US3039097A

US3039097A - Frequency-sensitive rapid-scanning antenna

Info

Publication number: US3039097A
Application number: US374708A
Authority: US
Inventors: Strumwasser Eric; Lester C Van Atta
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1953-08-17
Filing date: 1953-08-17
Publication date: 1962-06-12
Anticipated expiration: 1979-06-12

Description

June 12, 2 E. STRUMWASSER ETAL 3,039,097

FREQUENCY-SENSITIVE RAPID-SCANNING ANTENNA Filed Aug. 17, 1953 2 Sheets-Sheet 1 INVENTORS. LESTER C. VAN ATTA y ERIC STRuMwAssER HIS ATTORNEY. 2

June12,1962 ESTRUMWASSEFR ETAL 3,039,097

' FREQUENCY-SENSITIVE RAPID-SCANNING ANTENNA Filed Aug. 17, 1955 2 Sheets-Sheet 2 II E 1U INVENTORS.

' LE$TER C. VANATTA y ERK; STRuMWAsSER Hls ATM United States Fine 3,039,097 FREQUENCY-SENSITIVE RAPID-SCANNHJG ANTENNA Eric Strurnwasser, Los Angeles, and Lester C. Van Atta,

Pacific Palisades, Calif., assignors, by mesne assignments, to Hughes Aircraft Company, a corporation of Delaware Filed Aug. 17, 1953, Ser. No. 374,708 16 Claims. (Cl. 343-771) This invention relates to electromagnetic-wave radiators and receptors and more particularly to an antenna for scanning a given region in space with a beam of electromagnetic energy.

In a wave transmission system, such as a radar system, it is usually necessary to employ a narrow beam antenna which is capable of scanning a predetermined region in space. According to one method of scanning, generally referred to as mechanical scanning, the antenna structure is moved about a fixed point or axis in a predetermined geometrical pattern. However, rapid scanning in this manner with a highly concentrated beam often involves serious mechanical problems arising from antenna size and weight considerations.

In order to circumvent such problems, other methods of scanning have been devised which utilize a stationary scanning antenna. One of these is frequency controlled scanning; that is, scanning by means of periodic frequency variation. To accomplish this result, there is generally provided an antenna comprising a linear array of uniformly spaced radiators, each coupled at a different point to a common transmission line or waveguide. If the coupling points are separated by equal lengths of the waveguide, a change in the frequency of electromagnetic energy supplied at one end thereof causes a progressively incrasing phase shift in the energy which excites successive radiators. As a result, the beam produced by the radiators is angularly deflected with respect to the axis of the array, and scanning in a single plane, or so-called sector scanning, is readily accomplished.

Owing to the fact that the beam produced by the linear array of radiators is generally broad in a plane perpendicular to the axis of the array, it is often desirable to provide some means for narrowing it. This may be done most conveniently with a beam-forming reflector. In order for the reflector to be effective, however, it is necessary that the structure comprising the array of radiators present little obstruction to the reflected beam; that is, the reflector aperture may not be blocked appreciably. Because of this requirement, the combination of a frequency scanning array with a beam-forming reflector has proved to be most difficult in the past.

According to the present invention, however, there is provided an improved frequency controlled scanning antenna which eliminates, to a large extent, the problem of reflector aperture blocking. Briefly, the improved scanning antenna includes a linear array of radiators consisting of slots in a narrow wall of a length of rectangular waveguide. The waveguide is folded back upon itself at substantially regular intervals in a configuration similar to a serpentine. In terms of waveguide wavelengths, adjacent slots are separated by relatively long sections of waveguide as is required for relatively large angular deflections of the antenna beam with relatively small changes in frequency. Also, the spacial separation of adjacent slots is relatively small in terms of free space wavelengths so that a satisfactory radiation pattern may be obtained in a plane parallel to the axis of the array.

This waveguide configuration is adapted for use with a beam-forming reflector and yet does not obstruct the reflected beam by an amount suflicient to cause it to be dispersed and thereby seriously reduce the effectiveness of the reflector.

It is an object of this invention, threfore, to provide an improved frequency controlled scanning antenna,

It is another object of this invention to provide an improved frequency controlled scanning antenna which includes a linear array of slot radiators particularly adapted for operation in combination with a reflector.

It is a further object of this invention to provide an improved frequency controlled scanning antenna which includes a beam-forming reflector having its aperture substantially unobstructed.

