Compact Rat-Race Hybrid Coupler Implemented Through Artificial Left Handed and Right Handed Lines

In this work, a rat-race hybrid coupler based on left handed (LH) and right handed (RH) lines implemented by means of complementary split rings resonators (CSRRs) is designed and fabricated for the first time. The three 90deg transmission lines of the conventional device are replaced by RH artificial lines consisting on the combination of a CSRR and a shunt connected stub; the 270deg line is substituted by a -90deg LH line, where a CSRR is combined with a series gap. The resulting device is three times smaller than the conventional rat-race, the artificial lines do not include lumped elements, and device performance is good. Since dispersion in the artificial lines forming the device can be tailored, excellent characteristics in terms of phase-balance are obtained. These artificial lines can be applied to other microwave components. Size reduction and performance improvement are the key issues.