US3119081A

US3119081A - Microwave attenuator

Info

Publication number: US3119081A
Application number: US140467A
Authority: US
Inventors: Robert A Jordan
Original assignee: Lab For Electronics Inc
Current assignee: Laboratory For Electronics Inc
Priority date: 1961-09-25
Filing date: 1961-09-25
Publication date: 1964-01-21
Anticipated expiration: 1981-01-21

Description

Jan. 21, 1964 R. A. JORDAN 3,119,081

MICROWAVE ATTENUATOR Filed Sept. 25, 1961 2 Sheets-Sheet 1 FIG.|

INVENTOR. ROBERTA. JORDAN Jan. 21, 1964 R. A. JORDAN 7 3,119,081

MICROWAVE ATTENUATOR Filed Sept. 25, 1961 2 Sheets-Sheet 2 INVENTOR.

ROBERT A. JORDAN '7 AT ORNEY United States Patent 3,119,081 MICROWAVE ATTENUATOR Robert A. Jordan, Essex, Mass., assiguor to Laboratory for Electronics, Inc., Boston, Mass, a corporation of Delaware Filed Sept. 25, 1961, Ser. No. 140,467 1 Claim. (Cl. 333-81) This invention pertains generally to microwave transmission circuits and particularly to an improved attenuator adapted to insertion in a microwave transmission oncuit of the coaxial cable type.

It is known that selective attenuation of microwave energy is one to adjust the power level of such energy n the individual branches of a branched microwave circuit, or to or from a microwave component. Particular care must be taken, however, to avoid unwanted and undesirable effects. In particular it must be recognized that a satisfactory attenuator must not introduce undesired effects, as a phase shift dependent upon attenuation. Further, a satisfactory attenuator should be easy to manufacture and simple, yet dependable, in operation. Additionally, there is a great advantage to be gained if an attenuator may be continuously varied over a range of attenuation.

Therefore, it is a primary object of this invention to provide, for use in a microwave transmission circuit, an improved attenuator which may be fabricated using printed circuit techniques.

Another object of this invention is to provide an unproved, continuously adjustable microwave attenuator which has almost no effect on microwave energy except to change its power level.

Still another object of the invention is to provide an improved microwave attenuator which is simple and dependable in use.

These and other objects of the invention are attained generally by providing a photo-etched microwave attenuator in which a power absorbing element is movably supported in contact with a shaped conductor, such conductor being inserted in circuit with the center conductors of two sections of coaxial cable. Means are provided, also, to shield the power absorbing element and the shaped conductor so that the electrical characteristics of the sec tions of transmission line are unaffected, except as desired, by the attenuator.

For a more complete understanding of the invention, reference is now made to the following description of a preferred embodiment of the invention, and to the drawings, in which:

FIG. 1 is a perspective view of a microwave attenuator according to the invention; and,

FIG. 2 is an exploded view of the assembly shown in FIG. 1 to illustrate in detail the shape and disposition of the various elements making up that assembly.

A microwave signal entering the illustrated device on, say coaxial cable 11, may have its power level attenuated by any desired amount from zero to 25 to 40 db before leaving the device via a second coaxial cable 13. Obviously then, if the free end of coaxial cable 11 is connected to one of the output terminals of a microwave signal source (not shown), as, for example, a power divider, and if the free end of the coaxial cable 13 is connected to a circuit element (again not shown), as a driven element in an antenna array, the power level of the microwave signal at such a driven element with respect to the power level of the signal at the power divider may be adjusted as desired.

Any desired attenuation is here accomplished by shaping the various portions of the center conductor of the attenuator as illustrated, and at the same time, providing means for moving one such portion relative to another.

3,119,081 Patented Jan. 21, 1964 Thus, the center conductor of the illustrated attenuator is made up of length of an electrical conductor, preferably photo-etched and having parts indicated by the numerals 15, 17, 23 disposed, respectively, on a plate 25 and a plate 27 (all of which last named parts are electrical insulators) and means, described hereinafter, for rotating a disk 29 so as to move a semicircular attenuating section 30 with respect to lengths 17. It will be noted that while any known electrically insulating material may be used as the base material for plate 25, plate 27 and disk 29, it has been found that Rexolite, a material manufactured by the Rex Corporation of Acton, Massachusetts, is suited for the purpose, since the mechanical and electrical characteristics of Rexolite are quite well adapted to their illustrated application. It will also be noted that the various lengths of electrical conductors (as Well as the other electrically conductive portions of the attenuator presently to be described) may be copper, silver, aluminum or any other electrical conductive material and that the dimensions of the various elements, as the width and thicknes of the length of conductors 15, 17, 23 and the thickness of the

plates

25, 27 are matters of design. Fur ther, it should be noted that the semicircular attenuating section 30 may be any power absorbing material although, in the illustrated case, a sheet of so-called Filmed Mylar (consisting of a base of the plastic known in the art as Mylar, a product of E. I. du Pont de Nemours & Co., and a film of carbon electro deposited thereon) has been used. That is, the particular dimensions of the various elements may be varied, as is well known, to adapt the illustrated attenuator to use with transmission lines of differing characteristic impedances at dilfering frequencies. It is important only that length 17 be shaped so as to have a semicircular section 17a and that semicircular attenuating section 30 overlap the semicircular section 17a when disk 29 is inserted in a complementary opening 31 in plate 25.

