Design technique for meta-structure planar directional couplers with arbitrary coupling ratios

The design of directional coupler with arbitrary coupling ratios currently lacks a systematic process. This paper presents a design technique for meta-structure planar directional couplers that can achieve a wide range of arbitrary coupling ratios. Replacing the conventional transmission lines with a composite right/left-handed (CRLH) meta-structure, the proposed technique enables the use of one design parameter to achieve different coupling ratios. To demonstrate the technique, a 90° directional coupler operating at 2.45 GHz has been designed, fabricated and characterized. Simulated and measured results show good agreement.