Antennas and Access Points

Essential to any wireless network is the proper acquisition and placement of wireless antennas. Wireless networks today use three types of antennas:

• Omni-directional Also known as dipole antennas, omni-directional antennas are the most common. Omni-directional antennas radiate their energy equally in all directions. If you want to go greater distances, you can use a high-gain, omni-directional antenna, which offers greater horizontal coverage at the sacrifice of vertical coverage. High-gain omni-directional antennas provide coverage at right angles to the antennas. If you can mount the access point (AP) near the ceiling and tilt the antenna at a 45-degree angle, you can cover an entire room.

• Semi-directional Used when you need short or range bridging, such as between two buildings in close proximity to each other. These antennas direct their energy primarily in one general direction. Yagi, patch, and panel antennas are all types of semi-directional antennas.

• Highly directional Not used by client machines but rather for point-to-point bridges. These antennas can go long distances (up to 25 miles, so they are good for bridging buildings together). Because of the strength of these antennas, they are sometimes used to penetrate walls that other antennas are unable to. The challenge of these antennas is that they must be accurately positioned to provide a line-of-sight link between both antennas.

Omni-directional antennas are analogous to a light bulb in a house, providing a small range of light equally in all directions. Semi-directional antennas are like spotlights in that they generally spread a light in a single direction. Finally, highly directional antennas are like searchlights, offering a strong beam of light in a single direction.