How yagi antennas work
The Yagi-Uda array is one of the most common directional antennas on rooftops and towers. Here is the plain-language version of what those rods are doing.
The parts
- Driven element: The element connected to your coax or feedline — it launches or receives the radio wave.
- Reflector: Usually slightly longer, placed behind the driven element. It reinforces energy toward the front and reduces it out the back.
- Directors: Slightly shorter elements ahead of the driven element that help focus the beam forward.
- Boom: The cross-arm that holds spacing and alignment. Spacing is part of the design, not decoration.
Directionality & gain
Compared with an omnidirectional whip or simple dipole, a yagi concentrates energy into a forward lobe. That concentration is reported as gain (dBi or dBd). The tradeoff is beamwidth: higher-gain yagis are pickier about aiming. Miss the tower by tens of degrees and the TV pixelates or the repeater gets noisy.
Front-to-back ratio
A good yagi often rejects signals from behind better than from the sides. That helps when interference or unwanted stations sit behind you — useful for both OTA TV and ham work.
Why “one yagi” does not fit every hobby
Element lengths scale with wavelength. A TV yagi, a 70 cm ham yagi, and a 800 MHz cellular yagi are sized for different jobs even if they look similar in a product photo. Always match band and system impedance — see our OTA, ham, and cellular guides.