Adaptive doppler filter banks

Claim 2

A radar system for cancelling radar clutter with a minimum of hardware, said radar system having a radar signal with a doppler frequency space, a pulse repetition rate and an interpulse period, comprising; a radar echo signal input; an N subband doppler filter bank for dividing the doppler frequency space of said input signal into N frequency subbands and generating a separate subband output signal for each of said subbands. an M degree-of-freedom adaptive moving-target indicator circuit, where M is equal to or greater than one; means for obtaining a set of M+1 consecutive samples from each of said subband output signals, sampled at a rate of the radar system's pulse repetition rate divided by N; and means for consecutively applying each set of M+1 consecutive subband samples to said adaptive moving-target indicator circuit in a desired order to remove radar clutter.

Claim 3

A radar system as defined in claim 1, wherein said applying means comprises M+1 commutating switches, with each commutating switch having N positions, designated from 1 to N, commutating at the pulse repetition rate.

Claim 4

A radar system as defined in claim 2, wherein said sample obtaining means comprises N delay lines, a different one of said delay lines connected to delay a different separate subband output signal, each of said delay lines having M series-connected delays, wherein each of said M series-connected delays is equal to said radar interpulse period; and means for tapping the signal at the beginning, the end, and between said delays in each of said delay lines to obtain a set of M+1 tapped signals from each delay line, and for each set, applying each of said M+1 tapped signals in said set to the same numbered position of a different one of said M+1 commutating switches, with each different delay line set of tapped signals applied to a different numbered position of said commutating switches.

Claim 5

A radar system as defined in claim 3, wherein said N subband doppler filter bank is an N-point Fast Fourier Transform circuit for dividing the doppler frequency space into N equal, contiguous frequency subbands.

Claim 6

A radar system for cancelling radar clutter with a minimum of hardware, said radar system having a pulse repetition frequency and an interpulse period, comprising: an N-subband doppler filter bank circuit for dividing the doppler frequency space between zero frequency and the pulse repetition frequency for the radar system into N frequency subbands and generating a separate subband output signal at a different output port for each of said N frequency subbands; means for applying a radar echo signal to said doppler filter bank circuit; N delay lines, a different one of said delay lines connected to each of said separate subband output ports, each of said delay lines having M series connected delays, where M is equal to or greater than one, and wherein each of said M series-connected delays is equal to said radar interpulse period; M+1 commutating switches, with each commutating switch have N positions, numbered from 1 to N, commutating at the pulse repetition rate; means for tapping the signal at the beginning, the end and between said delays in each of said delay lines to obtain a set of M+1 tapped signals from each of said N delay lines, and for each set, applying each of said M+1 tapped signals in said set to the same numbered position of a different one of said M+1 commutating switches, with each different delay line set of tapped signals applied to a different numbered position of said commutating switches; and a single M degree-of-freedom moving-target indicator connected to each of said M+1 commutating switches for adaptively cancelling clutter in each of said frequency subbands.

Claim 7

A radar system for cancelling radar clutter with a minimum of hardware, said radar system having a pulse repetition frequency and an interpulse period, comprising: an N-subband doppler filter bank circuit for dividing the doppler frequency space between zero frequency and the pulse repetition frequency for the radar system into N frequency subbands and generating a separate subband output signal at a different output port for each of said N frequency subbands; means for applying a radar echo signal to said doppler filter bank circuit; N delay lines, a different one of said delay lines connected to each of said separate subband output ports, each of said delay lines having M series connected delays, where M is equal to or greater than one, and wherein each of said M series-connected delays is equal to said radar interpulse period; M+1 commutating switches, with each commutating switch have N positions, numbered from 1 to N, commutating at the pulse repetition rate; means for tapping the signal at the beginning, the end and between said delays in each of said delay lines to obtain a set of M+1 tapped signals from each of said N delay lines, and for each set, applying each of said M+1 tapped signals in said set to the same numbered position of a different one of said M+1 commutating switches, with each different delay line set of tapped signals applied to a different numbered position of said commutating switches; and a single M degree-of-freedom moving-target indicator connected to each of said M+1 commutating switches for adaptively cancelling clutter in each of said frequency subbands.

Claim 8

A radar system as defined in claim 5, wherein said N subband doppler filter bank is an N-point Fast Fourier Transform for dividing the radar's doppler frequency space into N equal, contiguous subbands.

Claim 9

A radar system as defined in claim 6, wherein M=1.

Claim 10

A radar system as defined in claim 6, wherein said moving target indicator is an open loop adaptive canceller.

Claim 11

A radar system as defined in claim 6, wherein said moving target indicator is a closed-loop adaptive canceller.

Claim 12

A radar system as defined in claim 6, wherein said moving target indicator uses sliding-window-derived weights.

Claim 15

A method as defined in claim 11, wherein said adaptively cancelling step includes the step of commutatively switching each set of M+1 consecutive subband samples consecutively to a single M+1 degree-of-freedom adaptive moving-target indicator circuit.