Broadband satellite payload architecture

A spacecraft includes a payload subsystem, the payload subsystem including a phased array of feed elements configured to illuminate an antenna reflector, a beam forming network (BFN) disposed proximate to the array of feed elements, and a plurality of power amplifiers disposed between the BFN and the array of feed elements. The BFN includes a plurality of variable amplitude and phase adjusting arrangements disposed between (i) m:1 power combiners that are communicatively coupled with the power amplifiers and (ii) at least one 1:n power splitter, where m is greater than 1, and n is greater than 2.

TECHNICAL FIELD

This invention relates generally to enabling an increased capacity broadband service from an Earth orbiting satellite, and particularly to a payload architecture for such a satellite.

BACKGROUND

The assignee of the present invention manufactures and deploys spacecraft for, inter alia, communications and broadcast services. Market demands for such spacecraft have imposed increasingly stringent requirements on spacecraft payloads. For example, broadband service providers desire spacecraft with increased data rate capacity at higher EIRP through each of an increased number of user spot beans operable from geosynchronous orbit altitudes in communication with small (<1 meter aperture) user terminals.

To meet the more stringent demands, a spacecraft capable of providing at least 500 Gbps total data bandwidth distributed across at least one hundred spot beams is desirable. The payload, desirably, should provide an aggregate effective isotropic radiated power (EIRP) in the forward direction of greater than 85 dBw so as to provide compatibility with user terminals having aperture diameters in the range of 0.5-1 meter.

Meeting the foregoing performance objectives with a conventional payload architecture while conforming to the mass and volume constraints imposed by conventional launch vehicles is infeasible. Thus, there is a need for a high power broadband spacecraft with an improved payload architecture.

SUMMARY

The present inventor has appreciated that a payload architecture for a satellite may be operable to provide, from an altitude over the earth of approximately 35,000 km, a combined forward and return data throughput exceeding 500 gigabits per second.

According to some implementations, the spacecraft includes a payload subsystem, the payload subsystem including a phased array of feed elements configured to illuminate an antenna reflector, a beam forming network (BFN) disposed proximate to the array of feed elements, and a plurality of power amplifiers disposed between the BFN and the array of feed elements. The BFN includes a plurality of variable amplitude and phase (VAP) adjusting arrangements disposed between (i) m:1 power combiners that are communicatively coupled with the power amplifiers and (ii) at least one 1:n power splitter, where m is greater than 1, and n is greater than 2.

In some examples, the beamforming coefficients of one or more of the VAP adjusting arrangements may be correctable by ground command. A failure of one or more of the power amplifiers may be compensatable by correcting, by ground command, the beamforming coefficients of one or more of the VAP adjusting arrangements.

In some examples, the plurality of power amplifiers in the beamforming network may be proximate to the array of feed elements.

In some examples, each VAP adjusting arrangement may be communicatively coupled with a single element, and at least some feed elements are coupled with multiple VAP adjusting arrangements. The phased array of feed elements may form a plurality of beams, each beam being formed by a center feed element, and six edge feed elements, the six edge feed elements being adjacent to and surrounding the center feed element. The center feed element may be communicatively coupled with a first VAP adjusting arrangement and each of the six edge feed elements may be communicatively coupled by way of respective ones of the m:1 power combiners with at least two VAP adjusting arrangements associated with adjacent beams that share the edge element.

In some examples, the respective ones of the m:1 power combiners may be proximate to the center feed element.

In some examples, m may equal 2 or 3 and n may equal 7.

In some examples, the BFN is configured to provide soft redundancy by allowing reoptimization of the beamforming coefficients in case of a failure of at least one of the power amplifiers.

According to some implementations, an apparatus includes a payload subsystem for a spacecraft, the payload subsystem including a phased array of feed elements configured to illuminate an antenna reflector, a beam forming network (BFN) disposed proximate to the array of feed elements, and a plurality of power amplifiers disposed between the BFN and the array of feed elements. The BFN includes a plurality of variable amplitude and phase (VAP) adjusting arrangements disposed between (i) m:1 power combiners that are communicatively coupled with the power amplifiers and (ii) at least one 1:n power splitter, where m is greater than 1, and n is greater than 2.

