Dispersion control of helical slow-wave structure by double-negative metamaterial loading

Abstract

A helix supported by a double-negative metamaterial (DNG-MMT) surrounding it, in a metal envelope, was field-analyzed to show that the shape of the dispersion is more sensitive to the value of the relative permittivity of the metamaterial (MMT) than that of its relative permeability. The field analysis was validated against equivalent circuit analysis as well as against simulation. The values of the MMT support parameters were adjusted to obtain nearly flat, rather slightly negative, dispersion characteristics together with a high value of the interaction impedance of the structure as required for a wideband traveling-wave amplifier. Unlike in a conventional traveling-wave tube, the flow of power of RF wave supported by DNG-MMT loaded helix was found to be in a direction opposite to that of the RF phase velocity of the wave supported by the structure resulting in a negative value of the interaction impedance of the structure suggesting that the device using a helix with double-negative MMT supports would operate in the backward-wave mode analogously to a reversed Cherenkov amplifier.

Keywords:

• Double-negative metamaterial
• backward-wave amplifier
• interaction impedance
• sheath helix model

Acknowledgment

The authors sincerely thank Dr SK Ghosh, Dr A Bera and N Purushothaman of CSIR-CEERI, Pilani, India for fruitful discussions.