The Truth About SWR, Resonance, and Efficient Radiation

SWR Isn’t the Whole Story

One of the most misunderstood aspects of antenna tuning is the role of SWR (Standing Wave Ratio). Many operators obsess over achieving a perfect 1:1 SWR, thinking it guarantees an efficient antenna. In truth, SWR only tells you how well your transmitter is matched to the feedline at a particular point. It doesn’t tell you anything about how well the antenna itself is radiating.

What matters more is the complex impedance of the antenna at the feedpoint. This includes both the resistive (R) and reactive (X) components. When X = 0, the antenna is said to be resonant at that frequency. But low SWR can exist even when X ≠ 0, especially if you're using a tuner or a long coax run that masks impedance transformations. In those cases, power transfer might look fine, but significant energy could be lost or reflected elsewhere in the system.

In short: SWR is a power transfer metric, not a tuning tool. To really know how your antenna is behaving, watch the reactance. If you're not looking at X, you're tuning blind.

Resonance Is Overrated

Another common misconception is that antennas must be resonant to work well. This simply isn't true.

Resonance is an electrical condition, not a requirement for efficient radiation. A non-resonant antenna that's well-matched can radiate just as effectively as a resonant one. In fact, many practical and high-performing antennas — like off-center-fed dipoles, long wires, and multiband verticals — are intentionally non-resonant.

What's far more important than resonance is the electrical length of the antenna. For example, a wire that's close to half a wavelength long will often radiate just as well whether it's resonant or not. The current distribution and resulting radiation pattern depend on geometry and length, not solely on achieving X = 0.

So while resonance can simplify matching, it is not a requirement for performance. Focusing purely on resonance can lead to impractical designs, forced compromises, or wasted potential.

The Bottom Line

  • Use SWR to monitor power transfer, but don’t rely on it as the sole indicator of antenna performance.
  • Always check impedance, especially the reactance component (X), when tuning.
  • Don’t be afraid of non-resonant antennas. With proper matching and feedline practices, they can perform just as well — or better.

Understanding these basics will help you move beyond myths and build antennas that truly work in the real world

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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.