Several varying types of antennas exist for WiFi, each with a specific purpose for how and when they should be used. Different types of antennas can be found anywhere from small office settings to outdoor camping grounds. While there are many types of antennas, all of them have the same purpose: producing radio waves to send information through the air. The three main antenna types are omnidirectional, semi-directional, and highly directional.
When you enter a home or office setting, you don't generally think about the type of antenna that is being used. This is because they are small - or not visible at all - and oftentimes built into the network’s router or access point. In these types of environments, omnidirectional antennas, specifically Dipole antennas, are commonly found. Similar to how a floor lamp radiates light, omnidirectional antennas radiate radio frequency (RF) in all directions. Another way to think about the coverage is to imagine putting a bagel on your finger as if it were a ring. Your finger is the antenna and the bagel is the coverage it provides. A perfect omnidirectional antenna would radiate RF signal like a theoretical isotropic radiator, meaning the signal is radiating equally in all directions.
This type of coverage is great for point-to-multipoint environments because it can be placed in the center of multiple client devices, providing central communications capabilities to all the surrounding clients. These antennas are great in office and home settings since their broad coverage allows clients to move around without losing signal. While not typically used for outdoor purposes, omnidirectional antennas can be used on top of a building to communicate with buildings on either side.
Semi-directional antennas are designed to direct the RF signal in a specific direction for point-to-point communication. Semi-directional antennas are used for short to medium distance communication indoors or outdoors. A good way to think of how the semi-directional antenna radiates RF is to think of it as a street lamp shining down on the street. It is common to use semi-directional antennas in a campus like environment since they can provide a network bridge between two buildings.
The main types of semi-directional antennas are Patch/Panel and Yagi. Patch/Panel antennas are generally found indoors and used to radiate into the forward space. A building with long hallways or shelves, such as retail stores, warehouses, libraries, or hospitals, that would block an omnidirectional antenna’s signal would benefit from a semi-directional antenna. A Patch/Panel antenna is placed high on the wall, aiming down an aisle or between rows of shelving. Since the antenna has a horizontal beam width of 180 degrees or less, there is plenty of necessary coverage with minimal bleed through. Yagi antennas span longer distances and are generally used in an outside environment. The main purpose of these antennas is to reach places that an omnidirectional antenna would not be able to reach.
Highly directional antennas are used for long distant point-to-point communication. They are used to bridge networks between two buildings that are far apart. Because these antennas are high gain, they provide the most focused and narrow beam width. Instead of a street light shining down, it is more of a spotlight shining in a specific direction. The two main highly directional antennas are Parabolic (Dish) and Grid. Dish antennas look similar to the TV dish antennas that you would find in a home but are often much larger in size. Grid antennas can also vary in size, but they look like a grill and are designed for outdoor environments with higher winds.
A third type of highly directional antenna is the Sector antenna. Sector antennas consist of a few highly directional antennas, placed back-to-back, that are working together to provide omnidirectional coverage. Each antenna that is part of the array provides a pie shaped coverage pattern. Sector antennas can be mounted high over the terrain and tilted slightly downward, with the tilt of each antenna at an appropriate angle for the terrain it is covering. While omnidirectional antennas can also be mounted high over the terrain, if it is tilted downward, the other side’s signal will be wasted up in the air. Therefore, the sector antennas are able to cover much larger areas because they can be directed in any direction the coverage is needed. Compared to omnidirectional antennas, sector antennas have greater throughput since there is more than one antenna in use. These antennas are generally used for cell phone coverage and at sports venues.
All antennas have their strengths and weaknesses. The omnidirectional antenna is great for general coverage and is more cost effective because of the general coverage it provides in a central location. The directional antennas are best for getting signal to a specific area, be it near or far. Having a basic understanding of different WiFi antenna types can be extremely beneficial when designing and building a wireless network.