In-Line Mixed Slots Coupled Bandpass Filters Based on Metal Integrated Suspended Line Processing Technology

This article introduces a novel approach to designing mixed coupled bandpass filters (BPFs) utilizing all-metal sheets processing technology. The proposed BPFs feature unique coupling configurations capable of achieving Chebyshev and elliptic functional filtering responses. Through the construction of multilayer metal integrated suspended lines (MISL) using thin metal sheets such as aluminum or copper, vertical miniaturization and the complete elimination of dielectric loss are made possible. The primary focus of this study is to analyze how MISL resonators establish coupling between each other and to investigate how this distinct coupling structure can be used to create transmission zeros (TZs) in in-line structure filters by employing mixed couplings. Three specific examples are thoroughly examined to demonstrate these concepts. To validate the practical feasibility of the design technology and coupling methods, three prototypes were synthesized, designed, fabricated, and tested in the C-band. The measured results exhibit a high degree of agreement with the simulated data, showing the exceptional performance characteristics of the MISL-based BPFs.