Narrowband beamformer using nonlinear oscillators

• US 6,473,362 B1
• Filed: 04/30/2001
• Issued: 10/29/2002
• Est. Priority Date: 04/30/2001
• Status: Expired due to Fees

• Current Assignee: Information Systems Laboratories, Inc.
• Original Assignee: Information Systems Laboratories, Inc.
• Inventors: Gabbay, Michael
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US09/846,592
• Publication Number:
  US 20020159335A1
• Time in Patent Office: 547 Days
• Field of Search: 367/905, 367/103, 367/119, 367/138, 342/354, 342/368, 342/379, 736/26
• US Class Current: 367/119
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H01Q 3/30 varying the relative phase between the radiating elements of an array H01Q3/2605, H01Q3/2658, H01Q3/2682, H01Q3/44 take precedence
• CPC Class Codes: H01Q 3/32 by mechanical means
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: Y10S 367/905 Side lobe reduction or shading

Abstract

A narrowband beamformer for extracting a mainbeam having a frequency, Ω, that is received at a beamsteered sensor array includes a plurality of nonlinear oscillators. Each nonlinear oscillator operates on a signal from one of the beamsteered sensors to produce a nonlinear oscillator output. A summer receives and sums all of the nonlinear oscillator outputs. Each nonlinear oscillator is coupled to at least one other nonlinear oscillator to create a signal in the summer output having a frequency of approximately, Ω, in response to receipt of the mainbeam signal by the sensor array. Further, the nonlinear oscillators are coupled to create a spectrum of signals in the summer output that are centered around a frequency, {overscore (ω)}, in response to receipt of a directional interference signal by the sensor array. A matched filter is used to isolate the frequency, Ω, to thus extract the mainbeam from the directional interference.

Claims

1. A receiver for receiving a mainbeam signal of approximate frequency, Ω

, in an environment containing directional interference signals of approximate frequency, Ω

, said receiver comprising;

a sensor array having a plurality of sensors;

a means for beamsteering said sensor array in the direction of the mainbeam;

a plurality of nonlinear oscillators, each said nonlinear oscillator connected to a said sensor to produce a nonlinear oscillator output;

a summer connected to each said nonlinear oscillator for receiving and summing said nonlinear oscillator outputs and creating a summer output;

at least one coupling circuit for coupling each said nonlinear oscillator to at least one other said nonlinear oscillator to cause a summer output having a frequency of approximately, Ω

, in response to receipt of the mainbeam signal by the sensor array and to cause a summer output having a frequency of approximately, {overscore (ω

)}, in response to receipt of a directional interference signal by the sensor array; and

a matched filter connected to said summer for receiving said summer output and separating said summer output into signals having an approximate frequency of Ω and

signals having an approximate frequency of {overscore (ω

)}.

2. A receiver as recited in claim 1 wherein said sensors are radiofrequency antennas.

3. A receiver as recited in claim 1 wherein said sensors are hydrophones.

4. A receiver as recited in claim 1 wherein said sensor array is a linear array.

5. A receiver as recited in claim 1 wherein said sensor array is a planar array.

6. A receiver as recited in claim 1 wherein said means for beamsteering said sensor array in the direction of the mainbeam comprises a plurality of delays, each said delay connected between a said sensor and a said nonlinear oscillator.

7. A receiver as recited in claim 1 wherein said frequency, {overscore (ω

)}, is the average of the natural frequencies for all said nonlinear oscillators.

8. A receiver as recited in claim 1 wherein said plurality of nonlinear oscillators are implemented on an analog VLSI chip.

9. A receiver as recited in claim 1 wherein the mainbeam signal has an approximate wavelength, λ

and wherein said sensors are spaced apart by a distance of approximately λ

/2.

10. A narrowband beamformer for operation on the output of a sensor array having a plurality of sensors, the sensor array being beamsteered in the direction of a mainbeam signal, each sensor for receiving the mainbeam signal of approximate frequency, Ω

, and sidelobe signals of approximate frequency, Ω

, said narrowband beamformer comprising;

a plurality of nonlinear oscillators, one said nonlinear oscillator connected to each sensor, each said nonlinear oscillator coupled to at least one other said nonlinear oscillator to allow each said nonlinear oscillator to create an output having a frequency of approximately, Ω

, in response to receipt of the mainbeam signal by the sensor array and to simultaneously allow each said nonlinear oscillator to create an output in a frequency spectrum that is centered on a frequency of approximately, {overscore (ω

)}, in response to receipt of a sidelobe signal by the sensor array;

a summer connected to each said nonlinear oscillator for receiving and summing said nonlinear oscillator outputs and creating a summer output; and

a matched filter connected to said summer for receiving said summer output and separating said summer output by frequency to distinguish the mainbeam signal from the sidelobe signals.

11. A narrowband beamformer as recited in claim 10 wherein said frequency, {overscore (ω

)}, is the average of the natural frequencies for all said nonlinear oscillators.

12. A narrowband beamformer as recited in claim 10 wherein said plurality of nonlinear oscillators are implemented on an analog VLSI chip.

13. A narrowband beamformer as recited in claim 10 wherein the plurality of sensors are arranged linearly in the sensor array with a second sensor juxtaposed between a first sensor and a third sensor;

and wherein a first said nonlinear oscillator having state vector, x₁, is connected to said first sensor, a second said nonlinear oscillator having state vector, x₂, is connected to said second sensor, and a third said nonlinear oscillator having state vector, x₃, is connected to said third sensor; and

wherein said second nonlinear oscillator is coupled to said first nonlinear oscillator and said third nonlinear oscillator according to the following relationship;

14. A narrowband beamformer as recited in claim 10 further comprising a plurality of weighting circuits, each said weighting circuit for multiplying each said nonlinear oscillator output by a weighing factor selected for each nonlinear oscillator prior to summation by said summer.

15. A method for beamforming the output of a plurality of beamsteered sensors comprising the steps of:

setting a critical phase lag, Δ

φ

_C;

providing a plurality of nonlinear oscillators;

connecting a separate said nonlinear oscillator to each beamsteered sensor;

coupling each said nonlinear oscillator to at least one other said nonlinear oscillator;

connecting each said nonlinear oscillator to a summer; and

adjusting the coupling strength between said coupled oscillators to cause said summer to output a signal having an approximate frequency, Ω

, in response to receipt of a signal having an approximate frequency, Ω

, by said beamsteered sensors when the phase lag, Δ

φ

, between any two beamsteered sensors is less than said critical phase lag, Δ

φ

_c, and to output a spectrum of signals centered on an approximate frequency, {overscore (ω

)}, in response to receipt of a signal of frequency, Ω

, by said beamsteered sensors when the phase lag, Δ

φ

, between any two beamsteered sensors is greater than said critical phase lag, Δ

φ

_c.

16. A method as recited in claim 15 further comprising the step of:

separating said summer output into signals having an approximate frequency Ω

, and signals centered on an approximate frequency, {overscore (ω

)}.

17. A method as recited in claim 16 wherein said separating step is performed using a matched filter.

18. A method as recited in claim 15 wherein said frequency, {overscore (ω

)}, is the average of the natural frequencies for all said nonlinear oscillators.