5.1.1 Ideal Frequency-Selective Filters Ideal bandstop filter h,e）+,e(e-8 01@Kw2 others hos n]=n] sinan sinaan ，-0<n<0 πn πn .Noncausal,not computationally realizable ◆no phase distortion 1H(el) -π-02 一0%0 0c2 8◆Ideal bandstop filter − 0  ( ) H ej 1 −c2 −c1 c1 c2 5.1.1 Ideal Frequency-Selective Filters 8 ◆Noncausal, not computationally realizable ◆no phase distortion   2 1 sin [ ] sin , bs c n c n n n n n n h      = + − −  ( ) ( ) ( )  0, | | 1 2 1, j c c b j hp j lp H es oth r H H e e s e         + = =