Band Stop Filters or or band-reject filters are used to block signals with a particular frequency range (or a particular set of frequencies). All signals in the stopband frequency range are attenuated and signals at other frequency ranges are allowed to pass with minimal losses. A bandstop filter is also known as a Notch Filter and these filters are formed by the combination of low pass and high pass filters with a parallel connection. They reject all frequencies that lie between the cut-off frequencies of the low-pass and high-pass filters. All frequencies that fall on either side of this range remain unattenuated.

Key Specifications:

Band Stop Frequency or Stopband Frequency: This is the frequency range that needs to be attenuated/blocked. So any signal in this frequency range will be attenuated by the filter. Some band stop filters have multiple band stop frequency bands, thereby blocking a set of frequencies. For example, if a filter has a band stop frequency from 1020 MHz to 1080 MHz. It will allow all frequencies up to 1020 MHz and above 1080 MHz to pass through.

Attenuation: This is the level of attenuation that any signal in the band stop region of the filter will experience. In an ideal world, this would be infinity, however, this is not the case in the real world - Values are usually above 15 dB here, the higher the better.

Insertion Loss: This is the loss that a signal in the passband of a Band Stop Filter experiences. The lower the insertion loss the better the filter.

Power Level: This is the maximum input power that the filter can handle.