S-Parameters

Model S-parameter network

• Library:

• RF Blockset / Circuit Envelope / Elements

• 

Description

The S-parameters block models a network defined by S-parameters in the RF Blockset™ circuit envelope simulation environment. The device can have up to 65 ports. For an introduction to RF simulation, see the example, Simulate High Frequency Components.

Note

If you specify more than eight ports, the block does not simulate noise.

The block models S-parameter data in the RF Blockset environment by fitting a rational function to the specified data. For more information about rational fitting of S-parameters, see the RF Toolbox™ rational function.

Note

During the fitting procedure, the block sets the TendsToZero and Qlimit properties of the rational object to false and inf, respectively.

S-parameters block mask icons are dynamic and indicate the current state of the applied noise parameter. This table shows you how the icons on this block vary based on the state of the Simulate noise parameter on the block.

Simulate noise: on	Simulate noise: off

Parameters

Main

Data source — Data source

Data file (default) | Network-parameters | Rational model

Data source for S-parameters behavior, specified as one of the following:

• Data file — Name of a Touchstone file with the extension.s2p. The block ignores noise and nonlinearity data in imported files.

• Network-parameters — Provide Network parameter data such as S-parameters, Y-parameters, and Z-parameters with corresponding Frequency and Reference impedance (ohms) for the s-parameters.

• Rational model — Provide values for Residues, Poles, and Direct feedthrough parameters which correspond to the equation for a rational model

  $$F(s)=\left({\displaystyle \sum _{k=1}^n\frac{C_k}{s-A_k}+D}\right)\begin{array}{cc},& s=j2\pi f\end{array}$$

  .In this rational model equation, each C_k is the residue of the pole A_k. If C_k is complex, a corresponding complex conjugate pole and residue must also be enumerated. This object has the properties C, A, and D. You can use these properties to specify the Residues, Poles, and Direct feedthrough parameters.

Data file — Name of network parameter data file

simrfV2_unitygain.s2p (default) | character vector

Name of network parameter data file, specified as a character vector.

Dependencies

To enable this parameter, select Data file in Data source tab.

Network parameter type — Network parameter type

S-parameters (default) | Y-parameters | Z-parameters

Network parameter type, specified as S-parameters, Y-parameters, or Z-parameters.

Dependencies

To enable this parameter, select Network-parameters in Data source tab.

Network-parameters — Network parameter values

[0 0;1 0] (default) | multidimensional array

Network parameter values specified as a multidimensional array. The third dimension of the S-parameter array must be the same length as the vector of frequencies specified by the Frequency parameter. The default values are different for S-parameters, Y-parameters, and Z-parameters respectively.

Dependencies

To enable this parameter, select Network-parameters in Data source tab.

Frequency (dB) — Frequency of network parameters

1e9 Hz (default) | scalar | vector | Hz | kHz | MHz | GHz

Frequency of network parameters, specified as a scalar or a vector in Hz.

Dependencies

To enable this parameter, select Network-parameters in Data source.

Reference Impedance(Ohm) — Reference impedance of network parameters

50 (default) | scalar

Reference impedance of network parameters, specified as a scalar.

Dependencies

To enable this parameter, select Network-parameters in Data source tab.

Residues — Residues in order of rational model

0 (default) | vector

Residues in order of rational model, specified as a vector.

Dependencies

To enable this parameter, select Rational model in Data source tab.

Poles — Residues in order of rational model

0 (default) | vector

Poles in order of rational model, specified as a vector.

Dependencies

To enable this parameter, select Rational model in Data source tab.

Direct feedthrough — Direct feedthrough

{0 0:1 0} (default) | array of vectors

Direct feedthrough, specified as an array vector.

Dependencies

To enable this parameter, select Rational model in Data source tab. .

Simulate noise — Generate thermal noise waves

off (default) | on

Choose this parameter to generate thermal noise waves [1]. Clear this parameter to stop simulating noise. For more information see, Generate Thermal Noise.

