r is invited to refer to these articles to go into the details of the theory. However, the papers do not focus on the physical processes that underlie the results of the theory. In the following, some key points of the theory will be recalled with the aim of clarifying these aspects. As preliminary step, let us consider the field on an observation curve S. The phase of the field in a point depends on two effects. The first one is the value of the current distribution on the source. Note that information is encoded in the current distribution. Consequently, this effect must be "preserved" in the field representation. The second one depends on the delay of propagation and hence on the geometry of the source and on the position of the observation point. Let us focus our attention on the consequences of the delay, whose effect in the harmonic domain is a phase shift. The phase variation of the field on S depends on the geometry of the source and of the observation curve. Since information is not encoded in the shape of the source and of the observation curve, the effect of the geometry can be subtracted from the phase of the field without losing information. There is a further effect of the phase that is relevant in a bandlimited represen- tation of the field. To clarify this effect, let us consider a linear source and a linear observation domain parallel to the linear source. The dimension of the source seen from a point along the observation line decreases when the point moves away from the position in front of the source. Intuitively, the source seen from the position of the observation point becomes "smaller," and its ability to transmit information 2 Information Flows at the DPL Level Fig. 2.6 Relevant for the bandlimited representation of the field; D is the domain containing the electromagnetic sources, bounded by the surface ; S is the observation curve; P(s) is the position of the observation point, wherein S is the curvilinear abscissa along the curve S2; t is the tangent to the curve So in the observation 