Wideband Bandpass Filter with High Selectivity and Wide Stopband Using Slow Wave Structure

A wideband bandpass filter with high passband selectivity and spurious response suppression is proposed. The filter consists of a pair of open stubs and two cascaded parallel coupled lines (PCL). A novel compact microstrip resonant cell (CMRC) with slow wave characteristic is applied to improve the width of the stopband. The proposed filter has a bandwidth of 4.2-9.2 GHz, and it has two transmission zeros near its passband, resulting in a sharp skirt. The return loss in the passband is better than 13 dB, and wide upper stopband with more than 20 dB attenuation up to more than 18 GHz. Experiment results of the fabricated filter show high consistency with the simulation.