Note

This parameter is disabled when you specify more than eight ports.

Ground and hide negative terminals — Ground RF circuit terminals

on (default) | off

Select this parameter to ground and hide the negative terminals. Clear this parameter to expose the negative terminals. By exposing these terminals, you can connect them to other parts of your model.

By default, this option is selected.

Modeling

Modeling options — Model S-parameters

Time-domain (rationalfit) (default) | Frequency-domain

Model S-parameters, specified as:

• Time-domain (rationalfit) technique creates an analytical rational model that approximates the whole range of the data. When modeling using Time domain, the Plot in Visualization tab plots the data defined in Data Source and the values in the rational function.

• Frequency-domain computes the baseband impulse response for each carrier frequency independently. This technique is based on convolution. There is an option to specify the duration of the impulse response. For more information, see Compare Time and Frequency Domain Simulation Options for S-parameters.

• For the Amplifier and S-parameters blocks, the default value is Time domain (rationalfit). For the Transmission Line block, the default value is Frequency domain.

Dependencies

To set this parameter, first select Data file or Network-parameters in Data source. This selection activates the Visualization Tab which contains Source of frequency data

Fitting options — Rational fit fitting options

Fit individually (default) | Share poles by column | Share all poles

Rational fit fitting options, specified as Fit individually, Share poles by column, or Share all poles.

Rational fitting results shows values of Number of independent fits, Number of required poles, and Relative error achieved (dB).

Dependencies

To set this parameter, select Time domain (rationalfit) in Modeling options.

Relative error desired (dB) — Relative error acceptable for the rational fit

-40 (default) | scalar

Relative error acceptable for the rational fit, specified as a scalar.

Dependencies

To set this parameter, select Time domain (rationalfit) in Modeling options.

Maximum number of poles — Maximum number of poles

48 (default) | positive scalar

Maximum number of poles to control over the fitting procedure, specified as a positive scalar. You can specify up to 99 poles.

Dependencies

To set this parameter, select Time domain (rationalfit) in Modeling options.

Automatically estimate impulse response duration — Automatically calculate impulse response

on | off

Select this parameter to automatically calculate impulse response. Clear this parameter to manually specify the impulse response duration using Impulse response duration.

Dependencies

To set this parameter, select Frequency domain in Modeling options.

Impulse response duration — Impulse response duration

1e-10 (default) | scalar

Impulse response duration, specified as a scalar.

Dependencies

To set this parameter, first select Frequency domain in Modeling options. Then, clear Automatically estimate impulse response duration.

Use only S-parameter magnitude with appropriate delay — Use only S-parameter magnitude with appropriate delay

off (default) | on

Select this parameter to ignore the S-parameter phase and to delay the impulse response by half its length. You can use this parameter to shape spectral content with filter effects by specifying only magnitude.

This parameter uses the magnitude of the original data to obtain the impulse response of the block. This impulse response is centered about the time sequence and adds an inherent delay of half the duration of the impulse response. In the frequency domain, this translates to a linear monotonic decrease in phase throughout the given spectrum.

Note

• This parameter is applicable only for S-parameter data modeled in the frequency domain and introduces an artificial delay to the system.

• Adding a time delay (or frequency phase variation) to the system can result in unexpected behaviors. For example, in an unmatched system, delayed signals are bounced back and added to the original signals.

Dependencies

To enable this parameter, set Modeling options to Frequency domain.

Visualization

Source of frequency data — Frequency data source

Extracted from data source (default) | User-defined

Frequency data source, specified as:

When Source of frequency data is Extracted from data source, the Data source must be set to Data file. Verify that the specified Data file contains frequency data.

When Source of frequency data is User-specified, specify a vector of frequencies in the Frequency data parameter. Also, specify units from the corresponding drop-down list.

