US2840787A

US2840787A - Hybrid tau type waveguide junction

Info

Publication number: US2840787A
Application number: US309086A
Authority: US
Inventors: Adcock Mack Donald; Louis A Kurtz
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1952-09-11
Filing date: 1952-09-11
Publication date: 1958-06-24
Anticipated expiration: 1975-06-24

Description

June 24, 1958 M. D. ADCOCK ETAL 2,840,787

HYBRID T TYPE WAVEGUIDE JUNCTION Filed Sept. 11, 1952 IN V EN TORS,

a am/Mn Z 4 Z W 24 f g r Y Z% w United States Patent HYBRID r TYPE WAVEGUIDE JUNCTION Mack Donald Adcock, Los Angeles, and Louis A. Kurtz,

Pacific Palisades, Califi, assig'nors, by mesne assignments, to Hughes Aircraft Company, a corporation of Delaware Application September 11, 1952, Serial No. 309,986

10 Claims. (Cl. 333-11) This invention relates to waveguides for electromagnetic waves, and more particularly to an improved waveguide structure of the hybrid T junction type.

As is well known to those skilled in the art, a hybrid T waveguide junction comprises two mutually perpendicular waveguide sections, each being joined at right angles to a third waveguide section, to forma common junction. One of the mutually perpendicular sections is designated as the E plane arm, and the other as the H plane arm, since the longitudinal axes of each of these sections, and the third section lie in a plane parallel to the electric vector, E, and the magnetic vector, H, respectively. The third section in effect forms two arms, one of which is a collinear extension of the other, these being usually designated as collinear arms, owing to their spacial relationship.

A waveguide junction of this type is characterized by the special manner in which it operates. That is, energy supplied to either the E or H plane arm is transmitted equally to independent, refiectionless loads terminating the collinear arms; and energy supplied simultaneously to both E and H plane arms is apportioned between the collinear arms according to the relative amplitudes and phases of input waves in the E and H plane arms, there being substantially no coupling between the E and H plane arms. Energy is similarly transmitted from one of the collinear arms to the E and H plane arms, provided that no energy is reflected from the junction. When such reflected energy is substantially eliminated, both collinear arms may be energized simultaneously, also with the result that energy is apportioned between the E and H plane arms according to the amplitude and phase relation of the input Waves supplied to each collinear arm.

In general, reactive elements, such as posts or irises,

are included in a hybrid T waveguide junction for the purpose of minimizing reflected energy. These elements provide reactances which compensate for the reactive effects produced by the electrically discontinuous junction of the waveguide sections, or arms. Under these conditions, the arms are said to be compensated, or matched. However, the arms of a conventional hybrid T junction can be effectively compensated or matched, in this manner, for operation over a relatively narrow band of frequencies only, whereas relatively broad band operation is desirable in many applications. This is because the electrical discontinuity of a conventional, unmatched, hybrid T waveguide junction is relatively large. In addition, conventional matching elements must form relatively large obstructions in the waveguide sections in order to provide the required amount of reactance. Consequently, the power handling capacity of a conventional matched hybrid T is correspondingly low, because in the vicinity of these matching elements, there exist high voltage gradients which may cause arcing.

It is also desirable in most applications of a hybrid T junction to minimize the coupling between the E and Hplane arms, which in practice, are not completely isolated. The extent to which these arms are isolated depends upon the electrical symmetry of the junction. Since, in general, electrical discontinuity creates electrical asymmetry, there is greater isolation of the E and H plane arms in a hybrid T type waveguide junction having a relatively small amount of electrical discontinuity.

Therefore, according to this invention, a novel arrangement of intersecting Waveguide sections -is utilized to provide an unmatched hybrid T type waveguide junction having a relatively small amount of electrical discontinuity thereby minimizing the amount of energy reflected. Accordingly, operation is obtainable with an increased amount of power, over a broader band of frequencies, and with a higher degree of isolation between the E and H plane arms.

In particular, four terminal waveguides are joined by means of a hollow uniconductor transitional waveguide section having an aperture therein. A first and a second of these waveguides are disposed at an angle in the range between 0 and approximately 90;a third Waveguide is disposed so that its longitudinal axis is cm planar and symmetrical with respect to the longitudinal axes of the first and second sections; and a fourth section extends perpendicular to the first, second, and third sections.

