Make Wi-Fi Visible #4 – Radio Frequency Diffraction

As we all know, Wi-Fi is amazing. The only thing is… it’s invisible.

So let’s start by explaining what makes Wi-Fi invisible? Wi-Fi uses radio frequencies electromagnetic waves to transfer information. These waves have wavelengths that are not within the visible space.

Light is also an electromagnetic wave. However, its wavelength is within the visible spectrum (between 330 nm and 700 nm). This is what make the light visible to the human eye. In fact, any electromagntic radiation having a wavelength between 330 nm and 700 nm is called “light” or to be precise “visible light”.

This means that we can explain Wi-Fi concepts using light analogies. In this set of articles, that is what we are going to do using simple drawings.

Episode #4 – Radio Frequency Diffraction

Radio waves tend to bend around sharp objects creating a new wave front. This phenomena is called diffraction. This allows the waves to go around an object and still reach a receiver. Diffraction is illustrated below:

Diffraction can be illustrated using sunlight going through a keyhole. A small portion of the sunlight going towards the door will go through the keyhole. At this moment, the shape of the wave is going to change and the light going inside will light up the room as illustrated below:

Diffraction, in combination with reflexion, allows Wi-Fi to go around objects in a typical indoor environment avoiding it from being totally blocked. This could be very good advantage if you think about it. However, everything has a cost. A diffracted wave is indeed losing power. This is an important fact to keep in mind! Another important fact to know about diffraction: the higher the frequency, the higher the loss. In Wi-Fi deployments, diffraction will, therefore, generate more loss on 5GHz transmissions than 2.4GHz transmissions.

Written by François Vergès

“Episode #1 – Radio Frequency Propagation” is still available!
“Episode #2 – Radio Frequency Reflection” is still available!
“Episode #3 – Radio Frequency Refraction” is still available!
“Episode #5 – Radio Frequency Scattering” coming next!

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