Coupled-line directional coupler based on Composite Right / Left-Handed coplanar waveguides

A broadside coupled (BSC) coupled-line directional coupler based on Composite Right/Left-Handed (CRLH) Coplanar Waveguide (CPW) is proposed. The CRLH CPW on both sides of the substrate comprises of series gap capacitor, broadside-coupled capacitor, and shunt meandering short-circuited stub inductor symmetrically. The new CRLH CPW coupler exhibits a quasi-0-dB coupling over a very wide bandwidth of 89.4% from 6.45 ~ 13.6 GHz centered at 8 GHz. It is also very compact and symmetrical compared with the conventional designs. An equivalent circuit model including series inductance, capacitance and shunt inductance and capacitance tank also has been established. Good agreement between the full-wave simulation and equivalent circuit model has been achieved and verified the effectiveness of the proposed circuit model.