Certified Wireless Network Administrator certifications are an invaluable asset in the enterprise networking job market.
According to Certification Magazine’s 2009 Salary Survey, CWNAs earn an average of $94,150 in the Unites States.
While many wireless technologies that are tested on the CWNA exams change rapidly as technology and security needs grow in terms of software and methods, there are some things that remain more or less unchanged as time goes by. One of them is hardware, which essentially consists of antennas and mounts, which have very few major revisions or updates.
Today we’ll take a look at the different types of wireless networking antennas as well as a few mounting methods for these antennas.
Types of Antennas
First, let’s go over the types of antennas available. There are only four or five types of antennas listed on the CWNA exam:
- Omni-directional antennas / Dipole antennas
- Semi-directional antennas
- Highly-directional antennas
- Sectorized antennas
Let’s look at each in more detail.
Dipole Antennas
Dipole antennas are much simpler than Omni-directional antennas, but at the same time, still considered Omni-directional.
The reason is, a Dipole antenna is simply a straight wire or pole which receives or transmits data in all directions, which technically qualifies it as Omni-directional.
However, the reason Dipole antennas are not professionally considered Omni-directional, is because although they do provide a very large range of current amplitude, the amplitude is decreased in range at the tips of the antenna.
While the sides maintain a very wide range, the ends are much smaller, and therefore do not receive/send as much current.
Omni-Directional Antennas
The first major type of antenna is the Omni-Directional antenna. This antenna is essentially a multi-dipole version of a Dipole antenna.
Omni-Directional antennas usually consist of multiple wires or poles that each acts as a Dipole antenna, but each in a different position to provide a wider coverage, thus making it omni-directional. Omni-directional antennas can be used to link multiple directional antennas in outdoor point-to-multipoint communication systems.
Wikipedia describes Omni-directional antenna radiation patterns as uniformly in one plane with a directive pattern shape in a perpendicular plane. This pattern is often described as “donut shaped”.
Semi-Directional Antennas
These types of antennas, along with Highly-Directional antennas are aimed to be directed towards one general direction. For example, in an office setting, a semi-directional WiFi antenna can be placed at the back of the office, facing forward to supply the office with network connectivity and internet.
The most common type of semi-directional antenna is the plate antenna. The plate antenna is (generally) a square piece of metal with the standard antenna wire lead soldered on.
In general, plate antennas supply the most powerful connection within 60 degrees of the antenna. The rest of the area provides a much weaker connection, if you look at further 60 degrees out, the connectivity is decreased by about 25%. Any further and you can see ranges from 75% less connectivity, to no connectivity at all.
The second most common semi-directional antenna is the Yagi-Uda antenna. This antenna consists of a dipole antenna along with multiple crossing sections, usually one deflector and one or more directors. Directors give the antenna a more directional throughput than a standard dipole antenna.
These antennas are generally used in longer range applications such as outdoor point-to-point access.
Highly-Directional Antennas
The most common highly-directional antenna is the Parabolic reflector. To put a clear picture in your mind, think satellite dishes.
Parabolic reflectors essentially do just as the name suggests, they reflect radiation into a center point, usually a center dipole. This focused current provides an extremely directional throughput that is only suitable for point-to-point communications with a clear line of sight.
Parabolic reflectors are also extremely susceptible to damage due to weather and wind pushing against them, especially when not properly or securely mounted. To combat this downside, many are built with holes in the reflector so that wind, rain and other elements can flow through without disturbing the antennas’ integrity or operation.
In terms of direction, let’s compare the parabolic reflector to a plate antenna. While the plate antenna maintains fairly open directional usage at 60 degrees, parabolic reflectors only offer about 5-25 degrees of directional usage with little to no room for error.
Because of the need for a clear line of sight, parabolic antennas should only be used in open or highly elevated areas with little to no obstructions in the way.
Sectorized Antennas
Sector antennas are simply multiple directional antennas in one antenna system. For example, a common sector antenna is created in a triangular shape using 3 directional rectangular plate antennas. This ensures three overlapping patterns providing a wide range of access.
Most sectorized antennas are able to provide (for the most part) a 360 degree range of coverage. While the range will likely go between 90% and 100% across the overlapping sections, sectorized antennas are still seen as a fairly good choice for both inside and outside wide access operation, even more-so than omni-directional antennas. Some antennas may consist of up to 6 sectors in practical uses.
Antenna Mounting
Although there are many ways to mount and set up antennas, today we’ll go over the three main methods for mounting and installing antennas as listed in the CWNA exam prep materials. These methods are as follows:
- Pole/mast mount
- Ceiling mount
- Wall mount
Pole/Mast Mounts
Pole/Mast mounts are essentially just as the name implies: antennas mounted on poles.
These poles can be secured on a rooftop, in the ground, or even secured to the side of a building. While height is an obvious advantage of pole mounting, a disadvantage is weather. Strong winds and other elements can cause poles to bend, mounting hardware to malfunction, etc.
One thing to remember about pole mounting is that due to the increased risk of lightning hitting the antenna, there is an increased safety hazard and you must be sure that it is properly grounded. Remember, even if you are an RF Engineer, it is a good idea to have a professional mount the antenna while you provide your expertise in what components are used and how.
Another important detail to remember is that while your antenna may be functional and safe, as with anything outdoors, there is still an issue with security. Always make sure the antenna is safe from not only the elements, but also theft.
Ceiling Mounts
Ceiling mounts are just what they sound like. In most cases, an omni-directional antenna is secured to the ceiling of a building.
Be sure to check with your client though, antennas aren’t exactly made for cosmetics and can be an eye sore. If you are working in somewhere like a hotel, discuss the possibilities of using more cosmetically appealing molded antennas that will do better in blending in with the wall, rather than protruding out.
Wall Mounts
Wall mounts are a lot like ceiling mounts. Obviously, these are installed on walls, rather than ceilings. Because of this, wall-mounts are usually directional, rather than omni-directional. This allows, as mentioned earlier, for an antenna to be mounted safely in the back of an office, and broadcast across the building.
You will want to figure out the best place to mount the directional antenna to provide access to anyone who needs access. One idea I’ve seen used is to mount the antenna in a corner, rather than the center of a wall, to ensure no blind-spots are created along-side the antenna.
Every little bit helps. Thanks Train Signal.