Enter any one of VSWR, Return Loss, or Reflection Coefficient into the Return Loss Calculator, and it works out the rest — giving you Mismatch Loss and Power Reflected alongside all three impedance mismatch values, with optional Source Impedance for a fuller picture.
VSWR
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Return Loss
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Reflection Coefficient
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Mismatch Loss
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Power Reflected
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VSWR (Voltage Standing-Wave Ratio) measures the severity of standing waves in a transmission line. It indicates how well the load impedance matches the transmission line impedance. A VSWR of 1:1 represents perfect matching, while higher ratios indicate greater mismatch and signal reflection.
Return Loss (dB) = 20 × log₁₀((VSWR + 1)/(VSWR - 1)). This logarithmic relationship shows that higher VSWR values correspond to lower return loss values in decibels.
Reflection coefficient (Γ) is the ratio of reflected voltage to incident voltage at the load. It ranges from 0 to 1, where 0 indicates perfect matching. VSWR = (1 + |Γ|)/(1 - |Γ|).
Mismatch loss is the power loss due to impedance mismatch between the transmission line and load. It's calculated as: Mismatch Loss (dB) = -10 × log₁₀(1 - |Γ|²), where Γ is the reflection coefficient.
High VSWR is caused by impedance mismatch between the transmission line and load. Common causes include damaged cables, loose connections, incorrect antenna impedance, or components with different characteristic impedances.
For most RF applications, VSWR < 1.5:1 is excellent, 1.5-2:1 is good, and 2-3:1 is acceptable. Critical applications may require VSWR < 1.2:1, while some broadcast applications can tolerate up to 1.8:1.
Return loss in dB is related to percentage power reflected. For example, 10 dB return loss means 10% of power is reflected, while 20 dB return loss means only 1% is reflected. Higher return loss values indicate better impedance matching.
50 ohms became the standard because it provides a good balance between power handling capability and signal loss in coaxial cables. It's a compromise between 30 ohms (maximum power) and 77 ohms (minimum loss) for air-filled coaxial lines.