5.1.1 Ideal Frequency-Selective Filters ◆ Ideal bandstop filter 0,w<|w<w H others H W。0W 丌8 5.1.1 Ideal Frequency-Selective Filters ◆Ideal bandstop filter ( ) 1 2 0, 1, jw c c bs w w w H e others    =   − 0  ( ) jw H e 1 1 wc 1 − wc 2 wc 2 − wc