Patent ID: 8284000

Claim:
A resonator for a bandpass filter, comprising: a dielectric block; a first ground electrode and a second ground electrode provided on or in the dielectric block so as to oppose each other; a first via conductor provided in the dielectric block so as to extend in a direction orthogonal to faces of the first and second ground electrodes, and having a short-circuit end and an open end, the short-circuit end being connected to the first ground electrode, and the open end extending toward the second ground electrode; a second via conductor provided in the dielectric block so as to extend in the direction orthogonal to faces of the first and second ground electrodes, and having a short-circuit end and an open end, the short-circuit end being connected to the second ground electrode, and the open end extending toward the first ground electrode; a third via conductor provided in the dielectric block so as to extend in the direction orthogonal to faces of the first and second ground electrodes, and having a short-circuit end and an open end, the short-circuit end being connected to the first ground electrode, and the open end extending toward the second ground electrode; a fourth via conductor provided in the dielectric block so as to extend in the direction orthogonal to faces of the first and second ground electrodes, and having a short-circuit end and an open end, the short-circuit end being connected to the second ground electrode, and the open end extending toward the first ground electrode, a first capacitor electrode provided in the dielectric block, and connected to the first via conductor and the third via conductor; and a second capacitor electrode provided in the dielectric block, and connected to the second via conductor and the fourth via conductor, wherein every couple of via conductors immediately neighboring one another, selected from the first to fourth via conductors, are interdigitally coupled with each other, the interdigitally coupled via conductors have a first resonant mode resonating at a first resonance frequency f 1 which is higher than a resonance frequency f 0 determined by a physical length of each via conductors, and a second resonant mode resonating at a second resonance frequency f 2 which is lower than the resonance frequency f o and an operating frequency is set at the resonance frequency f 2 .