Adaptive clutter cancellation for synthetic aperture AMTI radar

• US 3,993,994 A
• Filed: 06/27/1975
• Issued: 11/23/1976
• Est. Priority Date: 06/27/1975
• 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.
• Primary Examiner(s): Tubbesing, T.H.
• Application Number:
  US05/590,973
• Time in Patent Office: 515 Days
• Field of Search: 343/5 CM, 343/7 A, 343/7.7
• US Class Current: 342/25.00B
• CPC Class Codes: G01S 13/5265 IF cancellers, e.g. TACCAR systems
• CPC Class Codes: G01S 13/9023 combined with interferometric techniques
• 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 7/2921 based on data belonging to one radar period

Abstract

Clutter cancellation between adjacent channels of a multichannel synthetic aperture AMTI radar is accomplished by delaying signals from the forward channel to coincide with signals from the aft channel and subtracting the outputs. Adverse effects from unknown, uncalibrated and time varying parameters are compensated for by adjusting the phase and amplitude of the aft channel coherent receiver output in response to the complex multiplier signal ω. The synthetic aperture processing circuit outputs of each channel are averaged over many range cells and summed to determine clutter magnitude. The complex multiplier signal ω is made to minimize the clutter magnitude by means of a steepest descent algorithm. A mathematical expression relating the complex multiplier signal ω to clutter magnitude for optimum clutter cancellation is developed and a circuit is provided for mechanizing the process.

Claims

1. In combination with a multichannel AMTI synthetic aperture radar system in which each channel includes a receive antenna, a coherent receiver connected thereto and a synthetic aperture processing circuit connected to process the output of said coherent receiver, clutter cancellation means for optimizing clutter cancellation between two adjacent channels comprising

means for delaying the output of the forward channel coherent receiver,

means for averaging the outputs of the adjacent channel synthetic aperture processing circuits over a multiplicity of range cells,

means for generating a clutter cancellation adjustment signal,

a first multiplier means for multiplying the clutter cancellation adjustment signal ω

with the output of the aft channel coherent receiver,

a second multiplier means for multiplying the averaged output of the aft channel synthetic aperture processing circuit with the clutter cancellation adjustment signal ω

, and

means for summing the product of said second multiplier means and the averaged output of the foward channel synthetic aperture processing circuit to obtain a clutter magnitude signal S_T, said clutter cancellation adjustment signal ω

being related to said clutter magnitude signal S_T in accordance with the expression ##EQU5##

2. In combination with a multichannel AMTI synthetic aperture radar system in which each channel includes a receive antenna, a coherent receiver connected thereto and a synthetic aperture processing circuit connected to process the output of the coherent receiver, means for maintaining optimum clutter cancellation between two adjacent channels comprising

a delay means connected between the forward channel coherent receiver and synthetic aperture processing circuit,

a first complex multiplier having two inputs and an output, a first input thereof being connected to the aft channel coherent receiver and the output being connected to the aft channel synthetic aperture processing circuit,

a first signal averaging means connected to the output of the forward channel synthetic aperture processing circuit,

a second signal averaging means connected to the output of the aft channel synthetic aperture processing circuit,

a signal complex conjugate transform means,

a scalor constant means,

second and third complex multipliers each having two inputs and an output,

first, second and third summing means, each having two inputs and an output,

a unit delay means, and an initial clutter cancellation signal source, the output of said first signal averaging means being connected to a first input of said third summing means, the output of said second signal averaging means being connected to said signal complex conjugate transform means and to a first input of said third complex multiplier, said second complex multiplier having its first input connected to the output of said signal complex conjugate transform means and its second input connected to the output of said third summing means, the output of said third complex multiplier being connected to the second input of said third summing means, said scalor constant means being connected between the output of said second complex multiplier and a first input of said first summing means, said unit delay means being connected between the output of said first summing means and a first input of said second summing means, said first input of said second summing means being connected to the second input of said first summing means, said second summing means having its second input connected to said initial clutter cancellation signal source and its output connected to the second input of said third complex multiplier and to the second input of said first complex multiplier.