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We investigate the problem of determining the number of degrees of freedom of radiated fields. In particular, this analysis concerns the determination of the 'information content' provided by the knowledge of the field over bounded observation domains located both in the Fresnel zone and in the near zone, when only a priori information about the geometrical parameters of the planar source and of the planar observation domains is known.First, we analyse the problem with reference to a single bounded rectilinear observation domain located either in the Fresnel zone or in the near zone.Second, we specify the conditions under which the knowledge of the field over a second rectilinear domain makes it possible to increase the information content of the data. It has been observed that for two domains located in the Fresnel zone the knowledge of the field over the second domain makes it possible to increase significantly the amount of independent information only if the angle subtended by such a domain is larger than that subtended by the first domain.In the near zone, it has been numerically observed that when the field is known over two domains, the number of degrees of freedom roughly agrees with the greatest of those associated to the single domains.

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