Subwavelength guiding of electromagnetic energy in waveguide filled with anisotropic mu-negative metamaterial

A counter-intuitive phenomenon of propagation below cut-off in a waveguide filled with an anisotropic mu-negative metamaterial is investigated analytically, numerically, and experimentally. It is shown that the equivalent plane waves that make up the waveguide mode are inhomogeneous, and this fact is responsible for subwavelength guiding of electromagnetic energy. It was also found that the microscopic ('in-cell') magnetic field distribution in a waveguide filled with split-ring resonators may significantly differ from the distribution in the homogenized waveguide. However, spatial averaging of a numerically calculated magnetic field across the unit cell yielded a distribution that was very similar to the distribution in the continuous mu-negative material. Experimental waveguides filled with split-ring resonators were prototyped in the 8-GHz band, and measurement results were found to be in good agreement with all analytical and numerical predictions. This shows that it is indeed possible to interpret the waveguide filled with split-ring resonators as a homogenized waveguide filled with a continuous anisotropic mu-negative metamaterial.