Synthesis of direct coupled pentaband bandstop filters using frequency transformation

This paper demonstrate an approach to acquire coupling matrices for direct coupled Pentaband bandstop filter with asymmetric responses. There are different approaches to implement pentaband 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 pentaband bandstop filter. By properly combining several single-band filtering functions, the pentaband filtering function are generated. For easy tuning, filter has been synthesized in cul-de-sac topology which eliminates the need for diagonal couplings. Finally 20-pole symmetric pentaband bandstop filters has been synthesized.