Metamaterial-based wideband rat-race hybrid coupler using slow wave lines

摘要

Based on derived convenient design equations for slow wave transmission lines and metamaterial line, a very compact and wideband rat-race hybrid coupler is proposed using three -900; slow wave lines and one +900; metamaterial line. The closed-form solutions for circuit parameters based on both phase and phase slope matching conditions are derived. At the design frequency of 2 GHz, the size of the proposed coupler is about 2.0 7; 2.0 cm, which is a 85% reduction compared with the conventional one. In addition, the phase balance bandwidths based on ȦA;S21 - ȦA;S31 (0 1; 100;) and ȦA;S24 - ȦA;S34 (180 1; 100;) have been found to be 150 and 125%, which are 1.8 and 3.0 7; improvements compared with those of the conventional one. The measured results are in reasonable agreement with the circuit- and EM-simulated ones.