Matlab Model Rf

rfbudget Element Objects

Create and configure all rfbudget-compatible elements -- active components (amplifier, modulator, attenuator, phaseshift) and passive networks (seriesRLC, shuntRLC, lcladder, rffilter, nport, transmission lines). These are the building blocks for rfbudget cascade analysis and circuit composition.

Element Hierarchy

Active Elements

Passive / Data-Driven Elements

Transmission Lines

All are rfbudget-compatible 2-port: txlineDelayLossless, txlineDelayLossy, txlineMicrostrip, txlineCoaxial, txlineCPW, txlineStripline, txlineRLCGLine, txlineWRLGC, txlineWtable, txlineParallelPlate, txlineTwoWire.

Not rfbudget-compatible: resistor, capacitor, inductor, circuit -- primitive elements for circuit composition only.

amplifier

lna = amplifier('Gain', 15, 'NF', 2, 'OIP3', 35, 'Name', 'LNA');
ampFromFile = amplifier('FileName', 'default.s2p', 'Name', 'LNAMeasured');

Properties

Conventions: Amplifiers use output-referred (OIP3, OP1dB, OPsat). Mixers/modulators use input-referred (IIP3, IP1dB, IPsat).

'poly' vs 'cubic': 'poly' (default) uses ALL set compression params to fit a higher-order polynomial. 'cubic' uses only ONE param selected by Nonlinearity. Prefer 'poly'. See reference/amplifier-models.md for detailed compression parameter conventions.

modulator

downMixer = modulator('Gain', -6, 'NF', 10, 'OIP3', 20, ...
    'LO', 2.1e9, 'ConverterType', 'Down', 'Name', 'Mixer');

upMixer = modulator('Gain', -8, 'NF', 12, 'OIP3', 18, ...
    'LO', 1.5e9, 'ConverterType', 'Up', 'Name', 'UpConv');

Properties

Frequency Behavior

After a modulator, the signal frequency changes. In an rfbudget, subsequent stages operate at the converted frequency. For a down-converter: fOut = fIn - LO (or LO - fIn depending on sideband). For an up-converter: fOut = fIn + LO. Read b.OutputFrequency to see the frequency at each stage output.

rfelement

Use for cables, couplers, or any passive/active component defined by scalar specs:

atten = rfelement('Gain', -10, 'NF', 10, 'Name', 'Atten');
cable = rfelement('Gain', -1.5, 'NF', 1.5, 'Name', 'Cable');

Properties

Gotcha: For passive, NF must equal abs(Gain). A -3 dB attenuator has NF = 3 dB. Setting inconsistent values (e.g., Gain=-3, NF=0) produces incorrect budget results. Prefer attenuator which handles this automatically.

rfantenna

Models a transmit or receive antenna in an rfbudget chain, computing EIRP and received power from TxEIRP, PathLoss, and antenna Gain.

tx = rfantenna('Type', 'Transmitter', 'Gain', 6, 'Name', 'TxAnt');
rx = rfantenna('Type', 'Receiver', 'Gain', 3, 'TxEIRP', 30, ...
    'PathLoss', 60, 'Name', 'RxAnt');

Properties

Behavior in rfbudget

• Transmitter: Placed at end of chain. Adds antenna Gain to TransducerGain and OutputPower. EIRP = OutputPower at the antenna stage.

• Receiver: Placed at start of chain. Computes received power as TxEIRP - PathLoss + Gain. Adds 0 dB to TransducerGain. The AvailableInputPower argument to rfbudget is ignored (warning issued). The received power property is RxP.

• TransmitReceive: Can go anywhere in the chain. Gain must be 1x2 vector [TxGain RxGain].

% Receiver link budget: Rx computes its own input power
rx = rfantenna('Type', 'Receiver', 'Gain', 3, 'TxEIRP', 30, ...
    'PathLoss', 60, 'Name', 'RxAnt');
lna = amplifier('Gain', 15, 'NF', 2, 'OIP3', 35, 'Name', 'LNA');
b = rfbudget([rx lna], 2.4e9, -30, 10e6);
% Input power = TxEIRP - PathLoss + Gain = 30 - 60 + 3 = -27 dBm

Gotcha: Only one rfantenna element is allowed per rfbudget chain.

Gotcha: rfantenna is a 1-port element (2 terminals: p1+, p1-). In a circuit, use add(ckt, [1 0], ant) with 2 nodes, not 4.

Gotcha: You cannot call sparameters() directly on an rfbudget object. To extract S-parameters from a budget, first convert to a circuit: sp = sparameters(circuit(b), freq).

attenuator

A dedicated attenuator element that automatically handles NF derivation and impedance matching.

pad = attenuator('Attenuation', 6, 'Name', 'Pad6dB');
pad50to75 = attenuator('Attenuation', 10, 'Zin', 50, 'Zout', 75, 'Name', 'MatchPad');

Properties

In rfbudget, NF equals Attenuation automatically -- no manual NF setting needed.

