Waveguide Components Based on Multiple-Mode Resonators: Advances in Microwave Multiple-Mode Waveguide Components, Including Multiplexers, Three-State Diplexers, Crossovers, and Balanced/Unbalanced Elements

Waveguide components have been widely explored for several decades, due to their inherent merits of low insertion losses, high quality (Q) factors, and a significant power-handling capacity. Historically, cavity-based narrowband filters and multiplexers have been explored and designed for base stations and satellite applications. Compared with using single-mode resonators (SMRs), the implementation of multiple-mode resonators (MMRs) in waveguide structures is a promising solution to dramatically reduce the circuit volume and improve the frequency selectivity. Taking advantage of MMR techniques, various innovative waveguide structures have been proposed for a wide range of application scenarios. This article presents an overview of advances in microwave multiple-mode waveguide components, including narrow-, wide-, and multiband filters; multiplexers; three-state diplexers; crossovers; and balanced/unbalanced elements. Representative examples and their results are comprehensively discussed and summarized.