DETAILED DESCRIPTION

It will be understood that when a feature is referred to as being “connected” or “coupled” to another feature, it can be directly connected or coupled to the other feature, or intervening features may be present. Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. It will be understood that although the terms “first” and “second” are used herein to describe various features, these features should not be limited by these terms. These terms are used only to distinguish one feature from another feature. Thus, for example, a first user terminal could be termed a second user terminal, and similarly, a second user terminal may be termed a first user terminal without departing from the teachings of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The symbol “/” is also used as a shorthand notation for “and/or”.

The terms “spacecraft”, “satellite” and “vehicle” may be used interchangeably herein, and generally refer to any orbiting satellite or spacecraft system.

Referring toFIG. 1, a simplified diagram of a satellite communications network100is illustrated. The network includes a satellite111, which may be located, for example, at a geostationary orbital location or in a low earth orbit. The satellite111may be communicatively coupled, via at least one feeder link antenna121, to at least one gateway112and, via at least one user link antenna122to a plurality of user terminals116. The at least one gateway112may be coupled to a network such as, for example, the Internet. Each gateway112and the satellite111communicate over a feeder link113, which has both a forward uplink114and a return downlink115. The user terminals116and the satellite111communicate over a user link117that has both a forward downlink118and a return uplink119. The user link117and the feeder link113may operate in respective assigned frequency bands, referred to herein as the “user link band” and the “feeder link band”.

The satellite111will ordinarily include a payload subsystem for, inter alia, processing signals traveling between the at least one gateway112and the user terminals116. In some implementations, an architecture of the payload subsystem may provide dual frequency conversion and/or bandwidth aggregation as described in U.S. Pat. No. 8,660,482, assigned to the assignee of the present invention, the disclosure of which is hereby incorporated into the present application in its entirety. Put briefly, in such an architecture, the user link117includes a large number of small spot user antenna beams (“user spot beams”), not illustrated, communicatively coupled, on board the satellite111, to the feeder link113consisting of a smaller number of gateway antenna beams, not illustrated. The feeder link113accommodates substantially more bandwidth than any single user spot beam. The gateway antenna beam may carry aggregated signals for distribution to any of the large number of user spot beams. Feeder link signals received at a feed array of the at least one satellite feeder link antenna121may be amplified and down converted on the satellite as a block, to an intermediate frequency band substantially lower than the user link band. Advantageously, the down conversion is performed proximate to the satellite feeder link antenna feed array. The aggregated, down-converted signals may then be routed, at the intermediate frequency, through the satellite and processed for transmission by a satellite user link antenna feed array over the user link117. Prior to transmission over the user link117, the aggregated, down-converted signals are up-converted to the user link band. Advantageously, the up-conversion is performed proximate to the satellite user link antenna feed array. In an embodiment, intermediate frequency signals may be distributed, filtered and up-converted to the user link frequency band prior to high power amplification. The amplified signals may then be coupled with the individual user beam downlink feed elements of the user link antenna feed array.

In some implementations, feeder link signals received at the feed array of the at least one satellite feeder link antenna121may be amplified and directly converted to the user link band.

One or more of the at least one feeder link antenna121and the user link antenna122may include a high efficiency multi-beam antenna (MBA) system of the type disclosed in U.S. Pat. Pub. No. 2013/0154874 assigned to the assignee of the present invention, the disclosure of which is hereby incorporated into the present application in its entirety. The MBA antenna system may generate a set of user spot beams that define a coverage area which may extend, in aggregate, across a large region on the ground. MBA's providing wide-band communications services from a geosynchronous satellite conventionally provide contiguous coverage of a region with a triangular lattice of overlapping circular antenna beams. These beams are conventionally formed using a close packed array of circular feed elements, also centered on a triangular lattice. The feed elements illuminate, for example, offset fed parabolic reflectors to provide the desired antenna gain. The MBA system may provide within the coverage region, a number of spot beams, using a “multi-color”, frequency reuse scheme. The antenna reflector may be conventionally sized so as to produce a circular beam that is 4-4.5 dB down at the edge of coverage or may be substantially oversized with respect to that conventional design criterion. In some implementations, a subreflector may be disposed between the feed element array and the reflector. Moreover, the reflector and/or the subreflector, may not necessarily be parabolic, one or both may be otherwise shaped and/or flat.

