VSWR and Return loss Formula
Return loss (RL) and Voltage Standing Wave Ratio (VSWR) are both measurements used to quantify efficiency of power transfer in radio frequency (RF) and Microwave systems. They are related but represent same information in different ways.
Return Loss in dB : It is a measure of reflected power back from a discontinuity (e.g. connector,
impedance mismatch or component) in RF system. It is expressed in decibels (dB). Return loss formula is as follows.
RL (dB) = - 20 * Log10(|Γ|)
Γ represents reflection coefficient, which is complex ratio of reflected wave to incident wave
The higher values of return loss (dB) indicates better performance meaning that less power is being reflected.
VSWR : Voltage Standing Wave Ratio is another way to express the same information as
return loss but in different format. It is defined as ratio of maximum amplitude of standing wave to
the minimum amplitude. VSWR formula is as follows.
VSWR = (1 + |Γ|)/(1 - |Γ|)
VSWR provides simple way to describe how much power is being reflected versus transmitted.
VSWR values typically range from 1 to infinite. The higher values of VSWR
indicate more significant reflections.
VSWR = 1, indicates perfect match
VSWR = Infinite, complete reflection (i.e. all power reflected).
Return Loss (RL) and Voltage Standing Wave Ratio (VSWR) are related through a mathematical relationship. You can convert between RL and VSWR using above two formulas.
Return loss to VSWR calculator
Following calculator can be used to convert return loss in dB to corresponding VSWR.
VSWR Calculation Example :
Return loss in dB = 18
VSWR = 1.28
VSWR to Return loss calculator
Following calculator can be used to convert VSWR to corresponding return loss (RL).
Return loss calculation EXAMPLE :
VSWR = 1.1 Return loss in dB = 26.44
Conclusion : In summary, RL and VSWR formulas and calculators are valuable tools that enhance the efficiency, accuracy and consistency of RF engineering tasks such as measurement, analysis, troubleshooting and system design.
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