Stopband Expansion of Combline BPF

The design method of combline bandpass filter (BPF) with quarter-wave (λ/4) resonators is proposed in this report. The method allows us to provide a wide stopband while maintaining a uniform ripple level of a given value. The scientific basis of this method lies in the features of the trajectories of the antiresonance frequencies of combline resonators when changing the connection coordinates to them. The method is illustrated by the example of five-order BPF with inductive couplings. The simulation of frequency characteristics is presented.