On the complex nature of higher order modes in lossless nonreciprocal transversely magnetized waveguides

Propagation of nonreciprocal modes in transversely magnetized lossless nonreciprocal waveguides is analyzed. It is shown that purely evanescent modes cannot exist if the wave propagation is nonreciprocal. As a consequence of this, all the modes which do not support a net average power flux must be complex. These modes are called pseudo-evanescent complex modes. The meaning of the cutoff frequency concept of such pseudo-evanescent complex modes is also discussed.>