In accordance with the presently disclosed techniques, a payload architecture for a satellite may be operable to provide, from an altitude over the earth of approximately 35,000 km, a combined forward and return data throughput exceeding 500 gigabits per second. In some implementations, the payload architecture may be configured such that the forward uplink114and the forward downlink118are operable to provide approximately 150 GHz of bandwidth from the at least one gateway112to the user terminals116, while also being configured such that the return uplink119and the return downlink115are operable to provide approximately 75 GHz of bandwidth from the user terminals116to the gateway112.

In some implementations, usage of aggregate available bandwidth is optimized by frequency reuse of spatially isolated user downlink and uplink antenna beams. Spatial isolation may be achieved using a “multi-colored” frequency plan such that adjacent user beams do not operate with the same frequency sub-band and polarization. The frequency plan may be chosen to provide the desired bandwidth per beam and the antenna architecture may be chosen to provide both high efficiency and high co-polarized carrier-to-interference ratio (C/I) required to optimize capacity of an RF link design.

In some implementations, the bandwidth allocated to the feeder link113may be many times larger than the bandwidth allocated to the user link117in order to minimize the total number of gateways112required by the system100. For example, for a frequency plan that will support 1 GHz of forward downlink bandwidth for each user beam and 10 GHz of forward uplink bandwidth for each gateway, a gateway will support 10 user beams. An aggregate forward link bandwidth of 150 GHz would then require approximately 15 gateways112.

Thus, the presently disclosed techniques contemplate a payload architecture that is operable to provide hundreds of channels to and from hundreds of user beams and dozens of gateway beams. The spacecraft payload subsystem is contemplated to be operable with, low cost (small, low power) user terminals and conventional gateways. The spacecraft, including the payload subsystem, is sized to be compatible for launch by conventional launch vehicles, such as Proton, Ariane, Sea Launch, Atlas, Delta, H2, and Falcon. These objectives may be achieved by one or more of the following disclosed innovative techniques.

In some implementations, the allocated user bandwidth may be divided into three frequency sub-bands, where each sub-band is assigned to both polarizations producing six channel/polarization combinations (“colors”). Each beam may be assigned two opposite polarizations with different frequency sub-bands. This two of six color frequency plan provides three color reuse in each polarization and maximizes the bandwidth per beam at ⅔ of the allocated user spectrum for each beam in a contiguous cluster of beams. This frequency plan approach also provides the maximum capacity performance while substantially avoiding cross polarization interference.

In some implementations, the payload subsystem includes one or more MBA's. Each MBA may include a single parabolic reflector, fed by an active phased array of feed elements including one hundred or more feed elements. In some implementations, a sub-reflector may be disposed between the reflector and the active phased array. A number of spot beams may be formed, where each spot beam is formed by a respective cluster of feed elements. For example, referring now toFIG. 2, a first beam201may be formed by a cluster of seven feed elements, including feed element A, which may be referred to as the center feed element, and feed elements B, C, D, E, F, and G, which are adjacent to and surround feed element A. As will be described below, a large number of beams, similar to the first beam201may be provided by a feed array, such that the beams are contiguous or overlapping.

In the illustrated example, the first beam201is defined by seven approximately hexagonal regions, each associated with a respective feed element A, B . . . , G. However, it should be noted that feed element A, B . . . , G may have a square, rectangular, hexagonal or circular cross section, for example. Furthermore, the quantity of feed elements making up the beam, referred to generically herein as ‘n’, may be smaller or greater than seven. For example,FIG. 3illustrates an implementation where n=19.

For a given diameter of a reflector of an MBA system, a beam diameter and spacing may be determined for any particular desired operating frequency and antenna efficiency. An oversized reflector with respect to the chosen beam size may be used to increase antenna efficiency and beam isolation. Spacing between feed elements in the feed element array may be determined by the maximum size of the feed element for efficient beam forming and the size of the electronics package that is able to fit behind the feed elements.

