Main Content


Plot specified circuit object parameters using log scale for x-axis



lineseries = semilogx(h,parameter) plots the specified parameter in the default format using a logarithmic scale for the x-axis. h is the handle of a circuit (rfckt) object.

The semilogx method returns a column vector of handles to lineseries objects, one handle per line. This output is the same as the output returned by the MATLAB® semilogx function.

lineseries = semilogx(h,parameter1,...,parametern) plots the parameters parameter1, ..., parametern from the object h on an X-Y plane using a logarithmic scale for the x-axis.

lineseries = semilogx(h,parameter1,...,parametern,format) plots the parameters parameter1, ..., parametern in the specified format.


For all circuit objects except those that contain data from a data file, you must perform a frequency domain analysis with the analyze method before calling semilogx.

lineseries = semilogx(h,'parameter1',...,'parametern', format,x-axis parameter,x-axis format,'condition1',value1,..., 'conditionm',valuem, 'freq',freq,'pin',pin) plots the specified parameters at the specified operating conditions for the object h.


collapse all

Create an amplifier object from |default.s2p|.
amp = read(rfckt.amplifier,'default.s2p');

Plot S11 using log scale on x-axis.

lineseries = semilogx(amp,'S11')

lineseries = 
  Line (S_{11}) with properties:

              Color: [0 0.4470 0.7410]
          LineStyle: '-'
          LineWidth: 0.5000
             Marker: 'none'
         MarkerSize: 6
    MarkerFaceColor: 'none'
              XData: [1x191 double]
              YData: [1x191 double]
              ZData: [1x0 double]

  Show all properties

Input Arguments

collapse all

RF circuit or data object, specified as an object handle.

If h has multiple operating conditions, such as from a .p2d or .s2d file, the semilogx method operates as follows:

  • If you do not specify any operating conditions as arguments to the semilogx method, then the method plots the parameter values based on the currently selected operating condition.

  • If you specify one or more operating conditions, the semilogx method plots the parameter values based on those operating conditions.

  • When you use an operating condition for the xparameter input argument, the method plots the parameters for all operating condition values.

Format of the data to be plotted, specified as a character vector or string.

Example: lineseries = semilogy(h,'S11','Magnitude (linear)')

Valid parameters of circuit objects, specified as a character vector or string.

Use listparam(h) to get a list of valid parameters for a circuit object, h. Uselistformat(h,parameter) to see the legitimate formats for a specified parameter. The first listed format is the default for that parameter.

independent variable to use in plotting the specified parameters. Several xparameter values are available for all objects. When you import rfckt.amplifier, rfckt.mixer, or object specifications from a .p2d or .s2d file, you can also specify any operating conditions from the file that have numeric values, like bias.

This table shows the most commonly available parameters and the corresponding x-axis parameter values. The default values listed in the table are used if the xparameter is not specified.

Parameter Namex-axis parameter values
Pout, Phase, LS11, LS12, LS21, LS22Pin (default), Freq
S11, S12, S21, S22, NF, IIP3, OIP3, GroupDelay, VSWRIn, VSWROut, GammaIn, GammaOut, FMIN, GammaOPT, RN, TF1, TF2, Gt, Ga, Gp, Gmag, Gmsg, GammaMS, GammaML, K, Delta, Mu, MuPrimeFreq

Format used for the specified xparameter.

You do not need to specify x-axis format when xparameter is an operating condition.

This table shows the available x-axis format values that are available for the x-axis parameter values, along with the default values that are used if x-axis format is not specified.

x-axis parameter valuesx-axis format values
PindBm (default), mW, W, dBW

THz, GHz, MHz, KHz, Hz

By default, xformat is chosen to provide the best scaling for the given xparameter values.

AMMagnitude (decibels) (default), Magnitude (linear)

Name-Value Pair Arguments

Example: semilogy(h,'Pout','Pin','Freq',2.1e9)

Specify optional comma-separated pairs of Name,Value pair arguments. Name is the argument name and Value is the corresponding value. Name must appear inside single quotes (''). You can specify several name and value pair arguments in any order as Name1, Value1, ..., NameN, ValueN.

'condition1',value1, ..., conditionm,valuem are the optional condition/value pairs at which to plot the specified parameters. These pairs are usually operating conditions from a .p2d or .s2d file. For some parameters, you can specify a set of frequency or input power values at which to plot the specified parameter.

For example:

  • When plotting large-signal S-parameters as a function of input power, you can specify frequency points of interest using condition/value pairs.

  • When plotting large-signal S-parameters as a function of frequency, you can specify input power levels of interest using condition/value pairs.

  • When plotting parameters as a function of an operating condition, you can specify both frequency and input power values using condition/value pairs.

Frequency in Hz, specified as the comma-separated pair consisting of 'Freq' and a positive scalar.

Input power level, in dBm, specified as the comma-separated pair consisting of 'Pin' and a positive scalar.

Output Arguments

collapse all

Lineseries object, returned as a column vector of object handles.


  • Use the Property Editor (propertyeditor) or the MATLAB set function to change Line Properties. The reference pages for MATLAB functions such as figure, axes, and text also list available properties and provide links to more complete property descriptions.


    Use the MATLAB semilogx function to create a semi-log scale plot of network parameters that are specified as vector data and are not part of a circuit (rfckt) object or data (rfdata) object.

Introduced in R2007a