# S11 to dB Converter

Use this tool to convert Linear to dB values of S11.

The forward reflection coefficient S11 is a measure of impedance mismatch at a transition in an RF circuit.

Enter either one of the following

• Linear value of S11 (greater than 0 and less than 1)
• dB value of S11 (less than 0)

## Background

### What is S11?

For a two port network, S11 is the input reflection coefficient (also known as Î“ orÂ Gamma) with a value between 0 and 1.

S11 = b1/a1 (when port 2 is terminated – usually in 50 Î©) where a1 is the incident power on port 1 and b1 is the power reflected from port 1.

## Formula

if S11 is expressed as a linear quantity,

S11dB = 20*Log10(S11linear)

On the other hand, if S11 is expressed in dB

S11linear = 10(S11dB/20)

ðŸ’¡ S11 when expressed in dB is always a negative number

## Example Calculations

If the reflected signal b1 = 0, then all of the input signal a1 is transmitted forward and S11linear = 0; S11dB = -âˆž

If all of the input signal is reflected back, then b1=a1 and none of it is transmitted forward. This is the poorest match possible and the reflection coefficient S11linear = 1; S11dB = 0

The calculator can also be used to convert between linear and dB values of S21, S22 and S12.

## S11 for different RF components

The following table shows linear S11 values for various Radio Frequency modules