3 element yagi antenna calculator

What this 3 element Yagi calculator does

A 3 element Yagi antenna is one of the most popular directional antenna designs for ham radio, scanner projects, and DIY RF experimentation. It gives useful forward gain, decent front-to-back rejection, and remains mechanically simple enough for home construction.

This calculator provides a practical first-pass layout by estimating:

• Reflector length
• Driven element length
• Director length
• Element spacing on the boom
• Minimum boom length from reflector center to director center

How the math works

1) Wavelength from frequency

The free-space wavelength is estimated with:

• λ (meters) = 300 / f(MHz)

From there, half-wave is:

• Half-wave = 150 / f(MHz)

2) Driven element and parasitic element ratios

The calculator applies a user-selected correction factor to the half-wave value for real-world shortening effects, then derives parasitic elements with common practical ratios:

• Driven element = Half-wave × correction factor
• Reflector = Driven element × 1.05
• Director = Driven element × 0.95

3) Spacing assumptions

For a straightforward 3 element Yagi starting point:

• Reflector-to-driven spacing = 0.20λ
• Driven-to-director spacing = 0.15λ

These are standard hobbyist values that usually produce a stable pattern and a good tuning baseline.

Build and tuning guidance

Before cutting metal

• Pick the center frequency for your target band segment.
• Use straight, rigid elements (aluminum rod/tube is common).
• Mark boom positions from a single datum point to avoid cumulative measurement errors.
• Start with elements slightly longer (about 1-2%) and trim during tuning.

Feedpoint and matching notes

The driven element can be split-dipole style, folded dipole style, or adapted with a matching network (such as a gamma match). The exact feed method changes impedance behavior, so expect to do final trim and matching with an SWR meter or antenna analyzer.

• Use a current balun/choke at the feedpoint to reduce common-mode feedline current.
• Keep coax routing away from the element plane when possible.
• Tune the antenna in its real installation environment (height and nearby metal matter).

Expected performance (typical)

A well-tuned 3 element Yagi often delivers useful forward gain with a tighter pattern than a dipole, making it ideal for point-to-point contacts, fox hunts, weak-signal work, and directional receive improvement.

Worked example (conceptual)

If you design around 146.52 MHz with a 0.95 correction factor, the calculator returns a driven element just under one meter, with a slightly longer reflector and slightly shorter director. Spacing is derived from wavelength and gives you a practical boom layout to start construction quickly.

Common mistakes to avoid

• Using total element length formulas as half-length values by accident.
• Ignoring correction factor and cutting only from ideal free-space equations.
• Mounting the antenna near conductive objects during measurement.
• Skipping feedline choke/balun and misreading SWR behavior.
• Trying to tune with large trim cuts instead of tiny incremental adjustments.

Practical safety reminders

• Stay far from power lines during assembly and installation.
• Secure mast and guying hardware appropriately for wind loading.
• Ground and protect coax runs if the station setup requires lightning mitigation.
• Follow local regulations for transmitting frequencies and power levels.

Final note

This calculator is meant as a fast, practical design tool for a 3 element Yagi antenna. Real-world antenna behavior depends on element diameter, feed method, nearby structures, mounting height, and construction tolerances. Use the calculated dimensions as a strong starting baseline, then fine-tune for your exact operating conditions.