  The coherent radiation emitted by an electron bunch provides a diagnostic
signal that can be used to estimate its longitudinal distribution. Commonly
only the amplitude of the intensity spectrum can be measured and the associated
phase must be calculated to obtain the bunch profile. Very recently an
iterative method was proposed to retrieve this phase. However ambiguities
associated with non-uniqueness of the solution are always present in the phase
retrieval procedure. Here we present a method to overcome the ambiguity problem
by first performing multiple independent runs of the phase retrieval procedure
and then second, sorting the good solutions by mean of cross-correlation
analysis. Results obtained with simulated bunches of various shapes and
experimental measured spectra are presented, discussed and compared with the
established Kramers-Kronig method. It is shown that even when the effect of the
ambiguities is strong, as is the case for a double peak in the profile, the
cross-correlation post-processing is able to filter out unwanted solutions. We
show that, unlike the Kramers-Kronig method, the combined approach presented is
able to faithfully reconstruct complicated bunch profiles.
