f()=∑F Not =- 1 2 Snot at 2 jn∞1/2 jn∞1τ/2 71(-no1) 2元 nO,t 1 Sa(--) o1飞 2             = − −  =  =    −             − −       n n T E e e T jn E E e dt T F j n j n j n t n sin( ) ( ) ( ) / /   =− = n j n t f t Fn e 1 ( )  ( ) T1 n Sa    2