Extraction of modal parameters from state-space model

I have transformed my experiemtnal input - output responses data into a data object

Sample.Data=iddata(y,x,Ts);

where sampling frequency is 2048 Hz. I have then constructed state-space matrices of my system using an estimate 20th model order

ss.System = n4sid(Sample.Data,20,'Ts',Sample.Data.Ts);

How / what is the most efficient method of extracting the modal parameters frequencies (Hz), modal damping ratios (%) and mode shapes from the state-space matrices in matlab? To find the natural frequencies and damping ratios I have written the following however I seem to have issues with my modeshapes:

%Obtain the Eigenvalues and Eigenvectors

[V,D] = eig(ss.System.a);

%Ensure eigen values and vectors are sorted correctly

[d,ind] = sort(diag(D));EigenFreq= D(ind,ind);EigVector=V(:,ind);

% Calculate the frequencies and damping ratios from the eigenvalues of A

for jj=1:1:length(EigenFreq)

wk(jj)=abs(log(EigenFreq(jj,jj)))/Dt;

fk(jj)=wk(jj)/(2*pi);

Dk(jj)=-real(log(EigenFreq(jj,jj)))/(wk(jj)*Dt);

end

%Calculate the mode shapes from eigenvectors and C matrix

UnorderedEig(1:length(EigenFreq))=(ss.System.c*V)';

Phi=UnorderedEig(:,ind);

The mode shapes I obatin are complex numbers and I am unsure of how to convert them to real modeshapes.

Any help on the subject would be greatly appreciated. Thank you in advance