System for processing directional signals

• US 6,329,947 B2
• Filed: 10/12/1999
• Issued: 12/11/2001
• Est. Priority Date: 10/12/1999
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Smith, Mark D.
• Primary Examiner(s): Phan, Dao
• Application Number:
  US09/416,477
• Publication Number:
  US 20010040526A1
• Time in Patent Office: 791 Days
• Field of Search: 342/25, 342/418, 342/417, 342/424, 342/457, 342/451, 342/462
• US Class Current: 342/418
• CPC Class Codes: G01S 13/933 of aircraft or spacecraft
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/28 using amplitude comparison of signals derived simultaneously from receiving antennas or antenna systems having differently-oriented directivity characteristics

Abstract

A system for calculating the bearing of a signal source, with a directional antenna, provides corrections for distortion, such as due to a small fuselage of the monitoring aircraft and the elevation angle of an intruder aircraft with respect to the monitoring aircraft. A correction is applied to the bearing estimate that is based on relevant factors, such as the fuselage size and the elevation angle of the intruder aircraft. The correction can be calculated or applied through the use of a look-up table, which may be either pre-selected or selected after calculation of the elevation angle of the intruder aircraft.

Claims

1. A method for calculating a bearing of a signal source using a directional antenna having a plurality of receiving elements, comprising the steps of:

selecting a correction model from a plurality of correction models;

receiving a plurality of incoming signals with the receiving elements;

processing the incoming signals to produce a plurality of electrical connection signals, wherein each of the electrical connection signals corresponds to a different quadrant of a polar coordinate system and each of the electrical connection signals has an amplitude;

selecting the electrical connection signal with the strongest amplitude;

selecting the electrical connection signal with the second strongest amplitude;

identifying a first quadrant that contains the electrical connection signal with the strongest amplitude;

identifying a second quadrant that contains the electrical connection signal with the second strongest amplitude;

calculating an amplitude difference between the electrical connection signal with the strongest amplitude and the electrical connection signal with the second strongest amplitude;

applying a correction to the amplitude difference in order to obtain the bearing of the signal source, wherein the correction is determined by the correction model, the first quadrant, and the second quadrant.

2. The method according to claim 1, wherein the correction model comprises a look-up table.

3. The method according to claim 1, wherein the signal source comprises an intruder aircraft.

4. A method for calculating a bearing of a signal source using a directional antenna having a plurality of receiving elements, comprising the steps of:

receiving a plurality of incoming signals with the receiving elements;

processing the incoming signals to produce a plurality of electrical connection signals, wherein each of the electrical connection signals corresponds to a different quadrant of a polar coordinate system and each of the electrical connection signals has an amplitude;

selecting the electrical connection signal with the strongest amplitude;

selecting the electrical connection signal with the second strongest amplitude;

identifying a first quadrant that contains the electrical connection signal with the strongest amplitude;

identifying a second quadrant that contains the electrical connection signal with the second strongest amplitude;

calculating an amplitude difference between the electrical connection signal with the strongest amplitude and the electrical connection signal with the second strongest amplitude;

calculating an elevation angle of the signal source;

selecting a correction model from a plurality of correction models based on the elevation angle;

applying a correction to the amplitude difference in order to obtain the bearing of the signal source, wherein the correction is determined by the correction model, the first quadrant, and the second quadrant.

5. The method according to claim 4, wherein the selecting step of selecting a model further comprises selecting the correction model based on a fuselage size of a monitoring aircraft.

6. A system for determining a bearing to a radio signal source, the system comprising:

a. a first antenna having a maximum sensitivity in a first direction and providing in response to the signal source a first signal having a first amplitude, the first antenna being associated with a first ground plane;

b. a second antenna a having a maximum sensitivity in a second direction different from the first direction and providing in response to the signal source a second signal having a second amplitude, the second antenna being associated with a second ground plane;

c. a third antenna having a maximum sensitivity in a third direction different from the first direction and different from the second direction, and providing in response to the signal source a third signal having a third amplitude, the third antenna being associated with a third ground plane; and

d. a computer coupled to the first, second, and third antennas that determines a largest amplitude signal and a next-largest amplitude signal selected in response to the first, second, and third signals;

determines a difference between the largest amplitude signal and the next-largest amplitude signal; and

determines the bearing in accordance with a linear function of the difference, wherein the linear function has a slope in accordance with a difference between the respective ground planes associated with the largest amplitude signal and the next-largest amplitude signal.

7. The system of claim 6 wherein the first, second, and third antenna are mounted on a fuselage and the difference between the ground planes corresponds to a respective curvature of the fuselage along the respective direction.

