US2973518A - Corner reflector antenna - Google Patents

Description

Feb. 28, 1961 J. H. JENSEN CORNER REFLECTOR ANTENNA 3 Sheets-Sheet 1 Filed Sept. 25, 1957 INVENTOR. JACK H. JENSEN ATTORNEYS Feb. 28, 1961 J. JENSEN CORNER REFLECTOR ANTENNA 3 Sheets-Sheet 2 Filed Sept. 25, 1957 Fig. 6

IN V EN TOR.

s 5 Y m f J .M H In W 4 M Feb. 28, 1961 J. H. JENSEN 2,973,518

CORNER REFLECTOR ANTENNA Filed Sept. 25, 1957 5 Sheets-Sheet S VERTICAL PATTERN HORIZONTAL PATTERN INVENTOR. J4 CK H. JENSEN CORNER REFLECTOR ANTENNA Jack H. Jensen, 333 Westwind Drive, San Diego, Calif.

Filed Sept. 25, 1957, Ser. No. 686,266

6 Claims. (Cl. 343-837) (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. 4

The present invention relates to a corner reflector antenna and more particularly to an improved corner reflector antenna for radiating a directional type beam having a controllable beam tile.

My co-pending application Serial No. 649,576, filed March 29, 1957, now Patent No. 2,926,349 issued February 23, 1960, discloses a corner reflector antenna for radiating a directional type radar beam of an approximate 35 elevation. In using this antenna where a horizontal type beam is desired, it is necessary to tilt the whole antenna structure forward to an angle of an approximate 35. It is readily apparent that in many uses of the corner antenna, an antenna capable of being mounted in a horizontal position and yet radiate a horizontal beam is desirable. This is especially true when the antenna is mounted upon a rotatable pedestal.

The present invention is an improvement upon my prior corner reflector antenna in that it provides structural improvements which allow the antenna to project a directional type beam in a horizontal direction when the antenna is mounted upon a pedestal in a horizontal position, and further the invention permits the tilt of the directional beam to be selectively varied.

An object of the present invention is the provision of a corner reflector antenna having a directional type beam radiated in a horizontal direction relative to its finite ground plane.

Another object is to provide a corner reflector antenna with a beam having selective elevations.

A further object of the invention is the provision of a corner reflector antenna that radiates a directional type beam stabilized in a horizontal direction relative to its finite ground plane over a desired range of frequencies.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

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

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

Fig. 3 shows a top plan view of the antenna with the reflector unit removed;

Fig. 4 shows a section of the antenna and pedestal with the reflector unit removed taken on line 4-4 of Fig. 3 looking in the direction of the arrows;

Fig.5 is a diagrammatical end view of a parabolic cylinder illustrating that part of the cylinder from which Patented Feb. 28, 1961 ice Fig. 8 illustrates graphically the characteristics of the directional beam in the horizontal azimuth.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. l a parabolic corner reflector antenna 9 mounted on a swivel topped pedestal 18. The reflector portion of the antenna has two parabolic members 10 joined at substantially a angle by soldering or the like and Secured to plate 13 in a similar manner. Plate 13 provides added structural strength to the parabolic members in their mounted position, provides a horizontal attaching means for securing the members to the pedestal 18 and also cooperates with reflecting surfaces 23 in radiating and receiving radar energy. It is within the scope of the invention to not join the parabolic members together as shownin Figs. 1 and 2. The members may be separated at the corner of intersection as long as they are held at substantially a right angle and the corner ends positioned in close proximity. The allowable separation between the ends depends upon the parameters of the antenna and the effect the degree of separation has on the pattern. This latter elfect may be determined by experiment and it was found that the pattern characteristic became less desirable as the separation at the corner was increased. This result is evident as there will be radiation leakage through the gap causing increased losses to the rear of the antenna. I

Parabolic members 10 are symmetrical sections of a parabolic cylinder partially illustrated schematically in Fig. 5 as line 27. The cylinder section has the usual curvature formula of y equals 4fx, for the Origin at the vertex. The cylinders focal line 28 lies on the parabolas axis line 29. Parabolic member 10 used in the reflector array was removed from cylinder 27 as shown with its lower edge at the center point 30* of the parabolic cylinder. The members may be constructed of aluminum or the like or by light-weight fabrication techniques such as rodded construction or fiber glass honey-comb construction with important parts metal sprayed.

Plate 13 has a forward part 14 (see Figs. 1 and 2) that for-ms the sole of the reflecting unit. Sole 14 has a lip 15 that is downwardly inclined at an acute angle and has an arcuate edge, the radius of which generally extends from the radiator. The purpose of sole 14 and lip 15 will be explained in detail later.

Referring to Fig.4 ground plane member 12 is a radial extension of the outer conductor member 21 of the coaxial line that feeds high frequency current to radiator 11, and is supported at its outer edge by shoulder 33 of cylindrical member 30. The surface area of the ground plane member 12 is not critical as long as its area is suflicient to form an adequate support for ring 17 and the reflecting unit, and as long as it provides a ground plane surface surrounding radiator 11 that is sufiicient to close the immediate area between the parabolic members and thus reduce radiation leakage below the radiator. A circular bearing member 25 is attached to the upper and outer portion of cylinder 30 and supports rim structure 26 for free rotational movement relative to the cylinder 30 and ground plane member 12.

