Method and apparatus for performing bistatic radar functions

• US 20050237236A1
• Filed: 04/11/2005
• Published: 10/27/2005
• Est. Priority Date: 04/26/2004
• Status: Active Grant

• Current Assignee: Robert D. Budic
• Original Assignee: Robert D. Budic
• Inventors: Budic, Robert D.
• Granted Patent: US 7,038,618 B2
• Time in Patent Office: Days
• US Class Current: 342/159
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/225 with cyclic repetition of a non-uniform pulse sequence, e.g. staggered PRF
• CPC Class Codes: G01S 13/284 using coded pulses
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures
• CPC Class Codes: G01S 7/414 Discriminating targets with respect to background clutter

Abstract

A bistatic radar system having a transmitter that generates unique signals at spatially independent transmitter degrees of freedom and a receiver that filters the signal at each receiver degree of freedom into a group of signals identical in number to the number of transmitter degrees of freedom. The receiver formats the filtered signals into a 2-dimensional array of elements. The receiver rotates the array so that the new axes are aligned with the Doppler gradient. The data is then re-sampled and projected to linearize the clutter signal. The receiver may be integrated with a broad class of adaptive and non-adaptive clutter mitigation approaches such as electronic clutter tuning and projected bistatic space-time adaptive processing, or STAP.

Claims

1. A bistatic radar system comprising:

a transmitter comprising;

a programmable waveform generator for creating an array of multiple independent transmitter waveforms;

a plurality of RF sections for transmitting said independent transmitter waveforms, wherein said RF sections translate said array of transmitter waveforms from IF to RF, amplify said array of transmitter waveforms, and use phase shifts and channel weighting to displace, shape and steer an array of transmitter beams for said array of transmitter waveforms; and

a receiver comprising;

a plurality of RF sections for receiving a radar signal, wherein each said RF section amplifies an array of transmitted signals, translates said array of transmitted signals from RF to IF, and uses phase shifts and channel weighting to displace, shape and steer an array of receiver beams;

a plurality of digital elements for sampling and processing said array of receiver beams;

means for generating an array of waveforms identical to said array of transmitter waveforms;

a transmit aperture expansion on receive module for computing bistatic measurements;

means for reduced rank clutter mitigation; and

means for detecting a moving target.

2. A bistatic radar sensor according to claim 1, wherein said array of transmitter waveforms comprises at least one of:

(a) approximately orthogonal waveforms with a common center frequency;

(b) non-recurring waveforms with random or pseudo-random sample-to-sample phase with a common center frequency and (c) Vandermonde-LaGrange waveforms;

.

3. A bistatic radar sensor according to claim 1 wherein said plurality of receiver RF sections comprises at least one of (a) a plurality of sub-apertures with spatially separated phase centers through which said array of data are received;

and (b) a plurality of receiver beams with distinct beam centers or pointing direction through which said array of waveforms are received.

4. A bistatic radar sensor according to claim 1 wherein said means for generating an array of receiver waveforms comprises a programmable waveform generator for creating an array of waveforms identical to said transmitter waveforms.

5. A bistatic radar sensor according to claim 1 wherein said means for generating an array of receiver waveforms comprises:

a direct path antenna; and

a means for filtering data from said direct path antenna data into an array of waveforms identical to said transmitter waveforms.

6. A bistatic radar sensor according to claim 1, wherein said transmit aperture expansion on receive module comprises a means for decomposing a received signal into plurality of distributed bistatic measurements, wherein each of said plurality of distributed bistatic measurements comprises signal energy that has been scattered by a specific transmitter element and received by a specific receiver element.

7. A bistatic radar sensor according to claim 6, wherein each of said plurality of distributed bistatic measurements further comprises signal energy that has been delayed by a specific value relative to a direct path signal and Doppler shifted by a specific value relative to the direct path signal.

8. A bistatic radar sensor array according to claim 7 wherein said means for decomposing a received signal into plurality of distributed bistatic measurements comprises:

means for generating a Complex Ambiguity Function by filtering said array of radar signals into a plurality of signal components, each said signal component comprising energy delayed by a specific value and Doppler shifted by a specific value relative to the direct path signal;

means for filtering said Complex Ambiguity Function into a second plurality of signal components, each of said second plurality of signal components comprising energy scattered by a specific transmit element and received by a specific receiver element; and

means for generating a plurality of 4-dimensional labels for components of signal energy.

9. A bistatic radar sensor according to claim 6 wherein said plurality of generalized bistatic aperatures are coherent.

10. A bistatic radar sensor according to claim 7 wherein Characteristic Clutter Locus (after TAXO-R) is a plane or set of parallel planes in a 3-dimensional space-time aperture spanned by transmitter and receiver indices and Doppler measurements. The normal to the planes is delay independent.

11. A bistatic radar sensor according to claim 1 wherein said means for reduced rank clutter mitigation comprises:

means for bistatic aperture compression; and

means for STAP processing.

12. A bistatic radar sensor according to claim 11 wherein said means for bistatic aperture compression comprises:

means for defining coordinates for a generalized bistatic aperture;

means for rotating the generalized bistatic aperture;

means for defining coordinates for the rotated generalized bistatic aperture;

means for re-sampling signal data on the rotated generalized bistatic aperture;

means for defining steering vectors for the generalized bistatic aperture;

means for defining steering vectors for the rotated generalized bistatic aperture; and

means for projection.

13. A bistatic radar sensor according to claim 12 wherein said means for rotating said generalized bistatic aperture comprises:

means for computing a rotation angle; and

means for applying the rotation to the generalized bistatic coordinates.

14. A bistatic radar sensor according to claim 12 wherein said means for re-sampling signal data comprises:

means for selecting bistatic aperture samples in the rotated grid that are aligned with rotated coordinate axes;

means for determining coordinates of the generalized bistatic aperture samples in a rotated grid; and

means for interpolating values of signal data at samples in said rotated grid as a function of values of signal data at coordinates of an original grid.

15. A bistatic radar sensor according to claim 12 wherein said means for computing a steering vector comprises:

means defining coordinate samples for steering vectors associated with the generalized bistatic aperture;

means for defining coordinate samples for steering vectors associated with the rotated aperture;

means for computing the steering vectors as a function of coordinates; and

means for decomposition into vertical and horizontal steering vectors.

16. A bistatic radar sensor according to claim 12 wherein said means for projection comprises:

means for weighting signal data on the rotated grid by vertical steering vectors; and

means for summing weighted signal data along the horizontal axis of the rotated generalized bistatic aperture.

17. A bistatic radar sensor according to claim 11 wherein said means for bistatic aperture compression generates a line or set of parallel lines in a 2-dimensional space wherein the slope of the line or lines is delay independent.

18. A bistatic radar sensor according to claim 11, wherein said means for STAP processing comprises:

means for filtering signal data to form a lower-dimensional sub-space of signal data; and

means for application of STAP processing to the sub-space of projected data spanned by horizontal steering vectors.

19. A bistatic radar sensor according to claim 8, further comprising means for Reduced Rank STAP processing.

20. A method of filtering and processing a received radar signal comprising the steps of:

receiving an element-level radar signal;

splitting said element-level radar signal into a plurality of signal components, each said signal component comprising energy scattered by a specific transmit element-receiver-element pair;

forming a 2-D array of data associated with a plurality of transmitter and receiver degrees of freedom;

rotating said 2-D array of data;

re-sampling said array of data to find new degrees of freedom; and

using a projection to eliminate residual degrees of freedom.