Method for calibrating a wideband direction finding system

• US 6,700,537 B2
• Filed: 08/30/2001
• Issued: 03/02/2004
• Est. Priority Date: 08/31/2000
• Status: Active Grant

• Current Assignee: Her Majesty The Queen In Right of Canada As Represented By The Minister of National Defence
• Original Assignee: Her Majesty The Queen In Right of Canada As Represented By The Minister of National Defence
• Inventors: Patenaude, François, Dufour, Martial
• Primary Examiner(s): Phan, Dao
• Application Number:
  US09/941,706
• Publication Number:
  US 20030187601A1
• Time in Patent Office: 915 Days
• Field of Search: 342/165, 342/168, 342/174, 342/417, 342/418, 342/442
• US Class Current: 342/418
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/08 Means for reducing polarisation errors, e.g. by use of Adcock or spaced loop antenna systems
• CPC Class Codes: G01S 3/143 by vectorial combination of signals derived from differently oriented antennae

Abstract

The invention is a method of calibrating the sensor system of a wideband direction finder using a noise source. The sensor system includes at least two wideband tuners, and an analog/digital (A/D) converter connected to each wideband tuner. The calibration method involves selecting a common set of center frequencies for each of the wideband tuners. The wideband tuners receive a signal from the noise source on a per data frame basis. The passband of the received signal is then divided into a number of time-sampled data frames. For each time-sampled data frame, both a gain variation and a phase variation are calculated for the noise received at each wideband tuner. Gain and phase differences between the signal received by each wideband tuner within the same frame are compared. Based on the time-sampled data collected, the phase and gain differences for the signals received at the tuners which have not been previously mapped can be determined. As a result, this calibration method determines a series of calibration factors for each frame, and for a wide range of frequencies.

Claims

1. A method of calibrating a sensor system of a wideband direction finder having at least two antenna elements using a noise source, the direction finder having at least two arms, each arm having a wideband tuner for receiving a noise on a per data frame basis from the noise source, with each arm coupled to the data processing means, the method including the steps of:

a) selecting a set of centre frequencies common for all wideband tuners in the direction finder;

b) dividing a passband of the noise source into a number of time-sampled data frames, such that the dividing is dependent on the centre frequencies;

c) for each time-sampled data frame received by each arm;

c1) reading a gain and a phase of the noise at each wideband tuner for a given frequency;

c2) processing the gain and the phase for each time-sampled data frame, to transform the gain and the phase into the frequency domain and to obtain intermediate results;

c3) calculating a gain difference and a phase difference between the intermediate results output from each arm;

c4) repeating steps c1) to c3) for each given frequency in a chosen group of frequencies, the chosen group of frequencies being within a frequency range of the time-sample data frame; and

c5) averaging the gain and the phase difference obtained in step c4) for the time-sampled data frame to obtain a calibration factor having a gain component and a phase component; and

d) adjusting the sensor system based on the calibration factor;

wherein a passband of the noise source covers at least one portion of a desired radio frequency band.

2. A method of calibrating a sensor system of a wideband direction finder having at least two antenna elements by using a noise source, the direction finder having at least two arms, each arm, having a wideband tuner for receiving a noise signal on a per data frame basis from the noise source, and an analog/digital converter, the wideband tuner being coupled to the analog/digital converter, with each arm coupled to the data processing means through the analog/digital converter, the method including the steps of:

a) coupling the noise source to the each wideband tuner in each arm;

b) selecting a set of centre frequencies common for all wideband tuners in the direction finder;

c) dividing a passband of the nose source into a number of time sampled data frames, such that the dividing is dependent on the centre frequencies;

d) for each time-sampled data frame received by each arm;

d1) converting the noise signal into a digital noise signal for a given frequency;

d2) processing the digital noise signal to transform the digital noise signal into the frequency domain;

d3) reading a gain and a phase of a transformed digital noise signal for each time-sampled data frame to obtain intermediate results;

d4) calculating a gain difference and a phase difference between the intermediate results output from each arm;

d5) repeating steps d1) to d4) for each given frequency in a chosen group of frequencies, the chosen group of frequencies being within a frequency range of the time-sampled data frame;

d6) averaging the gain and the phase difference obtained in step d5) for the time-sampled data frame to obtain a calibration factor having a gain component and a phase component; and

e) adjusting the sensor system based on the calibration factor;

wherein a passband of the noise source covers at least one portion of a desired radio frequency band.

3. A method as defined in claim 2, wherein step d1) for a first time-sampled data frame is executed in parallel with step d2) for a second time-sampled data frame.

4. A method as defined in claim 2, wherein each wideband tuner receives a noise signal for the time-sampled data frame in a sequential order along the passband, such that frequencies covered by a succeeding time-sampled data frame are higher than frequencies covered by a preceding time-sampled data frame.

