What is Fractional Bandwidth?

So I keep hearing talk of 3:1 bandwidth or something similar at work but have no idea what that means. I know that they can use the formula below and get a percentage. But where does the Ration come from?

(F2-F1)/Fc = BW(%)

% or Ratio
5 or 1.05:1
10 or 1.11:1
20 or 1.22:1
30 or 1.35:1
40 or 1.50:1
50 or 1.67:1
60 or 1.85:1

Hi there

well for wideband antennas we normally use the ratio while for narrow band antennas we normally use the percentage using the formula mentioned by your.

for ratio we simply use : fh/fl



i hope this helps


regards

if this is the formula for ratio b.w then when a paper claim spiral antenna have 40:1 ratio what dose it mean?can you give an example so that i can understand plzzzzzzzzzz