RF Blockset™

Microstrip Transmission Line - Model microstrip transmission line

Library

Transmission Lines sublibrary of the Physical library

Description

The Microstrip Transmission Line block models the microstrip transmission line described in the block dialog in terms of its frequency-dependent S-parameters. A microstrip transmission line is shown in cross-section in the following figure. Its physical characteristics include the microstrip width (w), the microstrip thickness (t), the substrate height (d), and the relative permittivity constant ( ).

The block lets you model the transmission line as a stub or as a stubless line.

Stubless Transmission Line

If you model a microstrip transmission line as a stubless line, the Microstrip Transmission Line block first calculates the ABCD-parameters at each frequency contained in the modeling frequencies vector. It then uses the abcd2s function to convert the ABCD-parameters to S-parameters.

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

Z₀ and k are vectors whose elements correspond to the elements of f, a vector of modeling frequencies. Both can be expressed in terms of the specified conductor strip width, substrate height, conductor strip thickness, relative permittivity constant, conductivity, and dielectric loss tangent of the microstrip line, as described in [1].

The Microstrip Transmission Line block normalizes the resulting S-parameters to a reference impedance of 50 ohms.

Shunt and Series Stubs

If you model the transmission line as a shunt or series stub, the Microstrip Transmission Line block first calculates the ABCD-parameters at each frequency contained in the vector of modeling frequencies. It then uses the abcd2s function to convert the ABCD-parameters to S-parameters.

Shunt ABCD-Parameters

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

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

Series ABCD-Parameters

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

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

Dialog Box

Main Tab

Strip width (m): Width of the microstrip transmission line.
Substrate height (m): Thickness of the dielectric on which the microstrip resides.
Strip thickness (m): Physical thickness of the microstrip.
Relative permittivity constant: Relative permittivity of the dielectric expressed as the ratio of the permittivity of the dielectric to permittivity in free space .
Conductivity in conductor (S/m): Conductivity of the conductor in siemens per meter.
Loss tangent in dielectric: Loss angle tangent of the dielectric.
Transmission line length (m): Physical length of the transmission line.
Stub mode: Type of stub. Choices are Not a stub, Shunt, or Series.
Termination of stub: Stub termination for stub modes Shunt and Series. Choices are Open or Short. This parameter becomes visible only when Stub mode is set to Shunt or Series.

Visualization Tab

For information about plotting the transmission line parameters, see Plotting Model Data.

References

[1] Gupta, K.C., G. Ramesh, I. Bahl, and P. Bhartia, Microstrip Lines and Slotlines, Second Edition, Artech House, 1996. pp. 102-109.