If you pass struct() a cell array of data for a field, then it creates a struct array with the same size() as the size() of the cell array.
%setup to create cell arrays of data
N = 5;
spectras = arrayfun(@(n) randn(10,1), 1:N, 'uniform', 0);
freqs = arrayfun(@(n) sort(randi([0 999], 10, 1)), 1:N, 'uniform', 0);
%now that we have a cell arrays of data we can convert to struct array:
datastruct = struct('Spectra', spectras, 'freqs', freqs);
%verify that the struct is what we expect
whos datastruct
datastruct
datastruct(1).Spectra
spectras{1}
