Bi-directional coupler based on composite right/left-handed and artificial transmission lines

An artificial transmission line as a right-handed transmission line is edge-coupled with a CRLH-TL to realize coupling between the left-handed and the right-handed transmission line. The directional coupler is a compact planar structure with characteristics of backward and tight coupling. Experimental results show that a 10 dB coupling coefficient is achieved from 1.3 GHz to 1.8 GHz. The corresponding fractional bandwidth is about 32%, and the isolation is greater than 25 dB. Simulation results agree well with measured results. The directional coupler covers a wider coefficient range than the conventional one.