I don't know what you mean by a "structure" within Excel. But to output a string to Excel it has to be inside a MATLAB cell, not just a bare string or else each character of the string will go into a new cell in Excel.
e.g. (untested)
myArray = rand(20,2);
cellArray = {'column 1', 'Column 2'} % First row is column headers.
% The following rows are the numbers.
for row = 1 : size(myArray, 1)
cellArray{row+1, 1} = myArray(row,1);
cellArray{row+1, 2} = myArray(row,2);
end
xlswrite(filename, cellArray , 'A1');
