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Interpreting SWR correctly
What standing-wave ratio tells you about reflection, and which antenna properties it leaves unanswered.
Practice2 min readReviewed 15/10/2026
HB3YAQ · Ajdin HadzicLearning to take awayhttps://hb3yaq.ch/en/knowledge/swr-explained
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WHAT YOU WILL LEARN
- Convert SWR into reflected power.
- Distinguish matching from efficiency.
How standing waves arise
When a travelling wave meets a mismatched termination, part is reflected. Forward and reflected waves combine to create voltage maxima and minima along the line. Their ratio is SWR / standing wave ratioSWR is the ratio of maximum to minimum voltage on a line with standing waves. It is related to reflection caused by an impedance mismatch.Example & full explanation →. With a perfect match there is no reflected wave and the ratio is 1:1.
Reflection coefficient magnitude is |Γ| = (SWR−1)/(SWR+1). Its square is the reflected power fraction at the same reference plane. At SWR 2:1, |Γ| is one third, but the power fraction is only one ninth: about 11.11%. A voltage ratio must not be read directly as a power fraction.
SWR 2:1 does not mean a 50% loss
- |Γ| = (2 − 1) / (2 + 1) = 1/3
- Pr / Pf = (1/3)² = 1/9 ≈ 11.11 %
- Pr = 100 W × 1/9 ≈ 11.11 W
Quick check
Continue with SWR 2:1 →Mini-Circuits · VSWR ↗Does SWR 1:1 prove that an antenna radiates efficiently?
Reveal explanation
No. A matched dummy load can also have SWR 1:1 while turning power into heat. Matching and radiation efficiency are different properties.
Reflected does not mean dissipated
A reflected wave initially represents energy travelling backwards. How much becomes heat depends on the line, source, ImpedanceImpedance is complex opposition to alternating current: it includes resistance and a frequency-dependent reactance. Antenna input impedance is therefore more than a DC resistance reading.Example & full explanation → network and further reflections. A simple forward/reflected power calculation describes one reference plane, not complete station efficiency.
A dummy load can be very well matched while turning almost all input power into heat. Conversely, a radiating antenna with imperfect matching may still radiate much of the power it accepts. Low SWR is useful but proves neither high GainGain describes the ratio of output to input level. In a receiver it can occur before or after digitisation and is often expressed in dB.Example & full explanation → nor good range.
↑ Back to contentsMeasure at the right place
A lossy line attenuates both the outgoing and returning waves. SWR measured at the transmitter can consequently look better than at the antenna itself. Record measurement plane, cable and frequency. Also examine the response over the relevant range and investigate large changes when the cable moves.
↑ Back to contentsFrom reading to experimenting
SWR & reflection
SWR 2:1 means |Γ| = 1/3, approximately 11.11% reflected power and 9.54 dB return loss.
Open example with starting values →Standing-wave ratio: 2 : 1 · Forward power: 100 WThen change exactly one value. Compare the result and use the formula to explain why it changes. The model limits below the calculator also apply here.
Need a term explained?
These explanations help you keep reading.
Got the idea?
At 100 W forward power and SWR 2:1, what reflected power does the model give?
Show answer & explanation
About 11.11 W at the same reference plane. That does not automatically mean exactly 11.11 W is dissipated as heat.