Yagi calculator

v1.1.3

Single-band Yagi • reflector, split driven element and directors • insulated elements on a boom

01 Frequency & layout Centre frequency MHz Number of elements includes reflector & driven Drawing units

02 Element construction

Reflector Ø mm

Driven Ø mm

Directors Ø mm

Element material Driven feed gap mm

03 Design preference Element velocity / shortening multiplier

Leave at 1 for bare elements. Applied in addition to the diameter correction. This is not coax velocity factor.

Gain / bandwidth preference 50 / 50

Wider bandwidthHigher gain

Changes the starting lengths and spacings. Preference weights, not a specified dB/MHz ratio or verified optimisation.

04 Boom Boom diameter / width mm Overhang at each end mm

Elements must be electrically insulated and clear of the boom. Through-boom or bonded elements need a different model. Boom width is drawn but does not apply a tuning correction.

DIMENSIONED LAYOUT

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Preliminary geometry, not a validated antenna design. Gain, SWR, usable bandwidth and matching are not predicted. Simulate and measure before final cutting; leave trimming allowance.

Formulas, assumptions & accuracy

This calculator creates an editable starting layout for straight, constant-diameter elements. It does not solve electromagnetic coupling or optimise gain. The preference control blends two heuristic geometries; its percentages are weights, not a measured gain-to-bandwidth ratio.

Free-space wavelength λ = 299,792,458 / f (Hz). Diameter ratio q = d / λ. The illustrative end-effect factor K(q) = 0.98 − 0.015 log₁₀(1 + q / 0.0001). Each element length is λ × coefficient × K(q) × the entered element multiplier. This approximation is our layout heuristic, not a fit to the NBS design curves.

With g = gain preference / 100: reflector coefficient = 0.510 + 0.005g; driven = 0.490 − 0.005g; director i = 0.465 − 0.008g − (0.018 + 0.008g) × (i − 1) / max(1, directors − 1). Reflector-to-driven spacing = (0.18 + 0.02g)λ; driven-to-first-director = (0.12 + 0.03g)λ; subsequent director gaps = (0.18 + 0.10g)λ. These are unvalidated seed dimensions.

Material enters the conductor-loss calculation, not an arbitrary length multiplier: surface resistance Rs = √(πfμ₀ / σ), skin depth δ = √(1 / (πfμ₀σ)), and approximate driven-element loss Rloss = Rs × conducting length / (2πd), assuming a sinusoidal current. Conductivity presets at roughly 20°C: copper 58, aluminium 35, brass 15, nonmagnetic stainless 1.4 MS/m; alloys vary. This is an isolated-element loss indicator, not total Yagi efficiency or gain. Magnetic steel and coated wire are excluded.

Driven length is tip-to-tip including the gap; cut each half to (length − gap) / 2. Spacings are centre-to-centre. Boom length is reflector-to-last-director distance plus both overhangs. Position is measured from the rear boom end. Displayed rounding is not construction tolerance.

Element diameter, spacing and boom construction require proper design treatment: see NBS Technical Note 688: Yagi Antenna Design. Material conductivity and efficiency are discussed in Shahpari & Thiel (2015). Those references do not validate this heuristic.