VSWR
Power Loss Chart
How much power does VSWR actually cost you? This reference shows exactly how much transmitted power is lost to impedance mismatch at any VSWR. Use the calculator, study the chart, or scroll the full table.
VSWR Power Loss Calculator
Enter any VSWR value or drag the slider to instantly see the impact on transmitted power, reflected power, return loss, and mismatch loss.
Common VSWR Benchmarks
How much power is actually getting to your load? These are the numbers engineers reference most often.
0.01 dB mismatch loss
Excellent match
0.04 dB mismatch loss
Very good match
0.18 dB mismatch loss
Typical spec limit
0.51 dB mismatch loss
Antenna spec limit
1.25 dB mismatch loss
Poor match
VSWR vs. Power Loss Curve
Power delivered to the load drops rapidly as VSWR increases. The curve shows that keeping VSWR below 1.5:1 preserves over 96% of your transmitted power.
VSWR Power Loss Table
Full reference table showing VSWR, return loss, reflection coefficient, mismatch loss, and power transmitted/reflected. Filter by VSWR range or scroll the complete dataset.
| VSWR (Typ) |
Return Loss (dB) |
VSWR (dB) |
Voltage Refl Coefficient (Γ) |
Mismatch Loss (dB) |
Power Transmitted (%) |
Power Reflected (%) |
|---|
The Effect of VSWR on Transmitted Power
Every RF system has an impedance match at each connection point. When the impedance of a source, transmission line, and load are not perfectly matched, a portion of the transmitted signal is reflected back toward the source. VSWR (Voltage Standing Wave Ratio) quantifies this mismatch, and the resulting power loss is called mismatch loss.
Understanding this relationship is critical for system-level power budgets. A component with "only" a 2.0:1 VSWR is throwing away over 11% of your power before the signal even reaches the next stage.
The Core Equations
All the values in the table above are derived from a single parameter: the voltage reflection coefficient (Γ).
Return Loss = -20 × log10(|Γ|) [dB]
Mismatch Loss = -10 × log10(1 - |Γ|²) [dB]
Power Reflected = |Γ|² × 100 [%]
Power Transmitted = (1 - |Γ|²) × 100 [%]
VSWR (dB) = 20 × log10(VSWR)
Why This Matters in Practice
- High-power transmitters: In a 1 kW radar transmitter with VSWR 1.5:1 at the antenna feed, 40 watts of power reflects back into the transmitter. Over time, this reflected power heats components, degrades amplifier performance, and can trigger protection circuits.
- Satellite communications: Link budgets in satellite systems are calculated to fractions of a dB. A VSWR of 1.3:1 at each of four waveguide flanges in the feed chain adds approximately 0.12 dB of mismatch loss per junction, totaling nearly 0.5 dB across the chain.
- Test and measurement: When characterizing components on a network analyzer, the measurement port VSWR introduces uncertainty. A 1.2:1 source VSWR creates approximately ±0.04 dB of measurement uncertainty on any device under test.
VSWR Specification Benchmarks
- Below 1.1:1: Precision calibration standards and high-quality loads. Less than 0.2% power reflected.
- 1.1:1 to 1.2:1: High-performance connectors, adapters, and measurement cables. Standard for laboratory-grade equipment.
- 1.2:1 to 1.5:1: Standard specification for most commercial waveguide components, filters, and transitions. Acceptable for nearly all applications.
- 1.5:1 to 2.0:1: Typical antenna VSWR across full bandwidth. Broadband components often specify this range at band edges.
- Above 2.0:1: Generally considered poor for system use. Over 11% power reflected. May trigger transmitter protection foldback or shutdown.
Frequently Asked Questions
How much power is lost at VSWR 2.0?
At VSWR 2.0:1, the mismatch loss is 0.512 dB. This means 88.9% of the input power reaches the load, and 11.1% is reflected back toward the source. The reflection coefficient is 0.333 and the return loss is 9.54 dB.
What VSWR is acceptable for most RF systems?
For most systems, VSWR 1.5:1 or better is the standard acceptance threshold. At 1.5:1, you lose only 0.18 dB (4% of power). Precision measurement systems often require better than 1.2:1. Antennas typically specify 2.0:1 or better across their full operating bandwidth.
What is mismatch loss?
Mismatch loss is the fraction of power that fails to transfer from one stage to the next due to impedance mismatch. It is distinct from ohmic (dissipative) loss. The reflected power is not absorbed by the load; it travels back toward the source, where it may be re-reflected, absorbed by an isolator, or dissipated as heat in the source.
Does VSWR cause the same loss at all frequencies?
VSWR is frequency-dependent. A component may have 1.2:1 at the center of its band and 2.0:1 at the band edges. The power loss at each frequency corresponds to the VSWR at that frequency. When specifying system performance, always note the worst-case VSWR across the full operating bandwidth.
What happens to the reflected power?
Reflected power travels back toward the source. In most well-designed systems, an isolator or circulator absorbs the reflected power in a matched load. Without an isolator, the reflected power can re-enter the amplifier, causing gain compression, intermodulation products, or oscillation. High-power amplifiers include VSWR protection circuits that reduce output power or shut down when reflected power exceeds safe limits.