Patent ID: 6563455
Filing Date: 2003-05-13
Classification: G01S

Abstract:
A method of filtering radar source data comprising distance Doppler matrices X1 and X2 of two receiving channels, by Space-Time Adaptive Processing (STAP), wherein the data of the distance/Doppler matrices X1 and X2 of individual adjacent channels (left/right) as well as of sum and difference signals (&Sgr;/&Dgr;) are processed according to the same procedure, and wherein both computation of filter coefficients &agr;(i) and &bgr;(i), and filtering take place in the frequency domain, said method comprising:determining auto-correlations r11 and r22 and cross-correlations r12 of the signals X1 and X2 of both receiving channels, according to the following equations: r11&it;(i)=&Sum;j=1NRG&it;X1&it;(i,j)&CenterDot;X1*&it;(i,j)r22&it;(i)=&Sum;j=1NRG&it;X2&it;(i,j)&CenterDot;X2*&it;(i,j)r12&it;(i)=&Sum;j=1NRG&it;X1&it;(i,j)&CenterDot;X2*&it;(i,j)wherein X1 (i, j) is a complex range/Doppler matrix of a first of the two channels, X2 (i, j) is a complex range/Doppler matrix of a second of the two channels, NDZ is a number of Doppler cells, NRG is a number of range gates, and 1&lE;i&lE;NDZ;determining whether the first channel has the better signal-to-noise ratio according to the following condition max&it;(r11&it;(i)|1&leq;i&leq;NDZ)&Sum;i=1NDZ&it;r11&it;(i)>max&it;(r22&it;(i)|1&leq;i&leq;NDZ)&Sum;i=1NDZ&it;r22&it;(i);applying a selection rule which provides that if the first channel has the better signal-to-noise ratio, the filtering coefficients a (i) and b (i) are determined according to a(i)=âˆ’(2l+1) b&af;(i)=&Sum;k=NDZ-lNDZ+l&it;r12&af;((i+k-1)&it;mod&it;â€ƒ&it;NDZ+1)r22&af;((i+k-1)&it;mod&it;â€ƒ&it;NDZ+1)for 1&lE;i&lE;NDZ, and l=0, 1, 2, k being a summation index . . . ,and if the first channel does not have the better signal-to-noise ratio, the filtering coefficients a (i) and b (i) are determined according to a&af;(i)=&Sum;k=NDZ-lNDZ+l&it;r12*&af;((i+k-1)&it;mod&it;â€ƒ&it;NDZ+1)r11&af;((i+k-1)&it;mod&it;â€ƒ&it;NDZ+1)â€ƒb(i)=âˆ’(2l+1)for 1&lE;i&lE;NDZ, and l=0, 1, 2, k being a summation index . . . ;scaling the calculated coefficients a (i) and b (i) according Î±&it;(i)=a&it;(i)a&it;(i)&CenterDot;a*&it;(i)+b&it;(i)&CenterDot;b*&it;(i)Î²&it;(i)=b&it;(i)a&it;(i)&CenterDot;a*&it;(i)+b&it;(i)&CenterDot;b*&it;(i)for 1&lE;i&lE;NDZ; andfiltering the signals X1 and X2 in the frequency domain according to Yclutterfree(i,j)=&agr;(i)Â·X1(i,j)+&bgr;(i)Â·X2(i,j) wherein 1&lE;i&lE;NDZ and 1&lE;j&lE;NRG to provide a result matrix Yclutterfree which represents a range/Doppler matrix wherein echoes of stationary targets are suppressed and echoes of moving targets are coherently intensified.