Forward and backward waves propagation in an array of split-ring resonators

Simulation studies of resonator split-ring resonators inserted in a rectangular waveguide WR-90 are conducted to determine the nature of wave propagation linked to the electric and magnetic responses of a metamaterial array inserted in a WR-90 waveguide. As expected, magnetic transmission band (around 3.6 GHz) is of backward-wave character. However, to the right of the isolated magnetic-resonance mini-band, there appears a wider transmission band (4-8 GHz) with multiple ripples which are identified as being of forward and backward types alternately. Unlike previous works on SRR-loaded waveguides, in which all the transmission resonances in the second band have been classified as of the forward-type, the occurrence of backward-wave transmission peaks in the second transmission band, as it is demonstrated here, has never been reported.