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rfckt.microstrip

Microstrip transmission line

Description

Use the microstrip class to represent microstrip transmission lines characterized by line dimensions and optional stub properties.

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 (ε).

Creation

Syntax

h = rfckt.microstrip
h = rfckt.microstrip('Property1',value1,'Property2',value2,...)

Description

example

h = rfckt.microstrip returns a microstrip transmission line object whose properties are set to their default values.

h = rfckt.microstrip('Property1',value1,'Property2',value2,...) sets properties using one or more name-value pairs. You can specify multiple name-value pairs. Enclose each property name in a quote

Properties

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Computed S-parameters, noise figure, OIP3, and group delay values, specified as rfdata.data object. Analyzed Result is a read-only property. For more information refer, Algorithms

Data Types: function_handle

Relative permittivity of dielectric, specified as a scalar. The relative permittivity is the ratio of permittivity of the dielectric,$\epsilon$, to the permittivity in free space, ${\epsilon }_{0}$. The default value is 9.8.

Data Types: double

Dielectric thickness or physical height of the conductor, specified as a scalar in meters. The default value is 6.35e-4.

Data Types: double

Physical length of transmission, specified as a scalar in meters. The default value is 0.01.

Data Types: double

Loss angle tangent of dielectric, specified as a scalar. The default value is 0.

Data Types: double

Object name, specified as an 1-by-N character array. Name is a read-only property.

Data Types: char

Number of ports, specified as a positive integer. nportt is a read-only property. The default value is 2.

Data Types: double

Conductor conductivity, specified as a scalar in Siemens per meter (S/m). The default value is Inf.

Data Types: double

Type of stub, specified as one of the following values: 'NotaStub', 'Series', 'Shunt'.

Data Types: double

Stub transmission line termination, specified as one of the following values: 'NotaStub', 'Series', 'Shunt'.

Data Types: double

Physical thickness of microstrip, specified as a scalar in meters. The default value is 5.0e-6.

Data Types: double

Physical width of parallel-plate, specified as a scalar in meters. The default value is 6.0e-4.

Data Types: double

Object Functions

 analyze Analyze circuit object in frequency domain calculate Calculate specified parameters for circuit object circle Draw circles on Smith chart getz0 Characteristic impedance of transmission line object listformat List valid formats for specified circuit object parameter listparam List valid parameters for specified circuit object loglog Plot specified circuit object parameters using log-log scale plot Plot specified circuit object parameters on X-Y plane plotyy Plot specified object parameters with y-axes on both left and right sides polar Plot specified circuit object parameters on polar coordinates semilogx Plot specified circuit object parameters using log scale for x-axis semilogy Plot specified circuit object parameters using log scale for y-axis smith Plot specified circuit object parameters on Smith chart write Write RF data from circuit or data object to file

Examples

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Create a microstrip transmission line using rfckt.microstrip.

tx1=rfckt.microstrip('Thickness',0.0075e-6)
tx1 =

rfckt.microstrip with properties:

Width: 6.0000e-04
Height: 6.3500e-04
Thickness: 7.5000e-09
EpsilonR: 9.8000
LossTangent: 0
SigmaCond: Inf
LineLength: 0.0100
StubMode: 'NotAStub'
Termination: 'NotApplicable'
nPort: 2
AnalyzedResult: []
Name: 'Microstrip Transmission Line'

Algorithms

The analyze method treats the microstrip line as a 2-port linear network and models the line as a transmission line with optional stubs. The analyze method computes the AnalyzedResult property of the transmission line using the data stored in the rfckt.microstrip object properties as follows:

• If you model the transmission line as a stubless line, the analyze method 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 analyze method calculates the ABCD-parameters using the physical length of the transmission line, d, and the complex propagation constant, k, using the following equations:

$\begin{array}{l}A=\frac{{e}^{kd}+{e}^{-kd}}{2}\\ B=\frac{{Z}_{0}*\left({e}^{kd}-{e}^{-kd}\right)}{2}\\ C=\frac{{e}^{kd}-{e}^{-kd}}{2*{Z}_{0}}\\ D=\frac{{e}^{kd}+{e}^{-kd}}{2}\end{array}$

Z0 and k are vectors whose elements correspond to the elements of f, the vector of frequencies specified in the analyze input argument freq. 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].

• If you model the transmission line as a shunt or series stub, the analyze method first calculates the ABCD-parameters at the specified frequencies. It then uses the abcd2s function to convert the ABCD-parameters to S-parameters.

When you set the StubMode property to 'Shunt', the 2-port network consists of a stub transmission line that you can terminate with either a short circuit or an open circuit.

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

$\begin{array}{c}A=1\\ B=0\\ C=1/{Z}_{in}\\ D=1\end{array}$

When you set the StubMode property to 'Series', the 2-port network consists of a series transmission line that you can terminate with either a short circuit or an open circuit.

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

$\begin{array}{c}A=1\\ B={Z}_{in}\\ C=0\\ D=1\end{array}$

References

[1] Gupta, K. C., R. Garg, I. Bahl, and P. Bhartia, Microstrip Lines and Slotlines, 2nd Edition, Artech House, Inc., Norwood, MA, 1996.