Design of Novel Miniaturized Fractal-Shaped Branch-Line Couplers

Although miniaturized and fractal-shaped branch- line couplers have been reported by many researchers, their operating bandwidth are narrowed and shifted greatly, thus the application of these techniques were limited. In this paper, we present an exact design technique to obtain optimum compact and fractal-shaped branch-line coupler for a given frequency. As an example, three novel fractal-shaped branch-line couplers operated at 2.4 GHz using Koch fractal shapes of different iteration orders have been designed successfully, and the designed couplers all operate at the designed frequency and achieved a maximal 81.8% size reduction. And furthermore, the operating frequency and its bandwidth is virtually unaltered. The proposed method is verified by the measurement results.