Design of dual-band transmission line with flexible phase shifts and its applications

A novel dual-band transmission line with flexible phase shifts is presented. To realise dual-band operations, the proposed transmission line is constructed by series-connected coupled lines and open-ended stubs. Using this structure, flexible characteristic impedances and electrical lengths can be designed to operate at two frequencies. Moreover, the proposed dual-band transmission line features a wide range of realisable frequency ratios and a flexible structure. For practical applications, a planar dual-band 3 dB branch-line coupler operating at 2/5.2 GHz is designed using the proposed dual-band transmission line. The simulation and measurement results agree very well with the design theory.