Enter your Number of Stages (up to 4) along with each stage's Noise Figure and Gain, and this Noise Figure Calculator uses the Friis formula to compute your cascade's Total Noise Figure, Total Gain, and Total Noise Factor — so you can see exactly how much each stage degrades your system's overall signal quality.
Total Noise Figure
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Total Gain
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Total Noise Factor
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A cascaded noise figure calculator computes the total noise figure and gain of multiple RF stages connected in series. It uses Friis' formula to calculate how noise from each stage contributes to the overall system noise figure, accounting for the gain preceding each stage.
Gain is the amplification provided by each stage, measured in decibels (dB). For cascaded circuits, total gain is simply the sum of individual stage gains: Total Gain = Gain₁ + Gain₂ + Gain₃ + ... This applies because gains in dB add linearly when stages are connected in series.
Noise figure (NF) measures how much noise a component adds to the signal. For cascaded stages, total NF is calculated using Friis' formula: NF_total = NF₁ + (NF₂-1)/G₁ + (NF₃-1)/(G₁×G₂) + ..., where NF values are in linear scale and G represents linear gains.
The first stage has the greatest impact on total noise figure because its noise is not reduced by any preceding gain. Later stages contribute less to total noise figure since their noise contribution is divided by the cumulative gain of all preceding stages.
To minimize total noise figure: use a low-noise amplifier (LNA) as the first stage, maximize gain in early stages, and place high-gain stages before lossy components. The first stage should have the lowest possible noise figure and highest practical gain.
Noise factor (F) is the linear ratio of output noise to input noise, while noise figure (NF) is noise factor expressed in decibels: NF = 10×log₁₀(F). Noise factor is used in calculations, while noise figure is more convenient for specifications and measurements.
Yes, passive components like attenuators, filters, and cables can be included. For passive components, the noise figure equals the insertion loss (both in dB), and the gain is negative (equal to -insertion_loss). This accounts for both signal attenuation and noise degradation.
Negative gain (loss) is common in passive components like filters and attenuators. The calculator handles negative gains correctly in the Friis formula. Lossy stages after low-noise amplifiers can significantly impact total noise figure since they reduce the effective gain for subsequent stages.