> My understanding is that a dipole antenna is in the shape of a T where
> the length of each horizontal branch is equal to a quarter wavelength.
> So, for 2.4 GHz, each horizontal branch would be about 1.2 inches
> long. But I've seen articles and spec sheets that call the stock
> "rubber duck" antennas that come with many routers and client radios
> dipoles. They don't seem to be in the shape of a T at all. Rather they
> just seem to be a length of wire. What gives?

You're not wrong. The di-pole is both the centre conductor and the
outer conductor, one going one way, the other going the otherway.

With the rubber duck antenna's what they've done is essentially wrap the
coax back on itself by using a brass sleeve that fits over the outer
insulation. In effect the T is still there but the tail of the T fits
inside the brass tube.

Here are a couple of examples. Although I don't explicitly show the
dipole but you can see where it enters, a parabolic:-

http://www.nodomainname.co.uk/parabolic/parabolic.htm

and the guts of a PCI card being modified to stick in a laptop.

Underneath the heatshrink sleeving is a piece of brass tube that is
soldered inside to the coax braid, the centre conductor is then allowed
to protude the 1/4 wavelength amount, 31mm.

http://www.nodomainname.co.uk/dwl650g

Sorry, never got round to doing the page for the second one, just raw
pics.

David.