例:x(nm)=R(n),求: ()X(z) (2)X(eo) (3)令xw(n)= ∑xn+mN)R,(m求X,()=DFT[xxm,N=16 解: () X(2)=1z8 1-219 z>0 (2) X(ei)= -e-jo8 e。sin = 2 1-e-jo 2 (3) X(k)=X(e)儿w= π sin =e 2 k=0,1,2,.,15 sin k 16 20 例 ( ) ( ) 1 ( ) (2) ( ) j R XX 求 () 例: 8 () (), 1 () (2) ( ) (3) ( ) ( ) ( ) ( ) [ ( )], 16 j N NN N x n R n X z X e x n x n mN R n X k DFT x n N 求: () 令 ,求 m- 解: -8 1-z 解: (1) X z z 0 ( )= 1 (1) X z , z 0 1 z - ( ) - 8 j 1 j e 7 8 sin 2 j j 1 (2) X e ) 1 j ee ( 2 21 sin 2 j e 2 N j N k (3) X (k) X e ) | ( 2 7 16 sin 2 0, 1, 2, , 15 j k k e k 20 sin 16 k