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S21 Linear Magnitude
0.9441
S21 Linear Magnitude vs S11 (Return Loss at Port 1)
Formule
## Understanding S-Parameters Scattering parameters describe how RF energy propagates through a network. ### Parameter Meanings - **S11**: Input return loss (reflection at port 1) - **S21**: Forward transmission (gain or insertion loss) - **S12**: Reverse transmission (isolation) - **S22**: Output return loss (reflection at port 2) ### Conversion **Linear = 10^(dB/20)** (for voltage/amplitude) **dB = 20 x log10(Linear)** For passive devices, S21 is negative (loss). For amplifiers, S21 is positive (gain).
Exemple Résolu
A filter with S11=-15 dB, S21=-0.5 dB, S12=-30 dB, S22=-20 dB.
- 01S11 linear: 10^(-15/20) = 0.1778
- 02S21 linear: 10^(-0.5/20) = 0.9441
- 03S12 linear: 10^(-30/20) = 0.03162
- 04VSWR at port 1: (1+0.1778)/(1-0.1778) = 1.43
- 05Insertion loss: 0.5 dB
Questions Fréquentes
What does negative S21 mean?
For passive devices, S21 is negative (in dB) indicating insertion loss. For amplifiers, S21 is positive indicating gain.
What is good S11 for an amplifier?
S11 below -10 dB (VSWR < 2:1) is acceptable. Below -15 dB is good. Below -20 dB is excellent.
How are S-parameters measured?
Using a vector network analyzer (VNA) with calibrated test ports and known reference impedance (usually 50 ohms).
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