Frequency data — Frequency data range

[1e9:1e6:3e9] (default) | vector | Hz | kHz | MHz | GHz

Frequency data range, specified as a vector

Plot type — Type of data plot

X-Y plane (default) | Polar plane | Z Smith chart | Y Smith chart | ZY Smith chart

Type of data plot that you want to produce with your data specified as one of the following:

• X-Y plane — Generate a Cartesian plot of your data versus frequency. To create linear, semilog, or log-log plots, set the Y-axis scale and X-axis scale accordingly.

• Polar plane — Generate a polar plot of your data. The block plots only the range of data corresponding to the specified frequencies.

• Z smith chart, Y smith chart, and ZY smith chart — Generate a Smith^® chart. The block plots only the range of data corresponding to the specified frequencies.

Parameter 1 — Type of S-Parameters to plot

S11 (default) | SNN

Type of S-Parameters to plot, specified as SNN, where N is the number of ports in the s-parameters block.

Parameter 2 — Type of S-Parameters to plot

None (default) | SNN

Type of S-Parameters to plot, specified as SNN, where N is the number of ports in the s-parameters block.

Format1 — Plot format

Magnitude (decibels) (default) | Angle(degrees) | Real | Imaginary

Plot format, specified as Magnitude (decibels), Angle(degrees), Real, or Imaginary.

Format2 — Plot format

Magnitude (decibels) (default) | Angle(degrees) | Real | Imaginary

Plot format, specified as Magnitude (decibels), Angle(degrees), Real, or Imaginary.

Y-axis scale — Y-axis scale

Linear (default) | Logarithmic

Y-axis scale, specified as Linear or Logarithmic.

X-axis scale — X-axis scale

Linear (default) | Logarithmic

X-axis scale, specified as Linear or Logarithmic.

Plot — Plot specified data

button

Plot specified data using plot button.

Model Examples

Architectural Design of a Low IF Receiver System

Use the RF Blockset™ Circuit Envelope library to simulate the performance of a Low IF architecture with the following RF impairments: Component noise

Compare Time and Frequency Domain Simulation Options for S-parameters

Use two different options for modeling S-parameters with the RF Blockset™ Circuit Envelope library. The Time-domain (rationalfit) technique creates an analytical rational model that approximates the whole range of the data. This is a preferable technique when a good fit could be achieved with a small number of poles. When the data has a lot of details or high level of noise, this model becomes large and slow to simulate.

More About

Generate Thermal Noise

You can only generate thermal noise if the given S-parameters multiport components are passive.

To include the noise waves, the block augments the S-parameters equation:

$$b=Sa+c$$

• a and b — Customary wave vectors

• c — Noise wave vector

The noise wave vector, noise correlation matrix, and S-parameters have these relationships:

$$C_s=K*T(I-S{S}^{†})=\overline{c{c}^{†}}$$

where:

• K — Boltzmann's constant

• T — System temperature

• c — Noise wave vector

Compatibility Considerations

S-parameter network data construction in S-parameter block

Behavior changed in R2021b

Starting in R2021b, the Circuit Envelope library S-Parameters block uses the rational function to perform rational fitting to complex frequency-dependent data. The rational object provides improved fitting speed. The block also has a new parameter, Maximum number of poles, to provide additional control over the fitting procedure. You can specify up to 99 poles.

When you open a model created before R2021b containing the Circuit Envelope library S-parameter block, the software updates the extraction method to perform a rational fit with the new Maximum number of poles parameter. The output of the model gets refitted and the refitted output might differ from the output in previous releases.

S-parameter block icon updated

Behavior changed in R2021b

Starting in R2021b, the S-parametrs block icon has updated. The block icons are now dynamic and show the current state of the noise parameter.

When you open a model created before R2021b containing a S-parametrs block, the software replaces the block icon with the R2021b version.

References

[1] Wedge, Scott, and David Rutledge. “Wave Techniques for Noise Modeling and Measurement.” IEEE Transactions on Microwave Theory and Techniques 40, no. 11 (November 1992): 2004–12. https://doi.org/10.1109/22.168757.