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Docs Build & Assembly Ground Planes and Counterpoises

Ground Planes and Counterpoises

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Why a quarter-wave needs a ground plane, and how copper foil adds ~3 dBi

Ground Planes and Counterpoises

Overview

A quarter-wave monopole is only half an antenna - the other half is its ground plane. Without one, the feed becomes part of the antenna, which makes results unpredictable.

Quarter-Wave Theory

A 17.3 cm monopole at 433 MHz needs an electrically conductive counterpoise underneath to “reflect” the missing half-wave. The radio’s own ground pour is a small one; a larger plane performs better.

Adding a Ground Plane

MethodGain effect
No plane (bare wire)Baseline, unpredictable
Radio PCB ground onlySlightly better
Copper foil under the module+3 dBi typical
Full metal enclosure baseBest, if antenna exits above it

Practical Build

  1. Cut a square of copper tape or foil ~10 x 10 cm.
  2. Connect it to the module GND at the feed point.
  3. Mount the whip vertically above it.
  4. Keep the plane flat - folding it distorts the pattern.

Warning

The ground plane must be at the antenna feed, not shorting the SMA. Measure continuity: SMA center to the plane should NOT beep, SMA shield to plane should.