Investigation into a metamaterial supported helix slow-wave structure

A helix supported by a double-negative metamaterial in a metal envelope was analyzed in the sheath-helix model to explore its potential as the slow-wave structure of high efficiency backward-wave devices. The transmission line equivalent distributed line parameters of the structure were interpreted for the dispersion relation of the structure. The ratio of the envelope-to-helix radii was found to control the dispersion characteristics and hence the frequency range of backward wave interaction, a critical value of the ratio of radii corresponding to the existence of a non-propagating, leaky wave.