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

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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 }}

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A receiver that loses a few decibels before its first low-noise amplifier can miss weak signals even when the later gain lineup looks generous. Noise figure is the RF shorthand for that damage: it expresses how much a device or receiver chain degrades signal-to-noise ratio compared with an ideal noiseless device under the standard reference condition.

Receiver front ends are rarely a single device. An antenna path may include a switch, lightning protector, preselector, feedline, low-noise amplifier, mixer, IF filter, and gain block. Cascaded noise figure combines those stages in signal order, so the same parts can produce a different answer when a lossy filter moves from after the LNA to before it.

Core terms used in RF noise figure cascade estimates
Term	Plain meaning	Why it changes the receiver estimate
Noise figure	Signal-to-noise degradation expressed in dB.	Lower values preserve weak-signal margin before demodulation or measurement.
Gain	Amplification or loss through a stage.	Early gain reduces the input-referred effect of later noisy stages.
Insertion loss	Loss through a passive part such as a cable, switch, or filter.	Loss before the first active stage raises the cascade noise figure directly.
Bandwidth	The noise bandwidth used for the sensitivity estimate.	Wider bandwidth integrates more thermal noise even when noise figure is unchanged.
Required SNR	The signal-to-noise margin needed by the receiver or detector.	Higher SNR raises the minimum input signal above the noise floor.

Friis cascade arithmetic explains why early stages dominate. Added noise from a later stage is divided by all gain that came before it. Loss ahead of the first active stage does the opposite: it reduces the signal before useful gain appears and increases the input-referred noise budget almost one-for-one.

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

RF designers use cascade estimates when choosing LNA placement, deciding whether a preselector can sit before the first amplifier, comparing downconverter lineups, or checking whether an SDR front end has enough sensitivity for a channel bandwidth. The estimate is most useful when every datasheet number comes from the same frequency band, source impedance, temperature, and bias condition.

A cascade result does not settle receiver performance by itself. Antenna temperature, mismatch, compression, phase noise, image response, interference, fading, coding gain, and detector bandwidth can all change real signal recovery. Treat noise figure as the weak-signal starting point, then check the rest of the RF budget before committing hardware.

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, impedance environment, and operating condition whenever possible.

Choose a Cascade preset if one matches the receiver type, such as an SDR front end, LNA-first receiver, lossy feedline, satellite downconverter, or passive mixer chain. Editing a stage switches the lineup to a custom case while keeping the entered values.
In RF chain stages, set each stage role, name, gain, and noise figure. Enter 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 becomes 1.5 dB effective noise figure.
Use Add stage and 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.
Set 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 Noise figure target to the receiver or link-budget target. It does not change the Friis calculation, but it drives NF target margin, Stage Guidance, and the chart reference mark.
Open Advanced when the report assumptions need adjustment. Reference temperature changes equivalent input noise temperature and thermal noise density. Display precision changes rounded table and export values while the underlying calculation 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 compare Noise Budget, Stage Guidance, Friis Contribution Map, and Cascade Progression to find the dominant stage and the sensitivity impact.

If validation appears, fix the named input before using the result. Common causes are zero or negative bandwidth, 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 result is the total cascade noise figure referred to the chain input. Compare it with NF target margin before treating the design as acceptable. A positive margin means the selected target is met; a small positive margin still needs a frequency, temperature, and tolerance check.

How to read noise figure cascade outputs
Output	What it means	Best follow-up
Total cascade noise figure	Overall input-referred noise figure after all stage gains and noise factors are combined.	Confirm every stage value comes from the same frequency band and reference condition.
Friis Term	Each stage's excess noise after division by all prior gain.	Attack large early terms first 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.	Keep 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.	Compare sensitivity estimates only when 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 is unchanged.

Technical Details:

Noise factor is the linear ratio behind noise figure. A 3 dB noise figure is a noise factor of about 2, so the device roughly doubles the available input-referred noise power under the standard noise figure definition. Cascade arithmetic must use linear noise factors and linear power gains internally, then convert the final noise factor back to dB for RF budget work.

