Synthesis of Nonuniform TL Resonators for Bandpass Filters with Single Passband

This article proposes an approach that makes it possible to provide a single bandwidth in bandpass filter (BPF) based on transmission lines (TL) segments. All another (parasitic) bandwidths except for the main are suppressed. This BPF uses two types of resonators, which are interconnected by TL segments of half-wave length. Proposed resonators are included in the BPF as parallel stubs. Some resonators are nonuniform TL resonators with a shorted end, while others are uniform TL resonators with an open end. The effect of suppressing all parasitic bandwidths is achieved by a special mutual placement of resonant and antiresonant frequencies of resonators of two types. The traditional design, which uses couplings between resonators, is not applicable to the considered filters. Therefore, parameters of a single-band filter, which provide the required bandwidth, are determined numerically. In this way, dependences that allow calculating the filter parameters are constructed.