The older Cisco products all use a connector called RP-TNC – Reverse Polarity – Threaded Neill–Concelman. This is a 50Ohm coaxial connector. The Reverse Polarity means that the pins are on the device rather than on the cable. The cable contains holes. Generally, all antennas that say “TNC” and Cisco or Linksys are actually RP-TNC.
Antennas for the consumer router, the Linksys WRT54GL, which has removable antennae, are compatible with the Aironet 1200.
There are a few major types of antenna used with these WAPs.
The main type are the dipole or “duck” antennas. These look like rubber or plastic stubs around 5 inches long. Here’s someone who dissected one.
The other popular type are the omidirectional patch antennas, which are designed to be installed above the user.
The unidirectional patch antenna mounts on a wall. It’s usually square and encased in white plastic.
Omnidirectional dipole antennas look like ten inch batons, and can be mounted outdoors on a mast.
Yagi-Uda antennas look like ‘trees’ and are highly directional. Some are encased in plastic cylinders, for protection from the weather.
Antennas are designed for specific frequencies, and 802.11g operates in the 2.4GHz range. So you need to make sure you get 2.4GHz antennas.
The newer 802.11n operates in both 2.4 and 5GHz. 5GHz has a shorter wavelength, so requires a shorter antenna.
DIY antennas abound, but the easiest thing to do to boost signal is to use a reflector. They’re easy to make, cheap, and their operation is pretty obvious.
If you want to make an antenna, might as well go all the way and make the Yagi-Uda.