SIRIUS
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TECHNICAL REFERENCE MANUAL
6.1.3. Bandwidth
Bandwidth is the difference between the upper and lower frequencies in a continuous set of
frequencies. It is typically measured in hertz, and refers to the baseband bandwidth in the context of
this chapter: In the case of a low-pass filter or baseband signal, the bandwidth is equal to its upper
cut-off frequency.
If the maximum gain is 0 dB, the 3 dB bandwidth is the frequency range where the gain is more than
−3dB, or the attenuation is less than 3 dB.
The image below “3 dB Bandwidth” shows the definition of bandwidth (B) for a bandpass filter. f
0
is the
centre frequency, f
H
is the higher cut-off frequency, and f
L
is the lower cut-off frequency. The 0 dB level
is the level of the peak of the bandpass response, which is not necessarily located at the centre
frequency. Also the centre frequency is located at either the arithmetic or geometric mean of the upper
and lower cut-offs depending on context and conventions.
3 dB bandwidth
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