Page 138 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes Directional Links

Directional antennas are all the rage in networking applications where you want to hook up
branches of your network that are not in the same building. For instance, wireless links could be
used to cheaply connect sites in a Metropolitan Area Network; running cable through streets can
be very expensive. Alternatively, you could connect sites using a Virtual Private Network (VPN)
over the Internet or a “leased line” from an telecommunications provider.
Wireless provides a cheap solution but is considerably more difficult to troubleshoot. Consider
trying to move a building out of the way to see if the link quality improves. It is this reliability
issue that may rule out wireless for primary links, but still be useful as a backup or transient link.

Did u know? There are systems other than those in the 802.11 suite of protocols that
are designed for high-speed point-to-point wireless networking. 802.16 (WiMax) is a
Metropolitan Area Networking (MAN) standard designed for point-to-point applications
at a speed of up to 280Mbps. There are also laser-based point-to-point networking
technologies, but I won’t go into those here.

8.2.6 Semi-directional

Semi-directional antennas come in many different styles and shapes. Some semidirectional
antennas types frequently used with wireless LANs are Patch, Panel, and Yagi (pronounced
“YAH-gee”) antennas. All of these antennas are generally flat and designed for wall mounting.
Each type has different coverage characteristics. Figure 8.4 shows some examples of semi-
directional antennas.
Figure 8.4: Semi-directional Antennas

Sample semi-directional Antennas

Yagi Antenna Patch Antenna Panel Antenna

Source: http://docstore.mik.ua/univercd/cc/td/doc/product/access/mar_3200/wlsnotes/cfwlsmod.htm#wp1012118
These antennas direct the energy from the transmitter significantly more in one particular
direction rather than the uniform, circular pattern that is common with the omnidirectional
antenna. Semi-directional antennas often radiate in a hemispherical or cylindrical coverage
pattern as can be seen in Figure 8.5.

Figure 8.5: Semi-directional Antennas Coverage

Directional Patch Antenna Directional Yagi Antenna

Source: http://docstore.mik.ua/univercd/cc/td/doc/product/access/mar_3200/wlsnotes/cfwlsmod.htm#wp1012118

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