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 **Γ** or Gamma) with a value between 0 and 1.

**S11 = b1/a1** (when port 2 is terminated – usually in 50 Ω) 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,

**S11 _{dB} = 20*Log_{10}(S11_{linear})**

On the other hand, if S11 is expressed in dB

**S11 _{linear} = 10^{(S11dB/20)}**

**???? 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 ** S11_{linear} = 0**;

**S11**= -∞_{dB}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 ** S11_{linear} = 1**;

**S11**= 0_{dB}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

Module | Ideal S11 |

Lossless Transmission Line | 0 |

Attenuator (any dB loss) | 0 |

Amplifier (any dB gain) | 0 |

Filter in-band (LPF, BPF, HPF) | 0 |

Filter out-of-band (LPF, BPF, HPF) | 1 |