The focal length and offset of the reflector may be selected so as to produce a beam deviation factor such that the beam spacing in the focal plane is the square root of ‘N’ times the feed element spacing in the focal plane, where ‘N’ is the ratio of feed elements to formed beams in a sufficiently large triangular lattice of feed elements.

A better understanding of the term ‘N’ may be obtained by referring now toFIG. 4, which illustrates an example of a beam pattern where N=3. In the illustrated implementation, 37 feed elements include 13 center beam feed elements401(i), each associated with a formed beam402(i). Each center beam feed element may be related to a corresponding feed element, for example, center beam feed element401(14) corresponds with feed element14. The illustrated beam pattern, corresponding to 13 center beam feed elements, may represent a small subset of a contemplated spot beam coverage pattern that may include one hundred or more spot beams. It will be appreciated that, in the illustrated implementation, the number of feed elements (37) is approximately 3 times the number of center beam feed elements (13) and that for a sufficiently large number of feed elements arranged in the illustrated lattice pattern ofFIG. 4, the ratio of feed elements to center beam feed elements will closely approach three. Put another way, ‘N’ is simply the ratio of the area of a (dashed line) ‘beam’ hexagon410to the area of a (solid line) ‘element’ hexagon420.

Further illustrative examples are provided inFIG. 5, which depicts, in Detail A, an arrangement in which n=7 and N=4 and, in Detail B, an arrangement in which n=19 and N=12. Arrangements where n=37, and N=27 and similar, larger arrangements are also within the contemplation of the present disclosure.

In some implementations, the combination of n and N may be chosen to provide sufficient element beam pattern overlap to enable soft redundancy for element amplifiers. As used herein and in the claims the term “soft redundancy” means that in the event that one of the n amplifiers used to form the antenna beam fails, the beam shape may be reformed by re-optimizing the amplitude and phase coefficients to the remaining n−1 elements. Soft redundancy may obviate a need to provide spare amplifiers.

In some implementations, a high capacity broadband satellite may be configured to provide a user link by way of a large number of spot beams arranged in a triangular lattice similar to one or more of the examples illustrated hereinabove. Referring now toFIG. 6, satellite600may include a main body611and an offset fed reflector622. The reflector622is illuminated by a feed array624, which may be configured as an active phased array having some tens or hundreds of feed elements. For clarity of illustration, a single reflector620and a single feed array624, are depicted inFIG. 6, but it will appreciated that the satellite600may include two or more antennas systems each including a respective reflector and feed array.

Referring now toFIG. 7, a simplified block diagram of a portion of a payload subsystem of spacecraft600is illustrated. For simplicity of illustration, only forward path700of the payload system is illustrated. Data processed via forward path700may include data for each of a plurality of user spot beams. The data may have been modulated onto carriers at the gateway (not illustrated), and aggregated prior to being received by a feeder link antenna721.

At the spacecraft, the aggregated forward path data may be block down converted711to an intermediate frequency (IF). In an embodiment, the IF may be a substantially lower frequency than the frequency assigned to the user link. Following this down-conversion, the aggregated forward path data may be transported to the vicinity of the user link spot beam feed array. There, bandwidth for each individual user spot beam may be filtered out of the aggregate, up-converted to the user link frequency, and forwarded to a beam forming network (BFN)740.

Referring now to Detail A ofFIG. 7, the BFN740, in the illustrated implementation, is configured to perform seven element beam forming with three feed element spacing (n=7; N=3). The BFN740includes 1:7 power splitter742, commandable variable amplitude and phase (VAP) adjusting arrangements744, and 3:1 power combiners746. In some implementations, one or more of the VAP adjusting arrangements744may be implemented as a monolithic microwave integrated circuit (MMIC) chip. Each of seven VAP adjusting arrangements744is communicatively coupled with a single power amplifier750, which is communicatively coupled with a single corresponding feed element760. At least one power amplifier750may be communicatively coupled with the multiple VAP adjusting arrangements744by way of a respective 3:1 power combiner746, as described in more detail below in connection withFIGS. 8A and 8B.

