AMTI RADAR CLUTTER CANCELLING METHOD AND APPARATUS

• US 3,735,400 A
• Filed: 11/23/1971
• Issued: 05/22/1973
• Est. Priority Date: 11/23/1971
• Status: Expired due to Term

• Current Assignee: Carlyle J. Sletten, Holt F. Sheppard
• Original Assignee: Carlyle J. Sletten, Holt F. Sheppard
• Inventors: Sletten, Carlyle J., Holt, F. Sheppard
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/201,582
• Time in Patent Office: 546 Days
• Field of Search: 343/5CM,7.7,17.1R
• US Class Current: 342/161
• 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

Abstract

The locating and tracking of moving targets in ground clutter is accomplished by an airborne synthetic aperture radar system. Radar doppler echo signals are received simultaneously on three antennas disposed along the flight velocity vector of the aircraft. dispersive delay filters establish multiple narrow band channels for doppler signals in the clutter frequency spectrum and effect phase coincidence of such signals in each antenna. Clutter cancellation is accomplished by phase inverting the output of the center antenna and summing the outputs of adjacent antennas. Effective antenna gain and signal directivity on moving targets are increased by integrating many echoes following each filter. The doppler filters of the system are linked to the delay lines with an aircraft velocity dependent switch and gain adjusting means are provided for each antenna.

Claims

1. The method of cancelling clutter in an AMTI radar system comprising the steps of simultaneously receiving radar doppler echo signals on multiple radar antennas serially disposed in spaced relationship along the flight velocity vector of an AMTI radar bearing aircraft, separating the received doppler echo signals from each antenna into a multiplicity of narrow band clutter frequency spectrum signals and narrow band extra-clutter frequency spectrum signals, delaying the narrow band clutter frequency spectrum signals in each antenna channel to effect phase coincidence therebetween, effecting a 180* out of phase relationship between the clutter frequency spectrum signals of adjacent antennas, and summing the delayed, out of phase, clutter frequency spectrum signals of adjacent antennas.

2. An AMTI radar clutter cancelling system comprising first, second and third radar antennas serially disposed in spaced relationship along the flight velocity vector of an AMTI bearing aircraft, a filter means connected to each antenna for providing multiple narrow band doppler signal channels in the clutter frequency spectrum and narrow band doppler signal channels in the extra-clutter frequency spectrum, delay means connected to each clutter frequency spectrum channel adapted to effect phase coincidence between the doppler signals from each antenna, a phase-inverter connected to said second antenna, means for summing the delayed output of said first antenna and the phase-inverted, delayed output of said second antenna, and means for summing the delayed output of said third antenna and the phase-inverted, delayed output of said second antenna.

3. An AMTI radar clutter cancelling system as defined in claim 2 including switching means adapted to switch the outputs of said clutter frequency spectrum channels to appropriate selected delay means in response to changes in aircraft ground speed.

4. An AMTI radar clutter cancelling system as defined in claim 3 including gain adjusting means connected to said first and said third antennas.

5. An AMTI radar system comprising first, second and third radar antennas serially disposed in spaced relationship along the flight velocity vector of the AMTI radar bearing aircraft, a filter means connected to each antenna for providing multiple narrow band doppler signal channels in the clutter frequency spectrum and narrow band doppler signal channels in the extra-clutter frequency spectrum, delay means connected to each clutter frequency spectrum channel adapted to effect phase coiNcidence between the doppler signals from each antenna, a phase inverter connected to said second antenna, first summing means for summing the delayed output of said first antenna and the phase-inverted delayed output of said second antenna, second summing means for summing the delayed output of said third antenna and the phase-inverted delayed output of said second antenna, and phase comparison means adapted to compare the outputs of said first and second summing means and the outputs of the extra-clutter frequency spectrum narrow band doppler signal channels.

6. An AMTI radar system as defined in claim 5 including switching means adapted to switch the outputs of said clutter frequency spectrum channels to appropriate selected delay means in response to changes in aircraft ground speed.

7. An AMTI radar system as defined in claim 6 including gain adjusting means connected to said first and third antennas.

8. An AMTI radar system as defined in claim 7 including a moving range gate and integrating means connected between the outputs of each said first and second summing means and said phase comparison means.