liminfoRF Cascade Calculator
Free web tool: RF Cascade Calculator
Cascade Results
Total Gain
7.00 dB
Cascaded NF
8.33 dB
System OIP3
-17.85 dBm
System IIP3
-24.85 dBm
| Stage | Cum. Gain | Cum. NF |
|---|---|---|
| LNA | 15.00 dB | 1.20 dB |
| Filter | 13.00 dB | 2.59 dB |
| Mixer | 7.00 dB | 8.33 dB |
About RF Cascade Calculator
The RF Cascade Calculator performs a complete noise and linearity budget analysis for a multi-stage RF receiver chain. For each stage you define the gain in dB, noise figure (NF) in dB, and output third-order intercept point (OIP3) in dBm. The tool then applies the Friis formula for cascaded noise figure and the inverse-sum OIP3 cascade formula to compute system-level total gain, cascaded NF, system OIP3, and system IIP3.
RF engineers, microwave system designers, radar developers, software-defined radio (SDR) builders, and wireless communications students use this tool when designing low-noise receiver front-ends. Getting the cascaded noise figure right is critical for link budget calculations — the first-stage gain and NF dominate the total system noise performance, which is why LNA placement and specification matters most in the chain.
The tool supports five component type presets — LNA (15 dB gain, 1.2 dB NF, 20 dBm OIP3), Filter (-2 dB insertion loss), Mixer (-6 dB conversion gain, 8 dB NF, 15 dBm OIP3), Amplifier (20 dB gain, 3 dB NF), and Attenuator (-10 dB). Stages can be added, removed, reordered, and edited individually. A cumulative gain and NF table shows how the system metrics evolve stage by stage through the chain.
Key Features
- Multi-stage RF chain editor: add, remove, and edit any number of stages
- Friis formula for cascaded noise figure: NF_total = NF1 + (NF2-1)/G1 + (NF3-1)/(G1×G2) + ...
- Cascaded OIP3 calculation using inverse-power summation from output backwards
- System IIP3 derived from OIP3 minus total gain
- Per-stage cumulative gain and NF table to trace where noise and gain budget accumulate
- Component presets: LNA, Filter, Mixer, Amplifier, Attenuator with realistic default values
- 100% browser-based — all chain calculations run locally with no server dependency
- Dark mode support and responsive layout for bench and desk use
Frequently Asked Questions
What is the Friis formula for cascaded noise figure?
The Friis formula calculates the total system noise factor as: F_total = F1 + (F2-1)/G1 + (F3-1)/(G1×G2) + ... where F is the noise factor (linear, not dB) and G is the stage power gain (linear). The noise figure in dB is NF = 10×log10(F). The formula shows that early stages dominate the total noise, which is why a low-NF, high-gain LNA at the front of the chain is crucial.
What is OIP3 and why does it matter?
OIP3 (Output Third-Order Intercept Point) is a measure of a stage's linearity. It is the hypothetical output power level at which the third-order intermodulation distortion products would equal the fundamental output power. Higher OIP3 means better linearity. For a receiver chain, the cascaded OIP3 determines the maximum signal level the system can handle before significant distortion occurs.
How is the cascaded OIP3 calculated?
The cascaded OIP3 is calculated working backwards from the output stage. For a two-stage chain: 1/OIP3_cascade = 1/OIP3_2 + G2/OIP3_1. The general formula accumulates the inverse OIP3 contributions of all stages, weighted by the gain of all stages after them. Late stages in the chain with high gain tend to dominate the cascaded OIP3.
What is the difference between OIP3 and IIP3?
OIP3 (Output IP3) is referenced to the output port of the device. IIP3 (Input IP3) is referenced to the input port. They are related by: IIP3 (dBm) = OIP3 (dBm) - Gain (dB). System IIP3 is calculated as system OIP3 minus total chain gain. IIP3 is often the more useful specification for receiver design as it relates directly to the input signal level.
Why does LNA placement matter most in the chain?
According to the Friis formula, each stage's noise contribution is divided by the cumulative gain of all preceding stages. The first stage adds its full noise figure directly to the system. If the LNA has 15 dB of gain, the second stage's excess noise is reduced by a factor of 31.6 (10^1.5). This means the LNA's NF and gain specification is far more important than any later stage for overall system sensitivity.
What is a typical receiver chain configuration?
A typical RF receiver front-end starts with an antenna, followed by a bandpass filter (to reject out-of-band interference), then an LNA (to set system noise figure), another filter (image rejection or IF filter), a mixer (to downconvert the signal), and finally an IF amplifier. This tool's default three-stage chain (LNA → Filter → Mixer) represents this classic front-end architecture.
How do I use the attenuator preset?
The Attenuator preset (-10 dB gain, 10 dB NF, 50 dBm OIP3) models a passive attenuator pad. For a passive component, the noise figure in dB equals the insertion loss in dB, and OIP3 is very high (set to 50 dBm as a practical upper limit). Adding an attenuator at the input degrades the system NF directly by the attenuation value.
Can this calculator be used for transmitter chain analysis?
The tool is primarily designed for receiver chain analysis where cascaded NF dominates the design. Transmitter chain analysis focuses more on output power, efficiency, and spectral purity. However, the gain cascade (total gain) and OIP3 cascade calculations are mathematically valid for any amplifier chain regardless of whether it is in a receiver or transmitter.