The novel features which are believed to be characteristic of the 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 drawings in which:

FIG. 1 is a perspective view of the antenna according to the invention;

FIG. 2 is a plan view of the antenna according to the invention;

FIG. 3 is a fragmentary view of the feed structure employed in the antenna illustrated in FIGS. 1 and 2;

FIG. 4 is a sectional view of the feed structure taken on lines 44 of FIG. '3;

FIG. 5 is another sectional view of the feed structure taken on lines 5-5 of FIG. 3;

FIG. 6 is a perspective view similar to FIG. 1 illustrating a modification of the antenna also in accordance with the invention;

FIG. 7 is a plan view of the antenna illustrated in FIG. 6;

FIGS. 8 and 9 are plan views similar to FIG. 6 illustrating modifications of the feed structure further in accordance with the invention;

FIG. 10 is a fragmentary view of a further modification of the feed structure also in accordance with the invention; and

FIG. 11 is a sectional view of the feed structure taken on lines 11-11 of FIG. 10.

Referring to FIGS. 1 through 4, the frequency controlled scanning antenna in accordance with the invention comprises an improved feed structure 11 and a reflector 31. Included in the feed stmcture 11 is a folded length of rectangular waveguide 12 having

narrow walls

21, 22, input and

output ends

13 and 14, respectively, and provided with a series of radiating slots 18 linearly arrayed along an axis 19. The slots 18 extend across narrow wall 21 of the waveguide 12 and have a uniform center-to-center spacing equal to a distance 0 measured along the array axis 19. In addition, the centers of adjacent slots 18 are separated by equal lengths of the waveguide 12 as indicated by dimension d. Di mension c is made less than one wavelength in free space so that, in effect, only a single primary beam of radiant energy is produced by slots 18. Dimension d, however, is relatively large in terms of waveguide wavelengths to provide for relatively large angular deflections of the beam with relatively small changes in frequency. In order to arrange the slots, 18, in this manner, the waveguide 12 is formed in a configuration similar to a serpentine with

narrow waveguide walls

21 and 22, each being disposed in a single plane. More particularly,

the waveguide 12 is folded back upon itself at regular intervals to form a series of straight waveguide sections 15 aligned parallel to each other, and a series of U-shaped waveguide sections 16 interconnecting the straight sections 15. Each of the straight sections, 15, includes one of the slots, 18, centrally located in narrow wall 21. That is, the array axis 19, which joins the centers of spaces? 3 the slots 18, bisects the narrow wall 21 of each of the straight sections 15.

Each of the slots 18 is inclined with respect to the array axis 19 in order to control the amount of energy which it radiates. Thus the amount of energy contributed by a particular slot may be increased with increasing angles of inclination and decreased with decreasing angles of inclination. Although the exact amount by which slots 18 are inclined will depend to some extent on radiation pattern requirements, it generally will be necessary to increase the angle of inclination from slot to slot with increasing distance from the input end 13 of the waveguide 12. This is because less energy is available to those slots which are farthest removed from the input end 13 of waveguide 12. In addition, dimension d is made equal to an integral number of waveguide wavelengths at the center operating frequency andadjacent slots 18 are oppositely inclined, as shown in FIG. 3. In this way, a single beam of radiant energy is formed owing to the in-phase radiation of the slots at the center operating frequency and the progressive phase shift from slot to slot at other than the center operating frequency. That is to say, electromagnetic Waves propagating in waveguide 12 have a phase which differs by 360 degrees, or a multiple thereof, from one slot to the next because of dimension d. Owing to the U-shaped bends in the waveguide, however, the waves are periodically inverted so that, with respect to adjacent slots, they are apparently out of phase. Accordingly, adjacent slots 18 are coupled to waveguide 12 in a reverse phase relation, by virtue of their opposite inclinations, in order that they may radiate in phase at the center operating frequency. A similar result may also be obtained if dimension d is equal to an odd number of half waveguide wavelengths at the center operating frequency. In this case, however, all of the slots 18 would be inclined in the same direction. 1

