Study of Excitation of Nonreciprocal Complex and Backward Modes in Shielded Ferrite-Loaded Printed Lines

Abstract

This work studies the excitability of complex and backward modes in lossless nonreciprocal shielded printed lines. The surface current density produced by a delta-gap voltage source on the strip conductor of a ferrite loaded boxed microstrip is computed and then analyzed to obtain the excited modes that constitute the modal spectrum of the current density. With this method, complex modes are found to be excited individually in this structure, setting up the part of the modal spectrum that does not carry a net average active power flux and playing the same role as evanescent modes have in reciprocal structures. This purely reactive nature is verified by means of the computation of the complex power flux carried by these modes. In addition, backward modes with group velocity directed outward from the source are also excited by the source. These modes appear as a continuation of nonreciprocal complex modes after their attenuation constant goes to zero.