Patent ID: 7482898

Claim:
A filter comprising: a dielectric block; external conductors on faces other than one face of the dielectric block; an input-output electrode on a mounting surface perpendicular to the one face of the dielectric block, the input-output electrode being separated from the external conductors, the one face of the dielectric block is an open end face and a face opposing the open end face is a short-circuit face; a plurality of continuously arranged and step-shaped holes, which pass through the dielectric block between the open end face and the short-circuit face in parallel with the mounting surface, each respective step-shaped hole having a larger cross-section adjacent to the open end face and a smaller cross-section adjacent to the short-circuit face; inner conductors on internal surfaces of each of the plurality of step-shaped holes so as to form a plurality of resonator holes; respective open end-face electrodes on the open end face and electrically connected to the respective inner conductors of the plurality of resonator holes separately from the external conductor, wherein, in respective resonator holes positioned at both ends of the plurality of resonator holes, an axis of a first hole adjacent to the open end face is deviated from that of a second hole adjacent to the short-circuit face so that a distance on the open end surface between axes of the resonator holes positioned at both ends is greater than that on the short-circuit surface, wherein in the open end-face electrodes of the resonator holes positioned at both ends of the plurality of resonator holes, an area of an electrode adjacent to a central resonator hole of the plurality of resonator holes is greater than that of the electrode opposite thereto so as to generate a first capacitance between the open end-face electrodes of the resonator holes positioned at both ends of the plurality of resonator holes, and wherein the plurality of resonator holes are arranged such that a second capacitance generated between each open end electrode of the plurality of resonator holes and the external conductor and a third capacitance generated between the open end electrodes adjacent to each other are established so that inductive coupling is increased between neighboring resonator holes.