There are many different designs for antennas that Wi-Fi cards and access points can use.
Generally, antennas are either omnidirectional or directional.
Omnidirectional antennas are most commonly used with Wi-Fi cards and access points. These antennas send out radio waves in all directions equally on the horizontal plane but don't send out much in the way of signals vertically. The radiation pattern of an omnidirectional antenna looks like a doughnut, with the antenna in the center of the doughnut, as depicted in Figure 16.1.
Figure 16.2 shows a fairly standard omnidirectional antenna made by Maxrad, Inc., which is intended to work with Wi-Fi and the 2.4GHz spectrum and is mounted externally ...