US3672202A - Method of making waveguide bend - Google Patents

Abstract

A method of forming an H-plane or E-plane bend in a straight, hollow, rectangular waveguide is described which permits a decrease in the ''''a'''' or ''''b'''' dimension in going around the bend. In the practice of the method, part of one wall of the waveguide is deformed by a die to cause the wall portion to be sheared from the adjacent walls and pressed into the waveguide. The portions of the waveguide walls extending outside the deformed wall are cut away. Triangular segments are removed from the waveguide to form the guide into three sections. The three sections are then folded together to make the bend.

Description

United States Patent Barber [54] METHOD OF MAKING WAVEGUIDE BEND [72] Inventor: Wayne Barber, Bedford, Mass.

Microwave Development Laboratories, Inc., Needham Heights, Mass.

[22] Filed: Sept. 15, 1970 [21] Appl.No.: 72,279

[73] Assignee:

[ 51 June 27, 1972 3,016,081 l/l962 Gill ..72/369 3,072,870 l/1963 Walker ..333/93 BE 3,358,632 12/1967 Nemlich ..1 13/1 16 F Primary Examiner-Richard J. Herbst Attorney-Wolf, Greenfield & Sacks [57] ABSTRACT A method of forming an H-plane or E-plane bend in a straight, hollow, rectangular waveguide is described which permits a decrease in the a" or b" dimension in going around the bend. In the practice of the method, part of one wall of the waveguide is deformed by a die to cause the wall portion to be sheared from the adjacent walls and pressed into the waveguide. The portions of the waveguide walls extending outside the deformed wall are cut away. Triangular segments are removed from the waveguide to form the guide into three sections. The three sections are then folded together to make the bend.

2 Claims, 11 Drawing Figures PATENTEuJum 1912 3,672,202

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SHEET 3 BF 3 5y, 0%, WQLIOJA/ METHOD OF MAKING WAVEGUIDE BEND FIELD OF THE INVENTION This invention relates in general to the fabrication of bends in hollow, rectangular waveguide. More particularly, the invention pertains to a method of forming E-plane and l-I-plane bends in hollow rectangular waveguide having deformable walls.

DISCUSSION OF THE PRIOR ART In practice, the employment of a waveguide as a confining path for transmission of electromagnetic waves usually requires the waveguide to be bent as the path is seldom a straight line. Hollow, metallic waveguide of rectangular cross section is the type of waveguide most commonly used and bends in such waveguide may occur in the plane of either the electric or magnetic field. Where the bend occurs in the plane of the electric field it is termed an E-bend and, as a corollary, where the bends occurs in the plane of the magnetic field it is termed an I-I-bend.

Bends in waveguides, unless carefully fabricated, appear as discontinuities in the transmission line and cause undesired reflection of the wave energy. By curving the waveguide gradually to cause the radius of curvature to be large in relation to the wave length of the transmitted energy, a bend is produced having low reflectivity. Space requirements, in many instances, do not permit the use of bends of such gradual curvature and waveguide bends are known which turn more sharply and provide compensation to minimize the reflection of wave energy. Where the bend turns sharply, the bend is sometimes termed a waveguide corner.

Various types of E-plane and I-I-plane bends are depicted on page 204 of Principles and Applications of Waveguide Transmission, by George C. Southworth, published by Van Nostrand Co. In the Southworth book, FIG. 7.4l(c) shows a conventional E-plane bend having a 45 face, which at its narrowest point, reduces the b" dimension of the waveguide to b, where b is approximately equal to 0.86b. That FIG. also shows a conventional H-plane bend having a 45 face which, at its narrowest point, reduces the a dimension of the waveguide to a, where a, is approximately equal to 0.930. U.S. Pat. No. 3,072,870 discloses a waveguide bend in which a circular arc replaces the 45 surface and in which the corresponding narrowest point for the I-I-plane bend is approximately equal to 0.925a. Because dimensions in waveguide structures must be held to close tolerances, the complexity introduced by a decrease in the a dimension is going around the bend in an H-bend or the decrease in the b"dimension in going around the bend in an E-bend, has, because of lower production costs, resulted in such devices being produced chiefly by the metal casting techniques employed in foundry work. The bends produced by metal founding processes, are

- usually indi-vidual E-bend or l'I-bend units which are provided with flanges to enable the bends to be readily assembled with other waveguide sections. Straight hollow rectangular waveguide is, because of economic factors, usually made by the metal extrusion process. It has, therefore, been customary for a waveguide transmission line to be an assemblage of extruded straight sections and cast bent sections.

OBJECTIVES OF THE INVENTION The principal objective of the invention is to provide an inexpensive method for making E-plane and H-plane bends in hollow rectangular waveguide which permits precise control over the alteration of the a or b dimensions. Another objective of the invention is to provide a method for forming reduced dimension" E-plane and I-I-plane bends, in a waveguide without requiring those bends to be first fabricated as separated units. In the practice of invention, the bends are formed from straight rectangular waveguides. The invention permits an initially straight waveguide line to have integral E- plane and I-l-plane comers made in it without having to completely sever the line.

