matlab-analyze-rf-budget

RF Budget Analysis

Compute cascaded performance metrics (gain, noise figure, IP3, SNR, output power) through an RF signal chain using rfbudget.

When to Use

• Computing cascaded gain, noise figure, IP3, SNR through an RF signal chain
• Visualizing per-stage budget metrics with rfplot or show
• Comparing Friis vs HarmonicBalance solver accuracy
• Exporting RF systems to RF Blockset, Communications Toolbox, or MATLAB scripts
• Computing AM/PM compression tables or mismatch loss

When NOT to Use

• Creating or configuring rfbudget element objects -- use matlab-create-rfbudget-elements
• Composing arbitrary RF circuits with node wiring -- use matlab-compose-rf-circuit
• Time-domain simulation of RF systems -- use matlab-simulate-rf-system

Workflow

1. Define elements — Create RF elements (see matlab-create-rfbudget-elements skill)
2. Build budget — Pass element array, input frequency, power, and bandwidth to rfbudget
3. Inspect results — Read cumulative per-stage properties or use show for tabular view
4. Visualize — Plot with rfplot or smithplot
5. Export — Generate MATLAB script, RF Blockset model, or Communications Toolbox objects

Creating an RF Budget

lna = amplifier('Gain', 15, 'NF', 2, 'OIP3', 35, 'Name', 'LNA');
bpf = rfelement('Gain', -3, 'NF', 3, 'Name', 'BPF');
mix = modulator('Gain', -6, 'NF', 10, 'OIP3', 20, ...
    'LO', 2.1e9, 'ConverterType', 'Down', 'Name', 'Mixer');
ifAmp = amplifier('Gain', 20, 'NF', 4, 'OIP3', 30, 'Name', 'IFAmp');

b = rfbudget([lna bpf mix ifAmp], 2.4e9, -30, 10e6);

Constructor: rfbudget(elements, inputFreq, availInputPower_dBm, signalBW)

Key Properties (Read-Only Results)

All result properties return a vector with one value per stage (cumulative through the chain):

Property	Description	Units
TransducerGain	Cumulative gain at each stage	dB
NF	Cumulative noise figure	dB
OIP3	Cumulative output third-order intercept	dBm
IIP3	Cumulative input third-order intercept	dBm
OIP2	Cumulative output second-order intercept	dBm
IIP2	Cumulative input second-order intercept	dBm
OutputPower	Output power at each stage	dBm
OutputFrequency	Frequency at each stage output	Hz
SNR	Signal-to-noise ratio at each stage	dB
EIRP	Effective isotropic radiated power (with rfantenna)	dBm
Directivity	Antenna directivity (with rfantenna)	dB

System-level results are the last element of each vector:

systemGain = b.TransducerGain(end);    % Total chain gain in dB
systemNF = b.NF(end);                  % System noise figure in dB
systemOIP3 = b.OIP3(end);             % System OIP3 in dBm
systemSNR = b.SNR(end);               % Output SNR in dB

Input Properties (Read-Write)

Property	Description
Elements	Array of RF element objects
InputFrequency	Input signal frequency (Hz)
AvailableInputPower	Available input power (dBm)
SignalBandwidth	Signal bandwidth (Hz)
Solver	'Friis' (default) or 'HarmonicBalance'
AutoUpdate	true (default) — recompute on property change

Visualization

Tabular View

show(b);               % Opens interactive GUI table — no command-window output

Gotcha: show(b) opens a GUI table widget but produces no text in the command window. For programmatic access, use b.TransducerGain, b.NF, b.OIP3, b.OutputPower, etc.

RF Budget Analyzer App

rfBudgetAnalyzer(b);   % Launch interactive RF Budget Analyzer app with pre-loaded budget
rfBudgetAnalyzer;      % Launch empty app for manual entry

Plotting

rfplot(b, 'Pout');     % Output power per stage
rfplot(b, 'GainT');    % Transducer gain per stage
rfplot(b, 'NF');       % Noise figure per stage
rfplot(b, 'OIP3');     % OIP3 per stage
rfplot(b, 'IIP3');     % IIP3 per stage
rfplot(b, 'SNR');      % SNR per stage

Valid rfplot parameter strings: 'Pout', 'GainT', 'NF', 'OIP3', 'IIP3', 'SNR', 'Sparameters', 'OneTone', 'TwoTone'.