5. A method as defined in claim 2, wherein for each time-sampled frame, a scanning frequency region for the frame overlaps a portion of an immediately preceding frame and a portion of an immediately succeeding frame.

6. A method of calibrating a sensor system of a wideband direction finder having at least two antenna elements using a noise source, the direction finder having at least two arms, each arm having a wideband tuner for receiving a noise on a per data frame basis from the noise source, with each arm coupled to the data processing means, the method including the steps of:

a) selecting a set of centre frequencies common for all wideband tuners in the direction finder;

b) dividing a passband of the noise source into a number of time-sampled data frames such that the dividing is dependent on the centre frequencies;

c) for each time-sampled data frame received by each arm;

c1) reading a gain and a phase of the noise at each wideband tuner for a given frequency;

c2) processing the gain and the phase for each time-sampled data frame to transform the gain and the phase into the frequency domain and to obtain intermediate results;

c3) calculating a gain difference and a phase difference between the intermediate result output from each arm;

c4) repeating steps c1) to c3) for each given frequency in a chosen group of frequencies, the chosen group of frequencies being within a frequency range of the time-sample data frame;

c5) interpolating the gain and the phase difference obtained in step c4) for the time-sampled data frame to obtain a calibration factor for a frequency not part or the chosen group of frequencies, the calibration factor having a gain component and a phase component; and

d) adjusting the wideband tuners based on the calibration factor;

wherein a passband of the noise source covers at least ore portion of a desired radio frequency band.

7. A computer readable media having embodied thereon computer readable and computer executable instructions for a method of calibrating a sensor system of a wideband direction finder having at least two antenna elements using a noise source, the direction finder having at least two arms, each arm having a wideband tuner for receiving a noise on a per data frame basis from the noise source, with each arm coupled to the data processing means, the method including the steps of:

a) selecting a set of centre frequencies common for all wideband tuners in the direction finder;

b) dividing a passband of the noise source into a number of time-sampled data frames, such that the dividing is dependent on the centre frequencies;

c) for each time-sampled data frame received by each arm;

c1) reading a gain and a phase of the noise at each wideband tuner for a given frequency;

c2) processing the gain and the phase for each time-sampled data frame, to transform the gain and the phase into the frequency domain and to obtain intermediate results;

c3) calculating a gain difference and a phase difference between the intermediate results output from each arm;

c4) repeating steps c1) to c3) for each given frequency in a chosen group of frequencies, the chosen group of frequencies being within a frequency range of the time-sample data frame;

c5) averaging the gain and the phase difference obtained in step c4) for the time-sampled data frame to obtain a calibration factor having a gain component and a phase component; and

d) adjusting the wideband tuners based on the calibration factor;

wherein a passband of the noise source covers at least one portion of a desired radio frequency band.

8. A computer system constructed and configured to execute computer readable and computer executable instructions having embodied therein a method of calibrating a sensor system of a wideband direction finder having at least two antenna elements using a noise source, the direction finder having at least two arms, each arm having a wideband tuner for receiving a noise on a per data frame bases from the noise source, with each arm coupled to the data processing means, the method including the steps of:

a) selecting a set of centre frequencies common for all wideband tuners in the direction finder;

b) dividing a passband of the noise source into a number of time-sampled data frames, such that the dividing is dependent on the centre frequencies;

c) for each time-sampled data frame received by each arm;

c1) reading a gain and a phase of the noise at each wideband tuner for a given frequency;

c2) processing the gain and the phase for each time-sampled data frame, to transform the gain and the phase into the frequency domain and to obtain intermediate results;

c3) calculating a gain difference and a phase difference between the intermediate results output from each arm;

c4) repeating steps c1) to c3) for each given frequency in a chosen group of frequencies, the chosen group of frequencies being within a frequency range of the time-sample data frame;

c5) averaging the gain and the phase difference obtained in step c4) for the time-sampled data frame to obtain a calibration factor having a gain component and a phase component; and

d) adjusting the wideband tuners based on the calibration factor;

wherein a passband of the noise source covers at least one portion of a desired radio frequency band.

9. A system for calibrating a sensor system of a wideband direction finder having at least two antenna elements using a noise source, the direction finder having at least two arms, each arm having a wideband tuner for receiving a noise on a per data frame basis from the noise source, with each arm coupled to the data processing means, the system comprising:

means for selecting a set of centre frequencies common for all wideband tuners in the direction finder;

means for dividing a passband of the noise source into a number of time sampled data frames, such that the dividing is dependent on the centre frequencies;

means for reading a gain and a phase of the noise at each wideband tuner for a given frequency;

means for processing the gain and the phase for each time-sampled data frame, to transform the gain and the phase into the frequency domain and to obtain intermediate results;

means for calculating a gain difference and results output from each arm;

means for averaging the gain and the phase difference for the time-sampled data frame to obtain a calibration factor having a gain component and a phase component; and

means for adjusting the wideband tuners based on the calibration factor.