range stepwise from zero or a minimum amount of defocusing to a maximum amount of defocusing.

9. The satellite according to claim 8, wherein the satellite includes one or more switch matrices configured to control a mapping between service beam signals and corresponding clusters of component beam feeds, for selection of which service beam signal is associated with which cluster of component beam feeds.

10. The satellite according to any one of claims 1-9, wherein a third beamforming mode corresponds to the user- link antenna system being configured in a focused mode and wherein the plurality of beamforming circuits are configured by the controller for pass-through operation in which there is a one-to-one association between service beam signals and component beam feeds and each component beam correspondingly operates as a respective one of the service beams, and wherein the controller is configured to change from the third beamforming mode to the first or second beamfomiing mode responsive to onboard or ground-segment determination that one or more of the component beam feeds are inoperative.

11. A method of operating a satellite with adaptive beamforming, the satellite configured for operation in a satellite communications system and the method comprising providing a plurality of service beams for serving users in respective ones among a plurality of service beam areas corresponding to the plurality of service beams, each service beam associated with a respective service beam signal carrying user traffic to or from the users served by the service beam, and wherein the providing comprises: forming each service beam using a respective cluster of component beam feeds in a feed array of a user-link antenna system, each component beam feed providing a corresponding component beam and all respective clusters having a cluster size; andselecting a beamforming mode dynamically from at least first and second beamforming modes, and reconfiguring beamforming circuits included in a payload of the satellite, to change the cluster size according to the selected beamforming mode; wherein, for operation in the first beamforming mode, the method includes configuring the user- link antenna system in a first defocused configuration corresponding to a first amount of defocusing of the component beams with a corresponding first amount of component beam overlap and configuring the beamforming circuits to perform beamforming according to a first cluster size corresponding to the first amount of component beam overlap; and wherein, for operation in the second beamforming mode, the method includes configuring the user- link antenna system in a second defocused configuration corresponding to a greater second amount of defocusing of the component beams with a correspondingly greater second amount of component beam overlap and configuring the beamforming circuits to perform beamforming according to a larger second cluster size corresponding to the second amount of component beam overlap.

12. The method according to claim 11, wherein the first cluster size is three and the second cluster size is seven.

13. The method according to claim 11 or 12, wherein there is a plurality of beamforming modes and wherein the method includes changing from a currently selected beamfomiing mode to a newly selected beamforming mode responsive to at least one of: ground commands incoming to the satellite from a ground network of the satellite communications system, or onboard control processing.

14. The method according to claim 13, wherein the onboard control processing comprises determining that one or more the component beam feeds is inoperative.

15. The method according to any one of claims 11-14, wherein there is a third bcamforming mode defined in addition to the first and second beamforming modes, and wherein the method includes selecting the third beamforming mode as a default mode or as a change from the first or second beamforming modes and operating the satellite in the third beamforming mode by:configuring the user- link antenna system in a focused configuration in which the component beams are focused and have a minimum component beam overlap; and configuring the beamforming circuits in a pass-through configuration that provides a one- to-one mapping of service beam signals to component beam feeds, such that each service beam comprises one component beam.

16. A satellite communications system configured for adaptive beamforming and comprising: a satellite configured to serve users via a plurality of service beams, each service beam illuminating a respective service beam area containing one or more users and each service beam associated with a respective service beam signal carrying traffic for the users served by the service beam, and each service beam based on one or more ones among a plurality of component beams provided by a user-link antenna system of the satellite, each component beam corresponding to a component beam feed in a feed array of the user-link antenna system; a ground segment comprising a control system configured to select a beamforming mode used for providing the plurality of service beams, from among two or more beamforming modes corresponding to different focusing configurations of the user- link antenna system, the two or more beamforming modes including a first beamforming mode associated with a first defocused configuration of the userlink antenna system in which there is a first amount of defocusing of the component beams and a corresponding first amount of component beam overlap, and further including a second beamforming mode associated with a second defocused configuration of the user- link antenna system in which there is a greater second amount of defocusing of the component beams and a correspondingly greater second amount of component beam overlap; and wherein the satellite includes a controller configured to control a plurality of beamforming circuits in a pay load of the satellite to operate with a first bcamforming configuration responsive to selection of the first bcamforming mode, in which the plurality of beamforming circuits operate with a first cluster size in which each service beam is formed using a neighboring cluster of component beam feeds of the first cluster size, and to operate with a second beamforming configuration responsive to selection of the second beamforming mode, in which the plurality of beamforming circuits operate with a larger secondcluster size in which each service beam is formed using a neighboring cluster of component beam feeds of the second cluster size.

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