This is the most common design for Yagi antennas. Folded dipole has advantages over the dipole in greater bandwidth and higher impedance, and it can be more easily adjusted with a BalUn to 50Ω required by the most devices (this is not always correct. In many cases 28Ω antennas are a better choice).

For all the frequencies the principle is the same: there is one reflector that is behind dipole. Reflector has largest length of all the elements. After dipole come directors, each director further from the dipole is a bit shorter than the previous. Boom is the pipe that holds all the elements.

01 yagi

Elements of a Yagi antenna: A – folded dipole, B – reflector, D – feed point, C – directors

02 radiation pattern 03 radiation pattern

Radiation pattern for 7 element Yagi

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