It is most desirable that each of the slots 18 be substantially resonant or, in other words, present no reactive load to the waves propagating in the waveguide. Therefore the length of the slots must be equal to a distance in the order of one-half wavelength in free space. Assuming that conventional waveguide is utilized wherein the width of the narrow wall 21 is approximately threeeighths of a wavelength in free space, it is apparent that the required length of the slots Iii-may exceed the width of the narrow Wall 21. To overcome this difiiculty, and also to provide a mechanically rigid feed structure which is easily manufactured, the central portions of the straight waveguide sections are formed with a connecting member 23. Connecting member 23 comprises a rigid bar disposed so that its longitudinal axis bisects the longitudinal axes of :the straight sections 15. Included in connecting member 23 is a series of rectangular ducts having cross-sectional dimensions identical with those of the inside dimensions of waveguide 12. Each of the ducts is aligned with the interior of one of the straight sections 15, so as to form an integral portion thereof or, in effect, one continuous straight section of waveguide. The slots 18 may then be extended beyond the narrow wall 21 of the duct or Waveguide 15 in the form of

recesses

28 and 29 in connecting member 23, as shown in detail in FIG. 5. Recesses 2S and 29 which have a depth of approximately one-quarter wavelength in free space effectively lengthen the slots 18 so as to make them resonant. Of course other well known methods of accomplishing the same result may also be used. For example, the slots may be filled with a suitable dielectric material which decreases their resonant frequency, thereby effectively adding to their length. The method utilized in the invention is preferred, however, owing to the fact that the slots remain more nearly resonant over a wider band of frequencies.

As illustrated in FIGS. 1 through 4, there is also provided a cover 24 substantially enclosing the waveguide configuration 12, and thereby preventing energy radiated by the slots 18 from passing between the straight sections 15. The slots 18 are exposed by means of a rectangular aperture provided in the cover 24 and overlying connecting member 23. Joined to cover 24 is a. vane 20 for directing the energy radiated by the slots 18 towards reflector 31. Vane 20 comprises a plane reflecting surface of rectangular shape which projects over the slots 18. In particular, vane 20 is disposed parallel to the array axis 19 and at an acute angle with respect I to the slotted wall of connecting member 23. The distance from the array axis 19 to the apex of the angle formed by the junction of vane 20 and cover 24 is preferably in the order of one-half wavelength in free space.

Since feed structure 11 produces a fan-shaped beam which is broad in a plane perpendicular to the array axis 19, reflector 31 is used to narrow the beam in this plane. Reflector 31 comprises one half of a parabolic cylinder having

principal axes

32, 33 and a focal line 34. It is oriented so that the

principal axes

32, 33 are perpendicular to the array axis 19 and the plane of these axes substantially coincides with the plane of the narrow wall 21. In addition, focal line 34 is located at the mouth or aperture 36 of the horn-type structure formed by vane 20 and cover 24 as illustrated in detail in FIG. 4. Thus it is seen that the feed structure 11 is etfectively on edge with respect to reflector 31, and therefore does not obstruct appreciably the reflected beam which is formed thereby.

In operation electromagnetic wave energy is supplied to the input end 13 of the waveguide 12. This energy propagates in the waveguide 12 and is radiated in part by each of the slots 18 in a manner to form a directive beam which is narrow in a plane parallel to the array axis 19. The small amount of energy not radiated by the slots 18 may be absorbed by a dummy load coupled to the output end 14 of the Waveguide 12. This will prevent reflections and thereby improve the impedance characteristics of the slot array. Vane 2t) and cover member 24 form a horn-type structure for directing the beam towards the reflector 31. Owing to the parabolic shape of reflector 31, the beam also becomes narrow in a plane perpendicular to the array axis 19 upon reflection. That is to say, with the antenna oriented as shown in FIGS. 1 and 2, a highly concentrated beam is formed in a vertical plane by the linear array of slots 18, and in a horizontal plane by the reflector 3 1. This beam is angularly deflected in the vertical plane, or, in other words, scanned in elevation, by changing the frequency of the electromagnetic energy supplied to the input end 13 of the waveguide 15. The amount of angular deflection of the beam caused by a given change in frequency made be calculated with reference to the following equation:

A A) u,

=angular deflection of the beam from broadside (with respect to the principal axis 32 of FIG. 1)

c=spacial separation of the slots d=length of waveguide between adjacent slots A=wave1ength A =waveguide wavelength x =waveguide wavelength giving a broadside beam.

where FIGS. 6 and 7 illustrate a modification of the scanning antenna according to the invention and described in connection with FIGS. 1 through 5. As shown in FIGS. 6 and 7, feed structure 41 of the modified scanning antenna includes an additional linear array of slots 42 formed in narrow wall 22 of the waveguide 12 opposite to the array of slots 18. Slots 42 are exposed by means of an aperture in cover member 24 as are slots 18. Associated with slots 42 is a vane 43 identical with vane 20 illustrated in FIGS. 1, 2 and 3.

