US2926349A - Corner reflector antenna - Google Patents

Description

Feb. 23, 1960 Filed March 29, 1957 J. H. JENSEN 2,926,349

CORNER REFLECTOR ANTENNA 3 Sheets-Sheet l INVENTOR. JA CK H. JENSEN Feb. 23, 1960 J. H. JENSEN 2,926,349

CORNER REFLECTOR ANTENNA Filed March 29, 1957 3 Sheets-Sheet 2 Fig. 2

IN VEN TOR. JA CK H. JENSEN ATT RNEYS Feb. 23, 1960 Filed March 29, 1957 Fig. 5

AZIMUTH AZIMUTH J. H. JENSEN CORNER REFLECTOR ANTENNA Fig. 6

3 Sheets-Sheet IS AZIMUTH ELEVATION Fig.8

INVENTOR. JACK H JENSEN United States Patent. C

CORNER REFLECTOR ANTENNA Jack H. Jensen, San Diego, Calif.

Application March 29, 1957, Serial No. 649,576

12 Claims. (Cl. 343-840) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a corner reflector antenna and more particularly to a corner reflector antenna having parabolic side members for transmitting or receiving high frequency radiation having horizontal and vertical directivity.

Antenna devices utilizing reflector elements in conjunction with radiating elements to give directional beams are well known in the art. An example of one is the parabolic dish type reflector. The dish type reflector generally has a radiating element positioned at the focal point of the parabolic dish and a horizontal feed line leading thereto. The feed line usually passes through the dish and along its parabolic axis to the radiator. The dish type reflector can be designed to give a narrow beam having good horizontal and vertical directivity. However, antennas of this type have the limitations where a pencil type beam is desired, of having low relative gain or having high gain and relatively high side lobes or of being very large in size.

Another analogous directional beam type reflector is the corner reflector antenna. This type of antenna is easier to construct than the parabolic dish type and usually gives better gain than the general parabolic types. However, corner antennas known in the art, such as the corner antenna described in the Kraus patent, Patent No. 2,270,314, while giving a fairly narrow beam in the horizontal azimuth also radiates a wide beam in the vertical azimuth. Thus corner reflector antennas generally known in the art do not transmit the desired pencil type beam.

The antenna of the type disclosed herein comprises two symmetrical sections of a parabolic cylinder united in a general V shape and positioned on a ground plane. A radiator is positioned between the parabolic members and above the ground plane a distance that results in optimum impedance matching. The ground plane is a radial extension of the outer conductor member of the vertical coaxial feed to the radiator. In its normal operation, the radiator radiates high frequency waves which are reflected by the parabolic reflector surfaces to form a beam having the desired characteristics.

It is well known in the art of antennas having a directional beam that the requirement of maximum gain is incompatible with the requirement of minimum side lobes. Thus in any antenna of the directional type a certain balancing is required to provide an antenna having maximum gain with comparatively low side lobes. In this light the parabolic corner antenna is a distinctive advance in the art where a pencil type beam is required having high gain and low side lobes. A pencil type beam having high gain and low side lobes is generically desirable for directional or radar communication. An example of a more particular desirable use would be in radar detection to position targets in a fire control unit. In this latter instance, it is manifest that there be thegreatest 2,926,349 Patented Feb. 23, 1960 possible suppression of side lobes, as it confuses the fire control unit if a particular target gets in a side lobe. The parabolic corner reflector is also an extremely desirable addition to the art due to the excellent directional characteristics obtainable with a relatively small, in size, antenna that is simple to construct. These latter features are of particular advantage in increasing the efliciency and range of antennas on small ships.

The parabolic corner antenna radiates a beam having directional characteristics in the vertical and horizontal azimuth that is superior to the beam obtainable with a parabolic dish type or modifications thereof and further radiates a beam having greater gain with lower side lobes. The parabolic corner antenna also radiates a narrower beam in the horizontal and vertical azimuths than do the corner antennas generally known in the art. This is especially true with respect to the vertical azimuth. It also gives better gain and lower side lobes than is possible'with prior known corner antennas.

