A filter is used to allow wanted frequency components from the signals and eliminate unwanted frequencies. Filter circuits are used for combining the properties of low pass filter and high pass filter, which is known as a bandpass filter. A bandpass filter (BPF) allows signals between two precise frequencies to pass but separates signals at other frequencies. Some of these filters are involved in an external power source and utilize active components like transistors and ICs. It is what done in “tuning” the desired frequency, such as a radio or television signal. They have communication systems for selecting only specific signals from a variety of signals. Some of the types of filters are active or passive, time-variant or time-invariant, linearity-linear, or non-linear or digital filters. Some of the bandpass design can be done with external power as well as active components such as integrated circuits, transistors, known as an active bandpass filter. Similarly, some of the filters may use any kind of power source as well as passive components like capacitors and inductors. Such a filter is known as a passive filter. These filters are also described by three critical features: center wavelength (CWL)—the wavelength at the center of the passband, full width at half maximum (FWHM)—the bandwidth at 50% of the maximum transmission.
A bandpass filter is used in varied applications including wireless transmitters and wireless receivers to limit the bandwidth of the output signal to the minimum necessary. It allows signals within a preferred range of frequencies to be decoded while avoiding signals at redundant frequencies from getting through.
There are many types of bandpass filters such as SAW, Cavity, Notch, Ceramic, etc. There is also a number of variations in the construction of a bandpass filter and each has its advantages. Most reputed manufacturers offer a variety of options so that you can select the best-suited filter type for your application. For the selection of an ideal BPF, one needs to consider the application and configuration of the system where you plan to integrate the filter. The frequency of BPF is specified in two ways. The first method is simple where it is described as a minimum and maximum frequency. It will allow a signal between the minimum and maximum frequency to pass and attenuate any signals outside this range. The other method for specifying the frequency of BPF is to state a center frequency and the bandwidth, the passband can be calculated by min = Centre Frequency - BW/2 and max = Centre Frequency + BW/2.
Every filter has some loss of passband. The lower the insertion loss, the better will be the performance of the filter. Similarly, one needs to consider the level attenuation or isolation for any signal outside the passband. There are many leading manufacturers in the industry offering a range of bandpass filters. One can find and compare filter products across manufacturers.
