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function [type,freq,data,ref,comment]=read_touchstone( filename )
% [type,freq,data,ref]=read_touchstone( filename ) - read touchstone-file
% type (lowercase) 'z' for Z-Parameter touchstone-file
% freq vector of frequencies (in Hz)
% data (numports x numports x numfreq) matrix
% filename filename of the file to read
% ref reference impedance
% comment cell array of comment lines
%
% Version 16. Jun 2010
% 18. Aug 2010: comment lines
% 1. Sep 2010: BUGFIX: two-port files had S12 and S21 swapped!!!!!
% ATTENTION: higher than two-ports must be validated again!!!!!!!!!1
[fid, message] = fopen( filename, 'rt' );
if fid == -1
error( message );
end
comment = {};
% constants
DB = 0;
MA = 1;
RI = 2;
% number of ports (extract extension)
temp = lower(filename);
k = strfind(temp,'.');
if isempty(k)
error( 'filename has no extension' );
end
last_dot = k(length(k));
if length(temp) <= k
error( 'filename ends with "."' );
end
extension = temp(last_dot+1:length(temp));
if (lower(extension(1)) ~= 's') && (lower(extension(length(extension))) ~= 'p')
error( 'filename must have an extension like .s2p' );
end
num_ports = str2double(extension(2:length(extension)-1));
parameters_found = 0;
freq_nr = 1;
tline = fgetl(fid);
while ischar(tline)
tline = strtrim(tline);
if isempty(tline) || (tline(1) == '!')
% comment
if ~isempty(tline)
comment{end+1} = tline;
end
tline = fgetl(fid);
continue
end
if tline(1) == '#'
% found parameters
if parameters_found == 1
warning( 'additional parameter line found; expect garbage!' );
end
parameters_found = 1;
% parse parameters
[~,remain] = strtok(tline); % token is now '#'
[token,remain] = strtok(remain); % token is now the unit
unit = lower(token);
if strcmp(unit,'hz')
freq_mul = 1;
elseif strcmp(unit,'khz')
freq_mul = 1e3;
elseif strcmp(unit,'mhz')
freq_mul = 1e6;
elseif strcmp(unit,'ghz')
freq_mul = 1e9;
else
error( ['wrong unit: "' token '"'] );
end
[token,remain] = strtok(remain); % token is now the parameter type
type = lower(token);
[token,remain] = strtok(remain); % token is now the complex format
format = lower(token);
if strcmp(format,'ri')
format = RI;
elseif strcmp(format,'ma')
format = MA;
elseif strcmp(format,'db')
format = DB;
else
error( ['wrong complex format: "' format '"'] );
end
[token,remain] = strtok(remain); % token must be 'R'
if lower(token) ~= 'r'
error( 'incorrect file format' );
end
token = strtok(remain); % token is reference impedance
ref = str2double(token);
tline = fgetl(fid);
continue
end
% read data
clear 'cell_array';
cell_array = split( tline );
while length(cell_array) < 2*num_ports^2 + 1
temp_tline = fgetl(fid); %FIXME comments? empty lines?
cell_array = [cell_array,split( temp_tline )];
end
% now we have (at least) num_values values in cell_array
temp_freq = str2double(cell_array(1)) * freq_mul;
temp_data = zeros(num_ports);
for source = 1:num_ports
for dest = 1:num_ports
if num_ports ~= 2
pos = ((source-1)*num_ports + dest)*2;
else
% special file format for two-ports
pos = ((source-1)*2 + dest)*2;
end
if format == RI
temp_data(dest,source) = str2double(cell_array(pos)) + 1i*str2double(cell_array(pos+1));
elseif format == MA
temp_data(dest,source) = str2double(cell_array(pos)) * exp(1i*str2double(cell_array(pos+1))/180*pi);
%disp( [tline ' ### freq: ' num2str(temp_freq/1e9) ' S' num2str(source) num2str(dest) ' ' num2str(temp_data(dest,source))] );
%disp( ['pos: ' num2str(pos) ' cell_array: ' char(cell_array(pos))] );
elseif format == DB
temp_data(dest,source) = 10^(str2double(cell_array(pos))/20) * exp(1i*str2double(cell_array(pos+1))/180*pi);
end
end
end
% values are parsed, insert them into the freq and data arrays
freq(freq_nr) = temp_freq;
data(:,:,freq_nr) = temp_data;
freq_nr = freq_nr + 1;
% disp( ['frequency f=' num2str(temp_freq/1e9)] );
tline = fgetl(fid);
end
fclose( fid );
end %read_touchstone()
function cell_array=split( str )
cell_array = cell(0);
[token,remain] = strtok(str);
while ~isempty(token)
cell_array = [cell_array token];
[token,remain] = strtok(remain);
end
end
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