Download This Notebook: Plotting.ipynb



This tutorial describes skrf’s plotting features. If you would like to use skrf’s matplotlib interface with skrf styling, start with this

In [1]:
%matplotlib inline
import skrf as rf

Plotting Methods

Plotting functions are implemented as methods of the Network class.

  • Network.plot_s_re
  • Network.plot_s_im
  • Network.plot_s_mag
  • Network.plot_s_db

Similar methods exist for Impedance (Network.z) and Admittance Parameters (Network.y),

  • Network.plot_z_re
  • Network.plot_z_im
  • Network.plot_y_re
  • Network.plot_y_im

Smith Chart

As a first example, load a Network and plot all four s-parameters on the Smith chart.

In [2]:
from skrf import Network

ring_slot = Network('data/ring slot.s2p')
In [3]:

Another common option is to draw addmitance contours, instead of impedance. This is controled through the chart_type argument.

In [4]:

See skrf.plotting.smith() for more info on customizing the Smith Chart.

Complex Plane

Network parameters can also be plotted in the complex plane without a Smith Chart through Network.plot_s_complex.

In [5]:

from matplotlib import pyplot as plt
plt.axis('equal') # otherwise circles wont be circles
(-0.855165798772, 0.963732138327, -0.8760764348472001, 0.9024032182652001)


Scalar components of the complex network parameters can be plotted vs frequency as well. To plot the log-magnitude of the s-parameters vs. frequency,

In [6]:

When no arguments are passed to the plotting methods, all parameters are plotted. Single parameters can be plotted by passing indices m and n to the plotting commands (indexing start from 0). Comparing the simulated reflection coefficient off the ring slot to a measurement,

In [7]:
from import ring_slot_meas
ring_slot.plot_s_db(m=0,n=0, label='Theory')
ring_slot_meas.plot_s_db(m=0,n=0, label='Measurement')


Plot phase,

In [8]:

Or unwrapped phase,

In [9]:

Phase is radian (rad) is also available

Group Delay

A Network has a plot() method which creates a rectangular plot of the argument vs frequency. This can be used to make plots are arent ‘canned’. For example group delay

In [10]:
gd = abs(ring_slot.s21.group_delay) *1e9 # in ns

plt.ylabel('Group Delay (ns)')
plt.title('Group Delay of Ring Slot S21')
Text(0.5,1,'Group Delay of Ring Slot S21')

Impedance, Admittance

The components the Impendance and Admittance parameters can be plotted similarly,

In [11]:
In [12]:

Customizing Plots

The legend entries are automatically filled in with the Network’s The entry can be overidden by passing the label argument to the plot method.

In [13]:
ring_slot.plot_s_db(m=0,n=0, label = 'Simulation')

The frequency unit used on the x-axis is automatically filled in from the Networks Network.frequency.unit attribute. To change the label, change the frequency’s unit.

In [14]:
ring_slot.frequency.unit = 'mhz'

Other key word arguments given to the plotting methods are passed through to the matplotlib matplotlib.pyplot.plot function.

In [15]:
ring_slot.plot_s_db(m=0,n=0, linewidth = 3, linestyle = '--', label = 'Simulation')
ring_slot_meas.plot_s_db(m=0,n=0, marker = 'o', markevery = 10,label = 'Measured')


All components of the plots can be customized through matplotlib functions, and styles can be used with a context manager.

In [16]:
from matplotlib import pyplot as plt
from matplotlib import style

with style.context('seaborn-ticks'):
    plt.xlabel('Real Part');
    plt.ylabel('Imaginary Part');
    plt.title('Smith Chart With Legend Room');

Saving Plots

Plots can be saved in various file formats using the GUI provided by the matplotlib. However, skrf provides a convenience function, called skrf.plotting.save_all_figs, that allows all open figures to be saved to disk in multiple file formats, with filenames pulled from each figure’s title,

from skrf.plotting import save_all_figs
save_all_figs('data/', format=['png','eps','pdf'])

Adding Markers Post Plot

A common need is to make a color plot, interpretable in greyscale print. The skrf.plotting.add_markers_to_lines adds different markers each line in a plots after the plot has been made, which is usually when you remember to add them.

In [17]:
from skrf import plotting
with style.context('printable'):
    plt.legend() # have to re-generate legend

FileNotFoundError                         Traceback (most recent call last)
~/checkouts/ in use(style)
    110             try:
--> 111                 rc = rc_params_from_file(style, use_default_template=False)
    112                 _apply_style(rc)

~/checkouts/ in rc_params_from_file(fname, fail_on_error, use_default_template)
   1133     """
-> 1134     config_from_file = _rc_params_in_file(fname, fail_on_error)

~/checkouts/ in _rc_params_in_file(fname, fail_on_error)
   1049     rc_temp = {}
-> 1050     with _open_file_or_url(fname) as fd:
   1051         try:

~/checkouts/ in __enter__(self)
     58         try:
---> 59             return next(self.gen)
     60         except StopIteration:

~/checkouts/ in _open_file_or_url(fname)
   1034             encoding = "utf-8"
-> 1035         with, encoding=encoding) as f:
   1036             yield f

FileNotFoundError: [Errno 2] No such file or directory: 'printable'

During handling of the above exception, another exception occurred:

OSError                                   Traceback (most recent call last)
<ipython-input-17-4aa103b0c60f> in <module>()
      1 from skrf import plotting
----> 2 with style.context('printable'):
      3     ring_slot.plot_s_deg()
      4     plotting.add_markers_to_lines()
      5     plt.legend() # have to re-generate legend

~/checkouts/ in __enter__(self)
     57     def __enter__(self):
     58         try:
---> 59             return next(self.gen)
     60         except StopIteration:
     61             raise RuntimeError("generator didn't yield") from None

~/checkouts/ in context(style, after_reset)
    146         mpl.rcdefaults()
    147     try:
--> 148         use(style)
    149     except:
    150         # Restore original settings before raising errors during the update.

~/checkouts/ in use(style)
    115                     "{!r} not found in the style library and input is not a "
    116                     "valid URL or path; see `style.available` for list of "
--> 117                     "available styles".format(style))

OSError: 'printable' not found in the style library and input is not a valid URL or path; see `style.available` for list of available styles