× 之 十 十6 ∑ ∑ − = − = + = 1 2 0 2 2 1 2 0 2 1 ) ( ) ( N r rk N k N N r rk N Wr x W Wr x ) ( ) ( 2 1 k X W k X k N + = 1 0 − ≤ ≤ N k X1(k),X2(k)分别为偶数号序列和奇数号序列的N/2点 DFT,其周期均为N/2.  = + = + ) ( ) 2 ( ) ( ) 2 ( 2 2 1 1 k X N k X k X N k X k N N k N W W − = + 2 Q又