In this short video you will learn why radiation patterns of antennas are not stable over whole band width of operation. In the world of RF engineering, vast majority of parameters depend on frequency. Any and every RF device has properties that are changing with frequency. This is why very often an answer to RF related questions is: “it depends” :) . Understanding this simple and sometimes complicated fact is what RF engineers are paid for worldwide.

The gain of an antenna in datasheet is usually a single number - the peak gain at a particular frequency, which is rarely disclosed. The truth is, the gain of an antenna changes with frequency and angle. Describing gain by a single figure is therefore not enough.

When computers had low computational power, scientists displayed gain in two dimensional polar plots, because they are easy to draw on a paper. Today, 3D radiation diagrams are easy to produce and should be used because they provide complete information about gain.

Radiation diagram also changes with frequency. The shape and size of an antenna are usually fixed. But the wavelength of the feeding signal can change, which influences the radiation diagram. Some antennas - like patch arrays - are more prone to the diagram changes, while others, like horn antennas, are much more stable.

Why is stability of gain and radiation diagram important? Again, “it depends”.

Some antennas are used in a narrow bandwidth, so the frequency stability is not so important. Because most common antennas have stable performance over narrow frequency range, it is fairly easy to design a narrow band antenna.

To achieve stable performance over a wide bandwidth is a real challenge. Especially if we want an antenna to have stable gain and radiation diagram simultaneously.

In wireless networking for example, wideband performance, stability of gain and radiation pattern of sector antenna are important because the quality of delivered service directly depends on these parameters.

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0:00 Intro
0:29 Antenna Gain
0:44 Radiation pattern
1:07 Examples
1:19 Wideband VS Narrowband
1:40 WISP antennas

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