What is Notch Filter?

Notch filters are band-reject filters or stop band filters designed to provide maximum attenuation or rejection to a particular range of frequency. A band-reject filter with a narrow stop band is usually known as a notch filter.

The notch filter has two regions

Passband region: frequency range with minimum attenuation level (typically close to 0 dB).

Stop band region: frequency range with a maximum attenuation level. It is one of the specifications of the filter.

In electronic circuits, notch filters can be constructed using LC (Inductor and Capacitor) combination in Series and Shunt configuration. Below image shows electrical representation of notch filters in both configuration.

What are the specifications of a notch filter?

Stop band (bandwidth): the range of frequency it blocks/attenuates.

Passband range: the range of frequency it allows to pass through.

Insertion Loss: is the loss of the pass band region (typically very low IL for pass band frequency) and maximum attenuation level at the stop band.

Power: the highest power level filter can handle. The power level of the notch filter can vary depending on the applications and physical size of the filters.

Operating temperature: notch filters are designed to operate accurately within a temperature range.

Other specifications

Connector type: notch filters for RF test applications usually comes with an RF connector (SMA, N-type, etc.…). Miniaturized notch filters and SMD-sized filters are also available for various applications.

Package type: notch filters are available from millimeter size (used in RF modules) to a few inches long (used in high power applications).

Frequency Response of Notch filter

The above image shows the frequency response of the 750MHz notch filter. At 750Mhz, it has the highest attenuation and minimum attenuation for lower and higher frequency ranges.

Tunable Notch Filters (band reject)

Tunable notch filters are band-reject filters with tunable knobs or controls to shift the frequency high or low. These filters are specifically used in test environments where fine-tuning is necessary to avoid a certain frequency range.

Notch filters are used in a variety of applications including signal processing, signal detection, and signal filtering. This can be used to reduce noise in a signal or to reduce a signal’s bandwidth without changing the frequency. In some cases, notch filters are also used to limit the bandwidth of the signal, which can be used to reduce the frequency of the signal.

What are the applications of Notch filters?

In radio frequency communication

A notch filter can be used in RF modules to reduce the amount of noise that is picked up by the receiver. The notch filter is usually placed between the antenna and the receiver so that it can help reduce the noise.

It can be placed in the front end of the receiver as well. Notch filters are also used in radio frequency interference suppression. The filters are typically used to reduce the noise generated by the transmitter.

A radio-frequency notch filter is a device that blocks radio waves, preventing them from entering or exiting a certain area of an electronic circuit. The notch filter is usually used in protecting an electronic circuit from damaging radio-frequency radiation.

In RF test laboratories

The notch filter is used in the test laboratory to filter out interference from other equipment. Some complex test setup requires notch-off (filter) specific frequency to improve measurement accuracy.

Other applications

Some applications of radio frequency notch filters are in mobile phones, Wi-Fi routers, and two-way radios. Notch filters are used to remove interfering signals from a communication system.

Radio frequency notch filters are used in a variety of applications, including radio communications such as long-distance communications devices like ham radio, marine radio communication, etc.…

Notch filters are used in medical equipment,

In audio devices, notch filters are used to improve the sound quality of signals.