Any conventional matching arrangement, well known to the art, may be used to match this improved hybrid T type waveguide junction over a relatively broad band of frequencies, with a high degree of isolationbetween the E and H plane arms. However, a preferred matching arrangement is herein disclosed which is readily adjustable for optimum results. In particular, capacitive posts are located in the first and second Waveguides, and an inductive iris is provided in the fourth waveguide.

Therefore, it is an object of this invention to provide an improved hybrid T type waveguide junction which can be effectively matched over a relatively broad band of frequencies.

It is'another object to provide a hybrid T junction which has a relatively small amount of coupling between the E and H plane arms over a wide range of operating frequencies.

It is a further object to provide a hybrid T junction which is more easily manufactured than prior art devices of this type, and which, for many applications, is more readily adapted for connection with external microwave circuitry.

The novel features which are believed to be characteristic of this invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which:

Fig. l is a perspective view of an improved hybrid T type waveguide junction utilizing rectangular waveguide,

and embodying the present invention;

Fig. 2 is a perspective view of a modification of the improved hybrid T type waveguide junction illustrated in Fig. 1, in accordance with this invention;

Fig. 3 is a perspective view of another modification of the improved hybrid T type waveguide junction illustrated in Fig. 1, utilizing square waveguide, also in accordance with this invention; and

Fig. 4 is a perspective view of a further modification of the improved hybrid T type Waveguide junction of Fig. 1.

Referring now to the drawing wherein like elements are designated by the same reference characters, and particularly to Fig. 1, there is illustrated a waveguide structure of the hybrid T junction type including rectilinear

terminal waveguides

10, 20, 30, and 40. These waveguides need not be identical but are preferably recwalls may also be spaced a small distance apart.

tangular in cross section, having cross sectional or transverse dimensions of approximately the ratio 2:1; that is, the width of these sections is approximately twice their height. Waveguide has narrow walls, 11 and 12, and broad walls, 13 and 14. Similarly, waveguide 26 has narrow walls, 21 and 22, and broad walls, 23 and 24; waveguide 30 has narrow walls, 31 and 32, and broad walls, 33 and 34; and waveguide 40 has narrow walls, 41 and 42, and broad walls, 43 and 44. The exact dimensions of

waveguides

10, 20, 30, and 40 are determined with respect to the operating frequency to the end that only the TE mode be propagated in the waveguides. In this mode, the electric vector, E, extends between the broad, or horizontal walls of each of the waveguide sections, parallel to the narrow, or vertical walls as is well known.

Waveguides 10 and are parallel, narrow walls 11 and 21 of waveguides 10 and 20, respectively, being adjacent; and narrow walls 12 and 22 of waveguides 10 and 20, respectively, being remote. Although walls 11 and 21 are in actual contact, as illustrated in Fig. 1, these They may therefore be termed respective contiguous narrow walls. Waveguide is disposed so that its longitudinal axis is coplanar and symmetrical with respect to the longitudinal axes of waveguides 19 and 20

broad walls

13, 14, 23, 24, 33, 34 being parallel to each other and

narrow walls

11, 12, 21, 22, 31, 32 being parallel to each other. Waveguide preferably extends substantially perpendicular to

waveguides

10, 20, and 30, in such a mannerthat broad walls 43 and 44, of waveguide 40, are parallel to

narrow walls

31 and 32, of waveguide 30. The waveguide 30 may be considered to form a continuation of the waveguides 10 and 20 and its longitudinal axis to be coplanar and symmetrical with the longitudinal axes of the waveguides 10 and 20.

Waveguides

10, 20, 30, and 40 are interconnected by means of a hollow uniconduetor transitional waveguide section 60, comprising narrow walls, 61 and 62, and

broad walls

63, and 64; narrow wall 61 having the same dimensions as narrow wall 62, and broad wall 63 having the same dimensions as broad wall 64. Wall 61 includes straight portions, 71 and 72, and stepped portions, 73 and 74, at right angles to the straight portions. Wall 62 includes like portions which are disposed in the same manner. The transitional waveguide section provides an impedance matching coupling between the first and second waveguides, 10 and 20 respectively, and the third waveguide 30. r

