Antenna system and method for direction finding

• US 6,239,747 B1
• Filed: 03/11/1999
• Issued: 05/29/2001
• Est. Priority Date: 03/11/1999
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Kaminski, Walter Joseph
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/265,982
• Time in Patent Office: 810 Days
• Field of Search: 342/147, 342/156, 342/351, 342/417, 342/418-449, 342/450, 342/157, 342/368-377
• US Class Current: 342/442
• CPC Class Codes: G01S 3/023 Monitoring or calibrating
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems

Abstract

An array antenna for direction-finding includes antenna elements which define a triangular outline well-suited for meeting space constraints or reducing reflections from mounting conditions associated with the array antenna. The actual geometric configuration of the antenna elements is limited to certain triangular configurations with corresponding geometric correction factors to maintain the accuracy of estimating the angle of arrival. A processing system determines the appropriate angle of arrival based upon differential phases received in the antenna elements and the appropriate geometric correction factor.

Claims

1. An array antenna for direction finding of received signals, the array antenna comprising:

a plurality of antenna elements arranged to define vertices of a triangular outline with separations between the antenna elements;

at least one measuring device measuring differential phases between the received signals induced in at least a first pair of the antenna elements; and

a processing system for determining an angle of arrival of an incident electromagnetic field inducing the received signals in the antenna elements, based upon the measured differential phases and a geometric relationship between the antenna elements.

2. The array antenna according to claim 1 wherein the processing system determines the angle of arrival of the incident electromagnetic field based on the measured differential phases and an angular relationship between two sides of the triangular outline, and wherein the triangular outline comprises a nonorthogonal triangle with the separations determined based upon a frequency band of operation.

3. The array antenna according to claim 1 wherein

the processing system further comprises a user interface for selecting one geometric relationship of the antenna elements from a group of at least two geometric relationships; and

the processing system determines the angle of arrival of the incident electromagnetic field based on the measured differential phases and the selected geometric relationship.

4. The array antenna according to claim 1 wherein the at least one measuring device includes a first correlator for measuring a first differential phase between the first pair of the antenna elements and a second correlator for measuring a second differential phase between a second pair of the antenna elements sharing a common antenna element with the first pair.

5. The array antenna according to claim 4 wherein the processing system determines the angle of arrival based upon the equation:

α

=tan<sup>−

1</sup>(δ

₀/δ

₉₀), where a is the angle of arrival, δ

₀ is a function of the first differential phase and the second differential phase, and δ

₉₀ is a function of the first differential phase, the second differential phase and the geometric relationship between the antenna elements.

6. The array antenna according to claim 4 wherein the processing system determines the angle of arrival based upon the equation:

α

=tan<sup>−

1</sup>[2x(φ

₁+φ

₂)/(φ

₁−

φ

₂)] where a is the angle of arrival, φ

₁ is the first differential phase, φ

₂ is the second differential phase, and x is a geometric correction factor indicative of the geometric relationship between the antenna elements.

7. The array antenna according to claim 4 wherein the processing system calculates the angle of arrival based upon the equation:

α

=tan<sup>−

1</sup>[2x(φ

₁+φ

₂)/(φ

₁−

φ

₂)] where a is the angle of arrival, φ

₁ is the first differential phase, φ

₂ is the second differential phase, and x is a geometric correction factor indicative of the geometric relationship between the antenna elements and is equal to 0.5 sin β

/sin(90°

−

β

), wherein β

is an angle between adjacent sides of the triangular outline.

8. The array antenna according to claim 1 wherein the processing system determines the angle of arrival of the incident electromagnetic field based on the measured differential phases and a geometric correction factor indicative of the geometric relationship between the antenna elements, and the geometric correction factor comprises a ratio between a height distance, measured from an apex of two adjacent sides of the triangular outline to an opposite base side, and a length of the opposite base side of the triangular outline.

9. The array antenna according to claim 1 wherein

the processing system determines the angle of arrival of the incident electromagnetic field based on the measured differential phases and a geometric correction factor indicative of the geometric relationship between the antenna elements;

and

the antenna elements include a first antenna element, a second antenna element, and a third antenna element, a first separation between the first antenna element and the third antenna element, a second separation between the first antenna element and the second antenna element, and the third separation between the second antenna element and the third antenna element, and wherein sides coextensive with the first separation and the second separation form a beta angle for calculating the geometric correction factor.

10. The array according to claim 9 wherein

the beta angle is greater than sixty degrees, the second separation and the third separation being equal to or less than approximately one-half wavelength at the frequency band of operation;

and

the processing system calculates the geometric correction factor based upon the equation;

11. The array according to claim 9 wherein

the beta angle is generally equal to sixty degrees, the first separation, the second separation, and the third separation each being equal to or less than approximately one-half wavelength at the frequency of operation;

and

the processing system calculates the geometric correction factor based upon the equation;

x=0.5 sinβ

/sin(90°

−

β

), wherein x is the geometric correction factor and β

is the beta angle.