Although each of the arrays of

slots

18 and 42 is fed by waveguide -12, the feed structure 41 of the modified scanning antenna operates as if two feed structures, like feed structure 11 of FIGS. 1 through 5, were placed side by side. Consequently, there is provided a reflector 44 which is made up of two parabolic reflectors like reflector 31 of FIGS. 1 and 2. In particular, reflector 44 has two focal lines, 34 and 46, positioned at the respective apertures of the horn-type structures formed with

vanes

20, 43 and cover 24. Ordinarily, this would means that reflector 44 be comprised of two distinct halves separated by a distance corresponding to the spacial separation of focal lines 34 and 46. In order to form one continuous surface, however, reflector 44 includes a central portion parallel to the plane containing the focal lines 34 and 46. A reflector of this type is preferable as compared with a single parabolic cylinder reflector because of its superior. beam-forming properties. As shown in detail in FIG. 7, it has also been found desirable to taper to an edge the parallel surfaces of cover 24 overlying the

narrow walls

21 and 22 of the waveguide 12. That is, the portion of the feed structure 41 which is remote with re spect to reflector 44 is formed in the shape of a wedge in order to further minimize the effect of the feed structure 41 on the reflected beam.

FIGS. 8, 9, l and 11 illustrate modified reflecting means or primary reflectors which perform the same function as

vanes

20 and 43 of FIGS. and 6, and which are equally applicable to either the scanning antenna of FIGS. 1 through 5 or the modified scanning antenna illustrated in FIGS. 6 and 7. Referring particularly to FIG. 8, there are illustrated primary reflectors 50, each having an intermediate portion 51 disposed parallel and adjacent to one of the

slot arrays

18 and 42. Each intermediate portion 51 is joined to cover 24 by means of a connecting portion 52. Extending outwardly at an acute angle with respect to the

narrow walls

21 and 22 of the waveguide 15, in a manner somewhat similar to

vanes

21 and 43, are outer portions 53 which abut the intermediate portions 52 Referring now to FIG. 9, there is illustrated modified primary reflectors 55 similar to primary reflectors 50 of FIG. 8, but having a shorter outer portion 56. Operation like that of primary reflectors 50 of FIG. 8 is obtained, nevertheless, by the provision of slabs of dielectric material 57. Dielectric slabs 57 are situated between the intermediate portions 51' of primary reflectors 55 and the respective

narrow walls

21 and 22 of the waveguide 12. In addition, these slabs 57 are extended beyond intermediate portions 51' and outer portions 56 with a gradual reduction in their thickness.

FIGS. and 11 illustrate further reflecting means also in accordance with the invention. Rather than reflecting surfaces, there are provided additional arrays of

slots

58 and 59 adjacent to slots 42 and consisting of depressions formed in connecting member 23. Slots 58 are aligned parallel to the array axis 49 of slots 42 on one side thereof, while slots 59 are aligned in like fashion on the opposite side of array axis 49. In addition, the centers of adjacent ones of the

slots

42, 58 and 59 lie on a straight line which is perpendicular to the aray axis 49. The center-to-center spacing of adjacent ones of

slots

42 and 58 and also alots 42 and 59 is in the order of one-fourth wavelength In free space. Although

slots

58 and 59 do not communi- :ate with the interior of the waveguide 12, they are excited parasitically by slots 42 and operate as a director and a reflector. Accordingly, the energy radiated by slots 42 is beamed towards reflector 44 in the manner described in connection with vane 21 of FIGS. 1 through 3. Of course, identical arrays of parasitic slots would be used in connection with slots 18.

What is claimed is:

1. An antenna for scanning a desired region in space with a beam of electromagnetic wave energy in response to variations in wavelength of the electromagnetic waves, said antenna including a length of waveguide folded back upon itself at substantially regular intervals to form a continuous series of substantially U-shaped waveguide sections having their longitudinal axes disposed in a single plane, the arms of altefnate U-shap ed sections of said series being aligned substantially parallel to each other, said waveguide being provided with a linear array of apertures in a wall thereof parallel to the plane of the longitudinal axes of said waveguide sections, and said apertures being uniformly spaced along said waveguide wall at intervals of more than one waveguide wavelength of said electromagnetic waves.

2. An antenna according to claim 1 wherein said apertures are uniformly spaced from each other, adjacent ones of said apertures being separated by a distance of less than one wavelength in free space of said electro magnetic waves, said distance being measured along the axis of said array.

