SYSTEM FOR SIMPLIFICATION OF RECONFIGURABLE BEAM-FORMING NETWORK PROCESSING WITHIN A PHASED ARRAY ANTENNA FOR A TELECOMMUNICATIONS SATELLITE

• US 20100194629A1
• Filed: 07/18/2008
• Published: 08/05/2010
• Est. Priority Date: 07/20/2007
• Status: Active Grant

• Current Assignee: Astrium Limited (Airbus SE)
• Original Assignee: Astrium Limited (Airbus SE)
• Inventors: Craig, Antony Duncan, Stirland, Simon John
• Granted Patent: US 8,344,945 B2
• Time in Patent Office: Days
• US Class Current: 342/354
• CPC Class Codes: H01Q 1/288 Satellite antennas
• CPC Class Codes: H01Q 21/0006 Particular feeding systems
• CPC Class Codes: H01Q 21/061 Two dimensional planar arrays
• CPC Class Codes: H01Q 21/22 Antenna units of the array energised non-uniformly in amplitude or phase, e.g. tapered array or binomial array
• CPC Class Codes: H01Q 25/00 Antennas or antenna systems providing at least two radiating patterns arrangements for changing or varying the orientation or the shape of the directional pattern H01Q3/00
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H04B 7/18515 Transmission equipment in satellites or space-based relays

Abstract

A telecommunications satellite having a phased array antenna, wherein the beam-forming function within the phased array is simplified by partitioning it into two stages, in which the sub-array stage relates to a fixed, or infrequently changed, set of overlapping sub-arrays and the main stage provides the main pattern reconfiguration, typically in the form of multiple reconfigurable spot beams within a defined coverage region. The key advantage lies in the significant reduction in number of second stage beam-forming control points (at which independent amplitude and phase is applied) when compared with a conventional phased array (where amplitude and phase control is applied for each element of the array). The sub-array stage beam-forming may be implemented in analogue technology. The main beam-former may be implemented in digital technology, where the key processing functions of A/D or D/A conversion, frequency (de)multiplexing and digital beam-forming all scale with the number of control points.

Claims

1-37. -37. (canceled)

38. A method of beam-forming for an antenna of a telecommunications spacecraft, the antenna comprising a phased array antenna, and the antenna providing a plurality of communications beams within a predefined geographical region, the method comprising:

providing the phased array antenna as a plurality of antenna elements, each antenna element having an antenna element signal having a phase relationship and an amplitude relationship to the other element signals, and partitioning said antenna elements into a plurality of overlapping sub-arrays, each sub-array comprising a subset of all the antenna elements of the phased array, and at least some or all the antenna elements participating in more than one sub-array,

allocating to elements of each sub-array respective sub-array beam-forming weights, and allocating to each sub-array respective main beam-forming weights for said plurality of communications beams such that the composite radiation pattern of the antenna provides said plurality of communications beams within said region,

wherein said minimum antenna directivity value is determined by an optimisation process, involving changing, in iterations, of said sub-array beam-forming weights, together with determination of beam directivity at each said iteration.

39. A method according to claim 38, wherein said antenna is dimensioned to provide coverage over a global area, and said region comprises a limited part of said global area.

40. A method according to claim 39, wherein said region comprises two or more geographically separate areas.

41. A method according to claim 39, wherein said spacecraft is a geostationary satellite.

42. A method according to claim 38, wherein said beams are spot beams, each having at least a predetermined minimum antenna directivity value,

43. A method according to claim 38, wherein said main beam-forming weights are further optimised against a target combining edge-of-beam directivity and side lobe levels.

44. A method according to claim 38, wherein a set of weights is allocated to each sub-array, which is the same as sets assigned to the other sub-arrays.

45. A method according to claim 38, wherein said sub-array beam-forming weights are in analog form, and said main beam-forming weights are in digital form.

46. A phased array antenna, the antenna providing coverage over a predefined geographical region and providing a plurality of beams within said region, and comprising:

a plurality of antenna elements, each antenna element having an antenna element signal having a phase relationship and an amplitude relationship to the other element signals, and said antenna elements being partitioned into a plurality of overlapping sub-arrays, each sub-array comprising a subset of all the antenna elements of the phased array, and at least some of the antenna elements participating in more than one sub-array,

a sub-array beam-forming network which allocates to elements of each sub-array respective sub-array beam-forming weights, and

a main beam-forming network which allocates to each sub-array main beam-forming weights for each of said plurality of beams such as to produce said plurality of beams within said region

wherein sub-array beam-forming weights allocated to each sub-array have been optimised in order to attain a desired level of said directivity for said plurality of beams by an optimisation process wherein said sub-array beam-forming weights are changed in value in iterations, and at each iteration main beam-forming weight values allocated to said sub-arrays are determined.

47. A phased array antenna according to claim 46, wherein at least some of said beams has a said desired value of directivity, which is at least a predetermined minimum value.

48. A phased array antenna according to claim 46, wherein each said sub-array has an essentially similar set of sub-array beam-forming weights allocated to the other sub-arrays.

