Wireless Antennas for
WiMAX, Wi-Fi, Wireless LANs and 802.11 Networks

A wireless antenna focuses a radio signal in a specific direction and in a narrow beam. The increase in the signal power (compared to an omnidirectional antenna) when it is focused in the desired direction is called gain.

Antennas are tuned to operate on a specific group of frequencies. Other specific attributes such as beamwidth and gain are also fixed by the manufacturer. Antennas should be selected and placed according to your site and your application.

In general, the larger the antenna, the higher the gain and the larger the mast required. It is best to use the smallest antenna that will provide sufficient protection from interference and enough signal at the far end of the link to provide good reception even with fading.

Other considerations include antenna beamwidth, front-to-side ratios, front-to-back ratios, and cross-polarization rejection. Where interference from other licensees on the same channel or adjacent channels is an issue, narrow beamwidths, high front-to-back and front-to-side ratios, and high cross-polarization rejection are likely to be required. Even when other licensees are not an issue, if you are using a network deployment using the "cell" approach, all these considerations are still important to reduce interference between your own adjacent installations.

Antennas are an important part of a wireless system because it directs where a wireless signal is transmitted and it determines the direction that signals and noise are received from.

A short list of different types of antennas

Corner Reflector Antenna - A directional antenna that is made up of a dipole driven element mounted in front of a 60-degree or 90-degree corner-shaped reflecting element.

Dipole Antenna - A two-piece (di = two; pole=“pole” or “piece”) antenna that is the basic “building block” antenna element. A dipole is normally used as the “driven element” in most antenna systems. A dipole is made up of two ¼ wavelength-long antenna pieces arranged in a straight line. A coax transmission line feeds power to the middle of the dipole.

Directional Antennas - An antenna with a radiation pattern that concentrates both the transmitting and receiving signal power into one favored direction. The power gain (the increase in signal power in the favored direction) is measured in dbi or dbd.

Isotropic Antenna - An isotropic antenna is a theoretical antenna. If it existed in the real world, it would radiate a wireless signal equally in all directions (front, back, left, right, up, and down). The signal strength from a theoretical isotropic antenna is used as a reference level to measure the gain (focusing power) of real-world antennas.

Omnidirectional Antenna - An antenna with a radiation pattern that, when viewed from above, is equally strong in all directions.

Panel Antenna - A directional antenna made up of several phased driven elements mounted in front of a flat reflecting element. Panel antennas usually have a plastic or fiberglass cover that gives the antenna a panel-like appearance.

Parabolic Antenna - A directional antenna made up of a dipole driven element mounted in front of a parabolic-shaped reflector. The reflector may be either a solid metal “dish” or a dish-shaped screen made of metallic rods or mesh.

Patch Antenna - A smaller version of a directional panel antenna often used indoors.

Yagi Antenna - A directional antenna made up of one “driven element” that is connected to the transmission line and one or more “reflectors” (signal reflecting elements) and/or “directors” (signal directing elements).