1. A computer-implemented filtering method for attenuating clutter in a radar signal from a target to a radar system, said signal being received by an antenna coupled to said radar system, said method comprising: determining properties of a clutter correlation function R c of the antenna for continuous clutter of an unknown azimuth angle θ at a time interval τ by a continuous 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 a boresight angle of the antenna, {dot over (θ)} is an antenna rotation rate, g is an angularly varying 4-way voltage antenna pattern gain, and {dot over (φ)} is a phase change rate and accounts for a linear motion of the antenna in off-boresight directions, j≡√{square root over (−1)} is the imaginary number, and g* is the complex conjugate of said pattern gain g; 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, azimuth angle θ SLB is a side-lobe blanker azimuth angle limit, and T s is a pulse repetition interval; optimizing said clutter-to-noise ratio by a combination matrix: 
 ( R c +R n ) −1 M s =0, where R s = I γ ⁢ I is a noise correlation matrix with I as an identity matrix and γ is a clutter-to-noise ratio; and obtaining a filter signal for the radar system from said combination matrix with which to detect and measure the target.