Noise Figure Cascade Calculator

Cascade preset:

Start from a common front-end chain, then tune the stage gain and noise figure values from the datasheet or bench setup.

RF chain stages:

List the stages in signal order. Loss before the first LNA adds directly to the final noise figure.

Stage name:

Gain

Noise figure

Stage controls

Analysis bandwidth:

Use the IF, channel, FFT bin, or measurement bandwidth for the sensitivity estimate.

Required SNR:

Set 0 dB for noise-floor crossing, or use the demodulator/link requirement for receiver sensitivity.

Noise figure target:

Use the receiver or link budget target to see whether the current stage lineup has enough NF margin.

0.5 dB {{ targetNfDisplay }} 12 dB

{{ error }}

Reference temperature:

Changes equivalent input noise temperature and thermal noise density only.

Display precision:

Keep more decimals for small NF deltas or lab reports.

Stage	Role	Gain	Effective NF	Friis Term	Share	Cumulative Gain	Cascade NF	Copy
{{ row.stage }}	{{ row.role }}	{{ row.gain }}	{{ row.nf }}	{{ row.term }}	{{ row.share }}	{{ row.cumulativeGain }}	{{ row.cascadeNf }}

Metric	Value	Detail	Copy
{{ row.metric }}	{{ row.value }}	{{ row.detail }}

Check	Status	Action	Copy
{{ row.check }}	{{ row.status }}	{{ row.action }}

{{ jsonOutput }}

Export to PDF Fullscreen

Embed:

Customize

Include current inputs

Size

Advanced

Width

Height

Aspect ratio

Max height

Collapsible embed

Allow fullscreen

Referrer policy

Sandbox tokens

Noise figure describes how much an RF device or receiver chain degrades signal-to-noise ratio. A low noise figure means the chain adds relatively little noise of its own, which is why the number is central to weak-signal receivers, satellite downconverters, software-defined radio front ends, microwave instruments, and any link budget where sensitivity matters.

Cascaded noise figure is the combined noise figure of stages in signal order. A filter, switch, cable, low-noise amplifier, mixer, and IF amplifier may each have a datasheet gain and noise figure, but the first stages usually matter most. Loss before the first active gain stage raises the system noise figure directly, while later noise is divided by the gain that came before it.

RF receiver cascade showing front-end loss, LNA gain, later stages, and smaller later noise contributions.

The main engineering decision is usually not whether one part has the lowest possible noise figure in isolation. It is whether the lineup gives enough early gain, keeps pre-LNA loss low, preserves the required bandwidth, and still leaves enough sensitivity margin for the modulation, detector, or measurement you plan to use.

A calculated cascade is still a model. Datasheet numbers depend on frequency, temperature, impedance match, bias, measurement method, and production spread. Treat the result as a planning and comparison aid, then verify critical receiver designs with measured gain, noise figure, compression, and linearity data.

How to Use This Tool:

Build the receiver chain in the same order the RF signal sees it. Use stage values from the same frequency band and operating condition whenever possible.

Choose a Cascade preset for a starting point, such as an SDR receiver, LNA-first receiver, lossy feedline, satellite downconverter, or passive mixer chain. Editing any stage turns the lineup into a custom case without losing the entered values.
In RF chain stages, set each stage role, name, gain, and noise figure. Enter gain as positive dB for amplification and negative dB for loss. Passive loss and filter roles derive Noise figure from insertion loss, so a -1.5 dB passive stage displays 1.5 dB effective noise figure.
Use Add stage or Remove stage to model one to eight stages. Keep the order physical: antenna-side switch or filter first, then LNA, then later filters, mixers, and gain blocks.
Enter Analysis bandwidth in Hz, kHz, MHz, or GHz. Use the channel bandwidth, IF bandwidth, FFT bin, or measurement bandwidth that should define the integrated noise floor.
Set Required SNR for the receiver or detector. A 0 dB value estimates the noise-floor crossing point; a demodulator, link, or lab threshold usually needs a positive SNR margin.
Set the Noise figure target. It does not change the Friis calculation, but it drives the summary margin, guidance checks, and chart reference mark.
Open Advanced only when the reporting assumptions need adjustment. Reference temperature changes equivalent input noise temperature and thermal noise density. Display precision changes rounded table and export values, while the calculation itself keeps more precision.
Read Cascade Ledger first for each stage's effective noise figure, Friis term, contribution share, cumulative gain, and running cascade noise figure. Then use Noise Budget, Stage Guidance, Friis Contribution Map, and Cascade Progression to check the sensitivity and dominant stages.

If validation appears, fix the named input before using the result. Common causes are bandwidth at zero or below, a passive stage with positive gain, a negative active-stage noise figure, a reference temperature outside 1 K to 1000 K, or a stage count outside one to eight.

Interpreting Results:

The headline noise figure is the total cascade noise figure at the chain input. Compare it with NF target margin instead of reading it alone. A positive margin means the selected target is met; a small positive margin still deserves a frequency, temperature, and tolerance check.

