Name: 無線內部近場與遠場 (Inside Wireless: Nearfield vs Farfield)
Uploaded: 2024-12-26T06:57:20.000Z
Duration: 2 min 25 s

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

大家好，我是 RF elements 的 Sophie，今天我將談談近場和遠場。

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

如您所知，天線的近場和遠場是天線周圍兩個截然不同的區域，在這兩個區域中，天線的輻射特性有很大差異。

進階被動語態

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

近場又可分為反應近場和輻射近場。

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

現在，讓我們從我們最感興趣的遠場區域開始。

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.

它也被稱為輻射場或弗勞恩霍夫區域，是遠離天線的區域，在這裡電磁波已經充分發展，並表現出簡單、可預測的行為。

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

它們以平面波的形式傳播，電場和磁場相互垂直。

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

遠場區域由信號波長和天線尺寸確定。

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

d 的 2 次方除以 lambda 就是精確的計算公式，供各位書呆子參考。

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.

但一般來說，工作頻率為 5.5 GHz 的 30 度喇叭天線的遠場區域從 2 米處開始，一直延伸到無限遠處。

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

對於 24 dBi 增益的天線來說，這個距離是 6 米，而對於 20 dBi 增益的扇形天線來說，這個距離超過 20 米。

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

在另一側，離天線最近的是反應近場區域。

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.

在這一區域內的任何物體都會對天線的輻射圖和駐波比造成不可預測的變化，因為它本身就是天線的一部分。

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

對於前面提到的 30 度喇叭來說，這距離天線孔徑只有 0.3 米。

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

對於 24 dBi 增益的碟形天線來說，它的距離是 0.7 米，而對於 20 dBi 的貶值扇形天線來說，它的距離將近 2 米。

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

使用小尺寸天線時，保持無障礙的反應近場要簡單得多，從而可以進行更密集的配置。

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

最後，輻射近場是中間的區域。

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.

電磁場尚未整合到遠場結構中，但放置在這一區域的任何東西都足夠遠，不會對天線的性能產生直接影響。

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