Method and apparatus for improving the slowly moving target detection capability of an AMTI synthetic aperture radar

• US 4,086,590 A
• Filed: 01/21/1977
• Issued: 04/25/1978
• Est. Priority Date: 03/27/1975
• Status: Expired due to Term

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Goggins, William B. Jr.
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US05/761,507
• Time in Patent Office: 459 Days
• Field of Search: 343/5 CM
• US Class Current: 342/25.00B
• CPC Class Codes: G01S 13/4481 Monopulse hybrid systems, e.g. conopulse
• CPC Class Codes: G01S 13/449 Combined with MTI or Doppler processing circuits
• 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 13/9092 combined with monopulse techniques

Abstract

Detection of slowly moving and stationary targets that are normally obscured by ground clutter is accomplished by an AMTI synthetic aperture radar system that utilizes multiple receiving antennas mounted along the flight velocity vector of the radar bearing aircraft. Each antenna is separated by a distance d from each other. Synthetic arrays are formed by processing the radar returns from each antenna terminal. The radar PRF is controlled so that the aircraft flies a distance d during the interpulse period. The synthetic array outputs of adjacent pairs of antennas are subtracted to provide clutter cancellation. The resulting outputs from adjacent terminals can be used in a monopulse mode for angular discrimination.

Claims

1. The method of detecting slowly moving targers with a pulsed AMTI synthetic aperture radar system having multiple receiving antenna elements comprising the steps of

positioning said receiving antenna elements at equal separation distance d along the flight velocity vector V_o of the AMTI radar bearing aircraft,

controlling the PRF of said radar to maintain an interpulse period T of d/V_o, and

differencing the outputs of the synthetic aperture processing circuits of adjacent pairs of receiving antenna elements.

2. The method of detecting slowly moving targets as defined in claim 1 including the further step of

processing the differenced outputs of said synthetic aperture processing circuits with monopulse circuits for target angle determination.

3. The method of detecting slowly moving targets as defined in claim 2 including the further step of

providing simultaneous synthetic aperture processing means for targets travelling in a plurality of different discrete velocity ranges.

4. A pulsed AMTI synthetic aperture radar comprising

a multiplicity of receiving antenna elements spaced at equal separation distances d along the flight velocity vector V_o of the radar bearing aircraft,

aircraft velocity determining means,

Prf control means responsive to said aircraft velocity determining means and adapted to maintain a radar system interpulse period T of d/V_o,

synthetic aperture processing circuits connected to process received signals from said receiving antenna elements, and

clutter cancelling means connected to difference the outputs of the synthetic aperture processing circuits of adjacent pairs of receiving antenna elements.

5. A pulsed AMTI synthetic aperture radar as defined in claim 4 including monopulse circuits connected to process the outputs of said clutter cancelling means.

6. A pulsed AMTI synthetic aperture radar as defined in claim 5 wherein said synthetic aperture processing circuits include multiple synthetic aperture arrays effective to simultaneously detect targets travelling in different discrete velocity ranges.

7. A pulsed AMTI synthetic aperture radar comprising

first, second and third antenna elements spaced at equal distances d along the flight velocity vector V_o of the radar bearing aircraft,

a radar transmitter connected to transmit radar signals through as least one antenna element,

aircraft velocity determining means,

Prf control means responsive to said aircraft velocity determining means and adapted to maintain a radar system interpulse period T of d/V_o,

a coherent receiver connected to each antenna element,

a first synthetic aperture processing circuit connected to receive radar return signals from the coherent receiver connected to said first antenna element,

second and third synthetic aperture processing circuits connected to receive in parallel radar return signals from the coherent receiver connected to said second antenna element,

a fourth synthetic aperture processing circuit connected to receive radar return signals from the coherent receiver connected to said third antenna element,

a timing circuit, said timing circuit effecting the simultaneous formation of synthetic aperture arrays with said first and second synthetic aperture processing circuits and the simultaneous formation of synthetic aperture arrays with said third and fourth synthetic aperture processing circuits at a delayed time t_o equal to d/V_o,

a first array subtraction circuit connected to difference the outputs of said first and second synthetic aperture circuits,

a second array subtraction circuit connected to difference the outputs of said third and fourth synthetic aperture circuits, and

a monopulse circuit connected to process the outputs of said first and second array subtraction circuits.