Low cost angle of arrival measurement system

• US 6,255,991 B1
• Filed: 01/19/2000
• Issued: 07/03/2001
• Est. Priority Date: 01/19/2000
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Hedin, George L.
• Primary Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/487,507
• Time in Patent Office: 531 Days
• Field of Search: 342/156, 342/374, 342/424, 342/442, 342/444, 342/445
• US Class Current: 342/424
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured
• CPC Class Codes: H01Q 21/08 the units being spaced along or adjacent to a rectilinear path waveguide fed H01Q21/0037
• CPC Class Codes: H01Q 21/28 Combinations of substantially independent non-interacting antenna units or systems multiple beam H01Q25/00
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence
• CPC Class Codes: H01Q 21/293 one unit or more being an array of identical aerial elements adaptive arrays H01Q3/2605

Abstract

An interferometer antenna system (32) for measuring the angle of arrival of RF signals. The interferometer antenna system (32) includes a plurality of interferometer antenna elements (36) coupled to a first switching network (42). The first switching network (42) is coupled to only two interferometer receivers (44, 46). The first switching network (42) selectively connects the plurality of interferometer antenna elements (36) in pairs to the two interferometer receivers (44, 46) in a sequential manner, so that a phase difference is measured between the received signal for several of the pairs of the interferometer elements (36). Additionally, a plurality of guard antenna elements (38) are coupled to a second switching network (48). A single guard receiver (50) is coupled to the second switching network (48), where the second switching network (48) selectively connects one of the guard antenna elements (38) to the guard receiver (50) in a sequential manner. A controller (40) employs a suitable angle of arrival algorithm to generate a best estimate of the direction of the received signal based on the phase signals from the two interferometer receivers (44, 46) and the power signal from the guard receiver (50).

Claims

1. A system for determining angle of arrival measurements of a signal, said system comprising:

a plurality of interferometer antenna elements spaced apart from each other a predetermined distance and receiving the signal, said plurality of interferometer antenna elements being greater in number than two antenna elements;

a first switching network coupled to the plurality of interferometer antenna elements;

two interferometer receivers coupled to the first switching network, said first switching network selectively directing the received signal from two selected interferometer antenna elements to the two interferometer receivers in a sequential manner so that several pairs of the interferometer antenna elements are separately directed to the two interferometer receivers; and

a controller coupled to the interferometer receivers and determining a phase difference between measured phase differences of the two selected interferometer antenna elements, said controller subtracting a predicted phase difference from the determined phase difference to generate a nominal phase difference.

2. The system according to claim 1 wherein the interferometer antenna elements are arranged in a linear array.

3. A system according to claim 1 further comprising a plurality of guard antenna elements, a second switching network and a single guard receiver, said second switching network being coupled to the guard antenna elements and the guard receiver, and selectively directing the signal received by the guard antenna elements in a sequential and separate manner to the guard receiver, said controller being coupled to the guard receiver.

4. The system according to claim 1 wherein the nominal phase difference is compared to a threshold where phase differences below the threshold are accepted and phase differences above the threshold are rejected.

5. The system according to claim 1 wherein the controller performs a linear transform on the nominal phase difference to align phase trajectories with one coordinate axis and place ambiguities on other axes.

6. The system according to claim 1 wherein the antenna elements are positioned on an aircraft.

7. A system for determining direction of arrival of a received signal, said system comprising:

a plurality of interferometer antenna elements spaced apart from each other a predetermined distance and receiving the signal, said plurality of interferometer antenna elements being more than two antenna elements arranged in a linear array;

a first switching network coupled to the plurality of interferometer antenna elements;

only two interferometer receivers coupled to the first switching network, said first switching network selectively directing the received signals from two selected interferometer antenna elements to the two interferometer receivers in a sequential manner so that several pairs of the interferometer antenna elements are separately directed to the two interferometer receivers, said interferometer receivers measuring a phase difference therebetween;

four guard antenna elements oriented 90°

apart and receiving the signal;

a second switching network coupled to the four guard antenna elements;

a single guard receiver, said second switching network selectively directing the received signal from selected guard antenna elements in a sequential and separate manner to the guard receiver; and

a controller coupled to the interferometer receivers and the guard receiver, said controller determining a phase difference between the measured phase differences of the two selected interferometer elements and determining a power of the selected guard antenna element.

8. The system according to claim 7 wherein the controller subtracts a predicted phase difference from the determined phase difference to generate a nominal phase difference.

9. The system according to claim 8 wherein the nominal phase difference is compared to a threshold where phase differences below the threshold are accepted and phase differences above of the threshold are rejected.

