Click here to go to our basic concepts of microwave engineering page
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/FC
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 FL and FH:
BW%=2(FH/FL-1)/(FH/FL+1)
Where FH is the upper (higher) frequency and FL 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=(FH+FL)/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!