A compact microstrip crossover using NRI-TL metamaterial lines

A practical implementation of a miniaturized crossover is presented using negative-refractive-index transmission-line (NRI-TL) metamaterial lines. NRI-TL metamaterial theory has demonstrated that by loading a conventional transmission line with lumped LC elements, a large phase shift per-unit-length can be achieved. Employing this technique, the conventional microstrip transmission lines in a three-section branch-line coupler crossover are replaced with 90° NRI-TL lines, and thus a compact NRI-TL crossover with an area 47 times smaller than the area of its conventional counterpart is demonstrated. Measured results demonstrate that the proposed NRI-TL metamaterial crossover exhibits a −10 dB |S11| bandwidth of 33% and a |3 dB| |S31| bandwidth of 26% around 1 GHz.