Layered bandpass filter

• US 8,378,763 B2
• Filed: 09/24/2010
• Issued: 02/19/2013
• Est. Priority Date: 09/29/2009
• Status: Active Grant

• Current Assignee: TDK Corporation
• Original Assignee: TDK Corporation
• Inventors: Wakata, Eiko
• Primary Examiner(s): Takaoka, Dean O
• Application Number:
  US12/890,120
• Publication Number:
  US 20110074527A1
• Time in Patent Office: 879 Days
• Field of Search: 333/202, 333/204, 333/175, 333/185, 333/138
• US Class Current: 333/204
• CPC Class Codes: H01P 1/20345 Multilayer filters
• CPC Class Codes: H03H 7/0123 comprising distributed impedance elements together with lumped impedance elements
• CPC Class Codes: H03H 7/09 Filters comprising mutual inductance
• CPC Class Codes: H03H 7/1708 Comprising bridging elements, i.e. elements in a series path without own reference to ground and spanning branching nodes of another series path H03H7/07 takes precedence
• CPC Class Codes: H03H 7/1775 Parallel LC in shunt or branch path H03H7/1791 takes precedence
• CPC Class Codes: H03H 7/1783 Combined LC in series path
• CPC Class Codes: H03H 7/1791 Combined LC in shunt or branch path

Abstract

A bandpass filter includes three resonators of which adjacent two are electromagnetically coupled to each other, and two coupling paths connected in parallel for forming capacitive coupling between non-adjacent two of the resonators. Each of the two coupling paths includes at least one capacitor and an inductor connected in series. The two coupling paths function to form an attenuation pole at a frequency lower than the passband frequencies in the pass attenuation characteristics of the bandpass filter.

Claims

1. A layered bandpass filter comprising:

a layered structure including a plurality of dielectric layers stacked;

three or more resonators provided within the layered structure such that adjacent two of the resonators are electromagnetically coupled to each other; and

a plurality of coupling paths connected in parallel, for forming capacitive coupling between non-adjacent two of the resonators,

wherein each of the coupling paths includes at least one capacitor and an inductor connected in series.

2. The layered bandpass filter according to claim 1, wherein the three or more resonators and the plurality of coupling paths are each formed of a plurality of conductor layers provided within the layered structure.

3. The layered bandpass filter according to claim 1, wherein the plurality of coupling paths have respective different resonant frequencies.

4. The layered bandpass filter according to claim 1, wherein each of the three or more resonators is a quarter-wave resonator having an open end and a short-circuited end, and the plurality of coupling paths electrically connect the open ends of the non-adjacent two of the resonators to each other.

5. The layered bandpass filter according to claim 1, wherein the at least one capacitor is two capacitors, and the inductor electrically connects the two capacitors to each other.