Low probability of interception relative position determination system

• US 5,157,408 A
• Filed: 05/25/1990
• Issued: 10/20/1992
• Est. Priority Date: 05/25/1990
• Status: Expired due to Fees

• Current Assignee: NavCom Defense Electronics, Inc. (Transdigm Group Incorporated)
• Original Assignee: NavCom Defense Electronics, Inc. (Transdigm Group Incorporated)
• Inventors: Stahley, William, Wagner, Kenneth M., Van Cleave, James R.
• Primary Examiner(s): SWANN, TOD R
• Application Number:
  US07/528,807
• Time in Patent Office: 879 Days
• Field of Search: 342/399, 342/400, 342/401, 342/402, 342/403, 342/404, 342/405, 342/406, 342/49, 380/48, 380/33, 375/1
• US Class Current: 342/399
• CPC Class Codes: G01S 1/48 wherein the phase angle of the direction-dependent envelope signal is a multiple of the direction angle, e.g. for "fine" bearing indication TACAN

Abstract

A radio system for determining the range and bearing of mobile equipment, such as an aircraft, relative to reference equipment such as an aircraft carrier, with low probability of interception (LPI). The aircraft remains equipped with high power range and bearing determination equipment, such as TACAN equipment. Reference equipment transmits a LPI beacon, such as a pseudo noise code spread spectrum signal through a rotating beam antenna to amplitude modulate the beacon as a function of antenna orientation. The PN code is inverted as the antenna passes through a reference bearing. Mobile LPI equipment determines bearing and generates a high power signal, such as an emulated TACAN beacon signal. High power range and bearing equipment extracts bearing information from the emulated signal and display it. Range can be determined in a cooperative mode. Mobile LPI equipment transmits a LPI interrogation signal. Reference LPI equipment returns a LPI reply signal. Mobile LPI equipment determines range from the delay time, and generates a high power reply signal from which the high power range and bearing position determination means can extract and display range information.

Claims

1. A radio navigation system for determining the position of a mobile apparatus relative to a reference comprising:

position reference means for receiving an interrogation signal having low probability of interception (LPI TACAN) signal characteristic, for receiving standard TACAN interrogation signals, and for selectively transmitting either an LPI TACAN beacon signal or a standard TACAN beacon signal; and

mobile relative position determination means for selectively transmitting either an LPI TACAN interrogation signal or a standard TACAN interrogation signal, for selectively receiving either an LPI TACAN or a standard TACAN beacon signal, and for determining position relative to the position reference means from the selectively received LPI TACAN or standard TACAN beacon signal.

10. A system as in any of claims 1, 2, 3, 4, 4, 5, 6, 7, 8 or 9, wherein the reference means moves relative to the earth'"'"'s surface.

11. A system as in any of claims 1, 2 or 3 wherein an LPI TACAN signal is a spread spectrum signal.

12. A system as in claim 11 wherein an LPI signal is a pseudo noise coded spread spectrum signal.

13. A system as in claim 12 wherein:

the reference means further includes antenna means for transmitting a beacon with a rotating beam and means for inverting the PN code sequence periodically and synchronously with the antenna rotations; and

the mobile relative position reference means includes means for determining bearing from the amplitude of the beacon and from the inversion times of the PN code sequence of the beacon.

14. A system as in claim 13 wherein:

the reference means includes means for transmitting an LPI TACAN signal having a PN code sequence related in time with a PN code sequence of an LPI TACAN interrogation signal; and

the mobile relative position reference means includes means for determining the time delay between a transmitted TACAN LPI interrogation signal code sequence and the received LPI TACAN reply PN code sequence.

2. A radio navigation system for determining the position of a mobile apparatus relative to a reference comprising:

position reference means for receiving an interrogation signal having low probability of interception (LPI TACAN) signal characteristic, for receiving a standard TACAN interrogation signal and for selectively transmitting either a standard TACAN beacon signal or an LPI TACAN beacon signal; and

mobile relative position determination means for transmitting an LPI interrogation signal, for receiving an LPI TACAN beacon signal and for determining position relative to the reference means from the LPI TACAN beacon signal.

3. A radio navigation system for determining the position of a mobile apparatus relative a reference comprising:

position reference means for receiving an interrogation signal having low probability of interception (LPI TACAN) signal characteristic and for transmitting an LPI TACAN beacon signal; and

mobile relative position determination means for selectively transmitting either an LPI TACAN interrogation signal or a standard TACAN interrogation signal, for selectively receiving an LPI TACAN beacon signal or a standard TACAN beacon signal, and for determining position relative to the reference means from the selectively received LPI TACAN or standard TACAN beacon signal.

