A Distinctive Resonance: Multiband Bandpass Filter Design Techniques Using Multimode Resonators

It has been over a decade since stepped-impedance resonators (SIRs) first carved a niche in applications for multiband bandpass filter (BPF) design. This was the first class of resonator within the broad category of multimode resonator (MMR). Multiband filter design has seen subsequent development in other forms of MMRs, including stub-loaded resonators (SLRs), ring-loaded resonators, and the newly introduced fractal-shape resonators. In this article, we describe the different types of MMRs, along with their variations, that have led to emerging innovative design techniques for multiband BPFs.