Design of Compact Coaxial-Like Bandpass Filters Using Dielectric-Loaded Strip Resonator

Abstract

This paper presents a novel dielectric-loaded strip resonator (DLSR) with coaxial-like characteristic, comprising a metal strip attached on the surface of a high-permittivity dielectric rod. The strip of traditional strip-loaded dielectric resonator only functions as the perturbation for tuning the dielectric resonator mode. In particular, the dominant mode of the proposed DLSR stems from the strip and works as a quasi-λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> /4 resonator. It possesses very low resonant frequency with immense design freedom. The corresponding characteristics and frequency expressions of the strip mode are theoretically deduced and verified on the basis of the E-field distribution of the DLSR. For demonstration, a variety of single-ended inline filters are exploited using single-strip DLSRs with different deployments as well as the generation mechanism of transmission zeros is investigated. Furthermore, a simple modification with twin strips can serve for electrically small differential topology, highlighting the versatile design of the DLSR. Besides desirable differential-mode (DM) response, the differential DLSR filter manifests a large deviation between DM and common-mode (CM) frequencies, resulting in a satisfactory CM suppression in the DM passband. Good agreement between the simulation and the measurement validates the proposed methodology.