Super-compact multi-layered CRLH couplers designed in left-handed phase-advanced region

In this paper, two types of super-compact couplers, a branch line coupler and a rat-race coupler, are newly designed by replacing their -90° or -270° right-handed transmission lines (TLs) with +90° or +270° multi-layered (ML) composite right/left-handed (CRLH) TLs. Since the recent ML CRLH TLs have a broadband left-handed (LH) response with a well-balanced CRLH condition, these couplers also work in a LH phase-advance region, leading to significant size reduction from their original size. The overall dimension of the branch line coupler is 7.5 × 7.5 × 1.8 mm³ @2.3 GHz and that of the rat-race circuit is 4.0 × 8.0 × 2.9 mm³ @3.0 GHz, respectively.