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Transmission Line

Model transmission line

Library

Elements

Description

Use the Transmission Line block to model delayed-based, lumped, and distributed transmission lines. Mask dialog options will change automatically to accommodate model type selection.

Dialog Box and Parameters

Main Tab

Model type
  •  Delay-based and lossless

  •  Delay-based and lossy

  •  Lumped parameter L-section

  •  Lumped parameter pi-section

  •  Coaxial

  •  Coplanar waveguide

  •  Microstrip

  •  Two-wire

  •  Parallel plate

  •  Equation-based

  •  RLCG

Ground and hide negative terminals

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

By default, this check box is selected.

Parameter Calculations for Distributed Transmission Line

When modeling distributed transmission lines, the block first calculates ABCD-parameters at a set of internal frequencies. The ABCD-parameters are converted S-parameters for simulation.

The block calculates the ABCD-parameters from the physical length of the transmission line, d, and the complex propagation constant, k, using the following set of equations:

Transmission Line with Stub

When you set the Stub mode parameter in the mask dialog box to Shunt, the two-port network consists of a transmission line in series with a stub. You can terminate the stub with a short circuit or an open circuit as shown in the following figure.

Zin is the input impedance of the shunt circuit. The ABCD-parameters for the shunt stub are calculated as

When you set the Stub mode parameter in the mask dialog box to Series, the two-port network comprises a series transmission line. You can terminate this line with either a short circuit or an open circuit as shown here.

Zin is the input impedance of the series circuit. The ABCD-parameters for the series stub are:

Modeling Tab

Modeling options

Select Frequency domain or Time domain (rationalfit) from the drop-down list. Distributed transmission lines use S-parameter internal representation, while delay based and lumped employ a time domain representation. S-parameter modeling options in SimRF can be Time domain or Frequency domain. For an introduction to RF simulation and modeling options, see, Simulate High Frequency Components

For the Transmission Line block, the default value is Frequency domain.

Fitting options

This field displays when you select Time domain(rationalfit) as the modeling option. Valid values are Share all poles, Share poles by columns, and Fit individually.

For the Transmission Line block, the default value is Share all poles.

Relative error desired (dB)

This field displays when you select Time domain(rationalfit) as the modeling option. Enter the desired relative error in decibels (dB). The default value is -40.

Rational fitting results

These fields display the results of rational fitting when you select Time domain(rationalfit) as the modeling option.

Visualization Tab

Source of frequency data

The only option for Source of frequency data is User-specified. To plot, specify a vector of frequencies in the Frequency data parameter and select units.

Plot type

Specify the type of plot that you want to produce with your data. When you model using Frequency domain, Visualization tab plots only the data defined in Data Source. When you model using Time domain, Visualization tab plots the data defined in Data Source and the rationalfit values. The Plot type parameter provides the following options:

  • 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.

The default value is X-Y plane.

Parameter #

Specify the S-parameters to plot. From the Parameter1 and Parameter2 drop-down lists, select the S-parameters that you want to plot. If you specify two parameters, the block plots both parameters in a single window.

The default value for Parameter1 is S11. For the Transmission Line block, the default value for Parameter2 is S22.

Format #

For X-Y plots, format the units of the parameters to plot from the Format1 and Format2 drop-down lists. For polar plots and Smith charts, the formats are set automatically.

The default value is Magnitude (decibels).

Y-axis scale

Scale for the Y-axis.

The default value is Linear.

X-axis scale

Scale for the X-axis.

The default value is Linear.

Tip

In general, blocks that model delay effects rely on signal history. You can minimize numerical error that occur due to a lack of signal history at the start of a simulation. To do so, in the Configuration Parameters dialog box Solver pane you can specify an Initial step size. For models with delay-based Transmission Line blocks, use an initial step size that is less than the value of the Delay parameter.

Examples

The example, Transmission Lines, Delay-based and Lumped Models, shows how to use Delay-based and Lumped Transmission Line blocks.

References

[1] Sussman-Fort, S. E., and J. C. Hantgan. "SPICE Implementation of Lossy Transmission Line and Schottky Diode Models." IEEE Transactions on Microwave Theory and Techniques.Vol. 36, No.1, January 1988.

[2] Pozar, David M. Microwave Engineering. Hoboken, NJ: John Wiley & Sons, Inc., 2005.

[3] Gupta, K. C., Ramesh Garg, Inder Bahl, and Prakash Bhartia. Microstrip Lines and Slotlines, 2nd Edition, Norwood, MA: Artech House, Inc., 1996.

[4] Ludwig, Reinhold and Pavel Bretchko. RF Circuit Design: Theory and Applications. Englewood Cliffs: NJ: Prentice-Hall, 2000.

[5] True, Kenneth M. "Data Transmission Lines and Their Characteristics." National Semiconductor Application Note 806, April 1992.

See Also

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