Band pass filter is a frequency patrol picket in an electronic device. This “picket” would allow frequencies of a certain-calibrated/desired-bandwidth to pass through and prevent the unsolicited signals from getting through for further process.
Band pass filter is used in wireless communication transmitters and receivers. Rejection of non-calibrated frequencies helps the transmitter to limit the bandwidth of the output signals to the band allocated for the said transmission.
As a result, the transmitter in use is prevented from interfering among itself at one station and of the other stations too.
There are two types of band-passes-1) Narrow Band Pass and 2) Wide Band Pass. The narrow band-pass filter has a bandwidth small to the average frequency of the band and if the quality factor value is less than 10, it is a wide bandpass.
Further, band pass filter has two categories. 1) Active Band pass and 2) Passive Band pass.
Active bandpass has active components like operation amplifier (Op-Amp) along with resistors and capacitors. Passive band pass uses passive components resistors, capacitors, and inductors-Inductors are not used in active bandpass.
Ideal band pass filter would have a flat band and completely block frequencies outside the calibrated bandwidth-with no gain/attenuation across.
Practically, however, no bandpass is ideal as it doesn’t completely eliminate signals just outside the permitted bandwidth. This is known as filter roll-off.
However, designers/manufacturers succeed in keeping the roll-offs are kept as narrow as possible for the band pass filter to operate as per design. See the Raditek website.