US3134950A - Radio frequency attenuator - Google Patents

Description

May 26, 1964 E. J. COOK 3,1 4

RADIO FREQUENCY ATTENUATOR Filed March 24, 1961 INVENTOR: EDWARD J. COOK HI ATTORNEY.

United States Patent 3,134,950 RADIC FREQUENCY ATTENUATOR Edward J. Cook, Burnt Hills, N.Y., assignor to General Electric Company, a corporation of New York Filed Mar. 24, 1961, Ser. No. 8,045 3 Claims. (Cl. 333-81) My invention relates to radio frequency attenuators and pertains more particularly to new and improved means for effectively attenuating undesired radio frequency currents tending to travel along the direct current leads of high frequency electric discharge devices.

Many high frequency electric discharge devices, such as voltage tunable magnetrons, include several direct current supply leads either integrally formed with or connected to the direct current contacts of the devices. Due to various coupling mechanisms that can be present in such devices, radio frequency currents often tend to travel along or to be coupled out of the device through the direct current leads. For consistent performance and spectral regularity, it is desirable that this radio frequency power be attenuated. Additionally, it is desirable that means be provided which is effective for attenuating undesired radio frequency power on the direct current leads of an electric discharge device, and which is adapted for operating at high voltages and in rarefied atmospheres.

Accordingly, a primary object of my invention is to provide new and improved means for attenuating radio frequency current on a lead.

Another object of my invention is to provide new and improved attenuating means whereby attenuation of radio frequency current on a lead is greatly enhanced by improving the action of attenuating material on the electromagentic components of the radio frequency current.

Another object of my invention is to provide new and improved means effective for increasing the attenuation per unit length of a lead carrying radio frequency current to be attenuated.

Another object of my invention is to provide new and improved means for attenuating the radio frequency power on a lead with a minimum total mass of attenuating material.

Another object of my invention is to provide new and improved means for attenuating the radio frequency power on a lead with improvement in the voltage breakdown characteristics of the attenuator.

Another object of my invention is to provide a new and improved attenuator mount structure adapted for mounting a plurality of attenuators in mutually insulated spaced relation.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention I provide an electrical conductive lead having a section which is bared or devoid of any electrically insulative coating. Moulded about the bared section of the lead and in direct intimate contact therewith is a quantity of attenuating material characterized by high magnetic and high electrical lossiness at radio frequencies. The attenuating material is in sleeve-like form with a tapered end extending toward the generator of the radio frequency waves to be attenuated and, thus, is adapted for constituting a matched lossy element. In one form of my invention the portion of the lead imbedded in the attenuating material can be straight. Increased attenuation is obtainable by another form of my invention wherein the bared section imbedded in the attenuating material comprises a coiled section of the lead. Additionally, a modified form of my invention constitutes a mount construction for mount- 3,134,950 Patented May 26, 1964 ing a plurality of the described attenuators in a single structure and in a manner wherein the attenuators are mutually insulated and thus adapted for employment in constructions such as voltage tunable magnetron packages wherein normal operating voltages are substantially high. Additionally, my improved mount structure is particularly effective for resisting arcing over between leads and, thus, is adapted for applications in rarefied atmospheres.

For a better understanding of my invention reference may be had to the accompanying drawing in which:

FIGURE 1 is an enlarged sectional view of one form of my invention;

FIGURE 2 is an enlarged sectional view of a modified form of my invention; and

FIGURE 3 is an enlarged sectional view of a lead mount constructed according to my invention and adapted for facilitating mounting in mutually insulated relation a plurality of attenuators incorporating the other features of my invention.

Referring to the drawing, I have shown in FIGURE 1 a lead attenuator generally designated 1. The attenuator 1 comprises a length of lead 2 which has at least a section designated A which is bared or completely devoid of insulation. The remaining portion of the lead can be bared as shown or can be insulated.

Provided on the uninsulated or bared section A is a predetermined quantity of lossy material, or material characterized by high radio frequency attenuation capabilities. This material can advantageously be moulded as a generally cylindrical or sleeve member 3 about the lead for imbedding the Section A in the manner shown. Additionally, the lossy material is selected to have a maximum magnetic permeability and loss tangent. Further, the lossy material is selected to have a maximum dielectric constant and loss tagent, whereby it is adapted for being electrically lossy. I have found the attenuating materials available generally under the following designations and from the following sources to be satisfactorily employable in forming the member 3:

Material Source lolyiron Polyiron In operation, any radio frequency current on the lead is attenuated. This attenuation results to some extent from the electrical lossiness of the material of which sleeve member 3 is formed. However, to a much greater extent the attenuation is attributable to the high magnetic permeability of the sleeve member 3 and the effect thereof on the electromagnetic components of the radio frequency current on the lead.

Coatings of resistive material on a line operate on the electric field component in effecting attenuation. However, such coatings do not concentrate energy as does the attenuating material in my device. In my device, and as indicated above, attenuation resulting from operation of the electric field components is obtained. However, additionally, and very importantly, the high magnetic permeability of the sleeve material in my invention serves to concentrate the magnetic energy in the lossy region and, thus, has a greater attenuating effect per unit length of lead than would an attenuating structure wherein only resistance material is employed.

