Fractal-shaped UWB bandpass filter based on composite right/left handed transmission line

An ultra-wideband (UWB) bandpass filter is presented, with excellent passband performance and improved out-of-band sharpened rejection. It is constructed with Koch island-shaped stepped impedance lines and a composite right/left handed transmission line synthesised by etching a Koch fractal-shaped ring slot in the ground plane and a series capacitive gap in the conductor strip. The equivalent circuit model of the proposed structure is presented and the electrical parameters are also extracted. The UWB filter is designed and implemented to experimentally demonstrate the enhanced performance. Numerical and measurement results show that good performance, such as low return and insertion loss over the UWB passband and sharpened rejection skirts outside the UWB passband, is achieved. Furthermore, the structure is compact in size.