Fractional Bandwidth (FBW)

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The fractional bandwidth of an antenna is a measure of how wideband the antenna is. If the antenna operates at center frequency fc between lower frequency f1 and upper frequency f2 (where fc=(f1+f2)/2), then the fractional bandwidth FBW is given by:

fractional bandwidth is a function of the span and the center frequency

The fractional bandwidth varies between 0 and 2, and is often quoted as a percentage (between 0% and 200%). The higher the percentage, the wider the bandwidth.

Wideband antennas typically have a Fractional Bandwidth of 20% or more. Antennas with a FBW of greater than 50% are referred to as ultra-wideband antennas.

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