US3735305A

US3735305A - High power electrically variable inductor

Info

Publication number: US3735305A
Application number: US00290603A
Authority: US
Inventors: N Sinnott; H Jones
Original assignee: US Air Force
Current assignee: US Air Force
Priority date: 1972-09-20
Filing date: 1972-09-20
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22

Abstract

A high power electrically variable inductor includes a U-shaped ferrite core with an electromagnet and a permanent magnet attached to the U-core. The RF variable inductor winding is wound on a multiplicity of separate sections of the U-core. The area of the ferrite material at the RF winding is reduced to minimize the DC magnetic field.

Description

United States Patent Sinnott et al.

[ May 22, 1973 HIGH POWER ELECTRICALLY VARIABLE INDUCTOR Inventors: Norbert C. Sinnott, Adelphi, Mdx, Harold A. Jones, Jr., Thousand Oaks, Calif.

Assignee: The United States of America as represented by the Secretary of the Air Force, Washington, DC.

Filed: Sept. 20, 1972 Appl. No.: 290,603

U.S. Cl. ..336/1 10, 336/160, 336/172, 336/212 Int. Cl ..I-I01f 21/00 Field of Search ..336/1l0, 155, 160, 336/172, 212, 214, 215

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 763,497 12/1956 Great Britain ..336/l10 Primary Examiner-Thomas J. Kozma Att0rneyHarry A. Herbert, Jr. et a1.

[5 7] ABSTRACT A high power electrically variable inductor includes a U-shaped ferrite core with an electromagnet and a permanent magnet attached to the U-core. The RF variable inductor winding is wound on a multiplicity of separate sections of the U-core. The area of the ferrite material at the RF winding is reduced to minimize the DC magnetic field.

2 Claims, 2 Drawing Figures Patented May 22, 1973 HIGH POWER ELECTRICALLY VARIABLE INDUCTOR BACKGROUND OF THE INVENTION In the prior art, there is utilized high frequency saturable-core magnetic apparatus in which the inductance of a signal winding is controlled by varying the magnitude of a current through a control winding. In such magnetic control devices, called controllable or variable inductors, the control and signal windings are wound on portions of the same or magnetically interconnected ferromagnetic core structures. Variations in the current flowing through the control windings changes the degree of magnetic saturation of desired portions of the core structure, so varies the effective inductance of the signal winding. Thus, the magnitude of alternative current passed through the signal winding can be controlled in accordance with variations produced in the control current flowing through the control winding.

One of the uses of saturable-core magnetic devices exists in automatic tuning systems, for example, in tuning systems for HF or VHF power amplifiers or antennas. However, this requires high power electrically variable inductors and the prior art devices have limitations as to RF power handling capability of the RF inductor. Another limitation resides in the DC power requirements for the control winding. The present invention improves substantially the power handling capability of the RF inductor while simultaneously decreasing the DC power requirement of the control winding. Another advantage of the device of the present invention is its rapid tuning ability.

SUMMARY OF THE INVENTION A high power electrically variable inductor is provided. It is comprised of a U-shaped ferrite core with an electromagnet and permanent magnet attached to the U-core. A balanced RF variable inductor winding is wound on three (or more) separate sections of the U-core. The area of the ferrite material at the RF winding is reduced to minimize the DC magnetic field required for permeability tuning. A permanent magnet biases the ferrite material in the RF winding region to a lower permeability, higher Q state thus making possible lower RF loss. Increasing DC current in the electromagnet decreases the permeability further which changes the RF inductance.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a front view of the preferred embodiment excluding an RF inductor winding and shunt permanent magnet; and

FIG. 2 shows the side view of FIG. 1 including the RF inductor winding and shunt permanent magnet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now referring in detail to FIG. 1, there is shown U- shaped ferrite core 10 which is readily saturable. The area of U-shaped ferrite core 10 has been substantially reduced at

sections

10a, 10b, and 10c. I-Ioles 10d, le, and f have also been provided through U-shaped ferrite core 10 at

sections

10a, 10b, and 100, respectively. The RF inductor winding (not shown in FIG. 1) is wound utilizing

sections

10a, 10b, and 100, and associated

holes

10e, 10f, and 10d, respectively. Magnet steel bar 1 l is attached to

ends

12 and 13 of U-shaped ferrite core 10 by any suitable conventional means. Coil 14 is wound around magnet steel bar 11. Electromagnetic coil 14 is provided with terminals 15 which receives a variable DC input from any conventional source and operates as a control winding.

