In general, it won't work. You'll have high VSWR (reflected power), lousy gain, crummy radiation pattern, and a huge waste of time and effort. This isn't universally true as there are some very broadband antennas that will work on both bands.
So, what are you trying to accomplish and what do you have to work with?
Can you use a 5 ghz antenna in the 2.4 range and what will happen to gain. Thanks Ed
A full wave dipole is a *very* bad thing! The feed point impedance won't be anything like a half wave dipole... instead of a low impedance like the half wave dipole, it will be extremely high.
A half wave dipole, however, will work just fine at any *odd* multiple of the design frequency. Of course, the raditation pattern is not the same at any of those odd multiples, so if it is oriented correctly for any given direction at one frequency, it won't be at any of the other multiples in frequency.
To put it mildly, "takes special attention" was the operative phrase!
Depends on the design, but it probably won't be a good experience.
Antenna designs can be scaled in frequency, allowing you to take a design at
1 MHz and simply scale it up to 10 MHz, and so on, but for an antenna to operate on two bands so far apart, takes special attention, or luck. A half wave dipole for instance, becomes a full wave dipole at twice the original frequency, and that isn't a bad thing. A full wave loop becomes a two wave loop though, and that IS a bad thing.
Generally one made for only one frequency/band won't work very good, however they do make a few "dual band" antennas, for WiFi stuff that does both 2.4 and 5.
Think of it in more common terms..(not technically exact, but hopefully similar enuf to make sense and be understandable) They make VHF TV antennas, but if you try and use em for UHF, they sortof work-but not very good, however, they do also make combo VHF-UHF antennas, and those work pretty good in the correct bands.
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