A Band Pass Filter is an electronic device or circuit that acts as a gatekeeper, allowing signals that fall between two specific frequencies to pass while discriminating against signals at other frequencies. The range of frequencies that can pass through the filter is referred to as the passband.
Band pass filters are widely used in radio frequency transmitters and receivers. In a transmitter a band pass filter limits the bandwidth of the output signal, restricting the emission of undesired frequencies. In a receiver a band pass filter can be used to prevent unwanted signals being detected and processed. In both applications the band pass filter minimises interference, allowing communications to be optimised.