Adaptive moving target indicator (MTI) clutter rejection filter for radar systems

• US 20090109083A1
• Filed: 10/25/2007
• Published: 04/30/2009
• Est. Priority Date: 10/25/2007
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Tietjen, Byron W.
• Granted Patent: US 7,903,024 B2
• Time in Patent Office: Days
• US Class Current: 342/91
• CPC Class Codes: G01S 13/28 with time compression of received pulses
• CPC Class Codes: G01S 13/5244 Adaptive clutter cancellation specially adapted for airborne MTI, G01S13/5242
• CPC Class Codes: G01S 13/5246 post processors for coherent MTI discriminators, e.g. residue cancellers, CFAR after Doppler filters

Abstract

Apparatus for providing moving target indicator (MTI) filtering in the presence of clutter for a radar receiver employing digital pulse compression to provide at an output a compressed digital pulse for application to the input of a MTI digital filter, including a digital adaptive filter of the same weight as the MTI filter and operative to receive the compressed pulse to provide at outputs of the filter a set of weighted filter coefficients, wherein the weighted coefficients are applied to the MTI filter during a predetermined clutter mode.

Claims

1. Apparatus for providing moving target indicator (MTI) filtering in the presence of clutter for a radar receiver employing digital pulse compression to provide at an output a compressed digital pulse for application to the input of a MTI digital filter, comprising:

a digital adaptive filter of the same weight as said MTI filter and operative to receive said compressed pulse to provide at outputs of said filter a set of weighted filter coefficients, wherein said weighted coefficients are applied to said MTI filter during a predetermined clutter mode.

2. The apparatus according to claim 1, wherein said weighted coefficients are applied according to a switch.

3. The apparatus of claim 2, where said switch is operative in a first mode for applying a set of conventional weight coefficients to said MTI filter and operative in a second mode to apply said weighted coefficients from said adaptive filter to said MTI filter.

4. The apparatus according to claim 3, further comprising:

a threshold detector responsive to detected clutter to provide at an output a signal indicative of clutter above a predetermined level, said detector coupled to said switch to operate said switch in said second state to apply said weighted coefficients to said MTI filter.

5. The apparatus according to claim 3, wherein said digital MTI filter includes a N stage shift register, where N is a positive integer greater than 1 with each stage having an output with each output coupled to an input of an associated multiplier, with each multiplier having an input for receiving a multiplier coefficient wherein during said first mode said multipliers receive an associated conventional weight coefficient and during said second mode said multipliers receive an associated weight coefficient from said adaptive filter.

6. The apparatus according to claim 5, wherein N=5, whereby said MTI filter has a 5 stage shift register and said adaptive filter has a 5 stage shift register.

7. A method for providing moving target indicator (MTI) filtering in the presence of clutter for a digital pulse compression radar receiver having a digital MTI filter of the type including a N stage shift register with the output of each stage coupled to the input of a associated multiplier with another input of each multiplier receiving a coefficient for determining the filter response during radar operation;

the method comprising the steps of;

recalculating the coefficients for each multiplier during a determined large clutter mode, and

applying said recalculated coefficients to said multipliers during said large clutter mode.

8. The method according to claim 7, wherein the step of calculating includes,

employing a digital adaptive filter of the same weight as said MTI filter in said receiver, said adaptive filter receiving said compressed pulse and operative to generate a set of coefficients for said MTI filter multipliers,

determining a large clutter condition, and

applying said generated coefficients from said adaptive filter to said MTI filter during said large clutter condition.

9. The method according to claim 8, wherein N=5, wherein said digital MTI filter has a 5 stage shift register as does said adaptive filter.

10. A method for providing MTI filtering in the presence of clutter for a radar receiver employing digital pulse compression to provide at an output a compressed digital pulse for application to the input of a N state digital MTI filter, comprising the steps of:

using an adaptive digital filter of N stages,

applying said compressed digital pulse to the input of said adaptive digital filter to cause said adaptive digital filter to provide a set of N filter coefficients, and

applying said set of N filter coefficients to said MTI filter during a predetermined clutter mode.

11. The method according to claim 10, wherein said predetermined clutter mode is a large clutter mode when the clutter as detected from a radar clutter map processor exceeds a given threshold.