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RF TOOLS // RADIO FREQUENCY

GROUND PLANE CALC

Calculate dimensions for a Ground Plane antenna with 4 radials.
Enter frequency and wavelength submultiple — get all measurements and
the technical SVG drawing ready to print.

// Frequency
—
// Wavelength λ
—
// Submultiple
—
// Speed of light (c)
299.792.458 m/s
CALCULATION PARAMETERS
GROUND PLANE 4 RADIALS
Frequency —
Wavelength submultiple
Radial length +5%
+5%
Relative to the vertical element. Standard λ/4 GP: radials +5%
Velocity factor (Vf) 0.95
0.95
Bare copper wire ~0.95 · RG58 coax ~0.66 · Free air: 1.00
Radial angle (from horizontal plane)
// Results
Element mm cm m in ft
// Enter the parameters and press CALCULATE
// Technical drawing
// WAITING FOR CALCULATION GROUND PLANE 4 RADIALS
TECHNICAL NOTES
Velocity factor

The velocity factor (Vf) accounts for the fact that propagation speed in the conductor is lower than in free space. Bare metal wire typically uses 0.95. For purely theoretical calculations use 1.00.

Radial angle and impedance

For a λ/4 GP, horizontal radials (0°) → Z ≈ 36 Ω. Tilting them down to 45° → Z ≈ 50 Ω (direct match with 50 Ω coax). At 90° (vertical downward) → Z ≈ 75 Ω.

Radials 5% longer

Radials slightly longer than the vertical element improve the impedance match and reduce common-mode currents. For frequencies above 400 MHz, consider tightening construction tolerance.