This paper describes and implements an approach to the problem of determining the antenna aperture field distribution from only amplitude measurements of far-field pattern. We apply the quadratic approach for recovering the complex aperture field function from measurements of the pattern at different feed locations. The phase-retrieval procedure consists of minimizing a nonquadratic functional and a reliable iterative algorithm converging on the solution, regardless of the starting point, is thus obtained. This approach to phase-retrieval problem has been compared with well-known Misell algorithm. Also, the effectiveness of both algorithms has been verified by results of conventional with-phase holography with using the experimental data obtained on 70-meter mirror antenna.