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Antenna types

Good access point antennas are omni directional or sector types. An omni directional antenna has the advantage of quickly providing a large coverage area. The usage of sector antennas makes it possible to split the area around a node into several different independent parts. The main advantages of this approach are that while providing a stronger signal into the sectors, the access point node is able to handle more users (i.e. a larger total available bandwidth for that cell). A disadvantage of using sector antennas is that more wireless interfaces are needed and that interference can be a problem.

A point-to-point connection needs an antenna which directs all the radio frequency (RF) energy into one direction. The limiting factor for this antenna is mainly its size. High gain antennas reduce the chance of interference to other nodes or to the other antennas of the same node but are often quite large in size.

The key to a successful antenna setup for a given node location is in evaluating the simulation results together with the site survey details. After that, the cost factor is not to be neglected in the selection process. In some cases a home-made antenna can have a better price / performance ratio than a commercial one.

Clients need a directional antenna to connect to a node. There is no need for clients to be connected to more than one node at the same time. The main specification for the client antenna is the minimum gain that is needed to obtain a signal strong enough to make a good connection to an access point. Based on this gain, several different types of antennas are available. Other factors that determine the best antenna are the physical size, appearance and the cost of the antenna.

Simple antennas for use with access points [Omni], clients [Quad] or point-to-point connections [Yagi] can be made at home, keeping the price at the lowest possible level. Almost anything can be turned into an antenna. It has been shown that it is not difficult to make a WiFi antenna [Pringle]. The Wireless Leiden website has a large collection of antenna designs provided by users.

The layout of the Wireless Leiden network is designed on a typical client antenna gain of 7 dBi. Antennas with this gain are cheap and / or easy to construct.

next up previous
Next: Lightning protection Up: Antennas Previous: Antennas
Rudi van Drunen 2003-04-08