The height of transitional waveguide section 60, that is, the distance separating

broad walls

63 and 64, which are parallel, is equal to the height of the waveguides, 10, 20, and 30. The width of connecting chamber 60 at one of its ends, toward the right of Fig. 1, that is, the distance separating narrow wall portion 71 from the corresponding portion of wall 62 is substantially equal to the combined width of waveguides 10 and 20. Waveguides 10 and 20 are joined to this end of transitional waveguide section 60 in the following manner: broad wall 63 of transitional waveguide section 60 abuts, or extends in the same plane as broad walls 13 and 23, of waveguides 10 and 20, respectively; broad wall 64 of transitional waveguide section 60 similarly abuts broad walls 14 and 24, of waveguides 10 and 20, respectively; portion 71, of narrow walls 61 and the corresponding portion of wall 62, of transitional waveguide section 60, are disposed parallel to each other, and abut, or extend in the same plane as the remote narrow walls 12 and 22, respectively, of waveguides 10 and 20, respectively. Accordingly, transitional waveguide section 60 forms an enclosure which is an extension of waveguides 10 and 20, adjacent narrow walls 11 and 21, of waveguides 10 and 20, respectively, terminating at the entrance of transitional waveguide section 60. The width of transitional waveguide section 60 at the other of its ends, towards the left of Fig. l, is

substantially equal to the width of waveguide 30, to which it is joined in the following manner:

broad walls

63 and 64 of transitional,waveguide section 60 abut

broad walls

33 and 34, respectively, of waveguide 30; portion 73, of narrow walls 61, and the corresponding portion of wall 62, of transitional waveguide section 60, are coplanar with respect to each other, and are joined at right angles to the

narrow walls

31 and 32, respectively, of waveguide section 30. Thus, the width of transitional waveguide section 60 is reduced from approximately the combined width of waveguides 10 and 20 to the width of waveguide 31 by means of the steps in transitional waveguide section 60, provided by the stepped portions of

walls

61 and 62. A different arrangement of steps appropriate to accomplish this result may also be used, provided that the electrical discontinuity presented by transitional wave guide section 60 is minimized.

Waveguide 40 is connected to transitional waveguide section 60 by means of an opening or a suitable slot, centrally located in broad wallv 63 thereof. This opening is preferably rectangular, and of a size and outline conforming to the size and outline of waveguide 40.

Fig. 1 also illustrates a preferred arrangement of matching elements comprising screws, or posts, 16 and 26, and projections, 46 and 47. Screw 16 is centrally located in broad wall 13, of waveguide 10, in proximity to transitional waveguide section 60. Screw 26 is centrally located in broad wall 23 of waveguide 20, also in proximity to transitional waveguide section 69. Each of these screws projects a small amount into its respective waveguide in order to provide matching capacitive reactance. Projections 46 and 4'7, respectively, are aiiixcd to the narrow inner walls 41 and 42, respectively, of waveguide 48. These projections are equidistant from, and in proximity to wall 63, of transitional waveguide section 60, and form an iris which provides matching inductive reactance.

Referring to Fig. 2, the terminal waveguides of the hybrid T type waveguide junction, there illustrated, are disposed as in Fig. 1, except that waveguides 10 and 2t) diverge. That is, waveguides 1i) and 26 are separated by an acute angle, formed by the intersection of the adjacent narrow walls 11 and 21, of the respective waveguides. The waveguides 10 and 20 may therefore be said to have apexing narrow walls 11 and 21 respectively.

The waveguides are interconnected by means of a hollow uniconduetor transitional waveguide section, 80, comprising narrow walls, 81 and 82, and broad walls, 83 and 84. Transitional waveguide section is similar to transitional waveguide section 60, of Fig. 1, except that

narrow walls

81 and 82 are straight, and form an angle with the narrow walls 12 and 22 of waveguides 10 and 20, on the one hand, and with

narrow walls

31 and 32, of waveguide 30, on the other hand. That is, transitional waveguide section 80 reduces in the width from approximately the combined widths of waveguides 10 and 20, at one of its ends, to the width of waveguide 30, at the other one of its ends, by means of a continuous taper.

Transitional waveguide section 60, of Fig. 1 may also be used in place of transitional waveguide sections 80, of Fig. 2, and vice versa, since either transitional waveguide section is appropriate to interconnect the waveguides with a minimum of electrical discontinuity.

Referring to Fig. 3,

terminal waveguides

81, 82, 83, and 84 are square, having cross sectional, or transverse dimensions of the ratio 1:1. The exact dimensions of these waveguides are determined with respect to the operating frequency in the manner explained in connection with Fig. l, in order that only the TE mode be propagated.

