Half-Mode Dielectric-Filled Resonator and Its Application in Bandpass Filters

This article presents a novel design for half-mode (HM) dielectric-filled resonators based on the concept of virtual magnetic walls (VMWs). The underlying principles of the HM resonator are explored, along with a design methodology for implementing the VMW through an open aperture (OA) with no restrictions on the aspect ratio of the dielectric-filled resonator. The VMW implementation is analyzed using transmission line theory. Compared to conventional full-mode (FM) dielectric-filled resonators, the proposed HM dielectric-filled resonator achieves a 37% reduction in both size and weight. The HM resonator is fully compatible with the FM resonator in the design of bandpass filters (BPFs), offering enhanced flexibility in dimensional design. Additionally, the proposed design enables the integration of transmission zeros, which enhances out-of-band rejection performance. To validate the approach, both inline and folded fourth-order BPFs incorporating HM and FM dielectric-filled resonators were fabricated and experimentally tested. The experimental results confirm the effectiveness of the proposed design, demonstrating superior out-of-band suppression with flexibility dimensional design.