Nonreciprocal Field Displacement and Backward Waves in Azimuthally-Magnetised Semiconductor-Filled Coaxial Waveguide

The TM01, mode in a coaxial waveguide filled with a semiconductor magnetised with a uniform azimuthal static field has been rigorously analysed using confluent hypergeometric functions. Both branches of the ¿/ß diagram exhibit nonreciprocal propagation. This is shown for the first time to be due to nonreciprocal field displacement which, in turn, is due to the radial non-uniformity of the r.f. electric field. Power density distributions are presented for a specific InSb structure, and it is shown that negative power density can occur in certain annular regions of the coaxial cross-section. This leads to a physical explanation of backward-wave solutions which appear in specific parts of the ¿/ß diagram for one direction of magnetisation. The results may have implications for other non-uniform field structures, e.g. planar components.