3. An antenna according to claim 2 wherein said apertures are slots having their longitudinal axes disposed at an angle with respect to the axis of said array, the angle formed by the longitudinal axis of one of said slots and the axis of said array being substantially complementary with respect to the angle formed by the longitudinal axis of another one of said slots adjacent said one of said slots and the axis of said array.

4. An antenna having frequency controlled directive properties suitable for space scanning with a beam of electromagnetic wave energy, said antenna comprising a length of rectangular waveguide folded back upon itself at substantially regular intervals to form a continuous series of substantially straight waveguide sections having their longitudinal axes disposed in a single plane and aligned parallel to each other, and a series of U-shaped waveguide sections interconnecting said straight sections, said waveguide being provided with a linear array of slots in a wall thereof parallel to the plane of the longitudinal axes of said straight sections, said slots being uniformly spaced along the slotted waveguide Wall at intervals of more than one waveguide wavelength of the electromagnetic waves, and the centers of adjacent ones of said slots being separated by a fixed distance less than one wavelength in free space of the electromagnetic waves, said distance being measured along the axis of said array; and reflecting means joined to said slotted waveguide wall, said reflecting means and said slotted Waveguide wall forming a horn-type structure electrically coupled to said waveguide by means of said slots.

5. An antenna according to claim 4 wherein said reflecting means comprises a plane vane disposed parallel to the axis of said linear array and at an acute angle less than 45 with respect to said slotted waveguide wall, said vane projecting over said array.

6. An antenna according to claim 5 wherein said vane is joined to said slotted waveguide wall at a distance from the axis of said array equal to an integral number of half wavelengths in free space of the electromagnetic waves.

7. An antenna according to claim 4 wherein said reflecting means comprises a conductive member having an intermediate portion extending in a plane paralleland adjacent to the plane of said slotted Waveguide wall, an outer portion having a plane surface and extending outwardly at an acute angle with respect to said slotted it waveguide wall, and a connecting portion joining said first portion to said slotted Waveguide wall.

8. An antenna according to claim 7 including a layer of dielectric material interposed between the intermediate portion of said conductive member and said slotted waveguide wall, said dielectric layer projecting beyond the outer portion of said conductive member with a gradual decrease in its thickness.

9. An antenna having frequency controlled directive properties suitable for space scanning with a beam of electromagnetic Wave energy, said antenna comprising a length of rectangular waveguide folded back upon itself at substantially regular intervals to form a series of substantially straight waveguide sections having their longitudinal axes disposed in a single plane and aligned parallel to each other, and a series of U-shaped waveguide sections interconnecting said straight sections, said waveguide being provided with a first linear array of slots in a wall thereof parallel to the plane of the longitudinal axes of said straight sections, said slots being uniformly spaced along the slotted waveguide wall at intervals of more than one waveguide wavelength of said electromag netic waves, and the centers of adjacent ones of said slots being separated by a fixed distance of less than one wavelength in free space of said electromagnetic waves, said distance being measured along the axis of said first array, said waveguide including second and third linear arrays of parasitic radiating elements, the radiating elements of each of said second and third arrays consisting of slot-shaped recesses formed in said slotted waveguide Wall, and aligned parallel and adjacent to the axis of said first array, each of said slots being interposed between one of the recesses of said second array and one of the recesses of said third array.

10. An antenna for scanning a given region in space with a beam of electromagnetic wave energy in response to variations in wavelength of the electromagnetic waves, said antenna comprising a length of rectangular waveguide folded back upon itself at substantially regular intervals to form a series of substantially straight waveguide sections having their longitudinal axes disposed in a single plane and aligned parallel to each other, and a series of U-shaped waveguide sections interconnecting said straight sections, said waveguide being provided with a linear array of slots in a wall thereof parallel to the plane of the longitudinal axes of said straight sections, said slots being uniformly spaced along the slotted waveguide wall at intervals of more than one waveguide wavelength of said electromagnetic waves, and the centers of adjacent ones of said slots being separated by a fixed distance of less than one wavelength in free space of said electromagnetic waves, said distance being measured along the axis of said array; primary reflecting means joined to said slotted waveguide wall, said primary reflecting means and said slotted waveguide wall forming a horn-type structure electrically coupled to said waveguides by means of said slots and having a primary radiation pattern representative of a fan-shaped beam of radiant energy; and secondary reflecting means positioned in front of the aperture of said horn-type structure to form said fan-shaped beam into a pencil beam of radiant energy.

