Xa(Q2)=DTFTIxa (()]=xa(t)e 2丌 文(92)=D7F[合 △7(12)=D7FT[d1() ∑ 32[X(92)*A(2) ∫=。Xa(j(12-j)d0 24(22x5(2-A2-0 T T ∑X2(-jg2,)1 ( ) ( ) 2 Xa T j j j d         2 ( ) [ ( )] ( ) T T s k j DTFT t k T              1 ˆ ( ) [ ˆ ( )] [ ( )* ( )] 2 Xa a a T j DTFT x t X j j        1 2 [ ( ) ( ) ] 2 a s k X j k d T                  1 ( ) ( ) a s k X j k d T                1 ( ) a s k X j jk T        ( ) [ ( )] ( ) j t Xa a a j DTFT x t x t e dt        