Referring now toFIG. 8A, an illustration of an example beam forming network840will be described. In the illustrated example, the beam forming network840is configured to form the spot beam lattice pattern illustrated inFIG. 8B. For convenience, therefore, each feed element860illustrated inFIG. 8Ais assigned an identification number, (i.e., 6, 5, 10, 11, etc.) that corresponds to a numbered cell in the spot beam lattice pattern illustrated inFIG. 8B. The focal length and offset of the reflector620may be selected so as to produce a beam deviation factor such that the beam spacing in the focal plane is the square root of ‘N’ times the feed element spacing in the focal plane, where ‘N’ is the ratio of feed elements to formed beams in a sufficiently large triangular lattice of feed elements.

The beam forming network840includes 1:7 power splitters842. In the illustrated implementation, each of Beam1, centered at feed element19, Beam2, centered at feed element11, and Beam3, centered at feed element27, is associated with a respective 1:7 power splitter842. Each 1:7 power splitter842is communicatively coupled with seven respective VAP adjusting arrangements844. For convenience of nomenclature, each VAP adjusting arrangement is assigned an identifying number of the form X0Y, where X indicates the beam number associated with the 1:7 power splitter842to which the VAP adjusting arrangement844is coupled, and Y is an integer serial number 1, 2, 3, 4, 5, 6, or 7.

Each VAP adjusting arrangement844is communicatively coupled with a single 3:1 power combiner846. However, at least some of the 3:1 power combiners846are communicatively coupled with multiple VAP adjusting arrangements844. As a result, at least some feed elements860are communicatively coupled with multiple VAP adjusting arrangements844. In the illustrated implementation, for example, center feed elements11,19, and27are each communicatively coupled with a single VAP adjusting arrangement (respectively, VAP204, VAP104and VAP304, while “edge” feed elements (adjacent to and surrounding a respective center feed element) are communicatively coupled with three VAP adjusting arrangements844. A respective 3:1 power combiner846associated with each edge element of a beam may be proximate to the center feed element of the beam.

The above-described approach reduces the total number of feed elements for a contiguous cluster of beams formed with a single reflector while maintaining the same n-element feed cluster geometry required to form any single beam.

In some implementations, power amplifiers850may include solid-state power amplifiers (SSPAs). Each SSPA850may be disposed between and proximate to the 3:1 power combiners846and the feed elements860. In some implementations, the SSPA850may include gallium nitride semiconductors. Each feed element860may be communicatively coupled with a separate power amplifier850for each respective polarization at which the feed element860is intended to operate. The power amplifiers850, in some implementations, may be located very near to the feed elements860in order to minimize line losses.

Moreover, referring again toFIG. 7, it is contemplated that up converters731, the BFN740, and the power amplifiers750may be located in close proximity to the array of feed elements760. As a result, output waveguides, that would be required in the absence of the present teachings, may be omitted from forward path700. As a result, the number of components, mass and complexity of a phased array are all reduced.

According to the presently disclosed techniques, beamforming coefficients of beam amplitude and phase may be adjusted, by ground command, for example, for the beam location in the feed plane. As a result, relative to a single feed per beam multiple aperture predecessor design, a significant reduction in scan distortion and improvement in scan range and co-polarized C/I required by the two of six frequency plan may be obtained. In some implementations, this active phased array feed cluster architecture is coupled with a high efficiency single reflector MBA. The commandable nature of the presently disclosed BFN provides soft redundancy by allowing re-optimization of the beamforming coefficients in case of a power amplifier failure, thereby permitting to omit R-switches that would ordinarily be contemplated by the prior art.

Although the description above relates to a forward path of a satellite communication subsystem, it will be appreciated that the same architecture may be applied to the return path.

Thus, a high capacity broadband satellite payload architecture has been described. The foregoing merely illustrates principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise numerous systems and methods which, although not explicitly shown or described herein, embody said principles of the invention and are thus within the spirit and scope of the invention as defined by the following claims.