High Common-Mode Rejection Differential Filter Based on Coupled Lines

In this paper, a differential bandpass filter (BPF) based on enhanced coupling line structure has been suggested in this study. Two out-of-band transmission zeros are added to the differential mode by loading the coupling line at the output terminal, which raises the rectangular coefficient of the filter. Two common mode transmission zeros in the passband are additionally provided by the open/short stub that is already loaded at the output port. To accommodate the demands of various filter performances, the location of the transmission zeros can be modified by altering the values of the coupling lines' and stubs' impedances. Finally, the passband common mode suppression might be as high as 40 dB.