Referring to FIG. 2, there is shown a side view of FIG. 1 in which RF variable inductor winding 16 is clearly illustrated. Terminal 17 thereof receives the RF input signal and terminal 18 provides the RF output signal. Permanent magnet bar 19 is shown and may be attached by any suitable conventional means to U-shaped ferrite core 10. Bar 19 serves as a shunt magnet.

RF variable inductor winding 16 is a balanced winding. Equal number of turns appear on opposite sides of each of

holes

10d, 10e, and 10f. Three separate winding sections are series connected to form RF variable inductor 16 and is as illustrated in

sections

10a, 10b, and 100, and associated holes 10d, Ne, and 10f, respectively. The area of the ferrite material at

sections

10a, 10b, and 10 thus at the RF winding has been substantially reduced to minimize the DC magnetic field required for permeability tuning. Permanent magnet bar 19 biases the ferrite material in the RF winding region to a lower permeability, higher Q (lower RF loss), state. Increasing DC current in the electromagnet decreases the permeability still further which changes the RF inductance.

In the configuration shown in FIGS. 1 and 2, a 4 to 1 change in RF inductance with Q greater than over the entire range can be obtained with 1 watt of DC power used by the electromagnet for tuning. In addition, the RF induction can handle 320 volt-amperes (p It is emphasized that the use of a shunt permanent magnet reduces the required magnet DC tuning power. Still further, the series connection of three sections of the RF inductor, all of which are tuned by the same electromagnet increases the RF power handling capability of the RF inductor while reducing the required electromagnet tuning power.

It is claimed:

1. A high power electrically variable inductor comprising a U-shaped ferrite core having two arms, and a connecting member, said connecting member having first, second, and third sections with substantially reduced areas to minimize the DC magnetic field, each of said sections also having holes therethrough, a balanced RF variable inductor winding consisting of three series connected portions, each of said portions having an equal number of turns on opposite sides of the associated hole and wound on the associated section thereof, said balanced RF variable inductor winding including an input terminal for the reception of a high power RF input signal and an output terminal providing a high power RF output signal, an electromagnet attached across the ends of said two arms closing said U- shaped ferrite core, said electromagnet receiving a varying DC input signal thus operating to vary the magnitude of the inductance of said balanced RF variable inductor winding, and a shunt permanent magnet also attached to said U-shaped ferrite core biasing the ferrite material in the RF variable inductor winding region to a lower permeability.

2. A high power electrically variable inductor as de scribed in claim 1 wherein said electromagnet is comprised of a magnet steel bar and an electromagnet coil wound thereon.

Claims

1. A high power electrically variable inductor comprising a Ushaped ferrite core having two arms, and a connecting member, said connecting member having first, second, and third sections with substantially reduced areas to minimize the DC magnetic field, each of said sections also having holes therethrough, a balanced RF variable inductor winding consisting of three series connected portions, each of said portions having an equal number of turns on opposite sides of the associated hole and wound on the associated section thereof, said balanced RF variable inductor winding including an input terminal for the reception of a high power RF input signal and an output terminal providing a high power RF output signal, an electromagnet attached across the ends of said two arms closing said U-shaped ferrite core, said electromagnet receiving a varying DC input signal thus operating to vary the magnitude of the inductance of said balanced RF variable inductor winding, and a shunt permanent magnet also attached to said U-shaped ferrite core biasing the ferrite material in the RF variable inductor winding region to a lower permeability.

2. A high power electrically variable inductor as described in claim 1 wherein said electromagnet is comprised of a magnet steel bar and an electromagnet coil wound thereon.