sparameters

Calculate S-parameters for RF PCB objects

Since R2021b

Syntax

[sobj,fit] = sparameters(rfpcbobj,freq)

sobj = sparameters(___,Z0)

sobj = sparameters(___,Name=Value)

sobj = sparameters(data,freq)

sobj = sparameters(data,freq,Z0)

sobj = sparameters(filename)

Description

[sobj,fit] = sparameters(rfpcbobj,freq) calculates the S-parameters for the RF PCB object rfpcbobj over the specified frequency values.

sobj = sparameters(___,Z0) calculates the S-parameters for the reference impedance Z0.

sobj = sparameters(___,Name=Value) calculates S-parameters using one or more name-value arguments in addition to any of the input argument combinations in previous syntaxes

sobj = sparameters(data,freq) creates an S-parameter object from the S-parameter data provided in data over the specified frequencies values.

sobj = sparameters(data,freq,Z0) creates an S-parameter object for the reference impedance Z0.

sobj = sparameters(filename) creates an S-parameter object from the data provided in the Touchstone file specified in filename.

Examples

Calculate S-parameters for Wilkinson Power Splitter

Create a Wilkinson power splitter object.

rfpcbobj = wilkinsonSplitter;

Calculate the S-parameters for the Wilkinson power splitter at 2.4 GHz with the reference impedance of 50 ohms.

Sobj = sparameters(wilkinsonSplitter,2.4e9,50);

Plot the S-parameters using the rfplot function.

rfplot(Sobj)

Calculate S-Parameters of Right Angle Bend

Design a microstrip transmission line at 3 GHz with 75 ohms impedance.

m = microstripLine(Length=0.0379,Width=0.0027,Height=0.0016,GroundPlaneWidth=0.0133);

Create a right angle bend with length equal to half the length of the transmission line and width equal to the width of the transmission line.

layer2d = bendRightAngle( Length=[m.Length/2 m.Length/2],...
Width=[m.Width m.Width]);

Convert the right angle bend to a 3-D component.

robj = pcbComponent(layer2d);

Add thickness and substrate layers to the board.

robj.BoardThickness = m.Substrate.Thickness;
robj.Layers{2} = m.Substrate;

Define frequency points to calculate the S-parameters.

freq = (1:2:40)*100e6;

Calculate the S-parameters of the right angle bend using the behavioral model.

Sckt1 = sparameters(robj,freq,Behavioral=true);

Calculate the S-parameters of the right angle bend using the electromagnetic solver.

Sem1 = sparameters(robj,freq);

Plot the S-parameter data using the rfplot function.

rfplot(Sckt1,'abs','o')
hold on
rfplot(Sem1,'abs','s')

Compute RF PCB S Parameters Using Frequency Interpolation

This example computes the s parameters of an rfpcb object by using frequency interpolation with the sweep option name-value argument in the s parameters function. This method decreases computation time.

Create an RFPCB object

Use the design function to create a branch line coupler at 5 GHz.

b = design(couplerBranchline,5e9);

Compute and show the s parameters

Compute and display the s parameters of the coupler over a frequency range of 4.5 GHz to 5.5 GHz using the frequency interpolation with gradient calculation sweep option.

freq = [4.5e9,5.5e9];
sline = sparameters(b,freq,50,'SweepOption','interpWithGrad');
figure;
rfplot(sline)

S Parameters: Comparison of Full-Frequency Sweep vs. Frequency Interpolation Methods

This example compares s parameter calculations using full-frequency sweep vs. interpolatory sweep methods.

Create a RF PCB object

Use the design function to create a Wilkinson splitter with a specified frequency of 1.9 GHz.

splitter = design(wilkinsonSplitter, 1.9e9);

Calculate s parameters

Calculate s apameters of the splitter using three sweep options, over a frequency range of 1.5 GHz to 2.5 GHz.

First use a full-frequency sweep with 100 frequency points.

freq = linspace(1.5e9,2.5e9,100);
Sfull=sparameters(splitter,freq,'SweepOption','direct');

Next use interpolatory frequency sweep.

freqinterp = [1.5e9, 2.5e9];
Sinterp=sparameters(splitter,freqinterp,'SweepOption','interp');

Next use intepolation-with-gradient frequency sweep.

