METHOD OF DETERMINING THE DIRECTION OF ARRIVAL OF A HIGH-FREQUENCY ELECTROMAGNETIC WAVE

• US 20120086605A1
• Filed: 11/04/2009
• Published: 04/12/2012
• Est. Priority Date: 11/07/2008
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Merlet, Eric, Mesnage, Jean-Christophe, Rogier, Jean-Luc, Lecca, Arnaud
• Granted Patent: US 8,674,880 B2
• Time in Patent Office: Days
• 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 the measurements made by the antenna of a calibration signal which varies in its bearing and has a fixed or variable frequency;

in a phase of measuring detected signals;

acquiring the detected signals in at least one frequency channel;

for each frequency channel correlating the acquired signals with the recorded signals resulting from the frequency calibration close to f_i, and determining the direction of arrival of the signals by finding the bearing angle θ

for which the maximum correlation is obtained.

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

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

1, over a time interval Δ

t;

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

calculating a mean intercorrelation vector X by finding the mean of the p elementary intercorrelation vectors X_k calculated previously.

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

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

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

estimating the quality of a bearing measurement θ

, a quality score Q being assigned to the bearing measurement as a function of the level of the maximum correlation obtained, the quality score Q being an increasing monotonic function of the maximum correlation.

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

identifying erroneous measurements, a minimum threshold being chosen and a comparison being made between the minimum threshold and the quality score Q assigned to a measurement to identify a measurement whose quality score Q is below the threshold.

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

8. The method according to claim 1, wherein, in the calibration phase, the calibration signal is transmitted in such a way that the angle of elevation of arrival of the 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:

at an angle of elevation substantially equal to zero, defining a range of bearing directions [θ

_i;

θ

_f] to be monitored;

if signals are detected, executing the steps of the method of measuring the direction of arrival of signals according to claim 1;

if a signal is detected in the monitored range, triggering an alert command.

10. A goniometer using the measurement method according to claim 1.

11. A monitoring system positioned on a ship and using the method according to claim 9.