Dielectrical filters having resonators at a trap frequency where the even/odd mode impedances are both zero

摘要

A compact dielectric band elimination filter, which is composed of fewer components and can be produced in fewer production steps, uses a resonator apparatus having a dielectric block with a plurality of throughholes each containing an inner conductor and serving as a resonator. Capacitor electrodes are formed on a main surface of the block such that series-connected resonant capacitors are provided with the inner conductors inside the throughholes. The resonator apparatus is mounted on a substrate of a layered structure having an inductor thereon. Each trap frequency of the filter associated with one of the resonators can be adjusted by making adjustments on the associated resonator without affecting the characteristics of the adjacent resonators, by forming a larger-diameter part and a smaller-diameter part separated by a step inside each throughhole or by using a dielectric block having a wider part and a narrower part through which throughholes with a uniform inner diameter are formed, such that the even-mode input impedance and odd-mode input impedance of each resonator will be equal to zero at the trap frequency associated therewith.