Global convergence of phase retrieval by quadratic approach

The reliability of two different implementations of a quadratic phase retrieval approach to the problem of determining the far field of a radiating system from only square amplitude information on the near field zone is studied. The first implementation exploits square amplitude data over two scanning surfaces. The second one exploits the square amplitude of the voltages received by two different probes moving over a single scanning surface. It is pointed out how the diversity between the two scanning surface data or the two probes gives rise to "cancellation effects" which help in avoiding the local minima problem. Numerical examples are shown to discuss the global convergence properties of the two algorithms.