Design of mmWave Bandpass Filter Using Metal-Integrated Multimode Resonators Under Mixed Boundaries

In this paper, we, for the first time, introduce the multimode resonator (MMRs) based on metal-integrated suspended line (MISL) technology to design tri-mode bandpass filters (BPFs). By incorporating mixed boundary conditions and perturbations, we achieve precise control of multiple modes. Furthermore, based on various mode combinations, we design wideband a BPFs in the millimeter-wave frequencies. To verify the flexibility of our proposed MMRs and their advantages in BPFs design, we designed a tri-mode BPF operating at 22.50 GHz with third-order filtering responses. The proposed prototype was synthesized, simulated, fabricated, and measured. The experimental results demonstrate that our implemented filter not only exhibit low insertion loss but also show significant advantages in miniaturization—particularly in the planarization of metal-based BPFs.