Waveguides

81, 82, 83, and 84, respectively, are disposed in the same manner as

waveguides

10, 20, 30 and 40, of Fig. 1. These waveguides are interconnected by means of a hollow uniconduetor transitional waveguide section, 85, comprising narrow walls, 86 and 87, and broad walls, 88 and 89. Transitional waveguide section 85 is similar to transitional waveguide section 60, of Fig. 1, except that narrow walls 86 and 87 are curved. That is, transitional waveguide section 85 reduces in widths from approximately the combined width of

waveguides

81 and 32, at one of its ends, to the width of waveguide 83 at the other one of its ends, by means of inwardly curved narrow walls 86 and 87.

Transitional waveguide section 60, of Fig. 1, or transitional waveguide section 80, of Fig. 2, may also be used in place of transitional waveguide section 85, and vice versa, since either transitional waveguide section is appropriate to interconect the waveguides with a minimum of electrical discontinuity.

Referring to Fig. 4, another hollow uniconductor transitional waveguide section, 90, is illustrated, similar to transitional waveguide section 60, of Fig. 1, except that it is higher than

rectangular waveguides

10, 20 and 30. It is necessary, therefore, that transitional waveguide section 60 include end walls, 911 and 92. End wall 91 is provided with an opening which is preferably centrally located to receive waveguide 30, which is disposed as in Fig. 1. End wall 92 is provided with two centrally located and adjacent openings to receive waveguides and 20, which are also disposed as in Fig. 1. Waveguide 40 is connected to transitional waveguide section 90 as in Fig. 1. The exact height of transitional waveguide section 90 can best be determined experimentally, according to the operating frequency, and the size and shape of the waveguides utilizedv Any of these transitional waveguide sections could be stepped, in part, and tapered in part, or partly stepped and partly curved, or tapered in part, and curved, in part. Also,

waveguides

10, 20, 30, and 40, of Figs. 1, 2, and 4, may be used in place of waveguides S1, 82, 83, and 84, of Fig. 3, and vice versa, since either type of waveguide is appropriate for TE mode propagation. For the same reason, round or elliptical waveguides, or rectangular waveguides having other aspect ratios may also be utilized. The types of waveguide illustrated are preferred, however, since they are used predominately in microwave circuitry, and are therefore readily adapted for connection with other waveguides of similar type.

in operation,

waveguides

10, 20, and 30, of Figs. 1, 2, and 4, form the arms of an H plane junction, since the longitudinal axes of the waveguides lie in a plane parallel to the magnetic vector, H. Such a junction has the property that energy supplied to the H plane arm, waveguide 30, excites waves of equal phases in arms or waveguides it, and 20. Contra'riwise, waveguide sections it 20, and 40 may be regarded as forming the arms of an E plane junction, since the junction operates as if the longitudinal axes of the waveguides lay in a plane parallel to the electricvector, E. That is, energy supplied to the E plane arm, waveguide 40, excites waves of opposite phase in armsifi and 20. Consequently, energy supplied to either

arm

30 or 40 is transmitted equally to reilectionless loads terminating arms 10 and 20 there being substantially no direct coupling between

arms

30 and 40. Of course,

waveguides

81, 82, 83, 34 of Fig. 3 also operate in this same manner.

Efiective isolation of

arms

30 and 40 does not require that there be no reflected energy. However, in most applications of a hybrid T junction, it is desirable to eliminate reflected energy, that is to match the junction, in order to obtain so-called magic T operation. This means that it is then possible to transmit energy to

arms

30 and 40, equaily, from either of arms 10 or 20, with substantially no coupling therebetween. Thus, screws or posts and 2e are utilized to provide capacitive reactance appropriate to compensate, or match the electrical discontinuity of the H plane junction, that is, the junction of arms 10, and 30. In addition screws 16, 26 may be individually adjusted to accomplish maximum isolation of the H plane arm 30, and the E plane arm 40. Projections 46 and 47, on the other hand, comprise an inductive iris which provides inductive reactance. By means of this iris the E plane junction, that is, the junction of

arms

10, 20, and 40 is effectively matched.

