Broadband transmission below the cutoff frequency of a waveguide loaded with resonant scatterer arrays

A computer-aided method for the design of waveguide structures loaded with the arrays of metamaterial cells is described. Broadside coupled split ring resonators and Omega scatterers are chosen as the resonant metamaterial cells. By optimisation of the resonator geometry, the bandwidth of the transmission range below the cutoff frequency of the waveguide is enlarged compared with the results reported in the literature. The modes propagated below the waveguide cutoff possess a passband of the order of 30-50% and can be of the backward as well as of the forward type. The presented optimisation approach is based on the eigensolver simulations of a metamaterial unit cell. The designed metamaterial arrays are fabricated and measured. The experimental results are compared with the simulations validating the proposed design approach