A branch-line coupler with two arbitrary operating frequencies using left-handed transmission lines

A branch-line coupler (BLC) working at two arbitrary frequencies using left-handed (LH) transmission lines (TLs) is presented. The analysis of the structure is based on the even-odd mode analysis of the conventional BLC as well as a recently developed model for the LH-TL. We demonstrate that the two operating frequencies can be obtained by tuning the phase slope of the different line sections. A prototype is demonstrated by both simulation and measurement results. The operating frequencies of the two pass-bands are 920 MHz and 1740 MHz, respectively.