Miniaturized dual wideband bandpass filter with coupled ladder structure

A dual wideband filter utilizing a coupled ladder structure has been proposed in this paper. With the ladder structure which exhibits a slow-wave property, the size of the filter could be reduced. In addition, two additional transmission zeros were obtained due to the coupled ladder structure. Good frequency selectivity was achieved. The proposed circuit has been fabricated on a RO4003C substrate and could be operated at 1.82 GHz and 4.0 GHz. The measured fractional bandwidth are around 70.8% and 20.4% for return loss larger than 10 dB. The circuit occupied a small area which is around 0.08 λ × 0.314 λ at 1.86 GHz. Simulated and measured data are displayed and validate the operation of the filter.