ARRL Compendium 7 had an article that might be useful for your
application. The article, Untangling the Folded Unipole, by N7OP,
shows how to configure a folded unipole for use on several bands.
Folding the antenna raises the feed impedance, but does nothing for
the efficiency. Shorting the fold wires to the tower, as discussed in
the article, would be a convenient way to cover 3 bands.
The downside is that a matching system, would be required for each
band. The folded element exhibits inductive reactance, so it is
possible that only a series capacitor would be needed. Another
suggestion would be to use an auto tuner unless you plan to use power
of a KW or more. I am not aware of any reasonably priced tuners that
handle the legal limit.
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