Method of determining the direction of arrival of a high-frequency electromagnetic wave

• US 8,674,880 B2
• Filed: 11/04/2009
• Issued: 03/18/2014
• Est. Priority Date: 11/07/2008
• Status: Expired due to Fees

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Lecca, Arnaud, Merlet, Eric, Mesnage, Jean-Christophe, Rogier, Jean-Luc
• Primary Examiner(s): LIU, HARRY K
• Application Number:
  US13/128,345
• Publication Number:
  US 20120086605A1
• Time in Patent Office: 1,595 Days
• Field of Search: 342/441
• US Class Current: 342/441
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/085 by using spaced loop aerial systems
• CPC Class Codes: G01S 3/28 using amplitude comparison of signals derived simultaneously from receiving antennas or antenna systems having differently-oriented directivity characteristics
• CPC Class Codes: H01Q 21/205 providing an omnidirectional coverage turnstile aerials H01Q21/26
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

A method of measuring the direction of arrival θ of radio signals in the HF band received by a crossed loop antenna includes, in a preparatory calibration phase, acquiring and recording the measurements made by the antenna of a calibration signal which varies in its frequency and bearing angle; and in a measurement phase in which the bearing angle or angles of arrival of signals detected by the antenna is or are determined, acquiring the signals detected in at least one frequency channel, and then, for each frequency channel f_i, correlating the acquired signals with the recordings having frequencies close to f_i, resulting from the calibration, and determining the direction of arrival of the signals by finding the bearing angle θ for which the maximum correlation is reached.

Claims

1. A method of measuring a bearing angle of arrival θ

of HF band radio signals received by a crossed loop antenna or an Adcock antenna array, the method comprising;

in a preparatory calibration phase, acquiring and recording measurements, made by an antenna, of a calibration signal which has a variable bearing angle of arrival θ and

has a fixed or variable frequency; and

in a detected signals measurement phase;

acquiring detected signals in at least one frequency channel; and

for each frequency channel f_i, correlating the acquired detected signals with the recorded calibration signals resulting from a frequency calibration of approximately f_i, and determining, using a processor, the direction of arrival of the detected signals by finding the bearing angle of arrival θ

having the maximum correlation value.

2. The method according to claim 1, wherein each acquisition in the preparatory calibration phase is recorded in a table in the form of an intercorrelation vector, the intercorrelation vectors in the table being correlated with another intercorrelation vector obtained from the detected signals acquired in the detected signals measurement phase, the method further comprising calculating each of the intercorrelation vectors by:

acquiring, on a sine loop and a cosine loop of the antenna, N signal measurements, where N≧

1, over a time interval Δ

t;

calculating, for p measurements out of the N measurements, an elementary intercorrelation vector X_k; and

calculating a mean intercorrelation vector X by determining a mean of the p elementary intercorrelation vectors X_k.

3. The method according to claim 2, wherein the elementary intercorrelation vector X_k based on a measurement k is defined as:

4. The method according to claim 2, wherein a correlation criterion increases with a modulus of a scalar product of the intercorrelation vector of the detected signals and the intercorrelation vector of the calibration signals acquired during the preparatory calibration phase.

5. The method according to claim 1, further comprising:

estimating the quality of a bearing angle of arrival θ

measurement, a quality score Q being assigned to the bearing angle of arrival θ

measurement as a function of a level of the maximum correlation value, the quality score Q being an increasing monotonic function of the maximum correlation value.

6. The method according to claim 5, further comprising:

identifying erroneous measurements by receiving a minimum threshold and comparing the minimum threshold and the quality score Q assigned to the bearing angle of arrival θ

measurement to identify a bearing angle of arrival θ

measurement having a quality score Q below the minimum threshold.

7. The method according to claim 1, wherein the antenna is fixed on a ship, and the preparatory calibration phase is executed by transmitting signals from a fixed transmitter positioned substantially at sea level, so that the transmitted signals are received by the antenna at an elevation angle of substantially zero, the ship moving at a distance from the transmitter and the course of the ship being changed to vary the bearing angles of arrival θ

of the calibration signal with respect to the antenna.

8. The method according to claim 1, wherein, in the preparatory calibration phase, the calibration signal is transmitted so that an angle of elevation of arrival of the calibration signal at the crossed loop antenna is substantially constant.

9. A method of monitoring used on a platform at sea or on the ground, the method comprising:

defining, at an angle of elevation substantially equal to zero, a range of bearing angles to be monitored;

if the radio signals are detected, executing the method of measuring the bearing angle of arrival θ

of the radio signals according to claim 1; and

if a radio signal is detected in the monitored range of bearing angles, triggering an alert command.

10. A goniometer configured to execute the method of measuring the bearing angle of arrival θ

according to claim 1.

11. A monitoring system positioned on a ship, the monitoring system configured to execute the method of monitoring according to claim 9.

12. The method according to claim 1, wherein each acquisition in the preparatory calibration phase is made by acquiring, on a sine loop and a cosine loop of the antenna, N signal measurements, where N≧

1, over a time interval Δ

t.

