Theoretical and experimental study of the backward-wave radiation using resonant-type metamaterial transmission lines

Abstract

We investigate theoretically and experimentally the backward radiation of a type of negative-refractive-index (NRI) resonant-type metamaterial transmission lines (TL). The NRI TL goes beyond the bulk metamtaterials made of original split-ring resonator/wire and the NRI TLs using inter-digital capacitors and shorted stub inductors. The operation mechanism is investigated in depth behind a general composite right/left handed concept based on a TL theory and is interpreted from the perspective of field distributions, showing that the antiparallel phase and group velocities give rise to the full-space beam scanning peppery from backward, through broadside and finally to forward as frequency increases. In addition, we discuss the possible realizations by using complementary split ring resonators and other electrically smaller fractal-shaped resonators with different configurations. The fractal strategy certainly fulfills the challenging necessity of drastically increasing left handed capacitances and inductances in the homogenization process. In all cases, the resultant radiation is analogous to the reversed Cherenkov radiation. Moreover, the comprehensive theory established for a generic type of TL metamaterial paves the way for a round of antenna design, which is of a reference value.