The invention utilizes a vertical feed that is so positioned with respect to the parabolic members and ground plane that distortion in the beam pattern from the radiator and radiator supporting structure is not present to any appreciable degree. Distortion of this type is a disturbing factor in some reflector arrangements, such as where horizontal radiators are used in dish type reflectors. The relative freedom from distortion may be attributed to a certain extent to the positioning of the radiator, which allows freer radiation in all directions above the ground plane. This results in less concentration of radiated waves at the lower part of the reflector, and thus less wave conflict with the radiator and director structure. Further, freer radiation of the waves from the radiator in a generally vertical direction is one of the features which distinguishes the invention over antennas of the horn type. I

The parabolic corner reflector can also be used, by reducing its overall size, as a primary feed for any of the presently known reflectors, such as a parabolic dish or cylinder types or any appropriate reflector known in the art.

An object of the present invention is the provision of an antenna that will transmit or receive a radiation pattern having good directivity in the horizontal and vertical azimuth and also having high gain with low side lobes.

Another object is to provide an antenna that is capable of radiating a pencil type beam having high gain with low side lobes.

A further object of the invention is the provision of an antenna having good directional characteristics and yet having simplicity of design and construction and being relatively small in size.

Another object is to provide a new and improved antenna of the corner reflector type.

Another object is to provide an antenna which combines certain structures of antennas of the corner reflector and parabolic-types to produce improved beam characteristics.

Another object is to provide an antenna which in construction lends itself to light weight fabrication techniques.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawing, which illustrates a preferred embodiment, and wherein:

Fig. 1 shows a perspective view partly broken away of a preferred embodiment of the invention;

Fig. 2 shows a top plan view of the apparatus;

Fig. 3 shows a section of the device taken on the line 33 of Fig. 2 looking in the direction of the arrows;

Fig. 4 is a diagrammatical end view of a parabolic directional beam obtained in elevation.

Referring now to the drawings, whereinlike reference characters'designate like or correspondin'gipa'rts throughout the several views,'there is shown in Fig. l a parabolic corner'reflector antenna having two 'para'bolicmembers 9. The parabolic members 9 have'refiecting'surfaces 19 which in the specific embodiment are constructed of aluminum. However, the members lend themselves to lightweight fabrication techniques and they may beconstruct'ed by several alternate methods'sucha's rodd'ed'con- "struction (vertical rods), screened construction, or fiber glass honeycomb construction with the important parts metal sprayed. 'The'parabolic members 9 "are secured to plate 10, see Figs. 1 and 3,which lays substantially normal to the mer'nbers. The plate gives added structural "strength to the parabolic members in their mounted 'position and also provides a horizontal attaching means for securing the 'refiectorto the ground plane 13. Pl'atelt) 'rn'aybefixed to the ground plane '13 in any'well known manner. It may even be integral 'withth'e gro'un'dplane desired. In fixing plate 10 to the ground plane 13 there'should be good electrical conductivity'tlierebetween to assure a free flow of energy from the outerconductor of the coaxial feed line 14 to the parabolic members 9. Also it 'is desirable that there be no space between the bottom edge of the parabolic members and the ground plane that would allow radiation leakage to the rear of the antenna.

In the specific embodiment, the parabolic members are join'ed'as at 22. see Fig. 2, in any manner known in 'the art such as welding, 'solderingor the like. However, it is within the scope of the invention 'tha't'the members not be specifically joined as shown. The members may be separated at the corner as long as they remainin 'a close relationship. The actual distance of separation'desirable depends'upon'the parameters of 'the antenna involved and "the effect the degree of separation has on'the pattern. The elfect can be determined by experimentation and in the specific embodiment it was determined thatthe resulting pattern characteristic was less desira'blethe greater the separation at the corner. This is because, with each increase in separation at the corner, there was an increase in'radiation leakage between the member's causing losses to the rearof the antenna and adversely affecting the pattern.

