  In this paper, we address the problem of computing the dimension of data
space in phase retrieval problem. Starting from the quadratic formulation of
the phase retrieval,the analysis is performed in two steps. First, we exploit
the lifting technique to obtain a linear representation of the data. Later, we
evaluate the dimension of data space by computing analytically the number of
relevant singular values of the linear operator that represents the data. The
study is done with reference to a 2D scalar geometry consisting of an electric
current strip whose square amplitude of the electric radiated field is observed
on a twodimensional extended domain in Fresnel zone.
