Generate Smith chart and VSWR charts from .s1p files

smith_vswr.py

#!/usr/bin/env python3
#
# BSD 3-Clause License
# Copyright (c) 2022 Fred W6BSD All rights reserved.
#
# This program reads Touchstone files (.s1p) coming from any good
# antenna analyzer or VNA.  The the type of the data is limited to the
# format S,RI.
#
# You can go to https://0x9900.com/hustler-4btv-cleanup-tuning/ to see
# an example of images generated by this program.
#

import argparse
import os

import matplotlib.pyplot as plt
import skrf as rf

from matplotlib.ticker import MultipleLocator

DPI = 100

MAX_VSWR = 5
LINE_COLOR = "yellow"

MY_PARAMS = {
  "figure.dpi": DPI,
  "figure.figsize": [14, 6],
  "axes.labelsize": 10,
  "axes.grid" : True,
  "legend.fontsize": 8,
  "grid.color": "brown",
  "grid.linewidth": 1,
  "lines.linewidth": 1.5,
}

BANDS = [
 (1800, 2000, '160m'),
 (3500, 4000, '80m'),
 (5258, 5450, '60m'),
 (7000, 7300, '40m'),
 (10100, 10150, '30m'),
 (14000, 14350, '20m'),
 (18068, 18168, '17m'),
 (21000, 21450, '15m'),
 (24890, 24990, '12m'),
 (28000, 29700, '10m'),
 (50000, 54000, '6m'),
 (144000, 148000, '2m'),
]

plt.style.use('dark_background')
plt.rcParams.update(MY_PARAMS)

def open_network(s1p_file):
  return rf.Network(s1p_file)

def draw_smithvswr(dut, path, ext='png'):
  image = os.path.join(path, f"{dut.name}-smith-vswr.{ext}")
  fig, (ax1, ax2) = plt.subplots(1, 2)
  fig.suptitle(dut.name + "Smith Chart + VSWR")

  fmin = dut.frequency.f.min()
  fmax = dut.frequency.f.max()

  dut.plot_s_smith(ax=ax1, show_legend=True, color=LINE_COLOR)
  dut.plot_s_vswr(ax=ax2, color=LINE_COLOR)

  ax2.set_xlim(fmin, fmax)

  max_vswr = (1+dut.s_mag.max())/(1-dut.s_mag.max())
  if max_vswr < MAX_VSWR:
    ax2.set_ylim(1, MAX_VSWR)
    ax2.yaxis.set_minor_locator(MultipleLocator(.1))
    ax2.yaxis.set_major_locator(MultipleLocator(.5))
  else:
    ax2.set_ylim(1, max_vswr * 1.12)
    ax2.yaxis.set_minor_locator(MultipleLocator(1))
    ax2.yaxis.set_major_locator(MultipleLocator(5))

  ax2.axhline(y=3, linewidth=1.5, zorder=1, color='orange', linestyle="dotted")
  for low, high, _ in BANDS:
    ax2.axvspan(low*1000, high*1000, facecolor='lightgray', alpha=0.1)

  fig.text(0.01, 0.05, "Smith Chart By W6BSD - https://0x9900.com/", color='gray',
           rotation=90, fontsize=8)
  plt.tight_layout()
  fig.savefig(image, transparent=False, dpi=DPI)
  print(image)

def draw_rl(dut, path, ext='png'):
  image = os.path.join(path, f"{dut.name}-rl.{ext}")
  fmin = dut.frequency.f.min()
  fmax = dut.frequency.f.max()

  fig, ax = plt.subplots()
  fig.suptitle(dut.name + " - Return Loss (dB)")
  dut.plot_s_db(color=LINE_COLOR)

  for low, high, _ in BANDS:
    ax.axvspan(low*1000, high*1000, facecolor='lightgray', alpha=0.1)

  ax.axhline(y=-6, linewidth=1.5, zorder=1, color='orange', linestyle="dotted")
  ax.set_xlim(fmin, fmax)
  ax.set_ylim(top=0)

  fig.text(0.01, 0.05, "Smith Chart By W6BSD - https://0x9900.com/", color='gray',
           rotation=90, fontsize=8)
  plt.savefig(image, transparent=False, dpi=DPI)
  print(image)

def draw_vswr(dut, path, ext='png'):
  image = os.path.join(path, f"{dut.name}-vswr.{ext}")
  fmin = dut.frequency.f.min()
  fmax = dut.frequency.f.max()

  fig, ax = plt.subplots()
  fig.suptitle(dut.name + " - VSWR")
  dut.plot_s_vswr(color=LINE_COLOR)

  for low, high, _ in BANDS:
    ax.axvspan(low*1000, high*1000, facecolor='lightgray', alpha=0.1)

  ax.axhline(y=3, linewidth=1.5, zorder=1, color='orange', linestyle="dotted")
  max_vswr = (1+dut.s_mag.max())/(1-dut.s_mag.max())
  ax.set_ylim(1, 6 if max_vswr < 6 else max_vswr * 1.2)
  ax.set_xlim(fmin, fmax)

  fig.text(0.01, 0.05, "Smith Chart By W6BSD - https://0x9900.com/", color='gray',
           rotation=90, fontsize=8)
  plt.savefig(image, transparent=False)
  print(image)

def main():
  parser = argparse.ArgumentParser(description="Antenna Smith chart and VSWR chart")
  parser.add_argument('-V', '--version', action='version', version='%(prog)s 1.0')
  parser.add_argument('-f', '--file', required=True, help='s1p filename')
  parser.add_argument('-t', '--type', choices=['jpg', 'png', 'svg'], default='png',
                      help='image type [jpg, png, svg] (default: %(default)s)')
  opts = parser.parse_args()

  path = os.path.dirname(opts.file)
  dut = open_network(opts.file)
  draw_smithvswr(dut, path=path, ext=opts.type)
  draw_rl(dut, path=path, ext=opts.type)
  draw_vswr(dut, path=path, ext=opts.type)

if __name__ == "__main__":
  main()