RFReturn Loss vs VSWR: Understanding the Difference
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This page compares Return Loss vs VSWR and describes the difference between Return Loss and VSWR in tabular form with respect to various comparison parameters.
Introduction: Return loss and VSWR are important parameters used to measure the performance of RF devices and components. These parameters are measured using network analyzers.
These parameters indicate the amount of power transmitted and returned towards the source from the load due to impedance mismatching. Return loss is related to the reflection coefficient and VSWR (Voltage Standing Wave Ratio).
Return Loss
It is defined as the amount of reflected power due to impedance mismatch or discontinuity in the transmission path. It is expressed as the ratio of incident power to the reflected power. The reflection coefficient (Γ) is defined as the ratio of incident voltage to reflected voltage. It is related to return loss as follows:
- Return Loss (RL) = 10 * log(Pr/Pi)
- Return Loss (RL) in dB = -20* log(Γ)
Lesser value of return loss indicates higher impedance matching and vice versa.
VSWR
VSWR indicates the matching condition of the source (i.e., transmitter) with the load (i.e., Antenna). VSWR is the ratio of maximum voltage to minimum voltage along the path of the transmission line. VSWR and reflection coefficient can be expressed as follows:
- VSWR = Vmax/Vmin = (1 + Γ) / (1 - Γ)
- Γ = (VSWR - 1) /(VSWR +1 )
Where, ℾ = (ZL -ZO )/(ZL +ZO )
The figure-1 depicts mismatched condition between transceiver (as source) and antenna as load. Due to impedance mismatch, RF signal power is reflected back towards source (i.e. transmitter).
The figure-2 depicts matched condition between transceiver (as source) and antenna (as load). Due to perfect impedance matching, reflected signal power is zero or negligible.
More is the value of VSWR, higher will be the signal loss and lesser will be the power transmission efficiency. Both return loss and VSWR can be converted to each other as per above formula or equations.
Difference between Return Loss and VSWR
The following table mentions the difference between Return Loss and VSWR.
| Parameters | Return Loss (RL) | VSWR |
|---|---|---|
| Definition | The portion of RF signal reflected due to discontinuity in the transmission line is referred to as return loss. | The ratio of incident voltage and reflected voltage is referred to as VSWR. |
| Preferred industry | Cables | Connectors |
| Measurement type | Logarithmic | Linear |
| Application or usage | It is useful to display or measure very small amounts of reflections. | It is useful to display large amounts of reflections. |
| Formula | RL = 20 * Log10( (VSWR + 1)/(VSWR -1) ) | VSWR = ( (1 + 10RL/20 ) / (10RL/20 - 1) ) |
