What is a Notch Filter?

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- everything RF

Jul 25, 2021

A Notch Filter is also known as a Band Stop filter or Band Reject Filter. These filters reject/attenuate signals in a specific frequency band called the stop band frequency range and pass the signals above and below this band. For example, if a Notch Filter has a stop band frequency from 1500 MHz to 1550 MHz, it will pass all signals from DC to 1500 MHz and above 1550 MHz. It will only block those signals from 1500 MHz to 1550 MHz.

When selecting a Band Stop Filter or Notch Filter the following are important parameters to evaluate:

Stop Band Frequency: Any signal in this frequency range will be attenuated by the Notch Filter.

Attenuation/Rejection in the Stop Band: This is the level of attenuation that the filter will provide in the stop band. This is usually represented in dB.

Insertion Loss: This is the loss that the filter will provide outside the stop band. The lower the insertion loss outside the stop band the better. Insertion Loss is represented in dB.

Transition from Stopband to Passband: This may not be represented in the specs, however is important. It is a measure of how quickly the filter moves from the stop band to the passband. So if the stop band is 2300 to 2400 MHz. How quickly does it transition to having low loss. The quicker the transition the better.

Power Handling Capability of the Filter: This is the maximum power that the notch filter can handle.

Package Type: There are a number of form factors and package types in which these notch filters are available.

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