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

Syntax

h = rfckt.cpw

h = rfckt.cpw(Name,Value)

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

AnalyzedResult — Computed S-parameters, noise figure, OIP3, and group delay values

rfdata.data object

This property is read-only.

Computed S-parameters, noise figure, OIP3, and group delay values, specified as an rfdata.data object. For more information refer, Algorithms.

Data Types: function_handle

ConductorWidth — Physical width of conductor

scalar in meters

Physical width of conductor, specified as a scalar in meters. By default, the value is 0.6e-4.

Data Types: double

EpsilonR — Relative permittivity of dielectric

scalar

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, $${\epsilon }_0$$. By default, the value is 9.8.

Data Types: double

Height — Dielectric thickness or physical height of conductor

scalar in meters

Dielectric thickness or physical height of the conductor, specified as a scalar in meters. The default value is 0.635e-4.

Data Types: double

LineLength — Physical length of transmission

scalar in meters

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

Data Types: double

LossTangent — Loss angle tangent of dielectric

scalar

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

Data Types: double

Name — Name of coplanar waveguide transmission line object

1-by-N character array

This property is read-only.

Name of coplanar waveguide transmission line object, specified as a 1-by-N character array.

Data Types: char

nport — Number of ports

positive integer

This property is read-only.

Number of ports, specified as a positive integer.

Data Types: double

SigmaCond — Conductor conductivity

scalar in Siemens per meter

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

Data Types: double

StubMode — Type of stub

'NotaStub' | 'Series' | 'Shunt'

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

Data Types: double

SlotWidth — Physical width of slot

scalar in meters

Physical width of slot, specified as a scalar in meters. The default value is 0.2e-4.

Data Types: double

Termination — Stub transmission line termination

'NotApplicable' (default) | 'Open' | 'Short'

Stub transmission line termination, specified as one of the following values: 'NotApplicable', 'Open', 'Short'.

Data Types: double

Thickness — Physical thickness of conductor

scalar in meters

Physical thickness of conductor, specified as a scalar in meters. The default value is 0.005e-6.

Data Types: double

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 xy-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

Create Coplanar Waveguide Transmission Line

Create a coplanar waveguide transmission line using rfckt.cpw.

tx=rfckt.cpw('Thickness',0.0075e-6)

tx = 
   rfckt.cpw with properties:

    ConductorWidth: 6.0000e-04
         SlotWidth: 2.0000e-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: 'Coplanar Waveguide Transmission Line'

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:

  $$\begin{array}{l}A=\frac{e^{kd}+e^{-kd}}{2}\\ B=\frac{Z_0*\left(e^{kd}-e^{-kd}\right)}{2}\\ C=\frac{e^{kd}-e^{-kd}}{2*Z_0}\\ D=\frac{e^{kd}+e^{-kd}}{2}\end{array}$$

  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, 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_in 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 as shown in the following figure.

  

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

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

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