Discussion on coupling mechanism of asymmetric CRLH/RH TL coupler

A quasi 0-dB coupler composed of a composite right-/left-handed transmission line (CRLH TL) and a conventional right-handed transmission line (RH TL) is presented. This coupler is shown to exhibit broad bandwidth and tight coupling char acteristics. The circuit model and S-parameter results are also demonstrated. Another coupler with properly chosen loaded lumped-elements LL and CL in the CRLH TL is proposed to gain further understanding of the coupling mechanism. By adjusting the spacing between the CRLH TL and RH TL from 8 mm to 0.2 mm, it can be shown that backward coupling occurs in the left-handed region.