Ground Plane Antenna

Calculate ground plane antenna element and radial lengths for VHF, UHF, and other ham radio frequencies.

Ground Plane

A quarter-wave vertical with elevated radials. Downward-angled radials commonly help bring feed impedance closer to 50 ohms.

Band

Frequency (MHz)

Length Factor (%) Accounts for the typical shortening of a resonant element. Actual length varies with conductor and installation.

Number of Radials

Ground Plane Formula

These are the sizing relationships used by this calculator.

Wavelength

lambda (m) = 299.792458 / f(MHz)

Vertical Element

Vertical element = lambda / 4 * (Length factor (%) / 100)

Radials

Each radial = lambda / 4 * (Length factor (%) / 100)

FAQ

Does this ground plane calculator assume drooped radials?

It sizes the radiator and radials, and the notes explain the difference between drooped-radial and flat-radial feed impedance.

Is this mainly for VHF and UHF ground plane antennas?

It is commonly used that way, but the quarter-wave sizing logic applies to any frequency where the design is practical.

Antenna Calculators

Use these as starting dimensions

Real antennas still depend on environment, conductor diameter, insulation, feed method, and nearby structures. Expect to trim and retune.

Good field workflow

Cut slightly long when possible.
Measure with the feed system you will actually use.
Make small tuning changes and record each one.

Length factor note

This is a starting estimate for the shortening of a resonant element. Conductor size, insulation, mounting height, nearby structures, and feed arrangement can shift the final length.