Antenna Calculators

Calculate resonant lengths and basic parameters for common antennas: dipole, monopole, loop, folded dipole, Yagi, magnetic loop, inverted-V, 5/8λ, etc.

Velocity factor applies to wire shortening due to insulation/nearby objects. Default is free-space.

Half-wave dipole (center-fed)

Standard half-wave dipole resonant length and element half-length.
Formula: λ = 300 / f(MHz). Half-wave length ≈ 0.5 λ. Apply velocity factor and small end correction if needed.

Quarter-wave monopole (vertical, ground plane)

Monopole length is ~ λ/4. For ground-plane use 4 radials ≈ 0.48λ as a starting point if slanted down.

Folded dipole

Folded dipole is ≈ same length as half-wave dipole but has higher feedpoint impedance (~300 Ω for equal-conductor widths).

Full-wave loop (single-turn wire loop)

Resonant when circumference ≈ λ (full-wave) — common shapes: square, circular. Provide circumference and side length for square loop.

Small magnetic loop (hobbyist)

Magnetic loop: circumference ≈ 0.05–0.2 λ (tuned). This calculator gives circumference, diameter and a rough tuning capacitor range estimate (very approximate).
Note: magnetic loops are sensitive and need a high-voltage tuning capacitor; real design needs precise L/C modelling.

Inverted-V (dipole variant)

Center height and leg angle affect vertical/horizontal polarization mix and feed impedance.

5/8λ vertical (mobile/ground)

5/8 wave vertical gives more low-angle radiation. Needs proper matching coil/transformer; length ≈ 0.625 λ.

Simple 3-element Yagi-Uda (reflector + driven + director)

Gives approximate element lengths and spacings for a 3-element Yagi (HF/VHF typical rules of thumb).

End-Fed Half-Wave (EFHW) & long-wire

Calculates resonant lengths for 1/2, 1λ, 3/2λ, etc. Useful for long-wire and multiband single-wire antennas.