Bandwidth (signal processing)
It is typically measured in unit of hertz (symbol Hz).
It may refer more specifically to two subcategories: Passband bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a band-pass filter, a communication channel, or a signal spectrum.
[a] For example, a 3 kHz band can carry a telephone conversation whether that band is at baseband (as in a POTS telephone line) or modulated to some higher frequency.
In radio communications, for example, bandwidth is the frequency range occupied by a modulated carrier signal.
An FM radio receiver's tuner spans a limited range of frequencies.
A government agency (such as the Federal Communications Commission in the United States) may apportion the regionally available bandwidth to broadcast license holders so that their signals do not mutually interfere.
A less strict and more practically useful definition will refer to the frequencies beyond which performance is degraded.
In the context of Nyquist symbol rate or Shannon-Hartley channel capacity for communication systems it refers to passband bandwidth.
The Rayleigh bandwidth of a simple radar pulse is defined as the inverse of its duration.
The threshold value is often defined relative to the maximum value, and is most commonly the 3 dB point, that is the point where the spectral density is half its maximum value (or the spectral amplitude, in
The 3 dB bandwidth of an electronic filter or communication channel is the part of the system's frequency response that lies within 3 dB of the response at its peak, which, in the passband filter case, is typically at or near its center frequency, and in the low-pass filter is at or near its cutoff frequency.
This same half-power gain convention is also used in spectral width, and more generally for the extent of functions as full width at half maximum (FWHM).
In the stopband(s), the required attenuation in decibels is above a certain level, for example >100 dB.
In this case, the filter bandwidth corresponds to the passband width, which in this example is the 1 dB-bandwidth.
In signal processing and control theory the bandwidth is the frequency at which the closed-loop system gain drops 3 dB below peak.
In communication systems, in calculations of the Shannon–Hartley channel capacity, bandwidth refers to the 3 dB-bandwidth.
The fact that in equivalent baseband models of communication systems, the signal spectrum consists of both negative and positive frequencies, can lead to confusion about bandwidth since they are sometimes referred to only by the positive half, and one will occasionally see expressions such as
For instance, the baseband model of the signal would require a low-pass filter with cutoff frequency of at least
For instance, in the field of antennas the difficulty of constructing an antenna to meet a specified absolute bandwidth is easier at a higher frequency than at a lower frequency.
For this reason, bandwidth is often quoted relative to the frequency of operation which gives a better indication of the structure and sophistication needed for the circuit or device under consideration.
are the upper and lower frequency limits respectively of the band in question.
It more properly reflects the logarithmic relationship of fractional bandwidth with increasing frequency.
For wideband applications they diverge substantially with the arithmetic mean version approaching 2 in the limit and the geometric mean version approaching infinity.
Percent bandwidth is a less meaningful measure in wideband applications.
Ratio bandwidth is often expressed in octaves (i.e., as a frequency level) for wideband applications.
is the bandwidth of an ideal filter with rectangular frequency response centered on the system's central frequency that produces the same average power outgoing
The value of the noise equivalent bandwidth depends on the ideal filter reference gain used.
or in the time domain by exploiting the Parseval's theorem with the system impulse response
The same expression can be applied to bandpass systems by substituting the equivalent baseband frequency response for
In photonics, the term bandwidth carries a variety of meanings: A related concept is the spectral linewidth of the radiation emitted by excited atoms.