8. The system of claim 6 wherein two of the respective ground planes are effectively the same.

9. The system of claim 6 wherein the computer determines the bearing in accordance with instructions that implement the linear function as a formula.

10. The system of claim 6 wherein:

a. the computer comprises a look-up table; and

b. the look-up table comprises precalculated indicia of the linear function.

11. The system of claim 10 wherein the look-up table provides precalculated indicia of the linear function as indexed by the amplitude difference.

12. The system of claim 10 wherein the look-up table comprises:

a. first precalculated indicia of the linear function in accordance with a first slope, the first slope being in accordance with a first difference between the first ground plane and the second ground plane; and

b. second precalculated indicia of the linear function in accordance with a second slope, the second slope being in accordance with a second difference between the second ground plane and the third ground plane.

13. The system of claim 6 wherein:

a the computer comprises indicia of a plurality of slopes for determining the bearing; and

b. the computer is responsive to an input of the system to operate with a designated slope.

14. The system of claim 13 wherein the computer is responsive to the input upon association of the system with a particular fuselage.

16. The system of claim 13 wherein the indicia of the plurality of slopes comprises precalculated indicia of the linear function employing each slope of the plurality.

17. The system of claim 6 wherein:

a. the computer comprises indicia of a multiplicity of slopes, each slope for determining the bearing; and

b. the computer is responsive to an input of the system to operate with a designated plurality of slopes of the multiplicity.

18. The system of claim 17 wherein the computer is responsive to the input upon association of the system with a particular fuselage.

19. The system of claim 17 wherein the computer is responsive to the input from time to time during operation of the system.

20. The system of claim 17 wherein the designated plurality comprises indicia of slope in accordance with an elevation angle of horizon.

15. The system of clam 13 wherein the computer is responsive to the input from time to time during operation of the system.

21. A system for determining a bearing to a radio signal source, the system comprising:

a. a first antenna having a maximum sensitivity in a first direction and providing in response to the signal source a first signal having a first amplitude, the first antenna being associated with a first ground plane;

b. a second antenna having a maximum sensitivity in a second direction different from the first direction and providing in response to the signal source a second signal having a second amplitude, the second antenna being associated with a second ground plane;

c. a third antenna having a maximum sensitivity in a third direction different from the first direction and different from the second direction, and providing in response to the signal source a third signal having a third amplitude, the third antenna being associated with a third ground plane;

d. a ranging subsystem that determines a range to the signal source;

e. an altitude subsystem that determines an altitude of the system and an altitude of the signal source; and

f. a computer coupled to the first, second, and third antennas that determines a largest amplitude signal and a next-largest arm amplitude signal selected in response to the first, second, and third signals;

determines an amplitude difference between the largest amplitude signal and the next-largest amplitude signal;

determines an elevation angle of the signal source in accordance with the range to the signal source, the altitude of the system, and the altitude of the signal source; and

determines the bearing in accordance with a linger function of the amplitude difference, wherein the linear function has a slope in accordance with the elevation angle and in accordance with a difference between the respective ground planes associated with the largest amplitude signal and the next-largest amplitude signal.

22. The system of claim 21 wherein the altitude subsystem determines the altitude of the signal source in accordance with indicia of altitude provided by a transmission from the signal source.

23. The system of claim 21 wherein the first, second, and third antenna are mounted on a fuselage and the difference between the ground planes corresponds to a respective curvature of the fuselage along the respective direction.

24. The system of claim 21 wherein two of the respective ground planes are effectively the same.

25. The system of claim 21 wherein the computer determines the bearing in accordance with instructions that implement the linear function as a formula.

26. The system of claim 21 wherein:

a. the computer comprises a look-up table; and

b. the look-up table comprises precalculated indicia of the linear function.

27. The system of claim 26 wherein the look-up table provides precalculated indicia of the linear function as indexed by the amplitude difference.

28. The system of claim 26 wherein the look-up table comprises;

a. first precalculated indicia of the linear function in accordance with a first slope, the first slope being in accordance with a first difference between the first ground plane and the second ground plane; and

b. second precalculated indicia of the linear function in accordance with a second, the second slope being in accordance with a second difference between the second ground plane and the third ground plane.

29. The system of claim 21 wherein:

a. the computer comprise indicia of a plurality of slopes for determining the bearing; and

b. the computer is responsive to an input of the system to operate with a designated slope.

30. The system of claim 29 wherein the computer is responsive to the input upon association of the system with a particular fuselage.

31. The system of claim 29 wherein the computer is responsive to the input from time to time during operation of the system.

32. The system of claim 29 wherein the indicia of the plurality of slopes comprises precalculated indicia of the linear function employing each slope of the plurality.