The parabolic members are symmetrical sections of a parabolic cylinder. With referenceto Fig. 4, a parabolic "cylinder is shown schematically as line 30 and has the usual curvature formula of y 'equ'als 4fx,forthe origin nated by the intersection point 32. Thep'ar'abolic section used in the antenna was removed from the parabolic cylinder 30, and is designated 9. The location -of point36,

"whichis the lower edge of the removed parabolic section 9, is established by the angle which'line 35 makes with the axis line 31. Line 35 passes throughthe focal point 32 of theparaboliccylinder. In the preferredembodiment, angle 0 is 30 degrees. However, other sections of the parabolic cylinder maybe used thus-changing the =ness-of:plate -10. It thusfollows that=-the-horizontal axis at the vertex. The axis line 31 of the parabolic cylinder is shown passing through the cylinders focal line, desigplane 31 of the parabolic cylinder lies at an angle 0 with the ground plane. Inasmuch as the parabolic members 9 are fixed to plate 10 (see Fig. 3) and plate 10 in turn is secured to the ground plane, the bottom edge of the parabolic members 9 are spaced from the ground plane the thickness of plate 10. The focal point 32 of the parabolic cylinder, or the focal line considering the length of the parabolic cylinder, is located at the intersection of lines 31 and 35. Since the cylinders focal point lies on line 35, it is spaced above theground vplane a distance equal to the thickness of plate 10, as illustrated in Fig. 3 by point 33.

The two parabolic sections in the mounted position as shown in Figs. 1 through 3, have their -focal lines lying in the same plane. The two focal lines will intersectat a predetermined point between the parabolic segments'and the point will be located on a line that bisects the angle between the members. The point of intersection of the two focallines is the focal point for the 'two Iparabolic 'segme'ntstaken as a unit. This point is positioned inthe specific embodiment at point 33 in Fig. 3.

The ground plane 13 is a radial 'e'xten'sionof the outer conductor member 14 of the feed line to the radiator 11, "see Fig. 3.

The area of the radial extension -l3 is not necessarily critical as long as its area is sufiicient toform an adequate support'for plate 10, and as'lon'g as itprovides a ground plane surface surrounding 'the radiator sufiici'ent to enclose the immediate area'between theparabolic members to prevent radiation leakage below the radiator. The parabolic members'9 are ultimately secured to the radial extension 13 of the outer conductor member embodiment, angles of intersection of the two parabolic members in the neighborhood of degrees gave the optimum patterns desired. These angles are not to be considered critical, however, as any anglebetween 4510 degrees may be used taking into consideration that an increase in the angle above the range of 90 degrees may be expected to give a broader beam in the horizontal azimuth accompanied with less gain, and a decrease in the angle willgive a narrower beam with an increase-in the side lobes. For the 90 degrees corner angle used in the. preferred embodiment, the best efiiciency was obtained by a horizontal aperture distanceD of 3.1 wave lengths and a vertical height of the parabolic members H, see

Fig. 3, above the ground plane of 2.21 wave lengths. It is readily apparent that in'regard to the size of the specific embodiment, with any increase in the frequencyof the wave radiated there should be a corresponding increase or decrease in the overall dimensions of the unit to-get the optimum pattern.

It is emphasized at this point that to enable theinvention to be fully understood and carried into practical effect without difficulty, the parameters of the components shown in Figs. 1 through 4- and material to this invention,

by wayof example only, may have the'parametersgiven either above orsubsequently inthe disclosure.

Radiator 11, in thepreferredembodiment, is'of the "monopole type,:however, it may -be any-of the types known in the art such as a dipole'or the like. 'It is insulated from the-ground plane =13,-and'is spaced above it (see 'Fig. 3). The degree of spacing'of the radiator above the ground plane is generally determinable as being that height at which the optimum impedance matchingis obtained. In the specific embodiment the height of the phase center of the radiator above 'theground'plane-is of the orderof one'tenth of a wavelength an'd the top-of the radiator is ofthe order of one fifth of a wavelength. The

75 radiatons'height can be varied verticallytoobtainthe optimum impedance matching and small movements in this regard will not appreciably affect the pattern.

The radiators horizontal position with respect to the two parabolic members is on a line that bisects the angle of intersection of the members. It is spaced, in the preferred embodiment, .7 of a wave length from the corner of the reflector. This spacing gave the optimum pattern for the parameters used in the preferred embodiment.

