A broadband left-handed (LH) coupled-line backward coupler with arbitrary coupling level

A novel broadband left-handed (LH) coupled-line backward coupler with arbitrary coupling level is presented. This coupler is composed of two LH transmission lines (TL) constituted of series interdigital capacitors and shunt shorted-stub inductors. A quasi-0dB implementation of the coupler is demonstrated by simulation and measurement results, and shown to exhibit a bandwidth of 35% despite the relatively wide lines-gap of 0.3mm. An even/odd modes analysis is presented to explain the working principle of the component. A 3dB-quadrature implementation, with 37% bandwidth, is also demonstrated. Finally, parametric results illustrate the versatility of the LH coupler and its strongly enhanced backward coupling compared with the conventional coupled-line coupler.