A planar metamaterial co-directional coupler that couples power backwards

A metamaterial coupler made of a regular microstrip line and a negative-refractive-index (NRI) line is examined. Peculiar coupling effects are observed in which co-directional traveling waves result in contra-directional Poynting vectors on the lines thus leading to power being coupled backwards. This coupler demonstrates better performance in terms of coupled power and port isolation, but at a slightly reduced bandwidth, when compared to a commensurate regular microstrip coupled-line coupler.