GNU Octave script to test the de-embedding component

test_de_embedding.m

1;

% directory where qucsator and qucsconv are located
global qucsdir = "~/usr/local/bin/";

global freq = 1e9;

function val = isodd(n)
  val = (mod(n,2) == 1);
endfunction

function val = iseven(n)
  val = (mod(n,2) == 0);
endfunction

function Sr = randomS(n, spfname)
  % generate random S-parameters matrix
  global freq;
  Sr = randn(n) + j*randn(n);
  fsid = fopen(spfname, 'w');
  % write header
  fprintf(fsid, '# GHz S RI R 50\n');
  % write frequency
  fprintf(fsid, '%f\t', freq/1e9);
  for i = 1:n
    nv = 0;
    for j = 1:n
      fprintf(fsid, '%f %f\t', real(Sr(i,j)), imag(Sr(i,j)));
      nv = nv + 1;
      if (nv == 4)
        fprintf(fsid, '\n');
        nv = 0;
      endif
    endfor
    fprintf(fsid, '\n');
  endfor
  fclose(fsid);
endfunction

function maxdelta = test_de_embedding(nPorts)
  global freq;
  global qucsdir;
  % generate random S-parameters input
  spfname = sprintf('test.s%ip', nPorts);
  randomS(nPorts, spfname);

  % generate netlist
  fid = fopen('testnetlist.txt', 'w');

  % left-side sources
  for i = 1:2:nPorts
    fprintf(fid, 'Pac:P%i i%i gnd Num="%i" Z="50 Ohm" P="0 dBm" f="1 GHz" Temp="26.85"\n', i, i, i);
  endfor

  % right-side sources
  for i = 2:2:nPorts
    fprintf(fid, 'Pac:P%i o%i gnd Num="%i" Z="50 Ohm" P="0 dBm" f="1 GHz" Temp="26.85"\n', i, i, i);
  endfor

  % de-embedding component
  fprintf(fid, 'SPDfile:XD1');
  for i = 1:nPorts
    if isodd(i) % odd
      fprintf(fid, ' i%i', i);
    else % even
      fprintf(fid, ' m%i', i);
    endif
  endfor
  fprintf(fid, ' gnd File="{%s}" Data="rectangular" Interpolator="linear" duringDC="open"\n', spfname);

  % embedding component
  fprintf(fid, 'SPfile:X1');
  for i = 1:nPorts
    if (mod(i,2) == 1) % odd
      fprintf(fid, ' m%i', i+1);
    else % even
      fprintf(fid, ' o%i', i);
    endif
  endfor
  fprintf(fid, ' gnd File="{%s}" Data="rectangular" Interpolator="linear" duringDC="open"\n', spfname);

  % simulation component
  fprintf(fid, '.SP:SP1 Type="list" Values="[1 GHz; 2 GHz]" Noise="no" NoiseIP="1" NoiseOP="2" saveCVs="no" saveAll="no"\n');
  % apparently qucsconv does not work well with just a single frequency
  %fprintf(fid, '.SP:SP1 Type="const" Values="[1 GHz]" Noise="no" NoiseIP="1" NoiseOP="2" saveCVs="no" saveAll="no"\n');

  % done with test netlist file
  fclose(fid);

  % run qucsator
  [status, output] = system ([qucsdir "qucsator -i testnetlist.txt -o testnetlist.dat"]);
  % convert result to .mat format
  [status, output] = system ([qucsdir "qucsconv -if qucsdata -of matlab -i testnetlist.dat -o testnetlist.mat"]);
  % load results
  load("testnetlist.mat");

  % compute error
  %   S(n+1,n) and S(n,n+1) should be 1, all the others should be 0
  maxdelta = 0;
  % check results
  for i = 1:nPorts
    for j = 1:nPorts
      val = eval(sprintf('S_%i_%i(1)', i, j));
      %printf('S_%i_%i(1)=%f\n', i, j, val);
      if ((isodd(i) && (j == (i+1))) || (iseven(i) && (i == (j+1))))
        % S(n+1,n) and S(n,n+1) should be 1
        %printf('(1) S_%i_%i(1)=%f\n', i, j, val);
        delta = val - 1;
      else
        % others Snm should be 0
        %printf('(0) S_%i_%i(1)=%f\n', i, j, val);
        delta = val;
      endif
      if (abs(delta) > abs(maxdelta))
        maxdelta = delta;
      endif
    endfor
  endfor

  %printf('max delta = %e\n', maxdelta);
endfunction

% test de-embedding for a different number of ports
for p=2:2:40
  printf('[%i ports]\terror = %e\n', p, test_de_embedding(p));
endfor