A balun at RF frequencies is best done by passive means, like a toroid transformer. Just search for "antenna balun" on googly, I'm sure you get a lot of hits.
You can also buy an ARRL book or an ARRL antenna book. They explain this in detail.
Typically baluns are not meant to have such a wide band width.
Unless you use active components, or in corporate an unity gain
Distributive Amp to you balun. Most baluns(Passive Microwave/RF)
will work at Fo and will kinda work at 2*Fo, 3*Fo...
You should look online for a company and see if they have anything
with that wide of a band width.
Good luck.