Miniaturized dual-band ring coupler with arbitrary power divisions using composite right/left-handed transmission lines

In this paper, a ring coupler that allows for arbitrary power divisions in dual bands by use of the composite right/left-handed (CRLH) transmission structures is proposed. The presented 180° coupler is composed of four 50-Ω CRLH branch lines and its power division ratio at either frequency is a function of electrical lengths of the constituent transmission lines. Thus, large power divisions can be simply carried out by properly designing electrical lengths of the integral lines instead of applying high-impedance transmission lines, which is impractical as the division ratios increase. For demonstration purpose, two examples were experimentally developed to realize the division ratios of 9/3 dB and 6/6 dB at 0.9/1.8 GHz. Compared to the compact 0.9-GHz coupler based on similar design concept in the literature, the fabricated couplers show further size reduction up to 21%.