A compact planar wide-band balun with high isolation based on coupled-line and composite right–left-handed transmission line

A novel compact single-layer wide-band planar balun with high isolation is proposed. It is composed of a broadband coupled-line power divider and an improved phase shifter using coupled-line (CL) and composite right/left-handed transmission line (CRLH TL). The CRLH structure is used to realize the advanced phase response while the coupled-line power divider can be utilized to provide the performance of wide-band matching and isolation. For demonstration, a novel planar microstrip balun operating at ∼2.75 GHz is designed and implemented. The proposed balun has many advantages including compact single-layer structure, excellent return loss, high isolation, and perfect phase response. Finally, good agreements between the simulated and measured results verify this design. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:372–376, 2016