Design of Miniaturized Branch-Line Coupler Based on Novel Composite Right/Left-Handed Transmission Line Structure

A novel composite right/left-handed transmission line which includes interdigtial structure and double-spiral-defected resonant cell is proposed. The interdigital structure provides the impression of the negative-μ, and the double-spiral-defected resonant cell provides the impression of the negative-ε, so the proposed structure is composite right/left-handed structure. Then a miniaturized branch-line coupler using the proposed transmission line is designed. The designed coupler works at the left-handed bandwidth of the proposed composite right/left-handed transmission line, so it has a size reduction of 66% compared to the traditional branch-line coupler.