Additionally, and in recognition of the improvement in attenuation obtainable with a structure wherein the attenuating material operates on the magnetic components of the radio frequency current, I have provided the aboveing material.

mentioned direct intimate coextensive contact between the sleeve material and the bared section A of the lead 2. This construction affords a substantially tighter magnetic couple between the sleeve material and the electromagnetic field components of the radio frequency current, and the tighter magnetic coupling enhances greatly the capability of the sleeve material in operating on the magnetic field components for attenuating the radio frequency current.

Further, I have found that the tighter coupling obtained between the sleeve and lead when the sleeve material is moulded about the bared lead section enables me to provide an attenuator having a minimum total mass. This advantage is highly desirable where, due to space and wei ht considerations, the attenuator must be as small and light as possible. Additionally, in some applications, such asthe use of the attenuator on the direct current lead of a voltage tunable magnetron, it is desirable to keep the 'massto a minimum. Such a device is normally operated with the use of a static magnetic field extending therethrough and operation can be adversely affected by the near location of a substantial mass of magnetic permeability material.

In the prior art, a sleeve of attenuating material has been slipped over an insulative section of a lead.' In this form or structure the attenuating material is spaced from the wire by the thickness of the insulating material and aradio frequency leakage path between the wire and attenuating material exists. Additionally, a substantially looser coupling both electrically and magnetically results, and a substantially greater volume of attenuating material is required for attenuating a given radio frequency current. In my improved structure the attenuating material is in direct intimate contact with the bared section of the lead, with the desirable result that no radio frequency leakage can occur between the lead and attenuating material and tighter coupling results which, in turn, provides for greater attenuation with a reduced mass of attenuating material. 7

As also seen in FIGURE 1, the sleeve 3 is formed with a tapered end surface 4. The tapered end is provided for being directed toward the source or generator of the radio frequency wave to be attenuated. With the tapered end so oriented sleeve 3 constitutes a matched lossy element and serves to attenuate undesired radio frequency waves without causing undesired reflection thereof back toward the generator.

The tapered end 4 is particularly effective when its length, designated B in FIGURE 1, corresponds generally to, or is greater than, the wave length of the waves to be attenuated. If desired the taper length B can be made relatively long, whereby broadband matching is obtain able. However, the length B can also be made relatively short where attenuation of a very narrow band of frequencies is required and where it is desired to minimize the length and mass of the sleeve 3.

As noted above, the attenuating material is selected for maximum dielectric constant. In such material the Wave length of a radio frequency wave to be attenuated is substantially shorter than in free space. Thus, by emp'loying a maximum dielectric constant material, I am able to obtain the desired matching and attenuation with a minimum length of tapered section. This feature of my invention assists in enabling me to minimize the length and mass of the sleeve 3 required to effect attenuation of a given radio frequency current.

Illustrated in FIGURE 2 is a modified form of my structure designated 5. This form of my invention is particularly adapted for tightening the coupling between a bared section C of a lead 6 and a sleeve '7 of attenuat- In this embodiment the material of the sleeve 7 can be the same as that described above with respect to FIGURE 1 and the sleeve can also advantageously be moulded about the lead. Additionally, the sleeve 7 includes a tapered section 4' having a length designated D. In this embodiment the taper can be identical in structure and purpose to the tapered end 4 in FIGURE 1. However, the bared section C of this form of my invention constitutes a coiled portion of the lead. This construction provides for direct intimate contact or engagement between an increased length of the lead and the attenuating material. Thus, it afiords substantially increased coupling between the sleeve material and both the electrical and magnetic components of radio frequency waves on the lead. Accordingly, this form of my invention is adapted for increased attenuation effects and enables the employment of a reduced mass of attenuating material in obtaining a given degree of radio frequency attenuation.

Illustrated in FIGURE 3 is an attenuator mount construction generally designated 8 and adapted for mounting a plurality of my improved attenuators in mutually insulated spaced relation.

The mount construction 8 can be constructed to hold any number of attenuators. However, in FIGURE 3, I have illustrated an embodiment adapted for holding four attenuators constructed according to my invention as described above. The attenuators in FIGURE 3 are identical to that illustrated in FIGURE 1, however, it is to be understood that the attenuator 5 illustrated in FIG- URE 2 can be substituted for the ones illustrated in FIG- URE 3.

