Extension of Bandstop Filter Topology With Inter-Resonator Coupling Structures to Higher-Order Filters

This letter presents a rigorous extension of the concept for the bandstop filter (BSF) with inter-resonator couplings to a higher order filter. We show that a BSF topology with inter-resonator couplings can exhibit the frequency response that a conventional BSF topology without inter-resonator couplings generates. Equivalence between the coupling matrices of the two topologies are shown. As an example, this letter shows that fourth-order BSFs with and without inter-resonator couplings can exhibit identical frequency responses.