带通滤波器

带通滤波器是指能通过某一频率范围内的频率分量、但将其他范围的频率分量衰减到极低水平的滤波器，与带阻滤波器的概念相对。一个模拟带通滤波器的例子是电阻-电感-电容电路(RLC circuit)。这些滤波器也可以用低通滤波器同高通滤波器组合来产生.

An ideal filter would have a completely flat passband (e.g. with no gain/attenuation throughout), and would completely attenuate all frequencies outside the passband. Additionally, the transition out of the passband would be instantaneous in frequency. In practice, no bandpass filter is ideal. The filter does not attenuate all frequencies outside the desired frequency range completely; in particular there is a region just outside the intended pass band where frequencies are attenuated, but not rejected. This is known as the filter roll-off, and is usually expressed in dB of attenutation per octave of frequency. Generally, the design of a filter seeks to make the roll-off as narrow as possible and thus for the filter to perform as close as possible to its design. However, as the roll-off is made narrower, the passband is no longer flat — it begins to "ripple." This effect is particularly pronounced at the edge of the passband, an effect known as Gibbs phenomenon.

Outside of electronics and signal processing, one example of the use of band-pass filters is in the atmospheric sciences. It is common to band-pass filter recent meteorological data with a period range of, say 3 to 10 days, so that only cyclones remain as fluctuations in the data fields.

Between the lower cutoff frequency f₁ and the upper cutoff frequency f₂ of a frequency band is the resonant frequency, at which the gain of the filter is maximum. The bandwidth of the filter is simply the difference between f₂ and f₁.

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线性滤波器

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