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.

Worked Friis path:

A short three-stage path shows how prior gain changes the terms. With a -0.7 dB passive switch, a 20 dB LNA at 0.9 dB NF, and a -1.2 dB filter after the LNA, the later filter is divided by the gain already provided by the LNA. The partial cascade is about 1.61 dB NF before any mixer or IF gain is added.

Example Friis contribution path for an RF cascade
Stage	Prior gain	Effective NF	Friis term	Running cascade NF
Passive switch	0.00 dB	0.70 dB	0.1749	0.70 dB
LNA	-0.70 dB	0.90 dB	0.2706	1.60 dB
Post-LNA filter	19.30 dB	1.20 dB	0.0037	1.61 dB

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 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 behavior.
The cascade arithmetic uses the values in the browser without an upload step. Shared links, copied rows, downloaded tables, and JSON can still reveal entered stage names and stage values.

Advanced Tips:

Keep the stage order tied to the physical signal path. Moving a filter, switch, or feedline from after the LNA to before the LNA can change the total more than improving a later IF block by several dB.
Use the same frequency, impedance, bias, and temperature basis for every stage value. A low datasheet noise figure at one band can make the cascade look better than a measured value at the actual operating channel.
Set Noise figure target from the receiver budget before comparing variants. The NF target margin row then separates a real pass or miss from a lineup that merely looks numerically low.
Use Friis Contribution Map to find the dominant excess-noise term, then use Cascade Progression to see where the running noise figure stops improving. The two charts answer different questions and should agree on the stage worth investigating first.
Raise Display precision when comparing two low-noise lineups that differ by only a few tenths of a dB, and include the JSON export with lab notes when the stage names or assumptions need to be reviewed later.

Worked Examples:

SDR front end with an input filter

An SDR chain with an antenna switch at -0.7 dB, an LNA at +20 dB and 0.9 dB NF, an image filter at -1.2 dB, a -6 dB mixer with 7 dB NF, and a +24 dB IF amplifier with 3 dB NF lands near Total cascade noise figure of 1.97 dB. With 200 kHz bandwidth, 10 dB required SNR, and a 2.5 dB target, Minimum input signal is about -109.00 dBm and NF target margin is about +0.53 dB. The LNA is the largest contributor at about 47.2%, while the antenna switch still contributes about 30.5% because it sits before the LNA.

Feedline loss before first gain

A -3 dB feedline before the LNA becomes 3.00 dB Effective NF. With 1 MHz bandwidth, 8 dB required SNR, and a 3.5 dB target, the feedline case shows Total cascade noise figure near 4.12 dB, NF target margin near -0.62 dB, and Minimum input signal near -101.86 dBm. Stage Guidance names the feedline as the dominant contributor at about 63.0%, which points to shortening the feedline, moving the LNA closer to the antenna, or reducing preselector loss.

Passive-stage validation

If a filter role is entered with +2 dB gain, validation reports that the passive stage must use zero or negative gain. Changing that stage to -2 dB represents 2 dB insertion loss, and Cascade Ledger shows 2.00 dB Effective NF for that stage. Moving the same -2 dB filter before the LNA raises Total cascade noise figure and Input-referred noise floor more than placing it after strong early gain.

FAQ:

Why can a small switch or cable loss matter so much?

Loss before the first active stage reduces the signal before useful gain appears. A 0.7 dB switch before the LNA can add nearly 0.7 dB to the cascade, while the same loss after strong early gain is divided down in the Friis terms.

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.

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.

What happens to entered stage values?

The cascade arithmetic uses the values in the browser without an upload step. Shared links, copied tables, downloaded documents, and JSON can 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:

Noise Figure, Keysight Technologies.
Noise Figure: Overview of Noise Measurement Methods, Tektronix.
Noise Figure Measurement Methods and Formulas, Analog Devices.
How does the insertion loss of a switch affect the overall system noise figure?, RF Essentials.