The electrical circuit through the attenuator is completed by providing a ground plane 33 on the plate 25 and a ground plane 35 on the plate 27 and an opening (not numbered) formed through ground plane 35 and the plate 27 to allow the center conductors of coaxial cables 11, 13 to project into contact, respectively with lengths 15, 23. Ground plane 33 and ground plane 35 are, of course, metallic, preferably being deposited as a film on

plates

25, 27 and photo-etched as indicated. The two planes further are electrically connected to each other and to the shields of coaxial cables 11, 13, as by a number of screws 37 (which also serve to hold the coaxial cables 11, 13 in place) in appropriately disposed openings through both

plates

25, 27. It is clear from the foregoing, therefore, that a complete electrical circuit is formed between both the shields and the center conductors of the coaxial cables 11, 13 when the elements are assembled into the unitary structure shown in FIG. 1.

Turning now to a description of the means for rotating disk 29 referred to hereinbefore, it may be seen that the disk 29 is attached, as by riveting to a metallic spur gear 39 having a root diameter greater than the diameter of opening 31. A shaft 41 is afiixed in any known manner centrally of the spur gear 39 and a helical spring 43 is fitted over the shaft 41. Thus, when the shaft 41 is fitted into a journal bearing 45 in a bridle 47 and the bridle 47 is mounted, as with screws, to the

plates

25, 27, the disk 29 is springily pressed into the opening 31, curved sections 17 being then forced into contact with semicircular attenuating section 30. At the same time, the peripheral portion of the side of the spur gear 39 adjacent to the disk 29 is pressed into contact with the underlying portions of the ground plane 33. A driving gear 49, meshing with spur gear 39 and supported on a shaft 51 fitted into a journal bearing 53 in the bridle 47 permits a Vernier 3 adjustment of the spur gear 39, and the parts carried thereby, to be made.

In practice, it is highly desirable that positive means be provided to limit rotation of the semicircular attenuating section 30. This is simply accomplished here by mounting stops 55 on the plate 25 and a cooperating arm 57 on the spur gear 39. Rotation of the spur gear, obviously, is then restricted to the sector between the stops 55 so that movement of the semicircular attenuating section 30 is limited.

It will be immediately obvious to those having skill in the art that many changes in the just described attenuator may be made without departing from the concept of the invention. For example, it may on occasion be desirable to provide a non-linear attenuator. This may be easily accomplished by merely replacing the contemplated linear power absorbing sheet with a sheet having a non-linear coating of carbon.

In view of the foregoing description of a preferred embodiment of the invention and of the obvious modifications which may be made therein without departing from the inventive concepts so disclosed, it is felt that the invention should be limited only by the spirit and scope of the appended claims.

What is claimed is:

An attenuator for use in a microwave transmission line including two coaxial cables, comprising: a first electrically insulating plate having a first electrically conductive coating deposited on its outside surface and a semicircular section of electrically conductive line deposited on its inside surface; means operative through the first electrically conductive coating and the first electrically insulating plate to connect the center conductor of a coaxial cable to the ends of the semicircular section of line; a second electrically insulating plate having a circular opening formed therethrough and an electrically conductive coating deposited on the outside surface thercof; an electrically insulating disk having a diameter less than the diameter of the circular opening and a semicircular sheet of microwave power absorbing material aifixed to one side thereof; an electrically conductive gear aflixed to the opopsite side of the electrically insulating disk, the root diameter of such gear being greater than the diameter of the circular opening; and means for mounting the first and the second insulating plate, the electrically insulating disk and the electrically conductive gear to establish a first movable electrical contact between the semicircular section of line and the semicircular sheet of microwave power absorbing material and a second movable contact between the peripheral portions of the electrically conductive gear and the there underlying portions of the electrically conductive coating on the second electrically insulating plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,909,736 Sommers et al Oct. 20, 1959 2,961,620 Sommers Nov. 22, 1960 2,961,621 Tannenbaum et al Nov. 22, 1960 2,961,622 Sommers Nov. 22, 1960 3,046,505 Wilson July 24, 1962