Cascade Noise Figure Calculator
Enter gain and noise figure for each stage in an RF chain (LNA, filters, mixers, IF amps, …). The calculator applies Friis' cascade formula to compute overall noise figure and per-stage contributions.
Stages (leave unused rows blank)
| Stage | Gain (dB) | Noise Figure (dB) |
|---|---|---|
| 1 | ||
| 2 | ||
| 3 | ||
| 4 | ||
| 5 | ||
| 6 |
Result will appear here.
Overall NF
—
Noise factor F
—
Total gain
—
Te @ 290 K
—
Friis' formula (linear): Ftotal = F1 + (F2 − 1)/G1 + (F3 − 1)/(G1G2) + …. Gains G are linear (power) gains corresponding to the specified dB values.
Per-Stage Contribution & Theory
Relative contribution of each stage to the overall noise figure:
| Stage | Gain (dB) | NF (dB) | Contribution to Ftotal (%) |
|---|
Key ideas:
- The first LNA dominates system NF, because later stages are divided by the power gain of all preceding stages.
- High gain and low NF in the first stage greatly reduce the impact of noisy mixers or IF amplifiers.
- Elements with loss (negative gain) placed before the LNA (e.g., filters, switches) strongly degrade the overall noise figure.
This tool assumes a reference temperature of 290 K and is intended as a design / teaching aid rather than a full system simulator.