Experimental observation of negative refraction index of wire-pair composite by phase shift of transmission

We designed and fabricated a wire-pair composite sample which has negative refraction index at about 7 GHz. We measured the dependence of the phase shift of transmission on the sample's length along the wave propagating and found abnormal phase shift in designed frequencies. The calculated band diagram along the wave propagation showed that in the vicinity of the designed frequencies the sample has negative group velocity. The experiment and band diagram calculations demonstrated that the designed sample is a negative index material.