Yagi-Uda Antenna
The Yagi-Uda antenna achieves directional gain through a driven dipole, a reflector element, and one or more directors. Gain scales approximately as 10 log₁₀(N) for large arrays. This calculator uses the NBS/Viezbicke empirical tables (Tech Note 688) optimised for d/λ = 0.0085 element diameter.
Equations & Parameters ▸
\(\text{Gain (dBi)} = \text{Gain (dBd)} + 2.15 \quad Z_{in}\approx 25\,\Omega\text{ (straight driven)}\)
| Reflector | Slightly longer than λ/2 (≈ 0.505λ), placed ~0.25λ behind driven element |
| Driven | ≈ 0.47λ half-wave dipole; feed point impedance ~25 Ω in array environment |
| Directors | Slightly shorter than λ/2 (≈ 0.43–0.46λ), spaced 0.25–0.42λ ahead of driven |
| F/B ratio | Front-to-back ratio; improves with more elements but saturates above ~7 |
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Diagram