Impedance Matching and VSWR VSWR and Return Loss Informational

How do I calculate the mismatch loss in dB from a known VSWR value?

Mismatch loss is the power lost due to reflection at an impedance discontinuity. It can be calculated directly from the VSWR value: (1) Formula: first, convert VSWR to reflection coefficient: Gamma = (VSWR - 1) / (VSWR + 1). Then calculate the mismatch loss: ML (dB) = -10 × log10(1 - Gamma²). The mismatch loss represents the fraction of incident power that is reflected back (not delivered to the load). (2) Common VSWR values and their mismatch loss: VSWR = 1.0: Gamma = 0, ML = 0 dB (perfect match). VSWR = 1.2: Gamma = 0.091, ML = 0.036 dB. VSWR = 1.5: Gamma = 0.200, ML = 0.177 dB. VSWR = 2.0: Gamma = 0.333, ML = 0.512 dB. VSWR = 3.0: Gamma = 0.500, ML = 1.25 dB. VSWR = 5.0: Gamma = 0.667, ML = 2.55 dB. VSWR = 10.0: Gamma = 0.818, ML = 4.81 dB. (3) Practical significance: at VSWR = 1.5: only 0.177 dB (4%) of the power is lost. This is generally acceptable for most RF systems. At VSWR = 2.0: 0.512 dB (11%) is lost. This is the typical maximum acceptable VSWR for most designs. At VSWR = 3.0: 1.25 dB (25%) is lost. This is typically unacceptable and indicates a serious mismatch. (4) Relationship to return loss: return loss (dB) = -20 × log10(Gamma). At VSWR = 2.0: RL = 9.54 dB. Mismatch loss can also be calculated from return loss: ML = -10 × log10(1 - 10^(-RL/10)).
Category: Impedance Matching and VSWR
Updated: April 2026
Product Tie-In: Connectors, Cable Assemblies, Attenuators

Mismatch Loss Calculation

Mismatch loss is a fundamental quantity in RF system design, appearing everywhere from antenna feedlines to cascaded amplifier chains.

ParameterL-NetworkPi/T-NetworkTransmission Line
BandwidthNarrow (<10%)Moderate (10-30%)Broad (>30%)
Components2 (L, C)3 (L, C, C or C, L, C)Stubs, lines
Q ControlFixed by impedance ratioAdjustableSet by line length
Frequency RangeDC-6 GHzDC-6 GHz1-100+ GHz
Design ComplexityLowMediumMedium-high
Common Questions

Frequently Asked Questions

Is mismatch loss the same as insertion loss?

No. Mismatch loss is the power lost due to reflection only (the reflected power returns to the source). Insertion loss includes: mismatch loss (reflected power) PLUS dissipative loss (power absorbed as heat in the component). For a lossless component (ideal cable, ideal connector): insertion loss = mismatch loss. For a lossy component (real cable, attenuator): insertion loss = mismatch loss + dissipative loss. Insertion loss is always greater than or equal to mismatch loss.

Does mismatch loss always waste power?

The reflected power is not necessarily wasted. It returns to the source. If the source is a matched amplifier: the reflected power is absorbed by the source impedance (converted to heat in the amplifier output stage). If the source is a circulator-isolated transmitter: the reflected power goes to the circulator load (absorbed harmlessly). If the source is a resonant antenna: the reflected power bounces back and forth, with some radiated on each pass. In all cases: the power delivered to the load is reduced by the mismatch loss.

How does mismatch loss affect noise figure?

A mismatch at the input of an LNA degrades the noise figure: NF_system = Loss_mismatch + NF_LNA (in dB, for a passive mismatch). At VSWR 2.0 (ML = 0.51 dB): NF increases by 0.51 dB. For a 0.5 dB NF LNA: total NF becomes 1.01 dB. This is significant for sensitive receivers (radio astronomy, satellite). Keep input VSWR < 1.5 for NF-critical applications.

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