Gotcha: When Zin != Zout, there is a minimum attenuation requirement. For example, Zin=50, Zout=75 requires Attenuation > 5.72 dB. MATLAB reports the exact threshold in the error message. Matched impedances (Zin == Zout) have no minimum.

phaseshift

Adds a frequency-independent phase shift with zero insertion loss.

ps = phaseshift('PhaseShift', 90, 'Name', 'PS90');

Properties

In rfbudget: Gain = 0 dB, NF = 0 dB (lossless). In S-parameters: |S21| = 1, angle(S21) = PhaseShift.

Gotcha: The PhaseShift value maps directly to the S21 phase angle (positive = phase lead, negative = phase lag). PhaseShift=45 gives angle(S21) = +45 deg.

nport

Use when you have measured or simulated S-parameter data. Accepts .s1p through any .snp Touchstone file:

filter = nport('passive.s2p', 'BPFilter');   % Name is positional (2nd arg)

% Or from a sparameters object
s = sparameters(data, freq, 50);
comp = nport(s, 'CustomComp');

• Accepts .s1p through .snp (1-port works in circuit, not rfbudget)

• .amp files NOT supported

• For multi-port: set Input and Output properties for rfbudget port selection

Multi-Port Selection

For components with more than 2 ports, specify which ports to use:

n = nport('default.s4p');
n.Input = 1;          % Input port number
n.Output = 3;         % Output port number
n.Termination = 50;   % Terminate unused ports

Creating nport from Synthetic Data

% Build a 4-port sparameters object (e.g., through-path on ports 1->3)
data = zeros(4, 4, 10);
data(3,1,:) = 0.8; data(1,3,:) = 0.8;  % S31=S13 (reciprocal through)
data(4,2,:) = 0.8; data(2,4,:) = 0.8;  % S42=S24 (second pair)
s4 = sparameters(data, linspace(1e9, 3e9, 10), 50);
comp = nport(s4, 'MyComp');
comp.Input = 1;
comp.Output = 3;

rffilter

bpf = rffilter('ResponseType', 'Bandpass', 'FilterType', 'Butterworth', ...
    'FilterOrder', 5, 'PassbandFrequency', [2.3e9 2.5e9], 'Name', 'BPF');

Key properties: ResponseType (Lowpass/Highpass/Bandpass/Bandstop), FilterType (Butterworth/Chebyshev/InverseChebyshev), FilterOrder, PassbandFrequency (scalar for LP/HP, 2-vector for BP/BS). See reference/rffilter-synthesis.md for full design options.

Gotcha: ResponseType is shape (Lowpass/Bandpass/etc.), FilterType is algorithm (Butterworth/Chebyshev). Using rffilter('FilterType', 'Bandpass') errors.

seriesRLC and shuntRLC

Series Elements (In-Line with Signal Path)

L1 = seriesRLC('L', 2.7e-9, 'Name', 'Lseries');          % Inductor only
C1 = seriesRLC('C', 1.2e-12, 'Name', 'DCBlock');          % DC blocking cap
R1 = seriesRLC('R', 50, 'Name', 'Rpad');                   % Resistor only
rlc = seriesRLC('R', 10, 'L', 1e-9, 'C', 0.5e-12, 'Name', 'RLC1');

Shunt Elements (To Ground)

Cbypass = shuntRLC('C', 100e-12, 'Name', 'Cbypass');       % Bypass cap
Lchoke = shuntRLC('L', 100e-9, 'Name', 'Lchoke');          % RF choke
Rterm = shuntRLC('R', 50, 'Name', 'Rterm');                 % Termination

Omitted values default to "absent": seriesRLC uses R=0, L=0, C=Inf (wire-through); shuntRLC uses R=Inf, L=Inf, C=0 (open-circuit).

rfbudget vs circuit Topology Difference

In rfbudget, shuntRLC is modeled as a 2-port inline element (computing insertion loss from its shunt impedance to ground). In a circuit object, add(ckt, [node 0], shuntRLC(...)) wires the element literally between a signal node and ground -- this is a different topology. For example, a bias-tee inductor (shuntRLC('L', 100e-9)) shows near-zero insertion loss in rfbudget at RF frequencies, but if wired as add(ckt, [2 0], ...) in a circuit it appears as a shunt path to ground and dominates the S21 response. Use rfbudget for cascade analysis of bias tees; use circuit only when modeling the full node-level topology.

Common Building Blocks

lcladder

LC ladder filter networks. Created from a topology string, inductor values, and capacitor values.

lc = lcladder('lowpasspi', [10e-9 10e-9], [1e-12 1e-12 1e-12], 'LPF');
lc = lcladder(rffilterObj, 'BPF');

Topologies

Gotcha: lcladder constructor is positional -- lcladder(topology, L, C, name), not name-value pairs.

Gotcha: Topology strings are all lowercase ('lowpasspi', 'bandpasstee'). Using mixed-case like 'LowpassPi' or abbreviations like 'CLC' errors with "not a valid LC Ladder topology."

