Investigation of Dispersion Control in Planar Rectangular Tape Helix Slow Wave Structure with Double-Positive Metamaterial Assistance

This paper presents, a modified dispersion characteristics of rectangular tape helix (RTH) slow wave structure (SWS) by using double-positive (DPS) metamaterial (MTM) loading for wideband applications. The limited operation bandwidth associated with the conventional RTH restricts the applications for wideband frequency range. Therefore, the DPS-MTM comprising an array of sub-wavelength square split-ring resonators (SSRR) is thoroughly investigated. A full wave simulation is performed to extract the effective material parameters and DPS-MTM is systematically loaded on the opposite faces of dielectric support rods of the RTH. The post integration of DPS-MTM offers a flat-to-slightly negative dispersion characteristics in forward-wave mode with simulated normalized phase velocity (averaged) of 5% over the entire bandwidth (1–10 GHz). The flat band range of the phase velocity curve exceeds 70% in the desired region (±5% margin), by varying number of Unit Cells (UCs). Hence, the proposed structure attains the intended flat dispersion along with high interaction impedance of SWS rendering it suitable for the wideband operation of traveling wave tube (TWT) amplifier.