LNA Noise Figure vs Source Match
An amplifier's noise figure is lowest only at one specific source reflection — the optimum Γopt — and rises with the mismatch from it, at a rate set by the equivalent noise resistance Rn. Given the four noise parameters and your presented source reflection ΓS, this computes the actual noise figure and the penalty above Fmin. This is the noise-match trade-off behind LNA design.
Equations & Parameters ▸
\(F = F_{\min} + \dfrac{4\,R_n/Z_0\,\left|\Gamma_S - \Gamma_{\text{opt}}\right|^2}{\left(1-|\Gamma_S|^2\right)\left|1+\Gamma_{\text{opt}}\right|^2}\)
| Fmin | Minimum noise figure of the device (dB), achieved at Γopt. |
| Rn | Equivalent noise resistance (Ω) — how fast NF rises with mismatch. |
| Γopt | Optimum source reflection (magnitude and angle in degrees). |
| ΓS | Source reflection actually presented (magnitude and angle). |
| Z0 | Reference impedance (Ω), default 50. |
References: D. M. Pozar, Microwave Engineering, 4th ed., Wiley, 2012. · G. Gonzalez, Microwave Transistor Amplifiers, 2nd ed., Prentice Hall, 1997.
Inputs
dB
Best-case NFΩ
Mismatch slopemag, angle°
mag, angle°
Ω
Default 50Results
Noise figure
NF at ΓS—
Noise factor F—
Mismatch
Penalty above Fmin—
|ΓS − Γopt|—
Diagram