It is to be understood that matching can also be accomplished by other matching arrangements well known to the art, since the matching of this hybrid T type waveguide junction is easily accomplished. This fact maybe illustrated by means of voltage standing wave ratio data which is a measure of reflected energy. That is, a voltage standing wave ratio equal to one occurs when no reflected energy is present; and anincreasingly greater voltage standing wave ratio occurs as the amount of reflected energy increases with respect to the amount of transmitted energy. Specifically, whereas the voltage standing wave ratio of a conventional, unmatched, hybrid T waveguide junction, designed for operation in the frequency range 8500 to 9500 me. (megacycles) exceeds 3.50, in the H plane arm, and 2.20 in the E plane arm, with approximately 30 db (decibels) isolation between these arms, the voltage standing wave ratio, over the same frequency range, of the unmatched hybrid T type waveguide junction according to this invention does not exceed 1.20, in the H plane arm, or 1.50, in the E plane arm, with 60 db (decibels) isolation between these arms. With the disclosed matching elements included in this hybrid T type waveguide junction, the voltage standing wave ratio is less than 1.08 in the H plane arm, and 1.10 in the E plane arm, over a comparable range of frequencies. Under these conditions, the waveguide junction may be operated with an amount of power in excess of 250 kw. (kilowatts). I

What is claimed as new is:

1. A waveguide structure of the hybrid T junction type comprising: first, second, third and fourth terminal hollow uniconductor rectilinear waveguides of rectangular cross section for transmitting electromagnetic waves in the TE mode only and a transitional hollow uniconductor waveguide section for providing an impedance matching coupling between said third waveguide and said first and second waveguides, said Waveguide section being provided with an aperture for coupling said fourth waveguide to said first and second waveguides, said first and said second waveguide having respective contiguous narrow walls, said first and said second waveguide being coupled to said waveguide section, said third waveguide being coupled to said waveguide section forming a continuation of said first and second waveguides and having its longitudinal axis coplanar and symmetrical with respect to the longitudinal axes of said first and second waveguides, and said fourth waveguide extending substantially perpendicular to said first, second and third waveguides, the respective broad walls of said first, second and third waveguides being coplanar and the narrow walls of said third waveguide extending in planes parallel to the broad walls of said fourth Waveguide.

2. A waveguide structure of the hybrid T junction type for transmitting electromagnetic waves in the TE mode only comprising: irst and second straight terminal hollow uniconductor waveguides of rectangular cross section separated by an angle in the range between 0 and approximately and having apexing adjacent narrow. walls; a third terminal hollow uniconductor waveguide or". rectangular cross section forming a continuation of said first and second waveguides and having its longitudinal axis coplanar and symmetrical with respect to the longitudinal axes of said first and second waveguides; a fourth terminal hollow uniconductor waveguide of rectangular cross section extending perpendicular to said first, second, and third waveguides, the respective broad Walls of said first, second and third waveguides being coplanar and the narrow walls of said third waveguide extending in planes parallel to the broad walls of said fourth waveguide, and a transitional hollow uniconductor waveguide section providing an impedance matching coupling between said third waveguide and said first and second Waveguides, said waveguide section being provided with an aperture for coupling said fourth waveguide to said first and second waveguides, whereby electromagnetic waves transmitted by said third waveguide excite electromagnetic waves of equal phase within said first and second waveguides and electromagnetic waves transmitted by said fourth waveguide excite electromagnetic waves of opposite phase within said first and second waveguides, whereby all of said waveguides in combination operate as a hybrid T waveguide junction.

3. A waveguide structure of the hybrid T junction type for transmitting electromagnetic waves in the TB mode only comprising: first and second straight terminal hollow uniconductor waveguides of rectangular cross section having respective contacting narrow walls; a third terminal hollow uniconductor waveguide of rectangular cross section having its longitudinal axis coplanar and symmetrical with respect to the longitudinal axes of said first and second waveguides and extending in a direction substantially opposite thereto; a fourth terminal hollow uniconductor waveguide of rectangular cross section extending perpendicular to said first, second, and third waveguides, the respective broad walls of said first, second and third waveguides being coplanar and the narrow walls of said third waveguide extending in planes parallel to the broad walls of said fourth waveguide; and a transitional hollow uniconductor waveguide section providing an impedance matching coupling between said third waveguide and said first and second Waveguides, said waveguide section being provided with an aperture for coupling said fourth waveguide to said first and second waveguides.

4. A waveguide structure according to claim 2, including matching means, cooperating with said terminal waveguides, to compensate for electrical discontinuities associated with the junction between said terminal waveguides and said transitional waveguide section.

