Percent bandwidth

Updated June 22, 2009

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Percentage bandwidth is a simple calculation, and gives a normalized measure of how much frequency variation a system or component can handle. As you go higher in frequency, the absolute bandwidth as a part will naturally increase, while its percent bandwidth will decrease.

If you know the center frequency and the bandwidth, the percent bandwidth is:

BW%=BW/F_C

Here "BW" is the absolute bandwidth and FC is the center frequency. Thus a filter with 1 GHz passband centered at 10 GHz will have 10% bandwidth, while a filter with 10 GHz bandwidth at 100 GHz will have the same 10%.

Alternatively, you can calculate BW% from two corner frequencies F_L and F_H:

BW%=2(F_H/F_L-1)/(F_H/F_L+1)

Where F_H is the upper (higher) frequency and F_L is the lower frequency of the passband. This is simple math, it is derived from the center frequency being the arithmetic average between the upper and lower corner frequencies:

FC=(F_H+F_L)/2

Here's an alternative calculation from Daniel:

BW%=2*(FH-FL)/(FH+FL)

or more consistent with the use of percent sign:

BW%=200%*(FH-FL)/(FH+FL)

Thanks!