A compact coupled-line forward coupler using composite right-/left-handed transmission lines

A novel coupled-line forward coupler using composite right-/left-handed transmission lines (CRLH TLs) is presented. Enhanced forward coupling is achieved with the coupled CRLH TLs which have a considerable difference of effective phase constants in the even/odd modes. A circuit model and a microstrip implementation of the proposed CRLH forward coupler are described. The 10-dB forward coupler is simulated and experimentally demonstrated in the S-band. Its coupled-line length is significantly reduced to half of the conventional right-handed forward coupler with the same coupling. The experimental results correspond with the simulated results.