Name: Inside Wireless: Nearfield vs Farfield
Uploaded: 2024-12-26T06:57:14.000Z
Duration: 2 min 25 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Hi everyone, I'm Sophie from RF elements and today I will talk about nearfield and farfield.

As you may know, antenna nearfield and farfield are two distinct regions around an antenna where the antenna's radiation properties differ significantly.

Advanced passive voice

The nearfield can be further divided into reactive nearfield and radiative nearfield.

Now let's start with the region that interests us the most, the farfield region.

Also known as the radiation field or the Fraunhofer region, it is the region far away from the antenna where the electromagnetic waves have fully developed and exhibit a simple, predictable behavior.

They propagate as planar waves with the electric and magnetic fields perpendicular to each other.

The farfield region is defined by the wavelength of the signal and the size of the antenna.

Two times d squared divided by lambda is then the exact formula for all you nerds out there.

But generally speaking, the farfield region of a 30-degree horn antenna operating at 5.5 GHz starts at 2 meters and extends to infinity.

For a 24 dBi gain dish it's 6 meters, and for a 20 dBi pejorative sector, this distance is over 20 meters.

On the other side, closest to the antenna we have the reactive nearfield region.

This is a place of electromagnetic chaos.

Any objects inside this region cause unpredictable changes to the antenna's radiation diagrams and VSWR, because it becomes a part of the antenna itself.

For a 30-degree horn like mentioned before, this comes out to be only 0.3 meters from the antenna aperture.

For a 24 dBi gain dish it's 0.7 meters, and for a 20 dBi pejorative sector, this extends to almost 2 meters.

Maintaining a reactive nearfield free of obstacles is much simpler with antennas with small form factors, enabling much denser collocation.

Finally, the radiative nearfield is the region in the middle.

The EM fields have not yet consolidated into the farfield structure, but anything placed in this region is far enough not to have a direct influence on the antenna's performance.

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