How to read noise figure cascade outputs
Output	What it means	What to verify
Total cascade noise figure	Overall input-referred noise figure after all stage gains and noise factors are combined.	Confirm every stage value belongs to the same frequency band and reference condition.
Friis Term	Each stage's excess noise after division by all prior gain.	Large early terms deserve the most attention because later changes may barely move the total.
Share	Percent of total excess noise factor attributed to that stage.	Use it to prioritize improvements, not as proof that other RF limits are harmless.
Equivalent input noise temperature	Noise factor expressed as an equivalent input temperature at the selected reference temperature.	Use the same reference temperature when comparing runs.
Input-referred noise floor	Thermal noise density plus bandwidth integration plus total noise figure.	Check that the bandwidth matches the real channel, IF filter, or measurement bin.
Minimum input signal	Input-referred noise floor plus the selected required SNR.	Do not compare sensitivity estimates unless bandwidth and required SNR match.
Dominant contributor	The stage with the largest share of excess noise factor.	Check whether pre-LNA loss, first-stage NF, or insufficient early gain is causing it.

NF target met is useful only for the target you entered. It does not prove that the receiver has enough linearity, gain flatness, image rejection, blocker tolerance, or antenna temperature margin. NF target missed usually points to early loss, weak first-stage gain, or a first active stage with too much noise figure.

For fair comparisons, keep stage order, bandwidth, required SNR, reference temperature, and target noise figure fixed. Changing bandwidth can move Input-referred noise floor and Minimum input signal even when the Friis cascade noise figure itself is unchanged.

Technical Details:

Noise factor is the linear form of noise figure. A 3 dB noise figure is a noise factor of about 2, which means the device roughly doubles the available input-referred noise power under the standard noise figure definition. Friis cascade analysis must use linear noise factors and linear power gains internally, then convert the final noise factor back to dB.

Signal order matters because each stage's added noise is referred back to the chain input. The first stage is divided by no prior gain. The second stage is divided by the first stage's linear gain. The third stage is divided by the product of the first two gains, and so on. Negative gain, such as insertion loss, becomes a linear gain below 1, so loss ahead of an LNA makes later contributions larger instead of smaller.

Formula Core:

The cascade uses Friis noise factor arithmetic, with all gain and noise figure inputs converted from dB before summing the terms.

\begin{array}{rcl} F_{n} & = & 10^{{NF}_{n} / 10} \\ G_{n} & = & 10^{g_{n} / 10} \\ F_{total} & = & F_{1} + \sum_{n = 2}^{N} \frac{F_{n} - 1}{\prod_{i = 1}^{n - 1} G_{i}} \\ {NF}_{total} & = & 10 \log_{10} (F_{total}) \end{array}

Here, NFn is the stage noise figure in dB, gn is the stage gain in dB, Fn is linear noise factor, and Gn is linear power gain. Passive loss is modeled at the selected reference temperature by setting effective noise figure equal to insertion loss. For example, a -2 dB passive filter uses an effective 2 dB noise figure.

Noise figure cascade variables and units
Quantity	Unit	Role in the calculation
Stage gain	dB	Positive for amplification and negative for loss; converted to linear gain before Friis terms are divided.
Effective NF	dB	Stage noise figure after passive-loss handling. Active stages use the entered stage noise figure.
Friis Term	linear factor	Stage excess noise factor divided by cumulative prior gain.
Cumulative gain	dB	Running sum of stage gains through the current stage.
Cascade NF	dB	Running noise figure after the current stage has been added.
Total noise factor	linear factor	One plus the summed excess-noise terms; converted to total cascade noise figure.

Noise floor and sensitivity estimates start from thermal noise density. At 290 K, the input thermal noise density is about -173.975 dBm/Hz. Changing the reference temperature shifts that density before bandwidth and cascade noise figure are added.

\begin{array}{rcl} N_{density} & = & - 173.975 + 10 \log_{10} (T / 290) \\ N_{input} & = & N_{density} + 10 \log_{10} (B) + {NF}_{total} \\ S_{min} & = & N_{input} + {SNR}_{required} \\ T_{e} & = & T (F_{total} - 1) \end{array}

In these equations, T is reference temperature in kelvin, B is analysis bandwidth in hertz, Ninput is the input-referred noise floor in dBm, Smin is the minimum input signal in dBm, and Te is equivalent input noise temperature. Output noise floor and output sensitivity are found by adding total cascade gain to the input-referred values.

Validation boundaries for noise figure cascade calculations
Input	Accepted values	Why it matters
RF chain stages	1 to 8 stages	Friis terms must follow a finite signal-order cascade.
Passive stage gain	Zero or negative dB	Passive stages represent insertion loss, so positive gain would contradict the passive-loss rule.
Active stage noise figure	Zero or greater	A negative noise figure would imply better than a noiseless reference in this model.
Analysis bandwidth	Greater than zero after unit conversion	Bandwidth is inside a logarithm when the thermal noise floor is integrated.
Required SNR	Zero or greater, with the visible control covering 0 to 80 dB	The required SNR raises the minimum input signal above the noise floor.
Noise figure target	Greater than zero	The target margin is calculated as target noise figure minus total cascade noise figure.
Reference temperature	1 K to 1000 K	The temperature changes thermal noise density and equivalent input noise temperature.