Sinterpgrad=sparameters(splitter,freqinterp,'SweepOption','interpWithGrad');

Visualize s parameters

Plot the reflection coefficient, S11, of all three calculation methods.

figure;
rfplot(Sfull,1,1,'o');
hold;

Current plot held

rfplot(Sinterp,1,1,'+');
rfplot(Sinterpgrad,1,1,'*');

Input Arguments

rfpcbobj — Input object

RF PCB object

Input object, specified as a RF PCB object. You can specify either a PCB component, a microstrip bend, or a trace. For complete list of PCB components, microstrip bends, and traces, see PCB Components Catalog and Custom Geometry and PCB Fabrication.

data — S-parameter data

array of complex numbers

S-parameter data, specified as an array of complex numbers of the size N-by-N-by-K, where K represents number of frequency points.

freq — S-parameter frequency

scalar | vector

S-parameter frequencies, specified as a scalar or vector of positive real numbers in the ascending order.

Z0 — Reference impedance

50 (default) | positive real scalar

Reference impedance in ohms, specified as a positive real scalar.

filename — Name of Touchstone file

character vector | string scalar

Name of the Touchstone file containing network parameter data, specified as a character vector or string scalar. If the file is in the current folder or in a folder on the MATLAB® path, specify the file name. If the file is not in the current folder or in a folder on the MATLAB path, then specify the full or relative path name.

Example: sobj = sparameters('defaultbandpass.s2p');

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: Sobj = sparameters(robj,freq,Behavioral=true)

Behavioral — Behavioral model of RF PCB component and bend

false or 0 (default) | true or 1

Behavioral model of an RF PCB component and bend, specified as true (1) or false (0). You can compute the behavioral model for these rfpcb objects:

Bends	bendRightAngle bendCurved bendMitered Note The sparameters function does not support the behavioral model for objects with unequal widths such as bendRightAngle, bendCurved, and bendMitered objects.
Traces	traceTee traceCross Note The sparameters function does not support the behavioral model for Asymmetric tee- and cross-junction traces.
Transmission line objects	microstripLine coplanarWaveguide
Inductor	spiralInductor
Capacitor	interdigitalCapacitor
Splitter and Couplers	couplerRatrace couplerBranchline wilkinsonSplitter wilkinsonSplitterWideband wilkinsonSplitterUnequal splitterTee
Filters	filterCoupledLine filterHairpin filterStepImpedanceLowPass filterStub
Stubs	stubRadialShunt
Phase Shifter	phaseShifter
Vias	viaSingleEnded

Note

• Before using the sparameters function to calculate S-parameters for bends and traces, convert bends and traces to PCB components using the pcbComponent function.

• The sparameters function does not support using the behavioral model argument for:

  • Objects with unequal widths like bendRightAngle, bendCurved, and bendMitered

  • Asymmetric tee and cross-junction traces

Example: Sobj = sparameters(microstripline,freq,Behavioral = true)

SweepOption — Sweep type

'direct' (default) | 'interp' | 'interpWithGrad'

Use 'SweepOption' to switch to an interpolating fast frequency sweep method that adaptively selects frequency points to generate the responses, specified as:

• 'direct' computes s parameters at each given frequency point.

• 'interp' uses interpolation to compute s parameters with the minimum possible set of frequency points within the given frequency range.

• 'interpWithGrad'used a gradient-based interpolation technique to compute s parameters with the minimum possible set of frequency points within the given frequency range.

The interpolating fast frequency sweep uses rational interpolation by specifying two frequency points that define the frequency range of interest .

Example: s = sparameters(microstripLine,[2e9,3e9],'sweepOption','interp')

Data Types: string

Output Arguments

sobj — S-parameters

S-parameter object

S-parameters, returned as an object with the following properties:

• NumPorts — Number of ports, N, returned as an integer. The function calculates this value automatically when you create the object.

• Frequencies — S-parameter frequency, returned as a scalar or row vector of length, K, in the ascending order. The function sets this property from the filename or freq input arguments.

• Parameters — S-parameters, returned as an N-by-N-by-K array of complex numbers. The function sets this property from the filename or data input arguments.

• Impedance — Reference impedance in ohms, returned as a positive real scalar. The function sets this property from the filename or Z0 input arguments. If you do not provide reference impedance the function uses a default value of 50.

fit — Rational approximation

rational class object

Rational approximation returned when SweepOption is interp or interpWithGrad.

References

[1] H. -B. Yuan, W. -T. Bao, C. H. Lee, B. F. Zinser, S. Campione and J. -F. Lee, A Method of Moments Wide Band Adaptive Rational Interpolation Method for High-Quality Factor Resonant Cavities, IEEE Transactions on Antennas and Propagation, vol. 70, no. 5, pp. 3595-3604, May 2022.

Version History

Introduced in R2021b

R2025a: Frequency interpolation

Use new name-value argument SweepOption to use adaptive frequency interpolation calculation method.