5. A waveguide structure according to claim 2, including matching elements comprising: a first conductive post projecting into said first waveguide; a second conductive post projecting into said second waveguide; and an iris formed in said fourth waveguide, each of said elements being located in proximity to said transitional waveguide section, said posts being disposed to provide capacitance reactance, and said iris being disposed to provide inductive reactance.

6. A waveguide structure according to claim 2 wherein said transitional waveguide section comprises a first and a second mutually perpendicular pair of walls, and wherein said first pair of walls is abutting and extending in planes of the respective pair of broad walls of said first, second, and third waveguides so as to form a continuous extension thereof.

7. A waveguide structure according to claim 6 wherein each one of said second pair of walls of said transitional waveguide section is identical with the other, and each one has straight portions disposed substantially parallel to each other, and stepped portions disposed substantially perpendicular to said straight portions so as to provide an electrically matched waveguide to waveguide transition from said first and second waveguides to said third waveguide.

8. A waveguide structure for transmitting electromagnetic waves in the TE mode only comprising: first, second, third and fourth terminal hollow rectilinear uniconductor waveguides; and a transitional hollow uniconductor waveguide section for coupling said third waveguide to said first and second waveguides, said waveguide section being provided with an aperture for coupling said fourth waveguide to said first and second waveguides, said first and second waveguides having respective contiguous narrow walls, said third waveguide having its longitudinal axis coplanar and symmetrical with respect to the longitudinalaxes of said first and second waveguides, and said fourth waveguide extending substantially perpendicular to said first, second and third waveguides, the respective broad walls of said first, second and third waveguides being coplanar and the narrow walls of said third waveguide extending in planes parallel to the broad walls of said fourth waveguide, whereby electromagnetic waves transmitted by said third waveguide excite electromagnetic waves of equal phase within said first and second waveguides, and electromagnetic waves transmitted by said fourth waveguide excite electromagnetic waves of opposite phase within said first and second waveguides.

9. A waveguide structure of the hybrid T junction type for transmitting electromagnetic waves in the TE mode only comprising: first and second terminal hollow uniconductor waveguides of rectangular cross section separated by an acute angle; a third terminal hollow uniconductor waveguide of rectangular cross section having its longitudinal axis coplanar and symmetrical with respect to the longitudinal axes of said first and second waveguides; a fourth terminal hollow uniconductor waveguide of rectangular cross section extending perpendicular to said first, second, and third waveguides, the respective broad walls of said first, second and third waveguides being coplanar and the respective narrow walls thereof extending in planes parallel to the broad walls of said fourth waveguide, and a transitional hollow uniconductor waveguide section providing an impedance matching coupling between said third waveguide and said first and second waveguides, said waveguide section being provided with an aperture for coupling said fourth waveguide to said first and second waveguides.

10. A waveguide structure according to claim 9 Wherein said transitional waveguide section is rectangular in cross section and includes a second pair of walls disposed at an acuate angle relative to each other so as to provide a continuous taper from the combined width of said first and second waveguides to the width of said third waveguide.

References Cited in the file of this patent UNITED STATES PATENTS 2,438,915 Hansen Apr. 6, 1948 2,445,895 Tyrrell July 27, 1948 2,531,447 Lewis Nov. 28, 1950 2,563,612 Nebel Aug. 7, 1951 2,643,295 Lippmann June 23, 1953 2,656,513 King Oct. 20, 1953 2,682,641 Sensiper June 29, 1954 2,704,351 Dicke Mar. 15, 1955 2,739,287 Riblet Mar. 20, 1956 2,764,740 Pratt Sept. 25, 1956 OTHER REFERENCES Hughes and Astrahan: The Duo-Mode Exciter, Proceedings of the I. R. E., vol. 37, No. 9, September 1949,

5 page 1031. (Copyin333-11.)

v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,840,787 June 24, 1958 Mack Donald Adcock et all,

a It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 56, for "reduces in the Width" read reduces in Width column 5, line 4, for "Widths from approximately the combined width of Wave-=" read Width from approximately the combined Widths of Wave p line 12,

for "interconect" read interconnect e Signed and sealed this 23rd day of December 19580 (SEAL) Attest:

KARL II, ,AXLINE Attesting Oflicer ROBERT c. WATSON Commissioner of Patents