The Yagi antenna consists of three main elements located in the same plane: a reflector, a dipole and a director.The dipole is selected at half the wavelength, the reflector is located behind it and it is slightly longer than the dipole, and the director is located in front of the dipole and it is slightly shorter than the dipole.This is a three-element Yagi antenna.The number of directors can reach 10 or more.This is a directional antenna.It should be directed in the right direction to the source of the signal during reception or to the correspondent during transmission.
The principle of operation: All three elements receive and emit this signal.That is, we can imagine that each element is a receiver of the signal and emits it as a transmitter. If all three radiations from the elements are in phase, the maximum signal is received at the receiver input; if they are out of phase, the signal will be minimal.By moving the director and the reflector, we adjust the phases.We need to adjust so that all three signals are in phase.That's when we can receive weak radio signals.Antenna elements can be thought of as mirrors that receive light and reflect it back. Similarly, a radio signal enters the antenna elements and is reflected. We need to adjust these signal reflections from the elements so that they are all in phase.
You can conduct a simple experiment.An incandescent lamp is a dipole.Install a reflector on the back of the lamp and a lens on the front of the lamp, this will be the director.
You can see a narrow beam of light coming from the lamp like in a flashlight.This is a visual analogue of the Yagi antenna.
For the experiment, I made a three-element Yagi antenna with a frequency of about 433MHz. For the three elements, I used a 2.26mm diameter copper wire.
An RG-58c/u coaxial cable with a wave resistance of 50 ohms was connected to the dipole.Yes, this is a bit wrong, you can not connect an unbalanced cable to a symmetrical dipole and the antenna resistance is about 75 ohms and the cable is 50 ohms.An RF transformer is needed for matching, otherwise the cable braid will emit a signal during transmission and such an antenna will be ineffective, but my antenna is working.
Here are the technical specifications of my antenna.The SWR is about 1.4 at a frequency of 433MHz and a resistance of about 40-45 ohms.The adjustment must be made by shifting the director and the reflector
Now check the antenna operation.To determine the radiation of the radio signal, I used a RF probe on an LED.First, just check the dipole without reflector and director.The range is about 20cm
A reflector was installed behind the dipole and the range became 30cm.
A director was installed in front of the dipole, and the range was 50 cm.It's working.Such an effective directional antenna can be completely manufactured independently.
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