"Marvin Rosen" wrote in message
...
Is there such a thing as a 2 mtr omnidirectional
vertical beam antenna?



You want an omnidirectional directional antenna?! Nope, there isn't any such
thing.

An omnidirectional antenna radiates equally in ALL directions. If you think
of all the power flowing into an antenna being radiated out, equally
illuminating every unit area of an imaginary sphere around the antenna, then
that's an isotropic radiator. Since ALL the input power is radiated, you
never get any more efficient than that.

If you distort the radiation pattern, so that power isn't equal for every
unit area of that sphere, you now have a directional antenna. You get an
apparent gain in a certain direction because you have "stolen" some power
from other directions. No free lunch, etc.

If you get sloppy with your definition of omnidirectional, you might try to
call something like a quarter-wave vertical rod above a ground plane is an
omnidirectional antenna. Assuming perfect construction, this antenna
radiates equally well in all azimuths. But it sure doesn't radiate equally
well at all elevations. Either way, this isn't a "beam" antenna.

And once you array a group of dipoles or loops to form a classic beam
antenna, you don't have omni-directional radiation vertically or
horizontally.


--
Ed
WB6WSN