Metamaterial microstrip backward couplers for fully planar fabrication techniques

A novel approach to obtain metamaterials in microwave planar circuit technology compatible with fully planar fabrication techniques is described. Microstrip lines with dual split ring resonators (SRRs) etched on the ground plane along with series capacitive gaps in the upper conductor strip are considered. The occurrence of left-handed (metamaterial) wave propagation in such media is demonstrated. Then, a metamaterial coupler made of a regular microstrip line and a left-handed microstrip line is examined. Co-directional traveling waves result in contra-directional Poynting vectors on the lines thus leading to power being coupled backwards. Backward coupling much tighter than that achievable with traditional (also backward) λ/4-couplers of the same inter-line distance is reported.