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A band pass filter is an electronic circuit or device which allows only signals between specific frequencies to pass through and attenuates/rejects frequencies outside the range. Band pass filters are largely used in wireless receivers and transmitters, but are also widely used in many areas of electronics.
Band pass filters are easy to design and construct, and need only minimal components to build. For a band pass filter, the most important parameters are:
There are basically two types of band pass filters: narrow band pass filters and wide band pass filters. Narrow band pass filters have the selectivity of quality factor Q greater than 10, and wide band pass filters have the selectivity of quality factor Q less than 10. Some band pass filters might need an external source of power and use active components like integrated circuits and transistors; these are known as active band pass filters. Some band pass filters do not need any external source of power and use mainly passive components like inductors and capacitors; these are known as passive band pass filters. Compared to passive band pass filters, active band pass filters have more effective performance.
A band pass filter is capable of optimizing the signal-to-noise ratio and improving receiver sensitivity. Band pass filters are used in RF applications where tuned circuits are needed. They are used in transmitters to limit the bandwidth of the output signal, so that the signals are only transmitted in the band allocated for the transmission and thus do not interfere with other stations. Band pass filters in receivers help to allow signals within the selected frequency range to get through and block signals of unwanted frequencies. Band pass filters are also used in other fields such as atmospheric sciences, neuroscience and astronomy. Optical band pass filters are used in astronomy, spectroscopy, imaging, clinical chemistry and microscopy.