VSWR and Return Loss Calculations

This VSWR calculator will calculate return loss, mismatch loss, loss in percentage and the reflection coefficient. As an added bonus, the results are modifiable and can calculate the other values. VSWR (Voltage Standing Wave Ratio) is the measure of how efficiently RF power is transmitted and is expressed as a ratio of the maximum to minimum amplitude (or the voltage or current) of the corresponding field components appearing on a line that feeds an antenna. In order to improve the VSWR, this calculator also has an extra input for adding an attenuator to improve or reduce the system VSWR.

Calculator:

VSWR Loss Calculator
VSWR		: 1
Modifiable Calculated Results
Return Loss (dB)		Mismatch Loss (dB)
Loss in %		Reflection Coefficient
VSWR Reduction using a matched attenuator (assuming a perfect 1:1 Attenuator)
Attenuator (dB)		Improved VSWR

Definitions:

VSWR (Voltage Standing Wave Ratio) is the measure of how efficiently RF power is transmitted and is expressed as a ratio of the maximum to minimum amplitude (or the voltage or current) of the corresponding field components appearing on a line that feeds an antenna.

Return Loss (R_L) is a amount of power that is lost to the load and returns back to the system as a reflection typically expressed in dB. A high return loss means more power is lost at the load.

Loss in % (L%) is the percentage of power that is lost to the load and returns back to the system as a reflection (It is expressed in %). A high % loss means more power is lost at the load.

Mismatch Loss (ML) is a measurement describing the amount of power that will not be available at the load due to the reflected wave. It indicates the amount of power lost in the system due to the mismatched impedances.

Reflection Coefficient (R_C) indicates how much of an electromagnetic wave is reflected by an impedance discontinuity in the transmission medium. It is a ratio of the amplitude of the reflected wave to the wave incident at the junction. The magnitude of the reflection coefficient does not depend on the length of the line, only the load impedance and the impedance of the transmission line.

Formulas:

Further Reading:

• Here is an Excel spreadsheet containing the VSWR calculations.
• An article that explains VSWR
• Here is a useful "cheat sheet" converting VSWR to the percentage of reflected power.

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VSWR Stands for 'Voltage Standing Wave Ratio' and is used in EMC to specify the effect of a mismatch presented to a test system signal. Here is a brief history and Explanation the term VSWR. [more...]

ust in case you don't care for mathematical equations, here's a little "cheat sheet" table to help understand the correlation of VSWR to the percentage of reflected power that will return. [more...]

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