Apparatus for providing desired coupling in dual-mode dielectric

Abstract

A dual-mode dielectric-resonator-loaded cavity filter comprises a generally cylindrical cavity, at least two longitudinally-spaced dielectric resonator elements coaxially aligned within the cavity, and at least one coupling obstacle disposed between the resonators and extending a distance from the cavity wall. The coupling obstacles are preferably conductive and are electrically connected to the cavity wall. However, the obstacles may be constructed of a dielectric material in some applications. Each obstacle may be aligned with one of the reference planes corresponding to a resonant mode of the resonators to effectively control or reduce the coupling between the parallel resonant modes of adjacent resonators. The reduction in coupling between resonant modes of adjacent resonators allows large coupling differentials to be produced, allowing a filter designer to implement a wide variety of high-performance filters without expensive irises. The coupling obstacle achieves the reduction in coupling without requiring large spacing between adjacent resonators. The coupling obstacles may be conveniently and inexpensively produced in bar, wire, hemi-disk, and other configurations. Several adjustments allow the resonators to be tuned, and the couplings to be adjusted, after the filter is assembled, reducing the complexity and expense of manufacture. In particular, the coupling obstacles arc mounted for limited translation along the longitudinal axis of the cavity, and for rotation about their own longitudinal axes, thereby adjusting the amount of coupling reduction they provide.