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Quarter-Wave Monopole

Vertical Antennas

A single vertical quarter-wavelength rod that works against a ground plane.

Band
LF to UHF (scaled to band)
Gain
~5.15 dBi over a perfect ground
Polarization
Vertical

Photos

Real-world photo of a Quarter-Wave Monopole in use
Real-world example. Source: Wikimedia Commons (Public domain; Edmund A. Laport).

Radiation / wave patterns

Idealized radiation pattern of the Quarter-Wave Monopole
Idealized azimuth radiation pattern (illustrative, generated). Radial scale in dB.

How & why it works

A monopole is effectively half of a dipole: a quarter-wave vertical element is mounted over a conducting ground plane, and the ground acts as an electrical mirror that reflects an 'image' of the element to complete the missing half. Because only half the structure is physically present, the radiation resistance is about 36 ohms and the pattern covers the upper half-space, radiating equally in all horizontal directions. The quality of the ground plane (radials, a vehicle body, or earth) strongly affects efficiency and the low-angle radiation that makes verticals good for distant contacts.

Real-world uses

AM broadcast towers, base-station whips, CB and amateur verticals, and handheld radios.