nanovna-saver/NanoVNASaver/Touchstone.py

#  NanoVNASaver
#  A python program to view and export Touchstone data from a NanoVNA
#  Copyright (C) 2019.  Rune B. Broberg
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See theen.DM00296349
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <https://www.gnu.org/licenses/>.
import logging
import cmath
from NanoVNASaver.RFTools import Datapoint

logger = logging.getLogger(__name__)


class Options:
    # Fun fact: In Touchstone 1.1 spec all params are optional unordered.
    # Just the line has to start with "#"
    UNIT_TO_FACTOR = {
        "ghz": 10**9,
        "mhz": 10**6,
        "khz": 10**3,
        "hz": 10**0,
    }

    def __init__(self):
        # set defaults
        self.factor = Options.UNIT_TO_FACTOR["ghz"]
        self.parameter = "s"
        self.format = "ma"
        self.resistance = 50

    def parse(self, line):
        if not line.startswith("#"):
            raise TypeError("Not an option line: " + line)
        pfact = pparam = pformat = presist = False
        params = iter(line[1:].lower().split())
        for p in params:
            if p in ("ghz", "mhz", "khz", "hz") and not pfact:
                self.factor = Options.UNIT_TO_FACTOR[p]
                pfact = True
            elif p in "syzgh" and not pparam:
                self.parameter = p
                pparam = True
            elif p in ("ma", "db", "ri") and not pformat:
                self.format = p
                pformat = True
            elif p == "r" and not presist:
                self.resistance = int(next(params))
            else:
                raise TypeError("Illegial option line: " + line)


class Touchstone:

    def __init__(self, filename):
        self.filename = filename
        self.s11data = []
        self.s21data = []
        self.s12data = []
        self.s22data = []
        self.comments = []
        self.opts = Options()

    def load(self):
        logger.info("Attempting to open file %s", self.filename)
        sdata = [[], [], [], []]  # at max 4 data pairs

        with open(self.filename, "r") as file:
            for line in file:
                line = line.strip()
                if line.startswith("!"):
                    logger.info(line)
                    self.comments.append(line)
                    continue
                break
            self.opts.parse(line)

            prev_freq = prev_len = 0
            for line in file:
                # ignore empty lines (even if not specified)
                if not line.strip():
                    continue

                # ignore comments at data end
                data = line.split('!')[0]
                data = data.split()
                freq, data = float(data[0]) * self.opts.factor, data[1:]
                data_len = len(data)

                # consistency checks
                if freq <= prev_freq:
                    raise TypeError("Frequeny not ascending: " + line)
                prev_freq = freq

                if prev_len == 0:
                    prev_len = data_len
                if data_len % 2:
                    raise TypeError("Data values aren't pairs: " + line)
                elif data_len != prev_len:
                    raise TypeError("Inconsistent number of pairs: " + line)

                data_list = iter(sdata)
                vals = iter(data)
                for v in vals:
                    if self.opts.format == "ri":
                        next(data_list).append(
                            Datapoint(freq, float(v), float(next(vals))))
                    if self.opts.format == "ma":
                        z = cmath.polar(float(v), float(next(vals)))
                        next(data_list).append(Datapoint(freq, z.real, z.imag))

                self.s11data, self.s21data, self.s12data, self.s22data = sdata[:]

    def setFilename(self, filename):
        self.filename = filename