Band rejection filter having a plurality of dielectric resonator with

Abstract

A band rejection filter includes at least of two dielectric resonators and an inductor. Each dielectric resonator is composed of a dielectric base formed as a rectangular prism and having a penetrating hole in a central portion, an inner conductive layer arranged on an inner side surface of the dielectric base, an outer conductive layer arranged on an outer side surface of the dielectric base, a connecting conductive layer arranged on one end surface of the dielectric base to connect the outer conductive layer and the inner conductive layer, an outer conductor layer cut-out groove formed on the outer side surface of the dielectric base, and an independent coupling electrode surrounded by the outer conductor layer cut-out groove on the dielectric base. The inductor connects the independent coupling electrode of the dielectric resonators, and the outer conductive layers of the dielectric resonators are connected with each other. The outer conductor layer cut-out groove is surrounded by the outer conductive layer, thus avoiding change in a resonance frequency in the band rejection filter. The outer end surface of the dielectric base is opened and is surrounded by the outer conductive layer thus avoiding change in attenuation characteristics of the band rejection filter.