13. A method of measuring a bearing angle of arrival θ

of HF band radio signals received by a crossed loop antenna or an Adcock antenna array, the method comprising;

in a preparatory calibration phase, acquiring and recording measurements, made by an antenna, of a calibration signal which has a variable bearing angle of arrival θ and

has a fixed or variable frequency; and

in a detected signals measurement phase;

acquiring detected signals in at least one frequency channel; and

for each frequency channel f_i, correlating the acquired detected signals with the recorded calibration signals resulting from a frequency calibration of approximately f_i, and determining, using a processor, the direction of arrival of the detected signals by finding the bearing angle of arrival θ

having the maximum correlation value,

wherein each acquisition in the preparatory calibration phase is recorded in a table in the form of an intercorrelation vector, the intercorrelation vectors in the table being correlated with another intercorrelation vector obtained from the detected signals acquired in the detected signals measurement phase,

the method further comprising calculating each of the intercorrelation vectors by;

acquiring, on a sine loop and a cosine loop of the antenna, N signal measurements, where N≧

1, over a time interval Δ

t;

calculating, for p measurements out of the N measurements, an elementary intercorrelation vector X_k; and

calculating a mean intercorrelation vector X by determining a mean of the p elementary intercorrelation vectors X_k.

14. The method according to claim 13, further comprising:

estimating the quality of a bearing angle of arrival θ

measurement, a quality score Q being assigned to the bearing angle of arrival θ

measurement as a function of a level of the maximum correlation value, the quality score Q being an increasing monotonic function of the maximum correlation value.

15. The method according to claim 14, further comprising:

identifying erroneous measurements by receiving a minimum threshold and comparing the minimum threshold and the quality score Q assigned to the bearing angle of arrival θ

measurement to identify a bearing angle of arrival θ

measurement having a quality score Q below the minimum threshold.

16. The method according to claim 13, wherein the antenna is fixed on a ship, and the preparatory calibration phase is executed by transmitting signals from a fixed transmitter positioned substantially at sea level, so that the transmitted signals are received by the antenna at an elevation angle of substantially zero, the ship moving at a distance from the transmitter and the course of the ship being changed to vary the bearing angles of arrival θ

of the calibration signal with respect to the antenna.

17. The method according to claim 13, wherein, in the preparatory calibration phase, the calibration signal is transmitted so that an angle of elevation of arrival of the calibration signal at the crossed loop antenna is substantially constant.

18. A method of monitoring used on a platform at sea or on the ground, the method comprising:

defining, at an angle of elevation substantially equal to zero, a range of bearing angles to be monitored;

if the radio signals are detected, executing the method of measuring the bearing angle of arrival θ

of the radio signals according to claim 13; and

if a radio signal is detected in the monitored range of bearing angles, triggering an alert command.

19. A goniometer configured to execute the method of measuring the bearing angle of arrival θ

according to claim 13.

20. A monitoring system positioned on a ship, the monitoring system configured to execute the method of monitoring according to claim 18.

21. A method of measuring a bearing angle of arrival θ

of HF band radio signals received by a crossed loop antenna or an Adcock antenna array, the method comprising;

in a preparatory calibration phase, acquiring and recording measurements, made by an antenna, of a calibration signal which has a variable bearing angle of arrival θ and

has a fixed or variable frequency;

in a detected signals measurement phase;

acquiring detected signals in at least one frequency channel, and

for each frequency channel f_i,correlating the acquired detected signals with the recorded calibration signals resulting from a frequency calibration of approximately f_i, and determining, using a processor, the direction of arrival of the detected signals by finding the bearing angle of arrival θ

having the maximum correlation value; and

estimating the quality of a bearing angle of arrival θ

measurement, a quality score Q being assigned to the bearing angle of arrival θ

measurement as a function of a level of the maximum correlation value, the quality score Q being an increasing monotonic function of the maximum correlation value.

22. The method according to claim 21, wherein each acquisition in the preparatory calibration phase is recorded in a table in the form of an intercorrelation vector, the intercorrelation vectors in the table being correlated with another intercorrelation vector obtained from the detected signals acquired in the detected signals measurement phase, the method further comprising calculating each of the intercorrelation vectors by:

acquiring, on a sine loop and a cosine loop of the antenna, N signal measurements, where N≧

1, over a time interval Δ

t;

calculating, for p measurements out of the N measurements, an elementary intercorrelation vector X_k; and

calculating a mean intercorrelation vector X by determining a mean of the p elementary intercorrelation vectors X_k.

23. The method according to claim 22, wherein the elementary intercorrelation vector X_k based on a measurement k is defined as:

24. The method according to claim 22, wherein a correlation criterion increases with a modulus of a scalar product of the intercorrelation vector of the detected signals and the intercorrelation vector of the calibration signals acquired during the preparatory calibration phase.

25. The method according to claim 21, wherein the antenna is fixed on a ship, and the preparatory calibration phase is executed by transmitting signals from a fixed transmitter positioned substantially at sea level, so that the transmitted signals are received by the antenna at an elevation angle of substantially zero, the ship moving at a distance from the transmitter and the course of the ship being changed to vary the bearing angles of arrival θ

of the calibration signal with respect to the antenna.

26. The method according to claim 21, wherein, in the preparatory calibration phase, the calibration signal is transmitted so that an angle of elevation of arrival of the calibration signal at the crossed loop antenna is substantially constant.

27. A method of monitoring used on a platform at sea or on the ground, the method comprising:

defining, at an angle of elevation substantially equal to zero, a range of bearing angles to be monitored;

if the radio signals are detected, executing the method of measuring the bearing angle of arrival θ

of the radio signals according to claim 21; and

if a radio signal is detected in the monitored range of bearing angles, triggering an alert command.

28. A goniometer configured to execute the method of measuring the bearing angle of arrival θ

according to claim 21.

29. A monitoring system positioned on a ship, the monitoring system configured to execute the method of monitoring according to claim 27.