4. A radio navigation system for determining relative bearing of a mobile apparatus relative to a reference comprising:

relative bearing reference means for selectively transmitting either a beacon signal having low probability of interception signal characteristics or a standard TACAN beacon;

mobile relative bearing determination means for receiving the LPI TACAN beacon and for determining relative bearing to the reference means from the LPI TACAN beacon.

15. A system as in any of claims 4, 5 or 6 wherein an LPI signal is a spread spectrum signal.

16. A system as in claim 15 wherein an LPI signal is a pseudo noise coded spread spectrum signal.

17. A system as in claim 16 wherein:

the reference means further includes antenna means for transmitting an LPI TACAN beacon with a rotating beam and means for inverting the PN code sequence of the beacon periodically and synchronously with the antenna rotations; and

the mobile relative position reference means includes means for determining bearing from the amplitude of the beacon and from the inversion times of the PN code sequence of the beacon.

5. A radio navigation system from determining bearing of a mobile apparatus relative to a reference comprising:

bearing reference means for transmitting a beacon signal having low probability of interception (LPI TACAN) signal characteristics; and

mobile relative bearing determination means for selectively receiving either the LPI TACAN beacon signal or a standard TACAN beacon signal and for determining relative bearing to the reference means from the selectively received LPI TACAN or standard TACAN beacon signal.

6. A radio navigation system for determining bearing parameters of a mobile apparatus relative to a reference comprising:

relative bearing reference means for selectively transmitting either a beacon signal having low probability of interception signal characteristics (LPI TACAN) or a standard TACAN beacon; and

mobile relative bearing determination means for selectively receiving either an LPI TACAN beacon or a standard TACAN beacon signal and for determining relative bearing to the bearing reference means from the selectively received LPI TACAN or TACAN beacon signal.

7. A radio navigation system comprising:

range reference means for receiving an interrogation signal having low probability of interception (LPI TACAN) signal characteristics, for receiving standard TACAN interrogation signals, and for selectively transmitting either an LPI TACAN reply signal or a standard TACAN reply signal; and

mobile relative range determination means for transmitting an LPI TACAN interrogation signal, for receiving the LPI TACAN reply signal, and for determining range to the reference means from the LPI TACAN reply signal.

18. A system as in any of claims 7, 8 or 9 wherein an LPI signal is a spread spectrum signal.

19. A system as in claim 18 wherein an LPI signal is a pseudo noise coded spread spectrum signal.

20. A system as in claim 19 wherein:

the reference means includes means for transmitting a PN code related in time with a PN code of an LPI interrogation signal; and

the mobile relative range determination means includes means for determining the time delay between a transmitted interrogation signal code sequence and the received reply PN code sequence.

8. A radio navigation system comprising:

range reference means for receiving an interrogation signal having low probability of interception (LPI TACAN) characteristics and for transmitting an LPI TACAN reply signal; and

mobile relative range determination means for selectively transmitting either an LPI TACAN interrogation signal or a standard TACAN interrogation signal, for receiving either an LPI TACAN reply signal or a standard TACAN reply signal, and for determining relative range to the reference means from the received LPI TACAN or standard TACAN reply signal.

9. A radio navigation system comprising:

range reference means for receiving an interrogation signal having low probability of interception (LPI TACAN) signal characteristics, for receiving standard TACAN interrogation signals, and for selectively transmitting either an LPI TACAN reply signal or a standard TACAN reply signal; and

mobile relative range determination means for selectively transmitting either an LPI TACAN interrogation signal or a standard TACAN interrogation signal, for selectively receiving either the LPI TACAN or standard TACAN reply signal, and for determining relative range to the reference means from the selectively received LPI TACAN or standard TACAN reply signal.

21. A method for determining relative bearing from a vehicle to a navigation reference site comprising steps of:

transmitting a spread spectrum interrogation signal from the vehicle to the navigation reference site,

transmitting a spread spectrum reply signal from the landing site to the vehicle such that the reply signal has a duty cycle at least an order of magnitude greater than that of a conventional TACAN beacon signal and the amplitude of the reply signal received at the vehicle varies as a function of the relative bearing between the vehicle and the navigation reference site; and

determining bearing from the vehicle to the navigation reference site from the amplitude of the spread spectrum reply signal.

23. A method as in claim 21 or 22 wherein the step of transmitting a spread spectrum reply signal includes a step of transmitting a pseudo noise coded spread spectrum reply signal.

25. A method as in claim 23 wherein:

the step of transmitting a spread spectrum interrogation signal includes a step of transmitting a pseudo noise coded interrogation signal; and

the step of transmitting a pseudo noise coded spread spectrum reply signal includes a step of transmitting a pseudo noise code sequence related in time to a pseudo noise code sequence of the interrogation signal.

