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)

Velocity Factor (%)

Number of Radials

These are the sizing relationships used by this calculator.

lambda (m) = 299.792458 / f(MHz) * VF

Vertical element = lambda / 4

Each radial = lambda / 4

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

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

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

Bare wire is commonly near 95%, but different conductors and insulated wire can shift the practical length enough to matter.