So we have to start now a new section, and in this section, I have to speak about the antennas that we have on the wireless, which is Wi-Fi, of course. So what are the different antennas that we have? More details will be provided during this section. Let’s start directly and do the explanation.

 

What is an Antenna?

The antenna is used to radiate electromagnetic energy in the air and receive electromagnetic energy from the environment. If we didn’t have antennas, we wouldn’t be able to use wireless technology. As we mentioned, we have the electromagnetic spectrum. The term “electromagnetic” means that we have electric and magnetic components.

The electric field will raise the magnetic field, and the magnetic field will raise the electric field. That’s how wireless signals are sent through the air. The antenna has two functions: to emit or transmit the electromagnetic field or energy and also to receive it. So that’s the main function of the antenna.

 

Frequency Ranges

Antennas use specific frequency ranges. For example, if you want to use 2.4 GHz on your wireless, you have to buy an antenna that works on 2.4 GHz. Alternatively, you may choose to use 5 GHz. There are also some antennas that can use both 2.4 GHz and 5 GHz nowadays.

When you conduct a site survey, you need to decide which frequencies you want to use and then purchase the antenna based on those frequencies.

 

Radiation Patterns

Each antenna has a radiation pattern, which indicates how the antenna transmits the waves. We will discuss radiation patterns shortly, but remember that we have two patterns here: the azimuth and the elevation, also known as horizontal and vertical patterns.

The azimuth pattern shows how the signal is being propagated when looking at the antenna from the top down. The elevation pattern indicates what it looks like when viewed from the side of the antenna.

Why is this important? For example, if you buy an omnidirectional antenna, the radiation pattern shows that it sends the signal in all directions, resembling a donut shape. In this case, the antenna should be placed somewhere in the center to ensure coverage in all directions.

On the other hand, if you purchase a parabolic antenna, it will focus the signal in a specific direction. Therefore, understanding the radiation pattern is essential when selecting the right antenna.

 

Types of Antennas

There are two main types of antennas: indoor and outdoor. Indoor antennas are typically built into access points designed for indoor use. Some indoor access points allow you to attach external antennas for potentially greater gain.

Outdoor antennas are generally used for bridging connections, for example, to create point-to-point links over several kilometers.

 

Omnidirectional Antennas

As mentioned, there are different types of antennas. One of them is the omnidirectional antenna. There are two types: normal and high-gain omnidirectional antennas.

Omnidirectional antennas radiate energy in all directions. When viewed from the top (the azimuth pattern), you can see that the signal is transmitted at all angles. The elevation pattern (the E-plane) shows the main lobes extending from the antenna.

Omnidirectional antennas are commonly deployed indoors, ideally placed in the center of a space for optimal coverage. For example, the Cisco Aironet 2.4 GHz antenna is a common omnidirectional antenna:

It operates at 2.4 GHz, has an impedance of 50 Ohms (which is standard for all wireless hardware), and provides a passive gain of 2 dBi. Passive gain means that the antenna itself boosts the signal when radio frequency waves reach it.

 

Semi-Directional Antennas

The second type of antenna we can discuss is the semi-directional antenna, which propagates RF energy in a horizontal pattern between 8 and 180 degrees, covering half the area of an omnidirectional antenna.

This type of antenna is beneficial in high-density environments, such as areas with many people, where you want to cover a specific area. You can mount the antenna on a wall or ceiling to provide coverage for the desired location.

 

Highly Directional Antennas

The third type of antenna is the highly directional antenna, which is used for outdoor wireless connections over long distances. These antennas are ideal for point-to-point or point-to-multipoint connections.

Three common types of highly directional antennas are parabolic dishes, grid antennas, and Yagi antennas. The difference lies in the amount of gain they provide, with parabolic dishes offering the highest gain, allowing for longer distances.

For instance, some companies have achieved point-to-point links of up to 300 kilometers using wireless parabolic dishes. The radiation pattern for these antennas is typically narrow, usually less than 50 degrees in both horizontal and vertical patterns, with passive gains ranging from 12 to 30 dBi.

To illustrate, if a parabolic dish has an output power of 100 milliwatts and a gain of 24 dBi, the radiated power becomes 25.6 watts, significantly higher than the original output power.

This increase in power is measured as Equivalent Isotropically Radiated Power (EIRP). When designing a wireless link, you must comply with country regulations regarding allowable transmission power. Calculating EIRP is crucial for ensuring compliance and effective performance.

 

Internal and External Antennas

You can have internal antennas that come built into devices, such as access points, and external antennas that need to be purchased separately. Internal antennas tend to be more cost-effective, while external antennas provide greater control over RF signals and coverage areas.

For example, if your internal antenna does not provide sufficient coverage, an external antenna with higher gain can be selected for improved performance. Most indoor deployments use internal antennas, although high-density environments may require external antennas.

 

Additional Radio Frequency Hardware

In addition to antennas, you need cables and connectors to connect the antenna to the access point, all of which should be 50-ohm compatible. Amplifiers may also be necessary to boost the signal. However, be cautious not to exceed the allowed power levels set by regulations.

Attenuators are another type of RF hardware that can reduce signal strength if the transmitted power exceeds allowable levels. These components are crucial for deploying effective wireless connectivity.

 

Conclusion

This concludes the discussion about antennas and related hardware. We covered radiation patterns, passive and active gains, and various types of antennas used in wireless connectivity. I hope this information was informative for you, and I look forward to seeing you in the upcoming lecture.