The formulas assume matched stages and small-signal gain values that are valid for the operating frequency. They do not model impedance mismatch, gain compression, image noise in mixers, frequency-dependent filter loss, blocker desensitization, antenna temperature, or noise-parameter effects under non-50-ohm source conditions.

Accuracy and Privacy Notes:

Use the result as an RF planning estimate, not as a replacement for calibrated noise-figure measurements or a full receiver design review.

Noise figure depends on frequency, source match, physical temperature, bias, and measurement method. Use values measured or specified under compatible conditions.
The passive-loss rule assumes the passive element is at the selected reference temperature. Hot feedlines, filters, switches, or attenuators can add more noise than the simple insertion-loss rule suggests.
The sensitivity estimate does not include antenna noise temperature, external interference, fading, coding gain, detector bandwidth shape, image responses, or real demodulator performance.
The calculation uses the values on the page. Shared links, copied rows, downloaded tables, and JSON can still reveal entered stage names and component values.

Worked Examples:

SDR receiver with an input filter

Start from the SDR receiver preset: antenna switch -0.7 dB, LNA +20 dB with 0.9 dB noise figure, image filter -1.2 dB, mixer -6 dB with 7 dB noise figure, and IF amplifier +24 dB with 3 dB noise figure. With 200 kHz bandwidth, 10 dB required SNR, and a 2.5 dB target, Total cascade noise figure is about 1.97 dB and Total cascade gain is +36.10 dB. Minimum input signal is about -109.00 dBm, and NF target margin is +0.53 dB. The Dominant contributor is the LNA at about 47.2% of the excess noise, with the antenna switch still contributing about 30.5% because it sits before the LNA.

Lossy feedline before the LNA

Choose the lossy feedline preset and keep the 1 MHz bandwidth, 8 dB required SNR, and 3.5 dB target. The first stage is a -3 dB feedline, so its Effective NF is 3.00 dB. The result shows Total cascade noise figure near 4.12 dB, NF target margin near -0.62 dB, and Minimum input signal near -101.86 dBm. In Stage Guidance, the feedline becomes the dominant contributor at about 63.0%, which points to reducing feedline, switch, or preselector loss before improving later stages.

Correcting a passive-stage entry

If a filter role is selected with +2 dB gain, validation reports that the passive stage must use zero or negative gain. Change that stage to -2 dB for a 2 dB insertion loss. The Cascade Ledger then shows Effective NF as 2.00 dB for that passive stage, and the stage's Friis Term updates based on the gain ahead of it. If the same -2 dB filter is moved before the LNA, expect Total cascade noise figure and Input-referred noise floor to rise more than when it is placed after strong early gain.

FAQ:

Why do later high-noise stages sometimes barely change the total?

Friis divides each later stage's excess noise factor by the product of all earlier linear gains. A noisy mixer after a strong LNA can have a small Friis Term, while a small loss before the LNA can be much more damaging.

Why does a passive filter show noise figure equal to loss?

For a passive lossy stage at the reference temperature, the noise figure in dB is modeled as its insertion loss in dB. Enter the stage gain as a negative number, such as -1.2 dB, and the effective noise figure becomes 1.2 dB.

Does changing bandwidth change the cascade noise figure?

No. Bandwidth changes Input-referred noise floor, Output noise floor, and Minimum input signal. The Friis-derived Total cascade noise figure depends on stage gain and noise figure, not the selected analysis bandwidth.

What should I fix first when the target is missed?

Start with Stage Guidance. If Pre-active loss is high, reduce switch, cable, or filter loss before the first active stage. If First active gain is low or the Dominant contributor is early, improve the first active stage before chasing later IF blocks.

Are my stage values uploaded for the calculation?

The cascade result is calculated from the values on the page. Treat shared links, copied tables, downloaded documents, and JSON as user-controlled outputs that may contain entered stage names, gains, noise figures, and bandwidth settings.

Glossary:

Noise figure: Signal-to-noise degradation expressed in dB for a device or cascade under the noise figure reference condition.
Noise factor: The linear form of noise figure, used directly in the Friis equation.
Friis Term: A stage's excess noise factor after division by the cumulative gain of all prior stages.
Insertion loss: Signal loss through a passive stage, entered as negative gain and modeled as equal noise figure at the reference temperature.
Equivalent input noise temperature: The temperature that would create the same added input-referred noise as the cascade noise factor.
Input-referred noise floor: The estimated noise power at the chain input after thermal density, bandwidth, and total cascade noise figure are combined.

References:

Fundamentals of RF and Microwave Noise Figure Measurements, Keysight Technologies.
Noise Figure Concepts, Power Gain, Lossy Components, and Cascaded Systems, All About Circuits, May 15, 2023.
Noise Figure Measurement Methods and Formulas, Analog Devices.
Facts About Noise Figure in 5G and Defense Systems, Qorvo.