The straps 16, Figs. 1 and 2, form an extension of plate and project from the bottom edge of the parabolic members; midway their length. The straps have no effect on the pattern in and of themselves but merely provide a slot 17 lying on and parallel to the line bisecting the cornerangle for positioning the parasitic director 12. The director is manipulated in the slot experimentally to a position giving the preferred pattern characteristic desired. The director 12 serves a useful adjunct to the antenna as it increases gain and decreases the side lobes. In the specific embodiment the director is located horizontally .6 of a wave length from the radiator and 1.3 wave lengths from the corner of the reflector. The optimum approximate height of the director in the preferred embodiment with respect to the ground plane is .39 of a wave length. The director can either be electrically connected to the outer conductor, as in the specific embodiment, or it can be insulated therefrom or suspended in space with respect thereto. The same pattern will result regardless of the method of support adopted. However, if the director is suspended or insulated, then a slight adjustment in its position relative to the radiator and reflector is necessary to obtain the optimum pattern. This adjustment is necessary to compensate for the capacitance effect that would arise. With the addition of the parasitic director 12 to the antenna, the phase center of the radiating elements is displaced to a point located between the radiator and the director.

The beam radiated from the preferred embodiment disclosed herein is tiltedupward 35 degrees from the horizontal. However, the pencil type beam radiated can be directed as desired with respect to the horizontal by manipulating the antenna unit itself. For example, if a beam parallel with the horizontal is desired, it may be obtained by merely tilting the antenna and thus the ground plane to an angle of 30 degrees with the horizontal.

The directional characteristics obtainable with the parabolic corner reflector are illustrated graphically in.

sent the characteristics of the beam wave in the azimuth plane for three frequencies, 8500 mc., 8950 mc., and 9400 mc. Each curve has approximately the same directional characteristic (23 degree azimuth beam width for 3 db down) but the curve obtained with a frequency of 8950 me. had the lowest side lobes (37 db down which is very good). It is apparent that for the parameters of the preferred embodiment, a frequency in the neighborhood of 8900 me. is the optimum radiation frequency. However, the curves in Figs. 5 and 7 illustrate that the parabolic corner reflector has flexibility with respect to the desirable beam characteristics obtained, thus facilitating the use of frequencies other than but near the optimum for a fixed set of parameters.

Fig. 8 illustrates graphically the beam pattern characteristics in elevation for a transmitting frequency of 8800 me. For 3 db down, a 27 degree vertical beam is obtained. The first degree side lobe for the vertical beam on the lower side of the beam is 14 db down, but the side lobes on the top of the beam are 33.5 db down. As the top of the vertical beam is the side of most importance, the overall vertical characteristic is very good. Generally the vertical width of the beam can be increased or decreased by increasing or decreasing the height of the parabolic members above the ground plane.

It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes 0f the disclosure, which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. An antenna having, in combination, a reflector means for transmitting or receiving directional high frequency waves including two parabolic members comprising two symmetrical segments of a parabolic cylinder intersecting a vertical plane at an angle of less than 180 on symmetrical contours to form a corner reflector, and a radiator whose axis is perpendicular to the focal lines of the parabolic segments for radiating high frequency waves and feeding said reflector means in a manner facilitating a high gain directional beam being radiated from said antenna.

2. An antenna having, in combination, reflector means for receiving or transmitting high frequency waves including two parabolic members, said parabolic members comprising two symmetrical segments of a parabolic cylinder intersecting in a vertical plane at an angle of less than 180 on symmetrical contours to form a corner reflector, and a radiator whose axis is perpendicular to the focal lines of the parabolic segments for radiating high frequency waves and feeding said reflector in a manner that a high gain directional beam is radiated from said antenna, and a ground plane means for opposing radiation leakage below the bottom edge of said parabolic members.

3. A corner antenna having, in combination, two parabolic members comprising two symmetrical segments of a parabolic cylinder intersecting at an angle less than 180 in a vertical plane on symmetrical contours to form a corner reflector and having'concave surfaces that are adjacent, means for radiating high frequency waves and feeding said parabolic members, said means including a radiator located between said members intermediate the vertex and aperture of said corner reflector said radiator being entirely disposed in a vertical plane a distance from the bottom edge of said members and below the top edge of said members.

