# rfckt.txline

General transmission line

## Description

Use the `rfckt.txline`

object to create transmission lines
that are characterized by line loss, line length, stub type, and
termination.

**Note**

`txlineEquationBased`

is recommended over
`rfckt.txline`

because it enables you to:

Create an equation-based transmission line. You can set the loss, the phase velocity, and the interpolation type in this object.

Build a

`circuit`

object with a equation-based transmission line.Model an equation-based transmission line element in an RF chain created using an

`rfbudget`

object or the RF Budget Analyzer app, and then export this element to RF Blockset™ or to`rfsystem`

System object™ for circuit envelope analysis.

* (since R2023b)*

## Creation

### Description

`h = rfckt.txline`

returns a transmission line object
whose properties are set to their default values.

`h = rfckt.txline(Name,Value)`

sets properties using
one or more name-value pairs. For example,
`rfckt.txline('Z0',75)`

creates a transmission line
object with characteristic impedance of 75 ohms. You can specify multiple
name-value pairs. Enclose each property name in a quote. Properties not
specified retain their default values.

## Properties

## Object Functions

`analyze` | Analyze RFCKT object in frequency domain |

`calculate` | Calculate specified parameters for rfckt objects or rfdata objects |

`plotyy` | Plot parameters of RF circuit or RF data on X-Y plane with two Y-axes |

`circle` | Draw circles on Smith Chart |

`loglog` | Plot specified circuit object parameters using log-log scale |

`plot` | Plot circuit object parameters on X-Y plane |

`listparam` | List valid parameters for specified circuit object |

`getz0` | Calculate characteristic impedance of RFCKT transmission line object |

`semilogx` | Plot RF circuit object parameters using log scale for
x-axis |

`semilogy` | Plot RF circuit object parameters using log scale for
y-axis |

`polar` | Plot specified object parameters on polar coordinates |

`smith` | Plot circuit object parameters on Smith chart |

`write` | Write RF data from circuit or data object to file |

## Examples

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

*Z*_{0}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*=*α*+_{a}*iβ*, where*α*is the attenuation coefficient and_{a}*β*is the wave number. The attenuation coefficient*α*is related to the specified loss,_{a}*α*, by$${\alpha}_{a}=-\mathrm{ln}\left({10}^{\alpha /20}\right)$$

The wave number

*β*is related to the specified phase velocity,*V*, by_{p}$$\beta =\frac{2\pi f}{{V}_{p}},$$

where

*f*is the frequency range specified in the`analyze`

input argument`freq`

. The phase velocity*V*is derived from the_{p}`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.*Z*is the input impedance of the shunt circuit. The ABCD-parameters for the shunt stub are calculated as:_{in}$$\begin{array}{c}A=1\\ B=0\\ C=1/{Z}_{in}\\ D=1\end{array}$$

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 as shown in the following figure.*Z*is the input impedance of the series circuit. The ABCD-parameters for the series stub are calculated as:_{in}$$\begin{array}{c}A=1\\ B={Z}_{in}\\ C=0\\ D=1\end{array}$$

## References

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

## Version History

**Introduced in R2009a**

## See Also

`rfckt.amplifier`

| `rfckt.cascade`

| `rfckt.coaxial`

| `rfckt.cpw`

| `rfckt.datafile`

| `rfckt.delay`

| `rfckt.hybrid`

| `rfckt.hybridg`

| `rfckt.mixer`

| `rfckt.microstrip`

| `rfckt.passive`

| `rfckt.parallel`

| `rfckt.parallelplate`

| `rfckt.rlcgline`

| `rfckt.series`

| `rfckt.seriesrlc`

| `rfckt.shuntrlc`

| `rfckt.twowire`