Transmission Lines

All transmission line objects are 2-port and rfbudget-compatible. Use LineLength for physical length (not Length). See reference/transmission-lines.md for all types and properties.

tl = txlineDelayLossless('Z0', 50, 'TimeDelay', 33e-12, 'Name', 'TL1');
rlcg = txlineRLCGLine('R', 0.5, 'L', 250e-9, 'C', 100e-12, 'G', 0, 'LineLength', 0.05);
tw = txlineWRLGC('Lo', 350e-9, 'Co', 130e-12, 'Ro', 2, 'Rs', 5e-4, 'Gd', 1e-11, ...
    'LineLength', 0.1, 'Name', 'WLine');

• All use LineLength for physical length (not Length)

• All constructors are name-value only (no positional)

• txlineWRLGC properties are Ro, Lo, Co, Go, Gd -- short forms R, L are ambiguous and error

Using in rfbudget

All elements plug directly into rfbudget's element array:

lna = amplifier('Name', 'LNA', 'Gain', 15, 'NF', 1.5, 'OIP3', 20);
dcblk = seriesRLC('C', 100e-12, 'Name', 'DCBlock');
bpf = lcladder(rffilter('ResponseType', 'Bandpass', 'FilterOrder', 3, ...
    'PassbandFrequency', [2.3e9 2.5e9]), 'BPF');

% Positional form: rfbudget(elements, freq, inputPower, signalBW)
b = rfbudget([dcblk lna bpf], 2.4e9, -30, 10e6);

% Name-value form (equivalent):
% b = rfbudget('Elements', [dcblk lna bpf], 'InputFrequency', 2.4e9, ...
%     'AvailableInputPower', -30, 'SignalBandwidth', 10e6);

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

Critical: SignalBandwidth (4th positional arg) is required for NF, IP3, and SNR computation. Without it, those fields remain empty.

Element Reuse Requires clone()

An element object cannot appear more than once in the same chain or across separate budgets. Use clone() every time you need a second instance:

% ERROR: same object used twice
% b = rfbudget([lna filter lna], 2.4e9, -30, 10e6);

% CORRECT: clone for the second use
b = rfbudget([lna filter clone(lna)], 2.4e9, -30, 10e6);

% CORRECT: reuse across two budgets
b1 = rfbudget(lna, 2.4e9, -30, 10e6);
b2 = rfbudget(clone(lna), 5.8e9, -30, 10e6);

circuit Objects Are NOT rfbudget-Compatible

A circuit object cannot be added to rfbudget directly. Workaround -- convert to nport via Touchstone:

% Build circuit
ckt = circuit('MyNetwork');
add(ckt, [1 2], seriesRLC('L', 10e-9, 'Name', 'L1'));
add(ckt, [2 0], shuntRLC('C', 1e-12, 'Name', 'C1'));
setports(ckt, [1 0], [2 0]);

% Convert to nport for rfbudget
s = sparameters(ckt, linspace(1e9, 6e9, 500));
outFile = 'mynetwork.s2p';
rfwrite(s, outFile, 'ForceOverwrite', true);
np = nport(outFile, 'MyNetwork');
% np works in rfbudget

Standalone S-Parameter Analysis

Any element can compute S-parameters directly without wrapping in a circuit:

freq = linspace(1e9, 10e9, 500);
s = sparameters(mstrip, freq);

figure;
tiledlayout(1, 2);
nexttile; rfplot(s, 2, 1); title('S21 -- Insertion Loss');
nexttile; rfplot(s, 1, 1); title('S11 -- Return Loss');

Gotchas

1. Name must be valid MATLAB identifier -- no spaces

2. Elements are handle objects -- modifying an element after adding it to a budget changes the budget; use clone for independent copies

3. Passive NF equals loss -- prefer attenuator

4. nport uses ports 1 (input) and 2 (output) by default -- for multi-port files, set Input and Output explicitly

5. nport Name is positional -- nport('file.s2p', 'MyName'), not NV syntax; nport('file.s2p', 'Name', 'X') sets Name to literal 'Name'

6. rffilter is ideal -- no parasitic effects

7. rfantenna is 1-port -- one per chain; in circuit use add(ckt, [1 0], ant) with 2 nodes

8. attenuator minimum for mismatched Z -- Zin=50, Zout=75 requires Attenuation > 5.72 dB; error message gives threshold

9. 'poly' vs 'cubic' -- 'poly' uses all params, 'cubic' uses one selected by Nonlinearity

10. lcladder constructor is positional -- lcladder(topology, L, C, name), not name-value pairs

11. lcladder topology strings all lowercase -- 'lowpasspi' not 'LowpassPi'

12. circuit objects don't work in rfbudget -- convert via nport + Touchstone

13. rfwrite blocks on existing files -- Always 'ForceOverwrite', true

14. phaseshift sign convention -- positive PhaseShift = positive S21 phase angle (phase lead)

15. Cannot call sparameters() on rfbudget -- convert to circuit first: sparameters(circuit(b), freq)

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