Backward waves in waveguides containing dielectric

A method is described for determining the conditions which ensure backward-wave propagation in dielectric-loaded inhomogeneous waveguide structures. It is established that backward-wave propagation can be ensured for the hybrid H11-mode in a circular waveguide containing an axial dielectric rod whose relative permittivity exceeds approximately 9.4. The possibility of other inhomogeneous-waveguide modes exhibiting backward-wave properties is also examined.