Merge pull request scikit-rf#1117 from Asachoo/TouchStoneFormat

Adding S-parameter definition in Touchstone V1 comment

skrf/io/touchstone.py

@@ -36,7 +36,7 @@
 
 import numpy as np
 
-from ..constants import FREQ_UNITS, S_DEF_HFSS_DEFAULT
+from ..constants import FREQ_UNITS, S_DEF_HFSS_DEFAULT, S_DEFINITIONS
 from ..media import DefinedGammaZ0
 from ..network import Network
 from ..util import get_fid
@@ -498,6 +498,10 @@ def load_file(self, fid: typing.TextIO):
 
             self.s_def = S_DEF_HFSS_DEFAULT
             self.has_hfss_port_impedances = True
+            # Load the reference impedance convention from the comments
+            for s_def in S_DEFINITIONS:
+                if f'S-parameter uses the {s_def} definition' in self.comments:
+                    self.s_def = s_def
         elif self.reference is None:
             self.z0 = np.broadcast_to(self.resistance, (len(state.f), state.rank)).copy()
         else:

skrf/network.py

@@ -2409,7 +2409,8 @@ def get_buffer() -> io.StringIO:
             # exactly this format, to work
             # [HZ/KHZ/MHZ/GHZ] [S/Y/Z/G/H] [MA/DB/RI] [R n]
             if write_z0:
-                output.write('!Data is not renormalized\n')
+                output.write('! Data is not renormalized\n')
+                output.write(f'! S-parameter uses the {self.s_def} definition\n')
                 output.write(f'# {ntwk.frequency.unit} S {form} R\n')
             else:
                 # Write "r_ref.real" instead of "r_ref", so we get a real number "a" instead

skrf/tests/test_network.py

@@ -1074,6 +1074,8 @@ def test_sparam_from_hfss_with_power_wave(self):
         ntwk_orig.write_touchstone(os.path.join(self.test_dir, pwfile_skrf), write_z0=True, form='RI')
         ntwk_skrf = rf.Network(os.path.join(self.test_dir, pwfile_skrf))
 
+        # check if the s_def could be correctly recovered from scikit-rf's Touchstone file
+        self.assertTrue(ntwk_orig.s_def == ntwk_skrf.s_def)
         self.assertTrue(ntwk_orig == ntwk_skrf)
 
     def test_network_from_z_or_y(self):

skrf/tests/tmp_skrf_oneport_powerwave.s1p

@@ -8,8 +8,9 @@
 ! YY = 1
 !Data is not renormalized
 !
-!Created with skrf (http://scikit-rf.org).
-!Data is not renormalized
+! Created with skrf (http://scikit-rf.org).
+! Data is not renormalized
+! S-parameter uses the power definition
 # GHz S RI R
 ! Port[1] = 1
 !freq ReS11 ImS11