% This is a script designed for testing the passivity of N-port
% S-parameters (In Touchstone format). It  the standard passivity criterion
%
% Re{eigenvalues (I - S*S')} > 0     (Eq 1)
%
% The script works in conjunction with the SXPParse routine written by
% Tudor Dima to read N-port Touchstone files into Matlab.
% The script then checks condition (Eq1) for each frequency point and reports if it is violated.
% In order to run the routine, first open your Touchstone S-parameter file
% and make sure to delete all comments after the specifier line (# MHz etc).
% The top of your file should look like following:
%
%   ! ...all comments here,
%   ! on as many lines as you wish...
%    # MHZ S RI R 50.00
%           
%   50.000       0.076584    -0.033951    [...etc...]
%
% In line 47 of this file (PassivityTest.m), enter the file name of your
% Touchstone file (...= SXPParse('FileName.s4p')
% Save and Close the m-file.
% Run PassivityTest.m
%
% This is a little fresh, so please let me know if you encounter any
% problems. My contact info:
%
% Gourgen Oganessyan
% Sr Electrical Engineer
% Molex Inc.,
% Connector Products Division
% 2222 Wellington Court
% Lisle, IL 60532
% phone: (630)-527-4287
% fax:   (630)-512-8620
% E-mail: goganessyan@molex.com
%
%Thanks to Brian O'Malley, Vince Cavanna, Ray Anderson and Tudor Dima for
%original insights.
%
clear;
nonpassive=0;
[data_f, data, noise_f, noise, Zo] = SXPParse('Test.s4p');
[M N] = size(data_f);
[L K] = size(data);
 for n = 1:N
S = data(:, :, n);

	mineigv = min(real(eig(eye(size(S))-S*S')));

	if mineigv < 0 
		sprintf('%s  %0.5g %s %d' , 'Non-Passive at Freq=',data_f(n),' Hz   min(Eigenval)=',mineigv)
		nonpassive=1;
		format short e;
		S

	elseif mineigv==0
		sprintf('%s  %0.5g %s %d' , 'Conditionally Passive at Freq=',data_f(n),' Hz ')
		nonpassive=1;
		format short e;
		S

	end;

if nonpassive ~= 1
sprintf('%s','S-Parameter Matrix is Passive')
end;

end;