Directional coupler including impedance matching and impedance transforming attenuator

• US 20100194489A1
• Filed: 01/30/2009
• Published: 08/05/2010
• Est. Priority Date: 01/30/2009
• Status: Active Grant

• Current Assignee: TDK Corporation
• Original Assignee: TDK Corporation
• Inventors: Costello, John, Kearns, Brian
• Granted Patent: US 7,961,064 B2
• Time in Patent Office: Days
• US Class Current: 333/116
• CPC Class Codes: H01P 5/184 the guides being strip lines or microstrips

Abstract

The present invention provides a compact weakly coupled directional coupler combined with an integrated impedance transformation and matching circuit where the impedance transformation and matching circuit facilitates the fabrication of a highly miniaturized directional coupler with optimum electrical performance where the physical dimensions of the coupled transmission lines fall inside the constraints of the fabrication process.

Claims

1. A directional coupler comprising a pair of coupled transmission lines, said pair of transmission lines being located in close proximity to each other so that they are electromagnetically coupled to each other, said pair of coupled transmission lines comprising a first transmission line and a second transmission line, said first transmission line comprising a first end, to which a first RF port is connected, and a second end to which a second RF port is connected, said second transmission line comprising a first end to which a third RF port is connected and a second end to which a fourth RF port is connected, so that an electrical signal fed to said first RF port produces a direct electrical signal at said second RF port, and a coupled RF signal at said third RF port, said pair of coupled transmission lines having an even mode impedance Z_0E and an odd mode impedance Z_0O;

said directional coupler further including a first impedance matching and impedance transforming attenuator connected at said third port which provides a level of attenuation and which transforms a reference impedance value Z₀ connected to a fifth RF port to a transformed impedance Z_P3 not equal to Z₀ which appears at said third RF port, the value of Z_P3 being given by;

2. The directional coupler of claim 1 wherein the product of said even mode impedance and said odd mode impedance of said pair coupled transmission lines has a value that is less than Z_O².

3. The directional coupler of claim 2 wherein Z_O=50Ω

.

4. The directional coupler of claim 1 wherein said pair of coupled transmission lines are broadside coupled.

5. The directional coupler of claim 1 wherein said pair of coupled transmission lines are edge coupled.

6. The directional coupler of claim 1 wherein said first impedance matching and impedance transforming attenuator comprises a PI network connected between said third and fifth ports.

7. The directional coupler of claim 1 wherein said first impedance matching and impedance transforming attenuator comprises a T network connected between said third and fifth ports.

8. The directional coupler of claim 1 said directional coupler further including a second impedance matching and impedance transforming attenuator connected at said fourth port which provides a level of attenuation and which transforms a reference impedance value Z₀ connected to a sixth RF port to a transformed impedance Z_P4 which appears at said fourth RF port and where the value of Z_P4 is equal to the value of Z_P3.

9. The directional coupler of claim 1 wherein said pair of transmission lines are incorporated within a layered structure, said layered structure comprising a plurality of patterned layers of a metallic material and at least one patterned layer of an insulating material.

10. The directional coupler of claim 9, wherein said layered structure is fabricated on an insulating substrate.

11. The directional coupler of claim 9 wherein one of said patterned layers of a metallic material comprises a patterned resistive film layer, said resistive film layer providing said first impedance matching and impedance transforming attenuator.

12. The directional coupler of claim 9, wherein said layered structure and said substrate are incorporated in a chip component.

13. The directional coupler of claim 1 wherein said pair of transmission lines are incorporated within a layered structure, said layered structure comprising a plurality of patterned layers of a metallic material interspersed with layers of an insulating material, said layered structure forming a chip component.

14. An electrical component comprising the directional coupler of claim 11 mounted on a carrier PCB, said carrier PCB providing conducting trace lines for feeding electrical signals to and from said RF ports of said directional coupler.

15. The directional coupler of claim 14, wherein said carrier PCB includes a ground plane for said pair of coupled transmission lines.

16. A power monitoring circuit including the directional coupler of claim 1.

17. An RF circuit including the directional coupler of claim 1.