Yagi Antenna Calculator

What Is a Yagi Antenna? A Yagi-Uda antenna is a directional beam antenna with multiple parallel dipole elements. Invented by Shintaro Uda and Hidetsugu Yagi (Japan, Tohoku University, 1926). One driven element (fed), one reflector behind it, and one or more directors in front. Gain increases with more elements, and each director adds roughly 1.5 to 2 dB.

Element Types Reflector: slightly longer than driven element (about 5% longer). Positioned behind. Driven element: half-wave dipole fed by coax (via matching network). Center of the array. Directors: slightly shorter than driven element (about 5.5% shorter for the first). Multiple directors increase gain. Typical spacing: 0.1 to 0.25 λ between elements. This calculator uses 0.2 λ throughout, which is the safe middle of that range and is what most amateur designs of this size use.

Classic Yagi Design Rules (Long-Yagi by DL6WU / ARRL) Driven element length: L = 141/f (meters) where f is frequency in MHz Reflector: 5% longer than driven element Director 1: about 5.5% shorter Each additional director: 1.5% shorter than the previous Boom length: 0.4 λ for 3-element, growing by 0.2 λ per director after that

Why 141 and not the dipole’s 142.65 A wire dipole is cut at 468/f feet, which is 142.65/f metres. A Yagi driven element is not wire, it is 6 to 10 mm aluminium tube, and a fatter conductor resonates short. That puts the driven element near 0.47 λ rather than 0.4755 λ, which is where 141/f comes from. The dipole calculator is the right one for a wire antenna; this one is right for tubing. The two disagreeing by 1.2% is the conductor diameter, not an error in either.

Gain vs Number of Elements 3-element Yagi: ~5–6 dBd (over dipole) 4-element: ~6.5–7.5 dBd 5-element: ~7.5–8.5 dBd 10-element: ~11–12 dBd Each doubling of boom length adds ~3 dB.

Common Amateur Radio Bands 2m (144 MHz): λ ≈ 2.08 m | 70cm (432 MHz): λ ≈ 0.69 m 10m (28 MHz): λ ≈ 10.7 m | 6m (50 MHz): λ ≈ 6.0 m 20m (14 MHz): λ ≈ 21.4 m (Yagi large; often rotatable beam antennas)