Antenna Gain vs. Near-Field Measurements: Understanding the Difference

In amateur radio, few topics are more misunderstood than antenna gain. A very common mistake is assuming that measuring field strength close to an antenna—inside the near field—can tell you how well it radiates into the far field. It cannot. Near-field strength has no meaningful correlation with far-field gain, efficiency, or pattern.

What Is Antenna Gain?

Antenna gain describes how effectively an antenna directs energy in a particular direction compared to an isotropic radiator. It is a far-field quantity only. This is where electromagnetic waves have fully formed and where the angular pattern is stable and physically meaningful.

High gain means more power is focused in a given direction — exactly what matters for DXing, contesting, and long-distance links.

Near Field vs. Far Field

The near field is the region around the antenna where energy is mostly reactive — stored and exchanged, not radiated. For small HF antennas, the boundary is roughly:

Near-field distance ≈ λ / (2π)

Inside this region:

• E and H fields are not in the 377 Ω free-space ratio.
• Energy is reactive — not power actually leaving the antenna.
• The spatial pattern does not resemble the radiation pattern.
• Readings can change dramatically with tiny probe movements.

In the far field:

• Fields become true traveling waves.
• E/H approaches 377 Ω.
• The beam pattern becomes stable and measurable.
• Power flow corresponds to real radiated energy.

Why Near-Field Measurements Mislead

Walking around an antenna with a handheld field-strength meter at 1–2 m tells you nothing about gain. Instead, it measures reactive coupling and nothing related to actual propagation.

• Your body distorts the very field you’re trying to measure.
• Inefficient antennas can show higher near-field levels.
• A dummy load can look “strong” locally yet radiate almost nothing.

A stronger near field often means more loss — not more radiation.

Example: a poorly grounded vertical with one or two radials will dump current into the soil. The meter goes wild near the antenna, but 10–20 dB of your power is simply heating dirt.

A “hot” antenna in the near field is not the same as a “good” antenna in the far field.

How to Measure Gain Properly

There are only four scientifically valid methods:

1. A calibrated far-field test range.
2. Comparing received signal strength from a distant known source.
3. Logged A/B measurements using an SDR or S-meter with stable propagation.
4. NEC or full-wave simulations matched to real installation conditions.

For HF, fast A/B switching with identical height, feed, and power is usually the most reliable method available to amateurs.

The “POTA Performer” Fallacy

Portable operators often assume a locally “strong” antenna must be good. But small verticals with weak radial systems produce intense near-field currents while radiating very poorly. You might see +10 dB on a handheld meter yet lose far more in actual radiated power.

Conclusion

Near-field strength is not an indicator of far-field performance. It cannot tell you anything about:

• gain
• efficiency
• takeoff angle
• radiation pattern
• front-to-back or front-to-side ratio

If you want to understand how your antenna really performs, measure or simulate its far-field behavior. That’s where DX happens—and where performance actually matters.

Bottom line: If you’re judging an antenna by what your near-field meter says at 1.5 m… you’re measuring the wrong thing.

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