A super-compact 0dB/3dB forward coupler composed of multi-layered CRLH transmission lines with double left-handed shunt-inductors

This paper proposes a super-compact 0dB/3dB forward coupler composed of symmetrically installed two multi-layered (ML) composite right-/left-handed (CRLH) transmission lines (TLs). Each CRLH TL has double left-handed shunt-inductors to produce a large phase difference between even and odd modes, leading to significant size-reduction of forward couplers. Utilizing an inherent superior feature of ML CRLH TLs, that is, a large electrical length can be provided by an extremely short physical length, a 0dB/3dB forward coupler is designed at 3.0 GHz and 4.0 GHz respectively with very short coupling length of 1.57 mm. The dimensions of the coupler is 5.0 × 7.0 × 2.85 mm³ with a dielectric material of ε_r=2.59.