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rfckt.txline

General transmission line

Description

Use the txline class to represent transmission lines that are characterized by line loss, line length, stub type, and termination.

Creation

Syntax

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

Description

example

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

h = rfckt.txline('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. This is a read-only property. For more information refer, Algorithms.

Data Types: function_handle

Frequency data for the RLCG values, specified as a M-element vector in Hz. The values must be positive and correspond to the order of loss and phase velocity values. By default, this property is empty.

Data Types: double

Interpolation method used in rfckt.rlcgline, specified as one of the following values:

MethodDescription
LinearLinear interpolation
SplineCubic spline interpolation
CubicPiecewise cubic Hermite interpolation

Data Types: char

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

Data Types: double

Reduction in strength of signal as it travels through the transmission line, specified as a nonnegative M-element vector in decibels per meter.

Data Types: double

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

Data Types: char

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

Data Types: double

Phase velocity or propagation velocity of a uniform plane wave on the transmission line specified as a M-element vector in meters/sec. The phase velocity values correspond to the frequency values. The default value is 299792458.

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

Characteristic impedance, specified as a vector in ohms. The default value is 50 ohms.

Data Types: double

Object Functions

analyzeAnalyze circuit object in frequency domain
calculateCalculate specified parameters for circuit object
circleDraw circles on Smith chart
getz0Characteristic impedance of transmission line object
listformatList valid formats for specified circuit object parameter
listparamList valid parameters for specified circuit object
loglogPlot specified circuit object parameters using log-log scale
plotPlot specified circuit object parameters on X-Y plane
plotyyPlot specified object parameters with y-axes on both left and right sides
polarPlot specified circuit object parameters on polar coordinates
semilogxPlot specified circuit object parameters using log scale for x-axis
semilogyPlot specified circuit object parameters using log scale for y-axis
smithPlot specified circuit object parameters on Smith chart
writeWrite RF data from circuit or data object to file

Examples

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Transmission Line Properties

trl = rfckt.txline('Z0',75)
trl = 

   rfckt.txline with properties:

        LineLength: 0.0100
          StubMode: 'NotAStub'
       Termination: 'NotApplicable'
              Freq: 1.0000e+09
                Z0: 75
                PV: 299792458
              Loss: 0
          IntpType: 'Linear'
             nPort: 2
    AnalyzedResult: []
              Name: 'Transmission Line'

Plot

f = [1e9:1.0e7:3e9];     % Simulation frequencies
analyze(trl,f);          % Do frequency domain analysis
figure
plot(trl,'s21','angle'); % Plot angle of S21

Algorithms

The analyze method treats the transmission line, which can be lossy or lossless, as a 2-port linear network. It computes the AnalyzedResult property of a stub or as a stubless line using the data stored in the rfckt.txline object properties as follows:

  • If you model the transmission line as a stub less 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:

    A=ekd+ekd2B=Z0*(ekdekd)2C=ekdekd2*Z0D=ekd+ekd2

    Z0 is the specified characteristic impedance. k is a vector whose elements correspond to the elements of the input vector freq. The analyze method calculates k from the specified properties as k = αa + , where αa is the attenuation coefficient and β is the wave number. The attenuation coefficient αa is related to the specified loss, α, by

    αa=ln(10α/20)

    The wave number β is related to the specified phase velocity, Vp, by

    β=2πfVp,

    where f is the frequency range specified in the analyze input argument freq. The phase velocity Vp is derived from the rfckt.txline object properties. It is also known as the wave propagation velocity.

  • 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 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:

    A=1B=0C=1/ZinD=1

    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 as shown in the following figure.

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

    A=1B=ZinC=0D=1

References

[1] Ludwig, R. and P. Bretchko, RF Circuit Design: Theory and Applications, Prentice-Hall, 2000.

Introduced in R2009a

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