No.

If you begin with a Yagi antenna made for exactly 1.2 GHz and *reduce*
the element length, element diameter, and element spacing all by a
factor of two, it would work at exactly 2.4 GHz. That's assuming that
the effect of the boom is negligible. If the boom is large enough to
have an effect (typically the case), you'll also have to reduce the
diameter of the boom by a factor of two.

There's an infinite number of other combinations which will work; for
example, you can leave the element and boom diameters the same and
change only the spacing and element length. But then the spacing and
element length will need to be changed by some factor other than two,
and there's no simple way to calculate the factor.

Roy Lewallen, W7EL

oldcrow wrote:
Hi!

If I was to take yagi antenna for 1.2 gHz and then double the length of
each element. Would that work on 2.4 gHz?

Bob