4. An antenna for receiving or transmitting a predetermined high frequency wave comprising reflector means including two parabolic members formed by two symmetrical segments of a parabolic cylinder, said parabolic members being substantially joined at an angle to provide a corner reflector of approximately degrees having adjacent concave surfaces to provide an aperture width 3.1 times the wave length of said predetermined high frequency wave, means for radiating high frequency waves and feeding said reflector, said last named means including a radiator located between said members in a manner that said antenna radiates a high gain directional beam, said last named means also including ground plane means positioned below the edge of said parabolic members and in close proximity thereto for opposing radiation leakage below saidparabolic members.

5. A corner antenna for receiving or transmitting a predetermined high frequency wave comprising two parabolic members formed from two symmetrical segments of a parabolic cylinder positioned in close proximity to provide a corner reflector, each said parabolic member having a focal line, said focal lines lying in the same plane and intersecting at a focal point between said parabolic members, ground plane means positioned below said parabolic members and in close proximity thereto for opposing radiation leakage below the bottom of said parabolic members, the heighth of the top of said parabolic members above said ground plane being 2.21 times the wave length of said predetermined high frequency wave and electromagnetic radiator means located on a line bisecting the angle between said members and positioned at a height relative to the ground plane that gives the best impedance matching.

6. A corner reflector antenna comprising two symmetrical segments of a parabolic cylinder intersecting at an angle less than 180 in a vertical plane on symmetrical contours to form a corner reflector having adjacent concave surface members, radiator means for feeding said reflector located between said members a distance from the intersection of said members that is less than the length of one of the members and spaced vertically from the bottom of said members a distance that allows the best impedance matching, vertical feed supply means adapted to feed said radiator means having an inner and outer conductor, said inner conductor connected to said radiator'means and said outer conductor connected to said members.

7. The combination of claim 6 wherein said outer conductor forms a means for opposing radiation leakage below said members in the immediate space therebetween. v 8. The combination of claim 6 including a parasitic director positioned a greater distance from the intersection of said members than said distance to said radiator.

9. A reflector adapted to receive and transmit high frequency waves, said reflector including two parabolic members formed from two symmetrical segments of a parabolic cylinder and aligned at an angle less than 180 in amanner that one corner end of one of said members is in close proximity with one corner end of the other of said members, said parabolic members each having a focal line, said focal lines intersecting at a focal point, said focal point lying in a plane that bisects said predetermined angle and is located a distance from said corner ends that is less than the length of one of said members.

I 10. A reflector adapted to receive or transmit high frequency waves having two parabolic members comprising two symmetrical segments of a parabolic cylinder substantially joined at an angle that is substantially normal and having concave surfaces that are adjacent, each of said members having a focal line and said focal lines lying in the same plane.

11. In an antenna, a reflector adapted to receive and transmit high frequency waves including two symmetrical sections ofa parabolic cylinder connected along their base lines to a ground plate, said parabolic sections aligned at a predetermined angle in a manner that one end of one of said sections is in close proximity with one end of the other of said section, each of said parabolic sections having a focal line, said focal lines lying in the ground plane and intersecting at a point between said members on a line bisecting said predetermined angle.

12. A corner reflector antenna for receiving or transmitting a selected high frequency wave comprising two symmetrical segments of a parabolic cylinder intersecting at an angle less than in a vertical plane to form a corner reflector, a ground plane, said reflector being attached to said ground plane, the aperture distance of said reflector being 3.1 times the wave length of. said selected high frequency wave, and the heighth of the seg ments above the ground plane being 2.21 times said wave length, and means for radiating high frequency waves and feeding said reflector.

References, Cited in the file of this patent UNITED STATES PATENTS 2,054,896 Dallenbach Sept. 22, 1936 2,408,373 Chu Oct. 1, 1946 2,421,593 Bishop June 3, 1947 2,421,988 Brown et al June 10, 1947 2,430,568 Hershberger Nov. 11, 1947 2,473,421 Fubini etal June 14, 1949 2,745,102 Norgorden May 8, 1956 FOREIGN PATENTS 436,355 Great Britain Oct. 9, 1935

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