Composite right-/left-handed coplanar waveguide ferrite forward coupled-line coupler

In this study, the authors present a novel compact non-reciprocal ferrite forward composite right-/left-handed (CRLH) coupled-line coupler (CLC). The proposed forward coupler is realised in coplanar waveguide configuration using series air gap capacitors and shunt planar segment inductors. A theoretical coupled mode analysis of a general non-ferrite CRLH forward CLC has been proposed. The mode analysis is then extended to ferrite CRLH forward CLC. The ferrite coupler´s performance has been further analysed numerically and verified experimentally. Both numerical and experimental results have shown that the coupler demonstrates non-reciprocal operation for both forward coupling and through propagations. The coupler can achieve ~10 dB forward coupling and through levels with non-reciprocity isolation up to 30 dB. Moreover, the coupler has high backward coupling isolation better than 20 dB and very compact size with coupling length = 0.08 λ₀ or (0.2 λ_g) at 8 GHz which is significantly smaller compared with any forward coupler reported to date in the similar operating frequency bands. Although, a conventional ferrite forward CLC can be non-reciprocal, it has long length, resulting in very high losses. This is not the case for the proposed CRLH coupler. Hence, the novelty and advantage of the coupler are its combined properties in compactness and non-reciprocity. Furthermore, the coupler requires very low external DC magnetic bias because of its much lower demagnetisation compared with the microstrip configuration.