SWR Reflected Power

P_refl = P_fwd × ((SWR−1)/(SWR+1))²

Quick answer

This calculator solves P_reflected = P_forward × ((SWR − 1) / (SWR + 1))² for Reflected Power. With Forward Power 22 W, SWR 0.5, the result is 2.444 W. It solves in 3 directions, so you can enter the values you have and get the one you need.

Calculator

Reflected Power (W)
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Formula

P_reflected = P_forward × ((SWR − 1) / (SWR + 1))²

Description

Standing Wave Ratio (SWR) measures the impedance mismatch between a transmission line and its load (antenna). When the antenna impedance does not match the feedline characteristic impedance, a portion of the forward power is reflected back toward the transmitter. The reflection coefficient Γ = (SWR-1)/(SWR+1) determines the fraction of voltage reflected, and the reflected power is proportional to Γ². An SWR of 1:1 means a perfect match with zero reflection, while higher SWR values indicate worse mismatch and more wasted power.

Variables

  • P_reflected — Power reflected back toward the transmitter (W)
  • P_forward — Power traveling toward the antenna (W)
  • SWR — Standing wave ratio (dimensionless, ≥ 1)

Practical Notes

SWR 1.5:1 reflects only 4% of power, SWR 2:1 reflects 11%, and SWR 3:1 reflects 25%. Most amateur transmitters can tolerate SWR up to 2:1 or 3:1 before automatically reducing power. The real concern with high SWR is increased feedline loss (lossy cable dissipates more power at high SWR) and voltage/current hot spots that can damage cable connectors. An antenna tuner at the transmitter improves the match seen by the transmitter but does not reduce feedline losses.

Symbols and units

Symbol Meaning Default unit Accepted units
P_refl Reflected Power W µW, mW, W, kW
P_fwd Forward Power W µW, mW, W, kW
SWR SWR — —

Step by step

  1. 1. What you know: Forward Power 22 W, SWR 0.5
  2. 2. The relation: P_reflected = P_forward × ((SWR − 1) / (SWR + 1))²
  3. 3. Substitute: P_fwd = 22 W, SWR = 0.5
  4. 4. Result: Reflected Power = 2.444 W

Worked examples

Minimum range

Given: Forward Power 22 mW, SWR 0.025

Result: Reflected Power = 19.91 mW

Low range

Given: Forward Power 0.22 W, SWR 0.25

Result: Reflected Power = 79.2 mW

Typical

Given: Forward Power 22 W, SWR 0.5

Result: Reflected Power = 2.444 W

High range

Given: Forward Power 2.2 kW, SWR 0.8

Result: Reflected Power = 27.16 W

Maximum range

Given: Forward Power 22 kW, SWR 8

Result: Reflected Power = 13.31 kW

Solving for each variable

Solve for Reflected Power

Forward Power 22 mW, SWR 0.025 → 19.91 mW

Solve for Forward Power

Reflected Power 10 mW, SWR 0.025 → 11.05 mW

Solve for SWR

Reflected Power 10 mW, Forward Power 22 mW → 5.139

How Reflected Power changes with Forward Power

Forward Power (input) Reflected Power (result)
4.84 W 10.98 mW
12.1 W 27.44 mW
24.2 W 54.88 mW
36.3 W 82.31 mW
48.4 W 109.8 mW
72.6 W 0.1646 W
96.8 W 0.2195 W
0.1936 kW 0.439 W
0.3388 kW 0.7683 W
0.484 kW 1.098 W

The same result in other units

Unit Value
µW 2444000
mW 2444
W 2.444
kW 0.002444

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Frequently asked questions

How do you calculate SWR Reflected Power?

Use P_reflected = P_forward × ((SWR − 1) / (SWR + 1))². With Forward Power 22 W, SWR 0.5, Reflected Power works out to 2.444 W.

What is the formula for SWR Reflected Power?

The formula is P_reflected = P_forward × ((SWR − 1) / (SWR + 1))². Standing Wave Ratio (SWR) measures the impedance mismatch between a transmission line and its load (antenna).

How do you find Forward Power when you know the other values?

Rearrange for Forward Power: with Reflected Power 10 mW, SWR 0.025, Forward Power is 11.05 mW.

How do you find SWR when you know the other values?

Rearrange for SWR: with Reflected Power 10 mW, Forward Power 22 mW, SWR is 5.139.

What units does SWR Reflected Power use?

Reflected Power is shown in µW, mW, W, kW. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

All Amateur Radio formulas →
Quarter-Wave Antenna Length Half-Wave Dipole Length Coaxial Stub Length (λ/4) Effective Isotropic Radiated Power SWR Reflected Power Antenna Beamwidth

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