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Quarter-Wave Monopole

Vertical Antennas Beginner VHF 🔧 Buildable at home

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

New to these diagrams? How to read a radiation pattern →

Radiation pattern of the Quarter-Wave Monopole
Antenna vertical, seen from above: equal in every horizontal direction (omnidirectional). The vertical (elevation) cut would be a half figure-eight hugging the horizon.

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.

Make one at home

A practical starting point — always trim and check SWR for your exact frequency.

See the finished antenna pictured above ↑.

A quarter-wave monopole is the simplest vertical — one rod working against a ground.

You’ll need

  • A vertical element (wire, rod, or telescoping whip): 71.5 ÷ f(MHz) metres
  • A ground: a metal vehicle roof, a ground plane, or radials
  • A coax connector (e.g. an SO-239) as the feed base

Build

  1. Connect the element to the coax centre conductor at the base.
  2. Connect the coax braid to the ground/radials.
  3. Mount it as high and clear as possible.

Tune

Feed impedance is ~36 Ω over a perfect ground. Trim the element for lowest SWR; a good ground system matters as much as the rod length.

Safety

  • Keep antennas well clear of power lines — never put one where it could fall onto or contact mains wiring.
  • Don’t transmit while anyone is close to the antenna; mind RF-exposure limits and your local licensing rules.
  • Ground masts and use coax surge protection where appropriate.
  • Cutting/soldering: eye protection and a ventilated space.