Butterworth filter characteristics
The Butterworth filter is characterized in that the frequency response curve in the passband is as flat as possible, without undulations, and gradually decreases to zero in the blocking band. On the Bode plot of the logarithmic diagonal frequency of the amplitude, starting from a certain corner frequency, the amplitude gradually decreases with the increase of the angular frequency, and tends to negative infinity.
The first-order Butterworth filter has a decay rate of 6 dB per octave and 20 dB per decade. The attenuation rate of the second-order Butterworth filter is 12 dB per octave, the attenuation rate of the third-order Butterworth filter is 18 dB per octave, and so on. Amplitude diagonal frequency of Butterworth filter
Monotonically decreasing, and also the only filter that maintains the same shape regardless of the order, amplitude versus angular frequency curve. Only the higher the filter order, the faster the amplitude attenuation in the blocking band. The higher-order amplitude diagonal frequency maps of other filters and the lower-order amplitude diagonal frequencies have different shapes.