12. The array antenna according to claim 9 wherein

the beta angle is less than sixty degrees, the first separation being less than or equal to approximately one-half wavelength at the frequency of operation;

and

the processing system calculatesling) the geometric correction factor corresponding to the beta angle.

13. A dual-band antenna for direction finding of received signals, the antenna comprising:

a first array for operating in a first frequency band, the first array having antenna elements arranged to define a first triangular outline with separations between the antenna elements;

a second array for operating in a second frequency band different from the first frequency band, the second array having antenna elements arranged to define a second triangular outline with separations between the antenna elements;

at least one measuring device measuring differential phases between the received signals induced in at least one pair of the antenna elements;

a processor for determining a first angle of arrival of a first electromagnetic field of the first frequency band and for determining a second angle of arrival of a second electromagnetic field within a second frequency band, based upon the measured differential phases and at least one of a first geometric correction factor indicative of a gometric relationship between the antenna elements defining the first triangular outline and a second geometric correction factor indicative of a geometric relationship between the antenna elements defining the second triangular outline, at least one of the first and second electromagnetic fields inducing the received signals in the antenna elements.

14. The dual-band antenna according to claim 13 wherein the second array shares common ones of the antenna elements with the first array for serving the first frequency band and the second frequency band.

15. The dual-band antenna according to claim 13 wherein

the at least one measuring device includes a first correlator for measuring a first differential phase in the first array between a first pair of the antenna elements and a second correlator for measuring a second differential phase in the first array between a second pair of the antenna elements; and

the processor calculates the first angle of arrival based upon the equation;

α

₁=tan<sup>−

1</sup>[2x₁(φ

₁+φ

₂)/(φ

₁−

φ

₂)] where α

₁ is the first angle of arrival, φ

₁ is the first differential phase, φ

₂ is the second differential phase, and x₁ is the first geometric correction factor.

16. The dual-band antenna according to claim 15 wherein

the at least one measuring device includes a third correlator for measuring a third differential phase in the second array between a third pair of the antenna elements and a fourth correlator for measuring a fourth differential phase in the second array between a fourth pair of the antenna elements;

and

the processor calculates the second angle of arrival based upon the equation;

α

₂=tan<sup>−

1</sup>[2x₂(φ

₃+φ

₄)/(φ

₃−

φ

₄)] where α

₂ is the angle of arrival, φ

₃ is the third differential phase, φ

₄ is the fourth differential phase, and x₂ is the second geometric correction factor.

17. The dual-band antenna according to claim 13 wherein the separations coincide with sides including a base side located between the common ones, a first adjacent side of the first triangular outline adjacent to the base side, a second adjacent side of the second triangular outline adjacent to the base side, the base side and the first adjacent side forming a first beta angle, the first geometric correction factor being determined based on the first beta angle, and the base side and the second adjacent side forming a second beta angle, the second geometric correction factor being determined based on the second beta angle.

18. The dual-band antenna according to claim 17 wherein if the first beta angle is less than 60 degrees, the base side is generally equal to or less than one-half wavelength at a highest frequency of operation of the first frequency band and the second frequency band.

19. The dual-band antenna according to claim 17 wherein if the first beta angle is equal to approximately 60 degrees, the sides of the first triangular outline are at least approximately equal to each other and the sides are less than or equal to approximately one-half wavelength at the first frequency band.

20. The dual-band antenna according to claim 19 wherein if the second beta angle is equal to approximately 60 degrees, the sides of the second triangular outline are at least approximately equal to each other and the sides are less than or equal to approximately one-half wavelength at the second frequency band.

21. The dual-band antenna according to claim 17 wherein if the first beta angle is greater than 60 degrees, each of the first adjacent side and a remaining side of the first triangular outline is generally equal to or less than one-half wavelength at the first frequency band.

22. A method for determining an angle of arrival of a received signal at an array antenna, the method comprising the steps of:

arranging a plurality of antenna elements to define vertices of a triangular outline in a plane, the triangular outline including sides coextensive with corresponding separations between the antenna elements;

measuring differential phases received between different pairs of the antenna elements;

calculating a geometric correction factor based on a geometric relationship existing between the antenna elements;

determining an angle of arrival of an electromagnetic field incident upon the antenna elements based on the measured differential phases and the calculated geometric correction factor.

23. The method according to claim 22 wherein the arranging step further comprises adjusting the triangular outline to meet a spatial area constraint for mounting the array antenna.

24. The method according to claim 22 wherein the arranging step further comprises adjusting a triangular area encompassed by the triangular outline to be less than or equal to an available area for mounting the array antenna.

25. The method according to claim 22 wherein the arranging step further comprises adjusting the triangular outline to reduce or eliminate reflection of electromagnetic energy from a metallic object which would otherwise interfere with the field incident upon the antenna elements.

26. The method according to claim 22 wherein the arranging step further comprises adjusting the triangular outline to reduce or eliminate reflection of electromagnetic energy from a tower which would otherwise interfere with the field incident upon the antenna elements.

27. The method according to claim 22 wherein the arranging step further comprises determining the separations between the antenna elements based upon a frequency band of operation.