RF tuning element

• US 5,115,217 A
• Filed: 12/06/1990
• Issued: 05/19/1992
• Est. Priority Date: 12/06/1990
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Lubecke, Victor M., McGrath, William R.
• Primary Examiner(s): GENSLER, PAUL L
• Application Number:
  US07/622,939
• Time in Patent Office: 530 Days
• Field of Search: 333/161, 333/205, 333/225, 333/235, 333/246, 333/253, 333/263, 455/325, 455/327, 455/330, 343/700 MS File
• US Class Current: 333/246
• CPC Class Codes: H01P 1/28 Short-circuiting plungers
• CPC Class Codes: H01P 5/04 with variable factor of coupling

Abstract

A device for tuning a circuit includes a substrate, a transmission line on the substrate that includes first and second conductors coupled to a circuit to be tuned, and a movable short-circuit for varying the impedance the transmission line presents to the circuit to be tuned. The movable short-circuit includes a dielectric layer disposed atop the transmission line and a distributed shorting element in the form of a conductive member that is configured to be slid along at least a portion of the transmission line atop the dielectric layer. The conductive member is configured to span the first and second conductors of the transmission line and to define at least a first opening that spans the two conductors so that the conductive member includes first and second sections separated by the first opening. The first and second sections of the conductive member combine with the first and second conductors of the transmission line to form first and second low impedance sections of transmission line, and the opening combines with the first and second conductors of the transmission line and the dielectric layer to form a first high impedance section of transmission line intermediate the first and second low impedance sections. Each of the first low impedance section and the first high impedance section have a length along the transmission line of approximately one-quarter wavelength, thus providing a periodic variation of transmission line impedance. That enhances reflection of rf power.

Claims

1. A device for tuning a circuit, comprising:

a substrate, a transmission line on the substrate that includes first and second conductors coupled to a circuit to be tuned, and means defining a movable short-circuit for varying the impedance the transmission line presents to the circuit to be tuned;

the means defining a movable short-circuit including a dielectric layer disposed atop the transmission line and a distributed shorting element in the form of a conductive member that is configured to be slid along at least a portion of the transmission line atop the dielectric layer;

the conductive member being configured to span the first and second conductors of the transmission line and to define at least a first opening that spans the two conductors so that the conductive member includes first and second sections separated by the first opening;

the first and second sections of the conductive member combining with the first and second conductors of the transmission line and the dielectric layer to form first and second low impedance sections of transmission line, and the opening combining with the first and second conductors of the transmission line to form a first high impedance section of transmission line intermediate the first and second low impedance sections; and

at least each of the first low impedance section and the first high impedance section having a length along the transmission line of approximately one-quarter wavelength, thus providing a periodic variation of transmission line impedance that enhances reflection of rf power.

2. A device as recited in claim 1, wherein the conductive member includes a rectangularly shaped plate of conductive material and the first opening is a rectangularly shaped opening in the plate.

3. A device as recited in claim 1, wherein:

the conductive member defines a second opening that spans the first and second conductors of the transmission line so that the conductive member includes first, second, and third sections such that the first and second sections are separated by the first opening and the second and third sections are separated the second opening;

the first, second, and third sections of the conductive member combine with the first and second conductors of the transmission line and the dielectric layer to form first, second, and third low impedance sections of transmission line, and the first and second openings combine with the first and second conductors of the transmission line to form first and second high impedance sections of transmission line intermediate the first, second, and third low impedance sections; and

at least each of the first and second low impedance sections and the first and second high impedance sections have a length along the transmission line approximately one-quarter wavelength, thus providing a periodic variation of transmission line impedance that enhances reflection of rf power.

4. A device as recited in claim 1, wherein the conductive member includes a rectangularly shaped plate of conductive material and the first and second openings are rectangularly shaped openings in the plate.

5. A device as recited in claim 1, wherein:

each of the first low impedance section and the first high impedance section have a length along the transmission line that is approximately one-quarter wavelength.

6. A device as recited in claim 1, wherein the transmission line is a coplanar strip transmission line.

7. A device as recited in claim 1, further comprising means for guiding the conductive member as the conductive member is moved along the transmission line.

8. A device as recited in claim 1, wherein the transmission line is a slotline.

9. A device for tuning a circuit, comprising:

a substrate;

a transmission line on the substrate, which transmission line is coupled to a circuit to be tuned; and

means defining a movable short-circuit for varying the impedance the transmission line presents to the circuit to be tuned;

the movable short-circuit including a conductive member that is configured to be moved to any of various locations along the transmission line and to provide a low impedance path across the transmission line at any such location to which it is moved;

wherein the transmission line is configured as a coplanar strip transmission line having first and second conductors separated by a space;

the substrate defines a slot in alignment with the space; and

the conductive member includes a protrusion configured to extend intermediate the first and second conductors into the slot in order to reduce the impedance of the low impedance path provided by the conductive member.

10. A device for tuning a circuit, comprising:

a substrate;

a transmission line on the substrate, which transmission line is coupled to a circuit to be tuned; and

means defining a movable short-circuit for varying the impedance the transmission line presents to the circuit to be tuned;

the movable short-circuit including a conductive member that is configured to be moved to any of various locations along the transmission line and to provide a low impedance path across the transmission line at any such location to which it is moved; and

the movable short circuit also including means for guiding the conductive member as the conductive member is moved along the transmission line;

wherein the conductive member includes a plate of conductive material that is configured to be slid along the transmission line; and

the means for guiding the conductive member includes two guide-rail structures mounted on the substrate that extend along opposite sides of the transmission line in order to retain the conductive member in alignment with the transmission line.

11. A device as recited in claim 10, wherein the conductive member is configured to provide a first low impedance section of transmission line followed by a first high impedance section of transmission line and a second low impedance section of transmission line followed by a second high impedance section of transmission line.

12. A planar circuit, comprising:

a substrate, a planar antenna circuit on the substrate, and means defining an adjustable tuning element on the substrate for tuning the planar antenna circuit;

the adjustable tuning element including a transmission line on the substrate that is coupled to the planar antenna circuit and a conductive member that is configured to be moved to any of various locations along the transmission line in order to provide a low impedance path across the transmission line at any such location to which it is moved;

wherein the planar antenna circuit includes a planar antenna and a SIS junction device.

13. A circuit as recited in claim 12, wherein the adjustable tuning element is configured as a shunt tuner.

14. A circuit as recited in claim 13, further comprising a second adjustable tuning element configured as a series tuner.