Ground, Mirrors, and Radials – Not All Grounds Are Equal

In antenna design, "ground" is one of the most misunderstood terms. It gets used interchangeably to mean soil, a radial field, a metal roof, or even a wire counterpoise. For a technically informed audience, it's worth dissecting the actual roles and behaviors of these different "grounds." Let's explore four key types:

Real Ground – The Dirt Beneath Us

Soil is lossy. Its resistance and dielectric properties vary wildly with moisture, mineral content, and composition. When RF current flows into real ground—as in a vertical without radials—it dissipates part of its energy as heat.

Real ground also distorts the current distribution. Because it's not a good conductor, the antenna's return current tries to find the least-bad path—often spreading laterally before closing the loop. This causes ground losses, radiation pattern distortion, and impedance unpredictability.

Soil isn't inherently part of a well-functioning RF system. It's just a lossy medium that happens to be under your antenna.

RF Mirrors – Conductive Planes in the Near and Far Field

Large conductive surfaces like metal roofs, solar panels, or even shipping containers create an "image" of your antenna. This image alters the radiation pattern, impedance, and polarization characteristics by reflecting RF fields—both near-field inductive and far-field radiative components.

Unlike radials, these structures don't provide a controlled return path for antenna current. Instead, they create interference—sometimes constructive, sometimes destructive—depending on their size, conductivity, distance (height), and orientation.

The effect is highly frequency and geometry dependent. A roof might improve low-band radiation but kill your take-off angle on 20m. It’s a double-edged sword—unpredictable and often misunderstood.

Radials – Managing Return Current and Field Symmetry

Radials do more than offer a return path. They serve multiple critical roles:

• Complete the circuit: For verticals and end-fed designs, radials provide a low-impedance return path for the displacement current.
• Control impedance: A well-designed radial field stabilizes feedpoint impedance across seasons and soil conditions.
• Reduce ground losses: The current returns through copper or aluminum, not soil. This improves efficiency.
• Field symmetry: They help balance the antenna's radiation pattern, reducing unwanted skew or asymmetry.

The number and length of radials depends on the band and the desired efficiency. For quarter-wave verticals, 16 or more full-size radials approach diminishing returns; for elevated radials, even fewer can be highly effective.

Counterpoises – Artificial Grounds in the Air

A counterpoise is a non-resonant conductor (wire, screen, or plate) that provides a return path for RF current when a true ground or radial system is impractical. Unlike radials that are often laid on or buried in the soil, counterpoises are usually elevated above the ground and work via capacitive coupling.

They’re especially useful in portable and compromised installations (e.g. rooftops, balconies, or poor soil conditions), offering a controlled return path and reducing interaction with lossy earth. However, they require careful attention to size, height, and symmetry to avoid excessive common-mode currents.

Safety Ground – A Different Beast Altogether

RF ground and safety ground are not the same thing.

Safety ground, or protective earth, is a low-impedance connection to prevent shock hazards. It is required by electrical safety codes and typically ties all exposed conductive parts to earth. RF currents, however, do not care about electrical codes—they follow the path of least impedance at RF, which is often not the green wire.

Connecting your station's chassis to safety ground does not ensure good RF behavior. In fact, in many cases it introduces unwanted common-mode paths. Always separate your RF and safety ground considerations—both are essential, but for different reasons.

⚠️ Note: To prevent ground loops when low-impedance bonding to the protective earth of your home is not possible, maintain a minimum distance of 15–20 meters between independent ground rods or ground systems. This reduces circulating current and potential differences during lightning events or high RF power operation.

Related Reading

• The Faraday Cloth Radial Myth – Why an inductive mesh isn't a substitute for radials
• ARRL & K6WX: “Ground” is a Myth – But There’s Much, Much More to the Story – An in-depth look at the confusion surrounding RF ground

Conclusion

Understanding the distinction between lossy soil, RF-reflective structures, engineered current paths like radials, and capacitive systems like counterpoises is crucial for efficient antenna design. True performance comes not from dumping RF into dirt or relying on conductive surfaces—but from deliberately managing current flow, symmetry, and environmental interactions.

Not all grounds are equal. And in RF, sometimes the best "ground" isn’t the ground at all.

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.