  Phase retrieval problems in antenna measurements arise when a reference phase
cannot be provided to all measurement locations. Phase retrieval algorithms
require sufficiently many independent measurement samples of the radiated
fields to be successful. Larger amounts of independent data may improve the
reconstruction of the phase information from magnitude-only measurements. We
show how the knowledge of relative phases among the spectral components of a
modulated signal at the individual measurement locations may be employed to
reconstruct the relative phases between different measurement locations at all
frequencies. Projection matrices map the estimated phases onto the space of
fields possibly generated by equivalent antenna under test (AUT) sources at all
frequencies. In this way, the phase of the reconstructed solution is not only
restricted by the measurement samples at one frequency, but by the samples at
allfrequencies simultaneously. The proposed method can increase the amount of
independent phase information even if all probes are located in the far field
of the AUT.
