Interference rejection GPS antenna system

• US 7,009,557 B2
• Filed: 07/11/2001
• Issued: 03/07/2006
• Est. Priority Date: 07/11/2001
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Kirchofer, Richard, Nielsen, Raymond
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/902,095
• Publication Number:
  US 20030011514A1
• Time in Patent Office: 1,700 Days
• Field of Search: 342/359, 342/357.06, 342/357.08, 342/357.11, 342/357.14
• US Class Current: 342/359
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking
• CPC Class Codes: G01S 19/28 Satellite selection
• CPC Class Codes: G01S 19/36 relating to the receiver frond end
• CPC Class Codes: H01Q 21/065 Patch antenna 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 3/2605 Array of radiating elements provided with a feedback control over the element weights, e.g. adaptive arrays
• CPC Class Codes: H01Q 9/0471 Non-planar, stepped or wedge-shaped patch

Abstract

The present invention relates to a method and apparatus for selectively receiving radio frequency (RF) signals which utilizes an array of antenna elements including a center antenna for receiving the RF signal, a navigational controller using coordinate information to determine pointing vectors pointing to respective RF signal sources, and beam-forming electronics connected to the array of antenna elements and the navigational controller for forming reception lobes. Each reception lobe points in the direction of a determined pointing vector. For accurate and precise measurements, a constant phase center is maintained by adjusting the center antenna to the same phase shift for each of the lobes and steering the lobes by adjusting the phase shift of the antenna elements surrounding the center antenna.

Claims

1. Apparatus for selectively receiving radio frequency (RF) signals, comprising:

an array of antenna elements for receiving the RF signals, said array including a center antenna and a group of antenna elements surrounding the center antenna;

a navigational controller for determining pointing vectors, each vector pointing to a respective source of a received RF signal, from coordinate information; and

beam-forming electronics connected to the array of antenna elements and the navigational controller for forming a reception lobe in the direction of each pointing vector, wherein a phase center for the array of antenna elements is maintained by adjusting the center antenna to a same phase shift for each of the reception lobes.

2. The apparatus of claim 1, wherein the elements of the array comprise dual-frequency patch elements.

3. The apparatus of claim 1, wherein the beam-forming electronics form the reception lobes by adjusting the phase of the elements of the array.

4. The apparatus of claim 1, further comprising an antenna output from the beam-forming electronics.

5. The apparatus of claim 1, wherein the elements of the array are arranged in a symmetric configuration.

6. The apparatus of claim 1, wherein the elements of the array are arranged in a radially symmetric configuration.

7. The apparatus of claim 1, wherein the RF signals comprise signals from at least one global positioning system (GPS) satellite and the pointing vector comprises a satellite pointing vector.

8. The apparatus of claim 1, wherein the reception lobes have a width of 25 degrees or less.

9. The apparatus of claim 1, wherein said beam-forming electronics comprises:

at least one phase shifter connected to the array of antenna elements for shifting the phase of the received RF signal; and

a beam-forming algorithm processor connected to the at least one phase shifter and the navigational controller for calculating an amount by which the at least one phase shifter shifts the received RF signals in response to the pointing vector.

10. The apparatus of claim 9, wherein the at least one phase shifter comprises an array of phase shifters.

11. The apparatus of claim 10, wherein said beam-forming electronics comprises a means for summing outputs of each phase shifter of the array of phase shifters.

12. The apparatus of claim 11, further comprising an antenna output from said means for summing outputs of each phase shifter, of the beam-forming electronics.

13. The apparatus of claim 9, wherein the output of the phase shifters constructively amplifies selectively received RF signals by an amplification factor by aligning selective reception lobes of each element of the array of antenna elements, while interference signals from undesired sources are combined by the phase shifters in a random manner, such that the interference signals experience essentially no amplification.

14. The apparatus of claim 13, wherein the constructive amplification amplifies desired, selectively received RF signals by at least 12 dB.

15. The apparatus of claim 13, wherein the interference signals have a strength of −

30 dB.

16. The apparatus of claim 1, wherein the navigational controller comprises:

a receiver for receiving RF signal transmissions conveying absolute position information of the apparatus;

an inertial measurement unit (IMU) for measuring changes in relative position of the apparatus; and

a navigation processor connected to the receiver, the IMU, and the beam-forming algorithm processor for receiving absolute and relative position information from the receiver and the IMU, and calculating the pointing vector from the absolute and relative position information, and transmitting the pointing vector to the beam-forming algorithm processor.