THE DRAWINGS The invention can be better understood from the exposition which follows when it is considered in conjunction with the accompanying drawings in which:

FIG. 1A depicts a prior art waveguide bend of the double miter type;

FIG. 1B depicts the double miter bend in developed form;

FIG. 2A illustrates a prior art waveguide bend of the single miter cutofi type;

FIG. 2B shows the single miter bend in developed form;

FIG. 3 depicts an l-I-plane bend made in accordance with the invention;

FIG. 4 shows the I-I-plane bend in developed form;

FIG. 4A is an enlarged section depicting the teardrop shape of the V-notch apex;

FIG. 5 shows a straight section of waveguide from which the I-I-plane bend is fabricated;

FIG. 6 depicts the formation of two apertures in the straight waveguide section;

FIG. 7 illustrates the step of lancing and forming a wall of the straight waveguide section; and

FIG. 8 shows the confinement of the waveguide section to prevent buckling of the walls during the lancing and forming operation.

Tl-IE EXPOSITION Corners fabricated from initially straight sections of hollow rectangular waveguide have principally been of the double miter type shown in FIG. 1A or of the single miter cutoff type depicted in FIG. 2A. In fabricating the double miter waveguide comer, two 45 Vees are cut into a straight waveguide member, as shown in FIG. IE, to divide the guide into three sections 1, 2, and 3. The three sections are folded about the apices of the Vees to cause the waveguide bend of FIG. 1A to be formed. The foregoing prior art method of producing a double miter waveguide comer does not permit a reduction in the waveguide dimensions in going around the bend and therefore, to compensate for impedance discontinuities, it is necessary to space the two miters by a mean distance L which is selected to cause the reflections from the miter interfaces to cancel in the desired transmission band.

The prior art method of forming the single miter cutoff corner of FIG. 2A permits an alteration in the a or b dimension of the waveguide at the bend. To form the single mitered comer, Vees are cut into a straight length of waveguide, as shown in FIG. 28, to divide the waveguide into two sections 4 and 5. The two sections are butted together and a 45 wall 6 is added to close the gap in the waveguide wall. The single miter cutofi' corner is difficult to fabricate because three separate pieces must be carefully fitted together to form the comer.

The invention is an improvement over the foregoing prior art methods of fabricating waveguide bends from a straight length of waveguide. The fabrication of an H-plane bend of the type shown in FIG. 3 of the drawings has been selected to illustrate the invention. The bend turns the wave energy through 90 without causing appreciable reflections. The inner narrow walls 7 and 8 form a sharp 90 comer. The interior of the corner, however, does not present a sharp edge but rather has a 45 facet 9. The outer narrow walls have a face 10 which is inclined 45 with respect to faces ll, 12. Faces 13, 14 are inclined 22% relative to face 10. The dimension a, measured between the facet 9 and the interior of wall 10, is the narrowest part of the bend and is approximately equal to 0.9530 where a is the width of the waveguide at the input or output ports. Thus the width of the waveguide varies from a to 0.9531: in proceeding around the bend.

The bend is developed by dropping lines L1 and L2 from the sharp comer perpendicular to walls 13 and 14. By cutting along lines L1 and L2, from the comer to the walls 13 and 14, the waveguide bend can be straightened to take the form shown in FIG. 4. In the developed or straightened form, the bend consists essentially of three sections S1, S2, S3 which are hinged at points H1 and H2. To conform the straight section of waveguide shown in FIG. 5, to the configuration of the developed bend of FIG. 4, it is necessary (l) to cause the narrow wall of the straight waveguide over the length I. to follow the contour indicated in section at 15a, (2) to remove the portion 16 of the broad walls which, as viewed in FIG. 5, extends below the contoured narrow wall, and (3) to remove two 45 wedges 17 and 18 from the waveguide so as to divide the waveguide into three sections.

1n the practice of the invention, the narrow wall 15 of the straight waveguide is brought to the desired contour by die forming. In the initial part of the die forming operation, the die causes the narrow wall to be sheared from the broad walls. The shearing step is referred to as lancing. After being lanced, the wall 15 is pressed between a pair of mating dies to cause the wall to deform and assume the shape of the die. The material of the waveguide wall must be sufficiently ductile to permit it to elongate and retain its new shape when removed from the die. Since appreciable forces are involved in deforming the waveguide wall, the die must be rigidly supported during the die forming operation.

The initial step in the process, as indicated in FIG. 6, is the formation of two apertures 19 and 20 in the narrow wall 21 of the straight waveguide. The apertures are located opposite the portion of the narrow wall which is to be lanced and die formed. The dimensions of the apertures 19 and 20 are not critical as the apertures merely serve as access holes for posts which support the die. However, the access holes 19 and 20 must leave intact that portion of the narrow wall 21 which is to form the corner facet 9. The access holes can be formed in a manner, such as by drilling, which avoids distortion of the waveguide. Preferably, the access holes are made by punching our portions of the wall.

