Design of asymmetric dual bandstop filter using coupling matrix approach

This paper demonstrate an approach to acquire coupling matrices for direct coupled dual bandstop filter with asymmetric responses. There are different approaches to implement dualband filters among which frequency transformation techniques is advantageous than other methods in terms of complexity to find the transfer functions. So it is applied here for finding the locations of poles and zeros of a direct coupled dual bandstop filter. By properly combining two single-band filtering functions, the dualband filtering function of different bandwidths are generated. For easy tuning, filter has been synthesized in cul-de-sac topology which eliminates the need for diagonal couplings. Finally 8-pole asymmetric dual bandstop filters has been synthesized.