High-frequency filter

• US 6,798,319 B2
• Filed: 10/02/2002
• Issued: 09/28/2004
• Est. Priority Date: 10/03/2001
• Status: Expired due to Fees

• Current Assignee: Masayoshi Aikawa, Nihon Dempa Kogyo Company Limited
• Original Assignee: Masayoshi Aikawa, Nihon Dempa Kogyo Company Limited
• Inventors: Kawamura, Yoshifumi, Aikawa, Masayoshi, Asamura, Fumio, Oita, Takeo, Nishiyama, Eisuke
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Glenn, Kimberly E
• Application Number:
  US10/262,909
• Publication Number:
  US 20030102942A1
• Time in Patent Office: 727 Days
• Field of Search: 333/205, 333/202, 333/175, 333/204, 333/219, 333/246, 333/995
• US Class Current: 333/204
• CPC Class Codes: H01P 1/2013 Coplanar line filters

Abstract

A high-frequency filter for use in a superhigh frequency band such as of microwaves and millimeter waves has a substrate, a metal conductor disposed on a first main surface of the substrate, a resonator comprising a transmission line of a coplanar structure which is made of the metal conductor, and input and output lines disposed on a second main surface of the substrate transversely across the resonator and electromagnetically coupled to the resonator. The resonator may be a coplanar line resonator (coplanar waveguide resonator) or a slot line resonator. The high-frequency filter has a steep attenuating gradient in filter characteristics. The high-frequency filter may be combined with variable-reactance devices such as variable-capacitance diodes for electronically controlling the filter characteristics.

Claims

1. A high-frequency filter comprising:

a substrate;

a metal conductor disposed on a first main surface of said substrate;

a resonator comprising a transmission line of a coplanar structure which is made of said metal conductor, said resonator including a slot line resonator having a transmission line as a slot line;

input and output lines disposed on a second main surface of said substrate transversely across said resonator and electromagnetically coupled to said resonator;

a pair of variable reactance elements having respective first polarity terminals and respective second polarity terminals, said first polarity terminals being connected to each other, and said second polarity terminals being connected to metal conductor portions which are located on opposite sides of an opening defined in said slot line, respectively; and

means for applying a control voltage between an interconnection point of said pair of variable-reactance elements and said metal conductor.

2. The high-frequency filter according to claim 1, wherein said

pair of variable-reactance elements are disposed over said opening defined in said slot line.

3. The high-frequency filter according to claim 2, wherein each of variable reactance devices comprises a variable-capacitance diode.

4. The high-frequency filter according to claim 1, wherein said input line corresponds to a first end of said slot line, and said output line corresponds to a second end of said slot line.

5. The high-frequency filter according to claim 4, wherein said input line and said output line extend in a direction substantially perpendicular to the direction in which said slot line extends.

6. The high-frequency filter according to claim 1, wherein said substrate comprises a dielectric substrate.

7. A high-frequency filter for use as a cascaded filter, comprising:

a substrate;

a metal conductor disposed on a first main surface of said substrate;

a plurality of resonators disposed on said first main surface and each comprising a transmission line of a coplanar structure which is made of said metal conductor, wherein each resonator includes a slot line resonator having a transmission line as a slot line, said slot line resonators extending substantially parallel to each other on said first main surface, overlapping each other, and having ends displaced from each other;

input and output lines disposed on a second main surface of said substrate transversely across said resonator and electromagnetically coupled to said resonator;

a coupling line disposed on said second main surface and electromagnetically coupling said slot line resonators;

a pair of variable reactance elements for each slot line connecting metal conductor portions which are disposed over an opening defined in said slot line and having respective first polarity terminals and respective second polarity terminals, said first polarity terminals being connected to each other, and said second polarity terminals being connected to metal conductor portions which are located on opposite sides of an opening defined in said slot line, respectively; and

means for applying a control voltage between an interconnection point of each pair of variable-reactance elements and said metal conductor.

8. The high-frequency filter according to claim 7, wherein said input line corresponds to a first end of said slot line, and said output line corresponds to a second end of said slot line.

9. A high-frequency filter comprising:

a substrate;

a metal conductor disposed on a first main surface of said substrate;

a resonator comprising a transmission line of a coplanar structure which is made of said metal conductor; and

input and output lines disposed on a second main surface of said substrate transversely across said resonator and electromagnetically coupled to said resonator;

wherein said resonator comprises a coplanar line resonator comprising a transmission line as a coplanar line.

10. The high-frequency filter according to claim 9, further comprising:

a pair of variable-reactance devices interconnecting opposite ends of a signal line disposed in an opening defined in said coplanar line and said metal conductor; and

means for applying a control voltage for said variable-reactance devices to an electric midpoint of said signal line.

11. The high-frequency filter according to claim 10, wherein each of variable-reactance devices comprises a variable-capacitance diode.

12. The high-frequency filter according to claim 9, for use as a cascaded filter, wherein said high-frequency filter has a plurality of said coplanar line resonators disposed on said first main surface and arranged in a longitudinal direction of said substrate, further comprising:

a coupling line disposed in said second main surface and electromagnetically coupling adjacent two of said coplanar line resonators.

13. The high-frequency filter according to claim 12, further comprising:

a pair of variable-reactance devices interconnecting opposite ends of a signal line disposed in an opening defined in said coplanar line and said metal conductor; and

means for applying a control voltage for said variable-reactance devices and said applying means are provided for each coplanar line resonator.

14. The high-frequency filter according to claim 13, wherein said input line has a closed loop corresponding to a first end of said signal line and an extension extending from said closed loop, and said output line has a closed loop corresponding to a second end of said digital line and an extension extending from said closed loop of the output line.

15. The high-frequency filter according to claim 12, wherein said coplanar line resonator comprises an opening defined in a ground conductor disposed on said first main surface and a signal line disposed in said opening, said signal line having open opposite ends.