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Yagi-Uda

Directional Antennas

A directional array of a driven dipole with parasitic reflector and directors.

Band: VHF/UHF (also HF beams)
Gain: ~7-15 dBi (depends on element count)
Polarization: Linear (matches the driven element)

Photos

Real-world photo of a Yagi-Uda in use — Real-world example. Source: Wikimedia Commons (CC BY-SA 3.0; Lz1aat).

Radiation / wave patterns

Idealized radiation pattern of the Yagi-Uda — Idealized azimuth radiation pattern (illustrative, generated). Radial scale in dB.

How & why it works

A Yagi-Uda adds parasitic elements around a driven dipole. A slightly longer reflector behind the driven element and one or more shorter directors in front reshape the radiation pattern by re-radiating the signal with phase shifts that reinforce energy in one direction and cancel it in others. Adding directors narrows the beam and increases forward gain.

Real-world uses

Rooftop TV reception, point-to-point amateur and commercial links, and direction finding.