Analysis of the Metal Plate Coupled Resonator With Its Compact In-Line Filter Design Applications

This article introduces and analyzes the modified metal plate coupled resonator (MPCR), which can be designed to exhibit distinctive nondegenerate dual-mode characteristics, i.e., having different resonating frequencies and presenting quasi-orthogonal features (e.g., no coupling). By employing different feeding methods, the MPCR can function as either a single-mode or dual-mode resonator, both of which are suited for the design of in-line filters with controllable transmission zeros (TZs). For the single-mode operation, new mixed-coupling-based in-line filters can be designed to yield noteworthy advancements compared to prior research, as these filters achieve arbitrary placement of TZs without necessitating any additional structures. For the dual-mode operation, more compact in-line filters based on transverse coupling topology for achieving quasi-elliptic function response can be designed. In general, all filters developed in this work provide the advantages of adjustable TZs and simple physical configurations. For the rapid prototyping and the experimental demonstration, certain ${C}$ -band filters were designed and manufactured using 3-D metal printing technology. Meanwhile, for the first time, the necessity of introducing post-magnetic tuning is validated and then applied to the mixed-coupled filters. As a result, all testing results showed consistency with the simulated ones.