10. The system according to claim 8 wherein the controller performs a linear transform on the nominal phase difference to align phase trajectories with one coordinate axis and place ambiguities on other axes.

11. The system according to claim 7 wherein the antenna elements are positioned on an aircraft.

12. A method of determining the angle of arrival of a signal, said method comprising the steps of:

selecting a first pair of interferometer antenna elements from a plurality of interferometer antenna elements;

connecting the first selected pair of interferometer antenna elements to a pair of interferometer receivers;

measuring the phase difference between signals received by the first selected interferometer elements;

subtracting a predicted phase difference from the measured phase difference between the signals received by the first selected interferometer elements to generate a nominal phase difference;

selecting a second pair of interferometer antenna elements from the plurality of interferometer antenna elements that is different than the first pair of interferometer antenna elements;

connecting the second selected pair of interferometer antenna elements to the same pair of interferometer receivers;

measuring the phase difference been signals received by the second selected interferometer elements; and

determining the angle of arrival of the signal received by the interferometer antenna elements based on the measured phase differences, said step of determining the angle of arriving including subtracting a predicted phase difference from each measured phase difference to generate a nominal phase difference.

13. The method according to claim 12 further comprising the steps of selecting a guard antenna element from a plurality of guard antenna elements, connecting the selected guard antenna element to a single guard receiver, measuring the signal power received by the selected guard antenna element, and sequentially repeating the steps of selecting a guard antenna elements, connecting the guard antenna element to the guard receiver and measuring the signal power received by the selected guard antenna sequentially for all of the plurality of guard antenna elements.

14. The method according to claim 12 further comprising the step of comparing the nominal phase difference to a threshold and rejecting the nominal phase difference if it is greater than the threshold.

15. The method according to claim 12 further composing the step of performing a linear transform on the nominal phase difference to align phase trajectories with one coordinate axes and place ambiguities on other axes.

16. A method of determining the angle of arrival of a signal, said method comprising the steps of:

providing at least two interferometer antenna elements;

measuring the phase of the signal received by each of the interferometer antenna elements;

determining the phase difference between the measured phases of the signals received by the interferometer elements; and

performing a linear transform on the phase difference to rotate phase trajectories represented by the phase difference to be aligned with a coordinate axis.

17. The method according to claim 16 further comprising the step of subtracting a predicted phase difference from the determined phase difference to generate a nominal phase difference, said step of performing a linear transform including performing the linear transform on the nominal phase difference.

18. The method according to claim 17 further comprising the step of comparing the nominal phase difference to a threshold and rejecting the nominal phase difference if it is greater than the threshold.

19. A system for determining angle of arrival measurements of a signal, said system comprising:

a plurality of interferometer antenna elements spaced apart from each other a predetermined distance and receiving the signal, said plurality of interferometer antenna elements being greater in number than two antenna elements;

a first switching network coupled to the plurality of interferometer antenna elements;

two interferometer receivers coupled to the first switching network, said first switching network selectively directing the received signal from two selected interferometer antenna elements to the two interferometer receivers in a sequential manner so that several pairs of the interferometer antenna elements are separately directed to the two interferometer receivers;

a plurality of guard antenna elements;

a second switching network coupled to the plurality of guard antenna elements;

a single guard receiver coupled to the second switching network, said single guard receiver selectively directing the signal received by the guard antenna elements in a sequential and separate manner to the guard receiver; and

a controller coupled to the interferometer receivers and the guard receiver, said controller determining a phase difference between measured phase differences of the two selected interferometer antenna elements.

20. A method of determining the angle of arrival of a signal, said method comprising the steps of:

selecting a first pair of interferometer antenna elements from a plurality of interferometer antenna elements;

connecting the first selected pair of interferometer antenna elements to a pair of interferometer receivers;

measuring the phase difference between signals received by the first selected interferometer elements;

selecting a second pair of interferometer antenna elements from the plurality of interferometer antenna elements that is different than the first pair of interferometer antenna elements;

connecting the second selected pair of interferometer antenna elements to the same pair of interferometer receivers;

measuring the phase difference between signals received by the second selected interferometer elements;

selecting a guard antenna element from a plurality of guard antenna elements;

connecting the selected guard antenna element to a single guard receiver;

measuring the signal power received by the selected guard antenna element;

sequentially repeating the steps of selecting a guard antenna element, connecting the guard antenna element to the guard receiver and measuring the signal power received by the selected guard antenna element sequentially for all of the plurality of guard antenna elements; and

determining the angle of arrival of the signal received by the interferometer antenna elements based on the measured phase differences.