The waveguide is then, as shown in FIG. 7, inserted over an arbor 22 having a die face 23 configured to the contour which the deformed wall is to assume. The arbor, as shown in FIG. 8, fits closely between the broad walls of the waveguide. The arbor and waveguide assemblage is placed upon a fixture having two upstanding posts 24, 25 which protrude through access holes 19 and 20 and provide rigid supports for the arbor.

A punch 26 having a die face 27 which mates with the die of the arbor is mounted to be pressed against the stationary die. In its descending stroke, the punch causes the narrow wall 15 to be sheared from the broad walls 28, 29 of the waveguide. To prevent the broad walls from buckling, the fixture has side supports 30, 31 which closely confine the broad walls and prevent them from spreading laterally. The punch forces the lanced narrow wall against the die face of the arbor and causes the narrow wall to be permanently deformed to the contour of the die. Upon withdrawal of the punch, the waveguide and arbor assemblage are lifted off the posts 24 and 25 and the waveguide is detached from the arbor.

Subsequently, two 45 V-notches are cut into the waveguide, as indicated in FIG. 4. The apex of each V- notched is not a sharp point but, as shown in the magnified view of FIG. 4A, is of a rounded or teardrop form. The vnotches have their true pointed apices about midway through the wall 15. The rounded apex of each V-notch is coincident with the true pointed apex and thus penetrates about half-way through the wall 15 to form a deep score in the wall around which the wall can be folded in the manner of a hinged joint. Before the wall can be folded however, it is necessary to cut away the portion 16 of the broad walls to conform the contour of those walls to the contour of wall 15.

The sections S1, S2, S3 are folded about hinges H1 and H2 to form the I-I-plane waveguide bend shown in FIG. 3. It has been found, when the sections are folded together, that the material of the wall tends to flow into the apices of the V- notches and fill the circular openings.

The folding assemblage is then brazed to seal the seams between the contiguous sections.

While the invention has been described as applied to the fabrication of a bend, it is apparent that the invention can be utilized to construct bends which turn the wave energy through greater or lesser angles. In view of the various ways in which the method can be used, it is not intended that the invention be limited to the precise operations described in the foregoing exposition but rather that the scope of the invention be delimited by the appended claims.

What is claimed is:

1. The method of forming a hollow rectangular waveguide I-I-plane or E-plane bend of the type having a decreased dimension in going around the bend, comprising the steps of l. forming access holes in the wall of a straight length of hollow rectangular waveguide, the access holes being opposite an intermediate portion of the opposite wall which is to be deformed,

2. inserting an arbor in the waveguide, the arbor having a die face shaped to the contour which the deformed wall is to assume,

3. supporting the arbor upon posts extending through the access holes,

4. driving a punch against the portion of the waveguide wall which is to be deformed to cause that wall portion to be sheared from the transverse walls and pressed into the waveguide against the die face of the arbor,

5. cutting V-notches into the waveguide to form a plurality of waveguide sections, the apices of the V-notches forming scores in the deformed wall,

6. removing portions of the transverse waveguide walls to cause those walls to conform to the contour of the deformed wall, and

7. bending the waveguide sections about the scores in the deformed wall to bring the sections together.

2. The method according to claim 1 wherein in step 5 two V-notches are cut into the waveguide to form three waveguide sections, and the score in the apex of each V-notch has a teardrop shaped cross-section.

Claims (8)

1. The method of forming a hollow rectangular waveguide H-plane or E-plane bend of the type having a decreased dimension in going around the bend, comprising the steps of 1. forming access holes in the wall of a straight length of hollow rectangular waveguide, the access holes being opposite an intermediate portion of the opposite wall which is to be deformed, 2. inserting an arbor in the waveguide, the arbor having a die face shaped to the contour which the deformed wall is to assume, 3. supporting the arbor upon posts extending through the access holes, 4. driving a punch against the portion of the waveguide wall which is to be deformed to cause that wall portion to be sheared from the transverse walls and pressed into the waveguide against the die face of the arbor, 5. cutting V-notches into the waveguide to form a plurality of waveguide sections, the apices of the V-notches forming scores in the deformed wall, 6. removing portions of the transverse waveguide walls to cause those walls to conform to the contour of the deformed wall, and 7. bending the waveguide sections about the scores in the deformed wall to bring the sections together.

2. inserting an arbor in the waveguide, the arbor having a die face shaped to the contour which the deformed wall is to assume,

2. The method according to claim 1 wherein in step 5 two V-notches are cut into the waveguide to form three waveguide sections, and the score in the apex of each V-notch has a teardrop shaped cross-section.

3. supporting the arbor upon posts extending through the access holes,

4. driving a punch against the portion of the waveguide wall which is to be deformed to cause that wall portion to be sheared from the transverse walls and pressed into the waveguide against the die face of the arbor,

5. cutting V-notches into the waveguide to form a plurality of waveguide sections, the apices of the V-notches forming scores in the deformed wall,

6. removing portions of the transverse waveguide walls to cause those walls to conform to the contour of the deformed wall, and

7. bending the waveguide sections about the scores in the deformed wall to bring the sections together.

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