Calculations and measurements of wire and/or split-ring negative index media

Broadband calculations (70 MHz–20 GHz) and measurements (2–15 GHz) were performed on planar stacks of two-dimensional double-split rings arrays interspersed with arrays of thin wires. Recent work on similar composite structures infers a negative index of refraction $\mathrm{}(n<\mathrm{}0\mathrm{})\mathrm{}$ over a narrow frequency range. We have performed finite-difference time-domain (FDTD) calculations on various combinations of ring geometries, wire arrays, and stack spacings. Excellent agreement was obtained between FDTD simulations and our measured transmission spectra. Examining the FDTD time progression of fields we find regions of both negative and positive indices as well as an inverse Doppler effect.