An Embedded Stub-Loaded Resonator in Dielectric Cavity for Compact Bandpass Filter Designs

This letter presents a novel embedded stub-loaded resonator (ESLR) implemented within a dielectric cavity for compact bandpass filter (BPF) designs. The proposed ESLR comprises a rectangular slot with an open-ended cylindrical stub positioned at its center. Both the slot and the stub are metallized and fully embedded in the dielectric cavity. Due to its embedded configuration, the ESLR is fabricated in two separate parts. The ESLR supports both odd and even modes, enabling dual-mode resonance within a single dielectric cavity. By cascading two ESLRs, a fourth-order BPF with a center frequency of 3.55 GHz is designed and experimentally validated. The filter exhibits two transmission zeros near the passband, significantly enhancing sideband selectivity. The proposed BPF offers key advantages of compact volume, lightweight, and low insertion loss, making it a promising candidate for the base station applications in the 5G and future communication systems.