Note: rfplot(b) with no parameter string plots S-parameters (like rfplot(sparametersObj)). To plot budget metrics, specify a parameter string: rfplot(b, 'Pout'), rfplot(b, 'GainT'), etc.

Note: 'OneTone' and 'TwoTone' require Solver='HarmonicBalance' — they error with "Harmonic balance solutions must be computed" if the Friis solver is active.

Polar and Smith Chart Visualization

Plot S-parameters of each cascade stage vs. frequency:

polar(b, 2, 2);        % S22 of each stage on a polar plot
smithplot(b, 1, 1);    % S11 reflection coefficient on Smith chart

Solvers

Solver	Use Case
'Friis' (default)	Linear cascade analysis — fast, sufficient for most system budgets
'HarmonicBalance'	Nonlinear analysis — more accurate than Friis, matches RF Blockset Circuit Envelope simulation

HarmonicBalance accounts for compression, intermodulation, and mixer spurs that Friis ignores. Use it when accuracy matters — the results match the highly accurate Circuit Envelope simulation in RF Blockset.

b = rfbudget(elements, 2.4e9, -30, 10e6, 'Solver', 'HarmonicBalance');

For HarmonicBalance, control harmonic content:

b = rfbudget(elements, 2.4e9, -30, 10e6, ...
    'Solver', 'HarmonicBalance', ...
    'HarmonicOrder', 3);

AM/PM Compression Table

Compute the system's AM/AM and AM/PM characteristic:

ampmTable = computeAMPMTable(b);
% ampmTable: M×3 matrix [Pin_dBm, Pout_dBm, PhaseShift_deg]

% With custom input power range
pinRange = -40:0.5:10;
ampmTable = computeAMPMTable(b, pinRange);

Mismatch Loss

ml = mismatchLoss(b, 1);     % Mismatch loss at stage 1 input boundary (per frequency)
ml = mismatchLoss(b, 2);     % Mismatch loss at stage 2 input boundary (per frequency)

Arguments: (rfbudgetObj, stageNum) — stageNum is required (1 to number of elements). Returns a vector of linear loss factors (one per frequency point, 0 to 1, where 1 = perfect match).

AutoUpdate and Manual Computation

By default, rfbudget recomputes whenever a property changes. For batch modifications, disable auto-update:

b = rfbudget(elements, 2.4e9, -30, 10e6, 'AutoUpdate', false);
b.InputFrequency = 5.8e9;
b.AvailableInputPower = -20;
computeBudget(b);     % Explicitly trigger computation

Export

MATLAB Script

exportScript(b);                   % Opens generated MATLAB script in the editor

RF Blockset (Simulink)

exportRFBlockset(b);               % Opens Simulink model with RF Blockset blocks

Communications Toolbox

exportReceiver(b);                 % Opens receiver configuration script in the editor
exportTransmitter(b);              % Opens transmitter configuration script in the editor

Circuit Object

c = circuit(b);     % Convert budget to circuit object for S-parameter analysis
s = sparameters(c, freq);

Gotchas

1. Elements cannot appear twice — The same element object cannot be used more than once, whether in the same chain (e.g., rfbudget([lna filt lna], ...)) or across separate budgets. Use clone(element) to create an independent copy: rfbudget([lna filt clone(lna)], ...).
2. Name must be valid MATLAB identifier — Element Name property cannot contain spaces or special characters. Use 'IFAmp' not 'IF Amp'.
3. Per-stage results are cumulative — TransducerGain, NF, OIP3 etc. are cumulative through the chain, not per-element deltas. The system result is always the last element.
4. rfplot default is S-parameters — rfplot(b) with no parameter string plots S-parameters. Specify a string for budget metrics: rfplot(b, 'Pout'), rfplot(b, 'GainT'), etc.
5. Frequency changes at mixers — OutputFrequency changes after a modulator element (down/up conversion). Subsequent stages operate at the new frequency.

Conventions

• Use tiledlayout/nexttile for multi-panel budget comparison plots
• Always label plots with units (dBm, dB, GHz)
• Use show(b) for quick inspection before plotting
• Name elements descriptively for readable show output

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Copyright 2026 The MathWorks, Inc.

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