The authors introduce an element that allows them to analyze two-dimensional diffraction problems in a circuital way. The circuital analysis of electromagnetic problems, together to the segmentation technique, allows one to analyse large problems, in an electromagnetic sense, with the additional advantage that a change in a material is readily computed. This makes this method very appropriate for its use in CAD tools. The problem of a sector considered as a quadripole is only presented, in such a way that we can set the advantages of the method. It is easy to see how we can enlarge the problem to a four-port net. Finally, we must say that only the TM case is presented.