11. An antenna for scanning a given region in space with a beam of electromagnetic wave energy in response to variations in wavelength of the electromagnetic waves, said antenna comprising a length of rectangular waveguide folded back upon itself at substantially regular intervals to form a continuous series of substantially U-shaped waveguide sections havings their longitudinal axes disposed in a single plane, the arms of alternate U-shaped waveguide sections having their longitudinal parallel to each other, said waveguide being provided with a linear array of slots in a wall thereof parallel to the plane of the longitudinal axes of said waveguide sections and said slots being uniformly spaced along said Waveguide wall at intervals of more than one waveguide wavelength of said electromagnetic waves, the centers of adja cent ones of said slots being separated by a fixed distance of less than one wavelength in free space of said electromagnetic waves, said distance being measured along the axis of said array, and the longitudinal axes of saidslots being disposed at an angle with respect to the axis of said array, the angle formed by the longitudinal axis of one of said Slots and the axis of said array being substantially the same as the angle formed by the longitudinal axis of another one of said slots adjacent said one of said slots and the axis of said array; primary reflecting means joined to said sloted waveguide wall, said primary reflecting means and said slotted waveguide wall forming a horntype structure electrically coupled to said waveguide by means of said slots having a primary radiation pattern representative of a fan-shaped beam of radiant energy; and secondary reflecting means positioned in front of the aperture of said horn-type structure to form said fanshaped beam into a pencil beam of radiant energy.

12. An antenna for scanning a desired region in space with a "beam of electromagnetic wave energy in response to variations in wavelength of the electromagnetic waves, said antenna comprising a length of rectangular waveguide folded back upon itself at substantially regular intervals to form a series of substantially straight waveguide sections having their longitudinal axes disposed in a single plane, and aligned parallel to each other, and a series of U-shaped waveguide sections interconnecting said straight sections, said waveguide being provided with a pair of linear arrays of slots in opposite walls thereof parallel to the plane of the longitudinal axes of said straight waveguide sections, the slots of said arrays being uniformly spaced along the respective slotted waveguide walls at intervals of more than one waveguide wavelength of said electromagnetic waves, and the centers of the slots of each of said arrays being spaced at uniform intervals of less than one wavelength in free space of said electromagnetic waves, said distance being measured along the axes of each of said arrays; and reflecting means joined to each of said slotted waveguide walls, said reflecting means and said sloted waveguide walls forming a pair of horn-type structures electrically coupled to said waveguide by means of said slots.

13. An antenna according to claim 12 including a cover member overlying said sloted waveguide Walls and provided with apertures for exposing said slots to substantially eliminate mutual coupling between said horntype structures.

14. An antenna according to claim 13 wherein said reflecting means comprises a pair of plane vanes, each disposed parallel to the axes of said linear arrays and at an acute angle less than 45 with respect to said respective slotted waveguide walls, said vanes projecting over the respective arrays of slots.

15. An antenna according to claim 14 including a reflector shaped substantially in the form of a parabolic cylinder and positioned in front of the apertures of said horn-type structures for increasing the directivity of said horn-type structures in a plane perpendicular to the axes of said arrays of slots.

16. An antenna for scanning a desired region in space with a beam of electromagnetic wave energy in response to variations in wavelength of the electromagnetic waves, said antenna comprising a length of rectangular waveguide folded back upon itself at substantially regular intervals to form a continuous series of substantially U-shaped wave-guide sections having their longitudinal axes disposed in a single plane, the arms of alternate U-shaped sections of said series being aligned substantially parallel to each other, said waveguide being provided with a pair of linear arrays of slots in opposite walls thereof parallel to the plane of the longitudinal axes of said waveguide sections, the slots of said arrays being spaced along the respective slotted waveguide walls at uniform t I u up said cover member forming a pair or-horn-type structures electrically coupled to said waveguide by means of said slots; and second reflecting means, shaped substantially in the form of a parabolic cylinder, said first and second reflecting means cooperating to increase the d ireetivity of the antenna in a plane perpendicular to the axes of said arrays of slots.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,039,097 June 12, 1962 Eric Strumwasser et a1.

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

Column 1, line 65 for "spacial" read spatial column 7, line 69, for "havings" read having same column 7, line 71, strike out "having their longitudinal" and insert of said series being aligned substantially column 8, line 16, after "slots" insert and same column 8, lines 42, and 46, for "sloted" read slotted Signed and sealed this 30th day of October 1962.

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD Attesfing Officer Commissioner of Patents