Two-channel array for moving target indications

• US 10,359,510 B2
• Filed: 01/26/2016
• Issued: 07/23/2019
• Est. Priority Date: 01/26/2016
• Status: Active Grant

• Current Assignee: Information Systems Laboratories, Inc.
• Original Assignee: Information Systems Laboratories, Inc.
• Inventors: Bergin, Jameson S.
• Primary Examiner(s): Gregory, Bernarr E
• Assistant Examiner(s): Pervin, Nuzhat
• Application Number:
  US15/006,860
• Publication Number:
  US 20170212217A1
• Time in Patent Office: 1,274 Days
• Field of Search: 342 25 B
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/0209 Systems with very large relative bandwidth, i.e. larger than 10 %, e.g. baseband, pulse, carrier-free, ultrawideband
• CPC Class Codes: G01S 13/9029 specially adapted for moving target detection within a single SAR image or within multiple SAR images taken at the same time
• CPC Class Codes: G01S 2013/0254 Active array antenna
• CPC Class Codes: G01S 2013/0272 Multifunction radar

Abstract

A radar antenna system includes a single transmitter for creating pulses from a wideband waveform. A splitter divides each pulse into half-power pulses, and sends them along respective paths. On one path, successive half-power pulses are alternately modulated with a phase shift ϕ_A or ϕ_F. On the other path, the half-power pulses are not modulated. Each modulated half-power pulse is then combined with an un-modulated half-power pulse to transmit pulses of a full aperture beam with either ϕ_A or ϕ_F. This establishes two degrees of freedom for the system. Two separate receivers then simultaneously receive the pulse echoes and a signal processor uses the consequent four degrees of freedom to create a radar indicator with mitigated clutter and useable azimuth estimation. A coherent processing interval can then be selected for multi-mode operation of the system.

Claims

1. A radar antenna system which comprises:

a generator for creating pulses of a wideband waveform;

a splitter for dividing each individual pulse into a first half-power pulse and a second half-power pulse;

circuitry for directing the first half-power pulse along a first path, and for directing the second half-power pulse along a second path;

a switch positioned on the first path to alternately modulate, in sequence, a first phase shift (ϕ

_A), and a second phase shift (ϕ

_F) on successive half-power pulses on the first path;

a means for combining the modulated half-power pulses from the first path with the un-modulated half-power pulses from the second path to alternately create a first full aperture beam having a unique steering direction determined by the phase shift (ϕ

_A), and a second full aperture beam having a unique steering direction determined by the phase shift (ϕ

_F);

a first receiver for receiving respective pulse echoes from the first full aperture beam and from the second full aperture beam to establish a first signal;

a second receiver for receiving respective pulse echoes from the first full aperture beam and second full aperture beam to establish a second signal; and

a signal processor for using the first and second signals to create a radar indicator.

2. A system as recited in claim 1 wherein the switch is a Single Pole Double Transmit (SPDT) switch.

3. A system as recited in claim 1 wherein a slow-time modulation is employed on half-power pulses on the first path.

4. A system as recited in claim 3 wherein the slow-time modulation is bi-phase.

5. A system as recited in claim 1 wherein a coherent processing interval is selected to mitigate clutter and minimize endo-clutter azimuth estimation.

6. A system as recited in claim 1 wherein the first receiver includes a means for reordering the first signal into a bifurcation, wherein the bifurcation comprises:

a first subset of pulses with each pulse having the first phase shift (ϕ

_A); and

a second subset of pulses with each pulse having the second phase shift (ϕ

_B), wherein the first subset combines with the second subset to establish two receive degrees of freedom for the first signal.

7. A system as recited in claim 6 wherein the second receiver includes a means for reordering the second signal into a bifurcation, wherein the bifurcation comprises:

a first subset of pulses with each pulse having the first phase shift (ϕ

_A); and

a second subset of pulses with each pulse having the second phase shift (ϕ

_B), wherein the first subset combines with the second subset to establish two receive degrees of freedom for the second signal.

8. A system as recited in claim 7 wherein the two receive degrees of freedom of the first signal, and the two receive degrees of freedom of the second signal, are used together to provide four degrees of freedom for creation of the radar indicator.

9. A method for operating a radar antenna system, wherein use of a transmitter in the system comprises the steps of:

generating a wideband waveform;

creating pulses of the waveform;

splitting each pulse into a first half-power pulse and a second half-power pulse;

directing a plurality of the first half-power pulse along a first path, and a plurality of the second half-power pulse along a second path;

alternately modulating, in sequence, a first phase shift (ϕ

_A) and a second phase shift (ϕ

_F)on successive first half-power pulses on the first path;

sequentially combining a modulated first half-power pulse from the first path with an un-modulated second half-power pulse from the second path to alternately create pulses for a first full aperture beam having a unique steering direction, and pulses for a second full aperture beam having a unique steering direction; and

alternately transmitting a respective pulse of the first full aperture beam and of the second full aperture beam.

10. A method as recited in claim 9 wherein receiving return signals (echoes) from the first full aperture beam and from the second full aperture beam comprises the steps of:

receiving the pulse echoes with respective phase shifts (ϕ

_A) and (ϕ

_F) at a first receiver to establish a first signal having two degrees of freedom;

receiving pulse echoes with respective phase shifts (ϕ

_A) and (ϕ

_F) at a second receiver to establish a second signal having two degrees of freedom; and

combining the first and second signals to use four degrees of freedom for creation of a radar indicator.

11. A method as recited in claim 10 further comprising the steps of:

reordering the first signal into a bifurcation having a first subset of pulses wherein each pulse has the first phase shift (ϕ

_A), and a second subset of pulses wherein each pulse has the second phase shift (ϕ

_B); and

separating the first subset from the second subset to establish two degrees of freedom for the first signal.

12. A method as recited in claim 11 further comprising the steps of:

reordering the second signal into a bifurcation having a first subset of pulses wherein each pulse has the first phase shift (ϕ

_A) , and a second subset of pulses wherein each pulse has the second phase shift (ϕ

_B); and

separating the second subset from the first subset to establish two degrees of freedom for the second signal.

13. A method as recited in claim 12 wherein the two degrees of freedom of the first signal, and the two degrees of freedom of the second signal, are used together in the combining step to provide four degrees of freedom for creation of the radar indicator.

14. A method as recited in claim 9 wherein the alternately modulating step is accomplished using a Single Pole Double Transmit (SPDT) switch.

15. A method as recited in claim 9 further comprising the step of selecting a coherent processing interval to mitigate clutter and minimize endo-clutter azimuth estimation.

16. A method as recited in claim 9 further comprising the step of selecting a coherent processing interval to selectively accommodate Synthetic Aperture Radar (SAR) and Ground Moving Target Indications (GMTI) operations.