Compact bandpass filter with wide stopband utilizing modified anti-parallel coupled-lines

A novel bandpass filter with a wide stopband is presented. The proposed filter mainly consists of modified anti-parallel coupled-lines and four open circuited stubs, which can generate multiple transmission zeros at the lower and upper stopbands. Therefore, a wide stopband characteristic can be achieved. The central frequency of this proposed filter, which is implemented on Roges 4350 substrate, is at 2.5 GHz with an insertion loss of less than 1.8 dB and a 3 dB bandwidth of 4%. Good suppressing of more than 28 dB is obtained in lower stopband from DC to 2.3 GHz, and the upper stopband has larger than 18 dB rejection in the range of 2.7 GHz to 10 GHz. Measured results show a good agreement with simulated results.