N/2仍为偶数,进一步分解:N/2→N/4 x1(2)=x3( 7=0,1,…,N/4-1 x(2+1)=x(0 X1(k)=X3(k)+WN24( X(k+)=X3(k)-Wk2X)k=0 N 4 x3(0)=x1(0)=x(0) X3(0) X1(0) 点 (1)=x1(2)=x(4) DET 3(1) x4(0)=x1(1)=x(2 X4(0) N X1(2) 点 x4(1)=x1(3)=x(6 DFT X4(D) X1(3) N/2 图4-3由两个N4点DFT组合成一个N2点DFT1 3 1 4 (2 ) ( ) (2 1) ( ) x l x l x l x l       l  0,1,...,N / 4 1 1 3 / 2 4 1 3 / 2 4 ( ) ( ) ( ) ( ) ( ) ( ) 4 k N k N X k X k W X k N X k X k W X k           0,1,..., 1 4 N k   N / 2仍为偶数，进一步分解：N / 2  N / 4