RF Blockset™

S-Parameters Passive Network - Model passive network using S-parameters

Library

Black Box Elements sublibrary of the Physical library

Description

The S-Parameters Passive Network block models the two-port passive network described in the block dialog box, in terms of its S-parameters and the frequencies and reference impedance of the S-parameters.

In the S-Parameters field of the block dialog box, provide the S-parameters for each of M frequencies as a 2-by-2-by-M array. In the Frequency field, specify the frequencies for the S-parameters as an M-element vector. The elements of the vector must be in the same order as the S-parameters. All frequencies must be positive. For example, the following figure shows the correspondence between the S-parameters array and the vector of frequencies.

The S-Parameters Passive Network block interpolates the given S-parameters to determine their values at the modeling frequencies. The modeling frequencies are determined by the Output Port block. See RF Blockset Algorithms for more details.

Dialog Box

Main Tab

S-Parameters

S-parameters for a two-port passive network in a 2-by-2-by-M array. M is the number of S-parameters.

Frequency (Hz)

Frequencies of the S-parameters as an M-element vector. The order of the frequencies must correspond to the order of the S-parameters in S-Parameters. All frequencies must be positive.

Reference impedance (ohms)

Reference impedance of the network as a scalar or a vector of length M. The value of this parameter can be real or complex. If you provide a scalar value, then that value is applied to all frequencies.

Interpolation method

The method used to interpolate the network parameters. The following table lists the available methods describes each one.

Method	Description
`Linear` (default)	Linear interpolation
`Spline`	Cubic spline interpolation
`Cubic`	Piecewise cubic Hermite interpolation

Visualization Tab

For information about plotting circuit parameters, see Plotting Model Data.

Examples

Plotting Parameters with the S-Parameters Passive Network Block

The following example specifies S-parameters [-.96-.23i, .03-.12i; .03-.12i, -.96-.23i] and [-.96-.11i, .02-.21i; .02-.21i, -.96-.11i] at frequencies 2.0 GHz and 2.1 GHz respectively. The example then plots these parameters.

The example first uses the MATLAB cat function to create the 2-by-2-by-2 S-parameters array.

cat(3,[-.96-.23i, .03-.12i; .03-.12i, -.96-.23i],...
      [-.96-.11i, .02-.21i; .02-.21i, -.96-.11i])

You could also use the MATLAB reshape function. The following command produces the same result as previous command.

reshape([-.96-.23i;.03-.12i;.03-.12i;-.96-.23i;...
         -.96-.11i;.02-.21i;.02-.21i;-.96-.11i],2,2,2)

Type the following command at the MATLAB prompt to create a variable called sparams that stores the values of the S-parameters.
```
sparams = cat(3,...
      [-.96-.23i, .03-.12i; .03-.12i, -.96-.23i],...
      [-.96-.11i, .02-.21i; .02-.21i, -.96-.11i])
```
Set the S-Parameters Passive Network block parameters on the Main tab as follows:
- Set the S-Parameters parameter to sparams.
- Set the Frequency (Hz) parameter to [2.0e9,2.1e9].
Click Apply. This action applies the specified settings.
Set the S-Parameters Passive Network block parameters on the Visualization tab as follows:
- In the Source of frequency data list, select User-specified.
- Set the Frequency data (Hz) parameter to [1.9e9:1.0e8:2.2e9].
- In the Y parameter1 list, select S21.
Click Plot. This action creates an X-Y Plane plot of the magnitude of the S₂₁ parameters, in decibels, in the frequency range 1.9 to 2.2 GHz.