Bandstop filters(BS) or bandstop filters select certain frequencies that should not enter the transmission path. They attenuate a certain frequency range while the remaining frequencies are transmitted.
The function of a bandstop filter is the reverse of that of a bandpass filter; physically, it is a parallel connection of a high-pass and a low-pass filter in which the restricted frequency range is suppressed.
Bandstop filters with extremely narrow frequency characteristics and high slope can also be notch filters. Such filters are used, among other things, in broadband networks and in local networks in broadband topology, where frequency ranges can be occupied twice by using several head-end stations.