Nonuniform TL Resonators Synthesis for Filters with Finite Number of Passbands

In this paper, we propose a new approach that allows implementing a finite number of passbands (2, 3, etc.) in transmission line bandpass filters (BPF), all other passbands being suppressed. In this approach, two types of resonators are used in BPFs, which are coupled by quarter-wave uniform segments. These resonators are included in the BPF circuit as stubs. One part of the resonators is uniform transmission line segments with open-circuited end. The other part of the resonators is nonuniform transmission line (TL) segments with short-circuited end. The effect of suppressing all passbands, with the exception of some, is achieved by special placement of resonant and antiresonant frequencies of nonuniform resonators. The task is to synthesize nonuniform transmission line resonators by input impedance with a special arrangement of zeros and poles.