# rfckt.cpw

Coplanar waveguide transmission line

## Description

Use the `rfckt.cpw`

object to create a coplanar waveguide
transmission line that is characterized by line dimensions, stub type, and
termination.

A coplanar waveguide transmission line is shown in cross-section in the following
figure. Its physical characteristics include the conductor width (*w*),
the conductor thickness (*t*), the slot width (*s*),
the substrate height (*d*), and the permittivity constant
(*ε*).

**Note**

`txlineCPW`

is recommended over `rfckt.cpw`

because
it enables you to:

Create a coplanar waveguide or conductor backed transmission line.

Build a

`circuit`

object with a coplanar waveguide or conductor backed transmission line.Input the

`txlineCPW`

object to the`coplanarWaveguide`

object from RF PCB Toolbox™ for EM modeling.Model a coplanar waveguide or conductor backed 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.cpw`

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

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

sets properties using one
or more name-value pairs. For example,
`rfckt.cpw('ConductorWidth',0.3)`

creates an RF
coplanar waveguide transmission line with a width of 0.3 meters. 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 |

`circle` | Draw circles on Smith Chart |

`extract` | Extract specified network parameters from rfckt object or data 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 circuit object parameters on X-Y plane |

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

`getop` | Display operating conditions |

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

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

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

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

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

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

`read` | Read RF data from file to new or existing circuit or data object |

`restore` | Restore data to original frequencies |

`getop` | Display operating conditions |

## Examples

## Algorithms

The `analyze`

method treats the transmission line as a 2-port linear
network. It computes the `AnalyzedResult`

property of a stub or as a
stub less line using the data stored in the `rfckt.cpw`

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}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, slot width, substrate height, conductor strip thickness, relative permittivity constant, conductivity and dielectric loss tangent of the transmission 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 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}$$\begin{array}{c}A=1\\ B={Z}_{in}\\ C=0\\ D=1\end{array}$$

The `analyze`

method uses the S-parameters to
calculate the group delay values at the frequencies specified in the
`analyze`

input argument `freq`

, as described in
the `analyze`

reference page.

## References

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

## Version History

**Introduced before R2006a**

## See Also

`rfckt.amplifier`

| `rfckt.cascade`

| `rfckt.coaxial`

| `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`

| `rfckt.txline`