ON THE INFORMATION-CONTENT OF THE RADIATED FIELDS IN THE NEAR ZONE OVER BOUNDED DOMAINS

We investigate the problem of determining the number of degrees of fre edom of radiated fields. In particular, this analysis concerns the det ermination of the 'information content' provided by the knowledge of t he field over bounded observation domains located both in the Fresnel zone and in the near zone, when only a priori information about the ge ometrical parameters of the planar source and of the planar observatio n domains is known. First, we analyse the problem with reference to a single bounded rectilinear observation domain located either in the Fr esnel zone or in the near zone. Second, we specify the conditions unde r which the knowledge of the field over a second rectilinear domain ma kes it possible to increase the information content of the data. It ha s been observed that for two domains located in the Fresnel zone the k nowledge of the field over the second domain makes it possible to incr ease significantly the amount of independent information only if the a ngle subtended by such a domain is larger than that subtended by the f irst domain. In the near zone, it has been numerically observed that w hen the field is known over two domains, the number of degrees of free dom roughly agrees with the greatest of those associated to the single domains.