33. The system of claim 21 wherein:

a. the computer comprises indicia of a multiplicity of slopes, each slope for effecting a respective linear function for determining the bearing; and

b. the computer is responsive to an input of the system to operate with a designated plurality of slopes of the multiplicity.

34. The system of claim 33 when the computer is responsive to the input upon association of the system with a particular fuselage.

35. The system of claim 33 wherein the computer is responsive to the input from time to time during operation of the system.

36. The system of claim 33 wherein the designated plurality comprises indicia of slope in accordance with an elevation angle of horizon.

37. A system for determining a bearing to a radio signal source, the system comprising;

a. a first antenna having a maximum sensitivity in a first direction and providing in response to the signal source a first signal having a first amplitude;

b. a second antenna having a maximum sensitivity in a second direction different from the firs direction and providing in response to the signal source a second signal having a second amplitude;

c. a ranging subsystem that determines a range to the signal source;

d. an altitude subsystem that determines an altitude of the system and an altitude of the signal source; and

e. a computer coupled to the first and second antennas that determines an amplitude difference between the first amplitude and the second amplitude;

determines an elevation angle of the signal source in accordance with the range to the signal source, the altitude of the system, and the altitude of the signal source; and

determines the bearing in accordance with a linear function of the amplitude difference, wherein the linear function has a slope in accordance with the elevation angle.

38. The system of claim 37 wherein the computer determines the bearing in accordance with instructions that implement the linear function as a formula.

39. The system of claim 37 wherein:

a. the computer comprises a look-up table; and

b. the look-up table comprises precalculated indicia of the linear function.

40. The system of claim 39 wherein the look-up table provides precalculated indicia of the linear function as indexed by the amplitude difference.

41. The system of claim 39 wherein the look-up table comprises:

a. first precalculated indicia of the linear function in accordance with a first slope, the first slope being in accordance with a first elevation angle; and

b. second precalculated indicia of the linear function in accordance with a second slope, the second slope being in accordance with a second elevation angle.

42. The system of claim 37 wherein;

a. the computer comprises indicia of a multiplicity of slopes for determining the bearing; and

b. the computer is responsive to an input of the system to operate with a designated plurality of slopes of the multiplicity.

43. The system of claim 42 wherein the computer is responsive to the input from time to time during operation of the system.

44. The system of claim 42 wherein the designated plurality comprises indicia of slope in accordance with an elevation angle of horizon.

45. A computer for use in aircraft, the computer comprising:

a. at least one input for accepting antenna signals; and

b. a memory comprising idicia of;

(1) a linear function having a slope; and

(2) instruction for determining a bearing, the instructions comprising;

determining an amplitude difference between a selected pair of the antenna signals;

determining a slope in accordance with indicia of a selected antenna signal of the pair of antenna signals; and

determining a bearing in accordance with the linear function, the amplitude difference, and the slope.

46. The computer of claim 45 wherein the step of determining a bearing further comprises determining the bearing in accordance with instructions that implement the linear function as a formula.

47. The computer of claim 45 wherein;

a. the memory further includes a look-up table; and

b. the step of determining the slope further comprises accessing the look-up table in accordance with indicia of the selected antenna signal.

48. The computer of claim 47 wherein the look-up table provides precalculated indicia of the linear function as indexed by the amplitude difference.

49. The computer of claim 47 wherein:

a the memory further comprises indicia of a plurality of slopes for determining the bearing; and

b. the computer is responsive to a second input to operate with a designated slope.

50. The computer of claim 49 wherein the computer is responsive to the second input upon association of the system with a particular fuselage.

51. The computer of claim 49 wherein the computer is responsive to the second input from time to time during operation of the system.

52. The computer of claim 49 wherein the indicia of the plurality of slopes comprises precalculated indicia of the linear function employing each slope of the plurality.

53. The computer of claim 47 wherein:

a. each antenna signal of the pair is associated with a respective antenna having a respective orientation; and

b. the look-up table provides precalculated indicia of the linear function as indexed by indicia of the respective orientation of each antenna associated with the pair of antenna signals.

54. The computer of claim 45 wherein:

a. the memory further comprises indicia of a multiplicity of slopes, each slope for determining the bearing; and

b. the computer is responsive to a second input to operate with a designated plurality of slopes of the multiplicity.

55. The computer of claim 54 wherein the computer is responsive to the second input upon association of the system with a particular fuselage.

56. The computer of claim 54 wherein the computer is responsive to the second input from time to time during operation of the system.

57. The computer of claim 54 wherein the designated plurality comprises indicia of slope in accordance with an elevation angle of horizon.