17. The apparatus of claim 16, wherein the receiver comprises a GPS receiver.

18. The apparatus of claim 17, wherein the GPS receiver contains satellite almanac information comprising location information of satellites.

19. The apparatus of claim 16, wherein the IMU comprises a vibrational sensor.

20. The apparatus of claim 16, wherein the IMU comprises a gyroscopic sensor.

21. The apparatus of claim 20, wherein the gyroscopic sensor comprises a laser gyroscopic sensor.

22. The apparatus of claim 16, wherein the IMU comprises an accelerometer.

23. The apparatus of claim 16, wherein the IMU is a micro-machined device.

24. The apparatus of claim 16, wherein the relative position information comprises a change in velocity.

25. The apparatus of claim 16, wherein the relative position information comprises a change in angle.

26. The apparatus of claim 1, wherein the navigation processor is connected to a host.

27. The apparatus of claim 26, wherein the connection with the host provides input and output (I/O) communications between the navigation processor and the host.

28. The apparatus of claim 1, wherein the pointing vector is updated using a pre-determined refresh rate.

29. The apparatus of claim 28, wherein refresh rate is 200 Hz.

30. The apparatus of claim 28, wherein the refresh rate corresponds to an update rate of the reception lobes.

31. A method for selectively receiving radio frequency (RF) signals, comprising the steps of:

receiving RF signals using an array of antenna elements including a center antenna and a group of antenna elements surrounding said center antenna;

determining pointing vectors from coordinate information, each pointing vector pointing to a source of one of the received RF signals; and

forming a reception lobe in the direction of each pointing vector, wherein the center antenna is adjusted to a same phase shift for each reception lobe to maintain a phase center for the array of antenna elements.

32. The method of claim 31, wherein the step of determining pointing vectors determines a satellite pointing vectors.

33. The method of claim 31, wherein the step of determining is accomplished using actual coordinate information.

34. The method of claim 31, wherein the step of determining is accomplished using relative coordinate information.

35. The method of claim 31, wherein the step of forming the reception lobes is accomplished by shifting the phase of an RF signal received in the step of receiving.

36. The method of claim 31, further comprising the steps of:

shifting the phase of signals from antenna elements in the array to obtain phase-shifted signals; and

summing the phase-shifted signals obtained in the step of shifting in a manner such that desired RF signals in the direction of each pointing vector are constructively summed, providing an effective amplification of the desired RF signals, while interference RF signals not in the direction of the pointing vectors are not effectively amplified due to random shifting of the interference RF signals.

37. Apparatus for selectively receiving radio frequency (RF) signals, comprising:

an array of antenna elements for receiving RF signals, said array including a center antenna and a group of antenna elements surrounding the center antenna;

a navigational controller comprising;

an inertial measurement unit (IMU) for measuring changes in relative position of the apparatus; and

a processor for determining pointing vectors based at least in part on coordinate information and the measured changes, wherein each said vector points to a source of a respective received RF signal; and

beam-forming electronics connected to the array of antenna elements and the navigational controller for forming a reception lobe of the antenna array for each determined pointing vector, wherein a phase center for the array of antenna elements is maintained by adjusting the center antenna to a same phase shift for each lobe.

38. The apparatus of claim 37, wherein the elements of the array comprise dual-frequency patch elements.

39. The apparatus of claim 37, wherein the beam-forming electronics form the reception lobes by adjusting the phase of the elements of the array.

40. The apparatus of claim 37, further comprising an antenna output from the beam-forming electronics.

41. The apparatus of claim 37, wherein the elements of the array are arranged in a symmetric configuration.

42. The apparatus of claim 37, wherein the elements of the array are arranged in a radially symmetric configuration.

43. The apparatus of claim 37, wherein the RF signals comprise signals from at least one global positioning system (GPS) satellite and the pointing vectors comprise a satellite pointing vectors.

