Explanation: an end-fire array consisting of an excited unit, a reflection unit and one or more steering units. 

Note: in fact, the reflection unit can be composed of some elements or a reflection surface. 

In the 1920s, Hideji Yagi and Taro Uda of Tohoku University in Japan invented the antenna, which is called Yagi Uda Antenna, or Yagi Antenna for short. 

The Yagi antenna does work. 

It has good directivity and higher gain than dipole antenna. 

The effect of using it for direction finding and long distance communication is very good. 

If equipped with elevation and azimuth rotation control devices, you can contact radio stations in all directions, including spacecraft, at will, and this feeling cannot be obtained from vertical antennas. 

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A typical Yagi antenna should have three pairs of vibrators, and the whole structure is in the shape of "king". 

The active oscillator, or main oscillator, connected to the feeder is one of the three pairs of vibrators, the middle one of the word "Wang". 

The reflector, which is slightly longer than the active oscillator, is called a reflector, which is on one side of the active oscillator and plays the role of weakening the radio waves transmitted from this direction or from the antenna; the deflector, which is slightly shorter than the active oscillator, is located on the other side of the active oscillator, and it can enhance the electric waves coming from this side or emitting in this direction. 

There can be many deflectors, each of which is slightly shorter than the adjacent one close to the active oscillator. 

The more deflectors, the sharper the direction and the higher the gain, but in fact, after more than four or five deflectors, the increase of this "benefit" is less obvious, while the problems such as large size, increased self-weight, higher requirements for material strength and higher cost are becoming more and more prominent. 

Usually a pair of five-unit Yagi (that is, three deflectors, a reflector and an active oscillator) is sufficient.