Bandpass filters are two-port devices that provide transmission at frequencies within the passband of the filter and attenuation of other frequencies outside of the band. A band pass filter is used to prevent interference of signals and effectively utilize a frequency. A bandpass filter is the parts used at the mobile radio communication base station such as a cellular mobile telephone, a personal communications service (PCS) and a wireless local loop (WLL), and a radio frequency (RF) band.
The role which a bandpass filter is to fulfill is transmitting to a few loss signals which lie in a desired frequency band while intercepting all the frequencies outside the desired band. A bandpass filter freely passes frequencies within specified range, while rejecting frequencies outside the specified limits, and can be designed to provide symmetric or asymmetric characteristics. In microwave communications, the microwave frequency spectrum has become severely crowded and has been subdivided into a vast number of different frequency bands.
Microwave bandpass filters provide an output signal only at a precise (narrow) frequency band. Also, the filter can be tuned to a precise frequency band with there being a separate filter for each precise frequency band. In the field of communications, performance of a filter determines an effective use of a frequency which is an important resource. A bandpass filter allows a narrow range of frequencies to pass through it unattenuated, and blocks out all other frequencies. This narrow range of frequencies is the filter's passband. In the satellite communications technology, band pass filters in the microwave range play an important role in the preselection of individual communication channels.