The mount structure comprises an electrically insulative body member 9 which can be formed of ceramic or any other suitable high dielectric strength insulative material. The body member 9 can be suitably mounted in any support such as a wall section It) of a voltage tunable magnetron cavity or operating magnet structure. Additionally, the insulative body member 9 includes a plurality of parallel bores generally designated 11. The bores 11 are each formed to include a counterbored section 12 wherein an attenuator 3 is positioned so that it is axially wholly contained in bore 11, i.e., the ends of the attenuator are spaced inwardly from the respective ends of the bores 11. In this structure the leads 2 each carry an insulative coating 13 which is stripped back to a point spaced from the body member 9. A cured quantity of insulative potting compound 14 is provided on the end surface of. the member 9 and includes portions 15 which extend into the bores 11 about the bared portions of the leads 2. On the opposite side of the member 9 a second quantity of cured potting compound designated 16.

is provided which includes portions 17 extending into the counterbores 12 about the bared sections of the leads 2. Thus, the attenuators 3 are sealed or encapsulated in the member 9 in a manner which adapts the resultant structure for rarificd atmosphere applications.

In constructing the described potted arrangement, I.

have found particularly eifective the potting compound referred to as General Electric Silicone Rubber-RTV-60 Catalytic 7 potting compound and which is available through the General Electric Co., Waterford, New York.

The sections or portions of the member 9 between the counterbores 32 are dimensioned and the body material is selected so as to withstand electrical breakdown between the adjacent attcnuator sleeves 3 at the normal operof my invention I do not desire my invention to be limited to the particular forms shown and described, and I intendby the appended claims to cover all modifications within the spirit and'scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A radio frequency attenuator for use with direct current leads adjacent an electrical discharge device, said attenuator consisting of a solid sleeve of a material adapted for attenuating radio frequency Waves, said attenuating material being characterized by having a high magnetic permeability and a high dielectric constant, an electrically conductive lead having a bared section imbedded in said attenuating material in direct intimate contact therewith, said contact providing tight coupling between said attenuating material and any radio frequency Wave on said lead, said sleeve having at least one externally tapered end, said tapered end being relatively long conpared with the Wavelength of radio frequency waves to be attenuated.

2. An attenuator mounting and encapsulating assembly for use with direct current leads of an electrical discharge device comprising in combination, an insulative member including a plurality of parallel bores extending therethrough, a plurality of attenuators each consisting of a solid sleeve of attenuating material and a conductive lead having a bared section extending through said attenuating material in direct intimate coextensive contact therewith over the length of said sleeve, said sleeves being of a high magnetic permeability material, at least one of said sleeves having at least one tapered end adapted to be directed to the source of radio frequency power to be attenuated 3. In a voltage tunable magnetron having direct current leads connected thereto, a plurality of attenuators for said leads, each attenuator consisting of a solid elongated quantity of attenuating material having at least one tapered end and characterized by high magnetic permeability and one of said D.C. leads extending through said attenuating material with at least in intermediate bared section in direct intimate contact therewith, the portion of said leads on one side of said attenuating material bearing an insulative coating, an insulative member having a plurality of parallel bores extending therethrough, each of said attenuators extending through one of said bores with the attenuating material thereof wholly positioned in said bores and the insulative coating thereon terminating at a point spaced from said insulative member, and a quantity of insulative potting material carried on each side of said insulative member and including portions extending into said bores in sealing relation about said bared sections of said leads, and said potting mate'- rial being in sealed overlapping relation with said insulative coatings.

References Cited in the file of this patent UNITED STATES PATENTS 1,926,807 Hansell Sept. 12, 1933 1,998,525 Russell Apr. 23, 1935 2,238,915 Peters Apr. 22, 1941 2,412,802 Ford Dec. 17, 1946 2,443,109 Linder June 8, 1948 2,538,771 Feenberg Ian. 23, 1951 2,610,250 Wheeler Sept. 9, 1952 2,782,381 Dyke Feb. 19, 1957 2,898,523 Charles Aug. 4, 1959 2,940,058 Foster June 7, 1960 3,002,162 Garstang Sept. 26, 1961 FOREIGN PATENTS 587,045 Great Britain Apr. 11, 1947

Claims (1)

1. A RADIO FREQUENCY ATTENUATOR FOR USE WITH DIRECT CURRENT LEADS ADJACENT AN ELECTRICAL DISCHARGE DEVICE, SAID ATTENUATOR CONSISTING OF A SOLID SLEEVE OF A MATERIAL ADAPTED FOR ATTENUATING RADIO FREQUENCY WAVES, SAID ATTENUATING MATERIAL BEING CHARACTERIZED BY HAVING A HIGH MAGNETIC PERMEABILITY AND A HIGH DIELECTRIC CONSTANT, AN ELECTRICALLY CONDUCTIVE LEAD HAVING A BARED SECTION IMBEDDED IN SAID ATTENUATING MATERIAL IN DIRECT INTIMATE CONTACT THEREWITH, SAID CONTACT PROVIDING TIGHT COUPLING BETWEEN SAID ATTENUATING MATERIAL AND ANY RADIO FREQUENCY WAVE ON SAID LEAD, SAID SLEEVE HAVING AT LEAST ONE EXTERNALLY TAPERED END, SAID TAPERED END BEING RELATIVELY LONG CONPARED WITH THE WAVELENGTH OF RADIO FREQUENCY WAVES TO BE ATTENUATED.

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