22. A method for determining relative range from a vehicle to a navigation reference site comprising steps of:

transmitting a spread spectrum interrogation signal from the vehicle to the navigation reference site,

transmitting a spread spectrum reply signal from the navigation reference site to the vehicle, said spread spectrum reply signal having a duty cycle at least an order of magnitude greater than that of a conventional TACAN beacon signal; and

determining range from the vehicle to the navigation reference site from the time delay between transmitting the spread spectrum interrogation signal from and receiving the spread spectrum reply signal at the vehicle.

24. A method as in claim 22 wherein the step of transmitting a pseudo noise coded spread spectrum signal includes steps of:

transmitting a pseudo noise coded spread spectrum signal through a rotating beam antenna; and

inverting the pseudo noise code synchronously with the antenna beam rotations.

26. A method for determining relative range and bearing from an aircraft to landing site comprising steps of:

transmitting a PN coded spread spectrum interrogation signal from the aircraft;

receiving the PN coded spread spectrum interrogation signal at the landing site;

transmitting a PN coded spread spectrum beacon signal from the landing site to the aircraft such that;

(1) the duty cycle of the PN coded spread spectrum beacon signal has a duty cycle at least an order of magnitude greater than that of a conventional TACAN beacon signal;

(2) the amplitude of the beacon received at the aircraft varies as a function of relative bearing of the aircraft to the landing site; and

(3) the delay between the time of transmission of an identifiable portion of the PN code of the interrogation signal and the time of arrival of an identifiable portion of the PN code of the beacon signal varies as a function of relative range of the aircraft to the landing site.

27. A radio navigation system for determining the position of a mobile apparatus relative to a reference comprising:

position reference means for receiving an interrogation signal having spread spectrum signal characteristics and for transmitting a spread spectrum beacon signal, said spread spectrum beacon signal having a duty cycle at least an order of magnitude greater than that of a conventional TACAN beacon signal; and

mobile relative position determination means for transmitting a spread spectrum interrogation signal, for receiving the spread spectrum beacon signal and for determining position relative to the position reference means from the spread spectrum beacon signal.

28. A system as in claim 27 wherein a spread spectrum signal is a pseudo noise coded signal.

29. A system as in claim 28 wherein:

the reference means includes antenna means for transmitting the beacon with a rotating beam and means for inverting the PN code sequence of the beacon periodically and synchronously with the antenna rotations; and

the mobile relative position reference means includes means for determining bearing from the amplitude of the beacon and from the inversion times of the PN code sequence of the beacon.

30. A system as in claim 29 wherein:

the reference means includes means for transmitting a spread spectrum beacon signal having a PN code sequence related in time with a PN code sequence of a spread spectrum interrogation signal; and

the mobile relative position reference means includes means for determining the time delay between a transmitted spread spectrum interrogation signal code sequence and the received spread spectrum beacon PN code sequence.

37. A system as in any of claims 27, 31 or 34 wherein the reference means moves relative to the earth'"'"'s surface.

31. A radio navigation system for determining relative bearing of a mobile apparatus relative to a reference comprising:

bearing reference means for transmitting a beacon signal having spread spectrum signal characteristics, said beacon signal having a duty cycle at least an order of magnitude greater than that of a conventional TACAN beacon signal; and

mobile relative bearing determination means for receiving the spread spectrum beacon signal and for determining relative bearing to the bearing reference means from the spread spectrum beacon signal.

32. A system as in claim 31 wherein a spread spectrum signal is a pseudo noise coded signal.

33. A system as in claim 32 wherein:

the reference means further includes antenna means for transmitting the beacon with a rotating beam and means for inverting the PN code sequence of the beacon periodically and synchronously with the antenna rotations; and

the mobile relative position reference means includes means for determining bearing from the amplitude of the beacon and from the inversion times of the PN code sequence of the beacon.

34. A radio navigation system comprising:

range reference means for receiving an interrogation signal having spread spectrum, characteristics and for transmitting a spread spectrum reply signal, said spread spectrum reply signal having a duty cycle at least an order of magnitude greater than that of a conventional TACAN beacon signal; and

mobile relative range determination means for transmitting a spread spectrum interrogantion signal, for receiving the spread spectrum reply signal and for determining range to the reference means from the spread spectrum reply signal.

35. A system as in claim 34 wherein a spread spectrum signal is a pseudo noise coded signal.

36. A system as in claim 35 wherein:

the reference means includes means for transmitting a spread spectrum reply signal having a PN code sequence related in time with a PN code sequence of a spread spectrum interrogation signal; and

the mobile relative range determination means includes means for determining the time delay between a transmitted spread spectrum interrogation signal PN code sequence and the received spread spectrum reply PN code sequence.