Solved !
As suggested by Doug in
The complete solution is
tall_str = sprintf(['\\fontsize{14}' blanks(1) '\\fontsize{11}']);
h = title({'Frequency vs. Beampattern - GA Array ' ;...
[tall_str 'Plane Wave on Cylinder (Diffraction+Free-Field) - \phi_{in}=90^{\circ}']},...
'FontWeight','bold',...
'FontSize',11,...
'FontName','Palatino Linotype');
The "tall_str" is a dummy string with a bigger size just to allocate more space.
Cheers,
Will