1. A computer-implemented filtering method for attenuating clutter from a radar signal from a target, said signal being received by an antenna, said method comprising: determining properties of a correlation function R c of the antenna for clutter of unknown azimuth angle θ by a relation: 
 R c (τ)=∫ g (θ−θ p ) g *(θ−θ p −τ{dot over (θ)})exp [− j τ{dot over (φ)}(θ−θ B −τ{dot over (θ)})] dθ, where θ p is a pointing angle of a beam from the antenna, θ B is boresight angle of the antenna, {dot over (θ)} is an antenna rotation rate, g is angularly varying two-way voltage antenna pattern gain, τ is time offset, and {dot over (φ)} is the phase change rate and accounts for the linear motion of the antenna in directions that are off-boresight, j≡√{square root over (−1)} is the imaginary number, and for clutter of known azimuth angle θ c : 
 R c (τ)= g (θ c −θ p ) g *(θ c −θ p −τ{dot over (θ)})exp [− j τφ(θ c −θ B −τ{dot over (θ)})], where g* is the complex conjugate of said pattern gain g; estimate target spectrum and correlation properties from radar as: R s ( τ ) = exp [ - j ( ω d τ ) ] 2 θ SLB ∫ θ p - θ SLB θ p + θ SLB exp [ - jτ ϕ. ( θ - θ B - τ θ. ) ] g ( θ - θ p ) g * ( θ - θ p - τ θ. )  θ where w d is the target's angular Doppler frequency and azimuth angle θ SLB is a side-lobe blanker azimuth angle limit; completing an interference correlation matrix using a clutter-to-noise ratio using associated correlation function R c ; and estimating said clutter-to-noise ratio for a signal correlation matrix: M s ( i , k ) = exp [ - j ( i - k ) T s ] 2 θ SLB R c [ ( i - k ) T s ] ; where i is the row index, k is the column number and T s is the time between pulses known as the pulse repetition interval.