Study of excitation of nonreciprocal complex and backward modes in shielded ferrite-loaded printed lines

This work studies the excitability of complex and backward modes in lossles s nonreciprocal shielded printed lines. The surface current density produce d 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, set ting up the part of the modal spectrum that does not carry a net average ac tive power flux and playing the same role as evanescent modes have in recip rocal structures. This purely reactive nature is verified by means of the c omputation of the complex power flux carried by these modes. In addition, b ackward modes with group velocity directed outward from the source are also excited by the source. These modes appear as a continuation of nonreciproc al complex modes after their attenuation constant goes to zero.