SPARAMS — MATLAB S-Parameter Toolbox

A not-particularly-efficient MATLAB class for reading, manipulating, converting, and plotting S-parameter data from Touchstone files (.s1p, .s2p, .s3p, .s4p). Supports up to 4-port measurements in RI, MA, and dB/Angle formats.

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Getting Started

Load from a Touchstone file

s = SPARAMS('myfile.s2p');

Create an empty object and assign data manually

s = SPARAMS();
s.setNumPorts(2);
s.setZ0(50);
s.f   = freq;   % frequency vector in Hz
s.S11 = s11;    % complex S-parameter vectors
s.S21 = s21;
% etc.

Copy an object (no pointer referencing)

s2 = s.copyobj();

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Properties

Property	Description
f	Frequency vector (Hz)
S11, S12, ... S44	Complex S-parameters (up to 4-port)
Z0	System reference impedance (e.g. 50 Ω)
numPorts	Number of ports (1–4)

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Methods

Setup & Configuration

s.setFile('filename.s2p')      % Load a new file into an existing object
s.setFreqUnits('GHz')          % Set frequency axis units for plotting (does not change data)
                               % Options: 'Hz', 'kHz', 'MHz', 'GHz'

Accessing Data

s11 = s.S11;                   % Get S11 as complex (R + jI)
[S, fActual] = s.toMat(freq)   % Get full S-matrix at a specified frequency
                               % (uses nearest frequency if exact match not found)

Plotting

s.plotdB('S11')                        % Plot a single parameter in dB
s.plotdB({'S11', 'S21'})               % Plot multiple parameters in dB
s.plotAlldB()                          % Plot all S-parameters in dB
s.plotPolar({'S11', 'S21'})            % Polar plot
s.plotSmith('S11')                     % Smith chart plot
s.plotDispersion()                     % Dispersion diagram (for unit cells, must be a two-port file)
s.plotDispersion('flip')               % Dispersion with flipped axes

Parameter Conversions

[Zin1, Zin2] = s.toInputImpedance()           % Input impedance at each port (assuming other port is terminated in Z0)
[A, B, C, D] = s.toABCDparams()               % ABCD parameters (all frequencies)
[A, B, C, D] = s.toABCDparams(freq)           % ABCD parameters at one frequency
[T11,T12,T21,T22] = s.toTParams()             % T-parameters (all frequencies)
[T11,T12,T21,T22] = s.toTParams(freq)         % T-parameters at one frequency
[Z11,Z12,Z21,Z22] = s.toZparams()             % Z-parameters
[Y11,Y12,Y21,Y22] = s.toYparams()             % Y-parameters

Manipulation

s.renorm(Z0new)      % Renormalize to a new reference impedance
                     % (also updates s.Z0 automatically)
                     % Note: overwrites original S-parameters
                     % Use copyobj() first to preserve originals
s.cascade(N)         % Cascade the unit cell N times (2-port only)
                     % Note: overwrites original S-parameters
                     % Use copyobj() first to preserve originals

Export

s.writeCSV('output.csv')    % Export S-parameter data to CSV
s.writeSNP('output')        % Write a new Touchstone file
                            % Extension (.s1p/.s2p/etc.) is added automatically
                            % Format is GHz, RI

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Static Methods

De-embedding

Remove error networks from a measurement to isolate the DUT:

P1 <-- err1 <--> DUT <--> err2 --> P2

sDUT = SPARAMS.deembed(err1, measured, err2);

Returns a new SPARAMS object representing the DUT.

General Matrix Conversions

Z = SPARAMS.s2z(S, Z0)              % S-matrix → Z-matrix
S = SPARAMS.z2s(Z, Z0)              % Z-matrix → S-matrix
[A,B,C,D] = SPARAMS.s2abcd(S, Z0)  % S-matrix → ABCD
[S11,S21,S12,S22] = SPARAMS.abcd2s(A, B, C, D, Z0)  % ABCD → S-parameters

Comparing Two Sets of S-parameters

SPARAMS.plotAnydB(obj1, {'S11','S21'}, obj2, {'S11','S21'});

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Example Workflow

% Load a 2-port measurement
s = SPARAMS('dut.s2p');
s.setFreqUnits('GHz');

% Plot S11 and S21
figure;
s.plotdB({'S11', 'S21'});
title('DUT S-Parameters');

% Get ABCD parameters and cascade 3x
sc = s.copyobj();
sc.cascade(3);

% Export result
sc.writeSNP('cascaded_3x');

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Supported File Formats

Format	Description
.s1p	1-port Touchstone
.s2p	2-port Touchstone
.s3p	3-port Touchstone
.s4p	4-port Touchstone

Data formats supported within files: RI (Real/Imaginary), MA (Magnitude/Angle), dB (dB/Angle).

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Notes

• cascade() and plotDispersion() are intended for 2-port unit cell measurements.
• renorm() is fully implemented for 1- and 2-port measurements.
• toZparams(), toYparams(), toABCDparams(), toInputImpedance() require 2-port data.
• When using cascade(), it is recommended to copyobj() first, as the method overwrites the object's S-parameters.