44. The apparatus of claim 37, wherein each reception lobe has a width of 25 degrees or less.

45. The apparatus of claim 37, wherein said beam-forming electronics comprises:

at least one phase shifter connected to the array of antenna elements for shifting the phase of the received RF signals; and

a beam-forming algorithm processor connected to the at least one phase shifter and the navigational controller for calculating an amount by which the at least one phase shifter shifts the received RF signals in response to the pointing vector.

46. The apparatus of claim 45, wherein the at least one phase shifter comprises an array of phase shifters.

47. The apparatus of claim 46, wherein said beam-forming electronics comprises a means for summing outputs of each phase shifter of the array of phase shifters.

48. The apparatus of claim 47, further comprising an antenna output from said means for summing outputs of each phase shifter, of the beam-forming electronics.

49. The apparatus of claim 45, wherein the output of the phase shifters constructively amplifies selectively received RF signals by an amplification factor by aligning selective reception lobes of each element of the array of antenna elements, while interference signals from undesired sources are combined by the phase shifters in a random maimer, such that the interference signals experience essentially no amplification.

50. The apparatus of claim 49, wherein the constructive amplification amplifies desired, selectively received RF signals by at least 12 dB.

51. The apparatus of claim 49, wherein the interference signals have a strength of −

30 dB.

52. The apparatus of claim 37, wherein the navigational controller further comprises a receiver for receiving RF signal transmissions conveying absolute position information of the apparatus.

53. The apparatus of claim 52, wherein the navigation processor is connected to the receiver and the IMU, determines a pointing vector by way of a calculation based on the actual and relative position information, and transmits the pointing vector to the beam-forming algorithm processor.

54. The apparatus of claim 52, wherein the receiver comprises a GPS receiver.

55. The apparatus of claim 54, wherein the GPS receiver contains satellite almanac information comprising location information of satellites.

56. The apparatus of claim 37, wherein the IMU comprises a vibrational sensor.

57. The apparatus of claim 37, wherein the IMU comprises a gyroscopic sensor.

58. The apparatus of claim 57, wherein the gyroscopic sensor comprises a laser gyroscopic sensor.

59. The apparatus of claim 37, wherein the IMU comprises an accelerometer.

60. The apparatus of claim 37, wherein the IMU is a micro-machined device.

61. The apparatus of claim 37, wherein the relative position information comprises a change in velocity.

62. The apparatus of claim 37, wherein the relative position information comprises a change in angle.

63. The apparatus of claim 37, wherein the navigation processor is connected to a host.

64. The apparatus of claim 63, wherein the connection with the host provides input and output (I/O) communications between the navigation processor and the host.

65. The apparatus of claim 37, wherein the pointing vector is updated using a pre-determined refresh rate.

66. The apparatus of claim 65, wherein refresh rate is 200 Hz.

67. A method for selectively receiving radio frequency (RF) signals, comprising the steps of:

receiving the RF signals using an antenna array having a center antenna;

determining actual coordinate information from information conveyed by the RF signals;

sensing at least one change between an inertial reference frame and a reference frame of the antenna;

determining relative coordinate information based on the sensed changes;

determining pointing vectors from the actual and the relative coordinate information, each said pointing vector pointing in the direction of a source one of the RF signals; and

for each pointing vector, forming a reception lobe in a direction of the pointing vector, wherein the center antenna is adjusted to a same phase shift for each reception lobe to maintain a phase center for the antenna.

68. The method of claim 67, wherein the step of determining pointing vectors determines a satellite pointing vectors.

69. The method of claim 67, wherein the received RF signals are transmitted from a global positioning system (GPS) satellite.

70. The method of claim 67, wherein the step of forming the reception lobe is accomplished by shifting the phase of an RF signal received in the step of receiving.

71. The method of claim 67, wherein a pointing vector is determined for different sources of the received RF signals, and the step of forming a reception lobe includes forming a reception lobe for each of the different RF sources.

72. The method of claim 71, wherein each of the plurality of RF signals sources corresponds to a different GPS satellite.

73. The method of claim 67, further comprising the steps of:

shifting the phase of signals from antenna elements in the array to obtain phase-shifted signals; and

summing the phase-shifted signals obtained in the step of shifting in a manner such that desired RF signals in the direction of each pointing vector are constructively summed, providing an effective amplification of the desired RF signals, while interference RF signals not in the direction of the pointing vectors are not effectively amplified due to random shifting of the interference RF signals.