49. A phased array antenna according to claim 46, wherein said sub-arrays have essentially a similar geometric configuration.

50. A phased array antenna according to any one of claim 46, wherein said beams are communication beams and the phased array antenna is for a telecommunications spacecraft.

51. A phased array antenna according to any one of claims claim 46, wherein said antenna is dimensioned to provide coverage over a global area, and said region comprise a limited part, or more than one part, of said global area.

52. A phased array antenna according to claim 51, wherein said spacecraft is a geostationary satellite.

53. A phased array antenna according to any of claim 46, wherein the phase array antenna is formed in two dimensions and each sub-array extends in both dimensions.

54. A phased array antenna according to any of claim 46, wherein sub-array beam-forming weights allocated to each sub-array have values which have been optimised in order to attain a desired level of said directivity for said plurality of beams by an optimisation process wherein said sub-array beam-forming weights are changed in value in iterations, and at each iteration main beam-forming weight values allocated to said sub-arrays are determined.

55. A phased array antenna according to any of claim 46, wherein said sub-array beam-forming network assigns to each sub-array a set of weights, which is the same as sets assigned to the other sub-arrays.

56. A phased array antenna according to any of claim 46, wherein said sub-array beam-forming network includes a respective analog phase shifting means and a respective analog gain shifting means coupled to each antenna element.

57. A phased array antenna according to any of claim 46, wherein the phased array antenna has a receive function, and said sub-array beam-forming network includes, for each sub-array, a signal combining means for the element signals of the sub-array to provide a combined output signal to a sub-array output port.

58. A phased array antenna according to any of claim 46, wherein the phased array antenna has a receive function, and including down-converting means for down-converting sub-array output signals, or for down-converting individual element signals.

59. A phased array antenna according to claim 57, including analog to digital conversion means for digitising the output signals of each sub-array, frequency demultiplexing means for demultiplexing each sub-array output signal into a plurality (K) of channels signals, and a respective digital beam-forming network for each of said plurality (K) of channels, coupled to receive the respective channel signal from each sub-array output, and arranged to apply a complex weight to each said channel signal, and to sum the weighted channel signals, to provide a channel output signal.

60. A phased array antenna according to claim 59, including a plurality of digital beam-forming networks for one of said plurality (K) of channels, for providing a plurality of channel outputs for that channel for frequency reuse.

61. A phased array antenna according to any of claim 46, including analog to digital conversion means for digitising the output signals of each sub-array, and including FFT means coupled to receive the digitised signals and incorporating said main beam-forming network, and arranged to provide an output representing an array of spot beams.

62. A phased array antenna according to any of claim 46, wherein the sub-array beam-forming network is in digital form.

63. A phased array antenna according to any of claim 46, wherein both the main beam-forming network and the sub-array beam-forming network are in analog form.

64. A phased array antenna according to any of claim 46, wherein the phased array antenna has a transmit function, and for each sub-array, said sub-array beam-forming network includes, a signal distribution means coupled to an input port of the sub-array for providing the element signals of the sub-array.

65. A phased array antenna according to claim 64, including a respective digital beam-forming network for each of a plurality (K) of communications channels, and arranged to apply a complex weight to each said channel signal, digital to analog means for each channel signal for converting the channel signal to analog form, and multiplexing means for combining said channel signals, and coupled to each said input port.

66. An optimisation process for determining beam-forming parameters of a phased array antenna, the antenna providing coverage over a predefined geographical region, and a plurality of beams within said region, the antenna having a plurality of antenna elements, each antenna element providing an antenna element signal having a phase relationship and an amplitude relationship to the other element signals, and the antenna elements being partitioned into a plurality of overlapping sub-arrays, each sub-array comprising a subset of all the antenna elements of the phased array, and at least some of the antenna elements participating in more than one sub-array, the optimisation process comprising:

a first step in which sub-array beam-forming weights allocated to each sub-array are set to initial values, and

a second step in which main beam-forming weight values allocated to said sub-arrays are determined, to provide values of directivity at the locations of at least some of said beams; and

iterating said first and second steps, involving changing the values of said sub-array beam-forming weights, until a desired level of said directivity for said beams is attained.

67. An optimisation process according to claim 66, wherein, in said second step, said main beam-forming weight values are determined, to provide peak values of directivity at said locations.

68. An optimisation process according to claim 66, including determining overall antenna size based on spot beam directivity requirement.

69. An optimisation process according to claim 66, including determining individual element size/spacing based on size of grating lobe exclusion zone.

70. An optimisation process according to any one of claim 66, including determining spacing of the ports of said sub-arrays from maximum size of said region.

72. An optimisation process according to any of claim 66, wherein initial weights within each sub-array are set as either all equal or to maximise minimum sub-array directivity in said region.

73. An optimisation process according to any of claim 66, including a further optimisation wherein said main beam-forming weights are optimised against a target combining edge-of-beam directivity and side lobe levels.