Ring 17 is mounted on rim 26 by means of screws as shown in Fig. 4. Plate 13 and sole 14 are fixed to ring 17 in a similar manner. This structural arrangement permits rotational movement by the reflector unit on pedestal 18. Ring 17 is spaced from the ground plane member 12 at points where the ring 17 overlaps the ground plane 12 such as at 31 in Fig. 4. For reasons to be explained in detail later, a capacitive effect between ring 17 and ground plane member 12 is necessary to the operation of the antenna. In the specific embodiment this capacitive effect is provided by the space between rim 26 and side in the following manner.

member 30 through bearing 25. Rim 26 is electrically connected to ring 17 and side member 30 is directly connected electrically to the ground plane member. Should the rotational feature of the antenna-pedestal combination not be desired, the hearing may be omitted and rim 26 and ground plane member 12 made integral. The required capacitive effect can then be provided by a thin layer of insulation between rim 26 and ring 17.

Radiator 11, in the preferred embodiment, is of the fat-door-knob monopole type. However, it may be one of other suitable types known in the art. It is insulated from the ground plane member 12 and spaced above it, see Fig. 4, an amount dependent upon the height at which optimum impedance matching is obtained. Once optimum impedance matching is obtained, small movement of the radiator vertically will not appreciably affect the pattern. The radiator is positioned horizontally between the parabolic members on a line bisecting the angle of intersection of the members.

Sole 14 and its lip 15 serve in the antenna structure as the finite ground plane which lowers the tilt of the beam radiated from the antenna unit to a horizontal direction If a flat, finite ground plane is used without a lip portion, high frequency waves radiated from the radiator and reflectors will travel along the upper surface of the finite ground plane. Upon reaching the outer edge of the finite ground plane a portion of the radiated waves will encompass the edge thereof and cause high frequency waves to travel in a direction toward the radiator and reflectors via the under surface of the finite ground plane. The action of the radiated waves in encircling the finite ground planes edge results in a cancellation effect on that portion of the total radiated beam that is immediately adjacent the upper surface of the finite ground plane. This cancellation effect creates an effective beam that is tilted upwardly relative to the finite ground plane. For example, in my co-pending application, there is disclosed therein an antenna utilizing a flat, finite ground plane without a lip portion that transmits a pencil type beam tilted upwardly 35 relative to the ground plane.

The addition of lip 15 to sole 14 transfers the rolling over the edge effect of the radiated waves from the sole member to the edge of the lip portion. Thus the lip portion functions as the edge portion of finite ground plane in this circumstance and the beam is tilted upwardly from the lip portion rather than from sole 14. Inasmuch as the lip portion is angled downwardly relative to the sole,

the resultant radiated beam is projected in a direction horizontal to the fiat surface portion'of sole 14.

In operation of the antenna, a change in frequency'of the radiated waves will cause a change in the tilt of the beam. To provide increased stability of the beam tilt and allow a broader range of frequencies to be transmitted, ring 17 was incorporated into the antenna structure.

Ring 17 is spaced from the ground plane member 12 providing a capacitive eflect therebetween. This capacitive effect is obtained in the specific embodiment by adjacent positioning of ring 17 and ground plane member 12 as at 31 in Fig. 4, and the spacing between members in ring bearings 25. The spacing of elements 12 and 17 through bearing 25 forms an RF choke joint, which prevents ring 17 from being electrically shorted to ground plane member 12. The impedance presented by this arrangement varies due to the varying width of ring 17. The exact theory of operation is not entirely understood. The capacitive effect plus the spacing of plate 13 of the radiating unit from the ground plane member 12 by ring 17, functions to correlate the phase of the current passing from the outer conductor 21 to the reflecting members and to sole 14 and lip 15.

Ring 17, see Fig. 3, is asymmetrical having a circular outer edge with an off-set circularhole 32 therein. The off-set center space allows one side A to be of greater width than the opposite side 13. The wider portion A 4 may be positioned on either the front or rear side of the reflector unit depending upon the parameters of the reflecting units used. In the specific embodiment side A is positioned on the rear side of the antenna.

The radiated r-adar beam may be maintained steadily in a horizontal position or it may be selectively raised or lowered through movement of the ring or parts thereof. Disk 17 is electrically connected to the reflector unit and while it may be fixed thereto or made integral therewith in a position that will hold the beam tilt to a horizontal position; to facilitate selective raising or lowering the tilt of the beam, the disk can also be made slidable relative to the reflector unit. This latter construction allows the ring to be moved forwardly or rearwardly relative to the reflecting unit and pedestal, causing a regulated lowering or raising of the beam tilt.

An alternative method of controlling the beam is to slidably move only a section 24 from ring 17, as shown in Fig. 6. In this manner the main body of ring 17 may be permanently secured to the antenna structure and the lowering or raising of the beam accomplished by sliding section 24 toward or away from the radiator 11.

Ring 17 may be considered a vernier to the sole 14 and its lip 15 in controlling the tilt of the beam and stabilizing it. Also the V-shaped space 22 (see Figs. 1- and 2) between the upper edges of the parabolic members functions to stabilize the beam as a further impedance mis-match correction factor.

Slot 19 in sole 14 has no effect on the pattern but merely provides means for variably positioning parasitic director 16. The director is moved in the slot experimentally to a position giving the pattern characteristic desired. It serves a useful adjunct to the antenna as it increases gain and decreases the side lobes and may be either electrically connected to the outer conductor, as in the specific embodiment, or it may 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 com pensate for the capacitance effect that would arise.

The directional characteristic obtainable with the parabolic corner reflector of this invention are illustrated graphically in Figs. 6 and 7. These curves represent the characteristics of the beam wave in vertical and horizontal azimuth plane for a frequency of 8800 me. and illustrate the pencil type beam obtained.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In an antenna, reflector means for transmitting or receiving directional high frequency waves including two parabolic members aligned in substantially a V-shape and finite ground plane means positioned between said members at their bottom edges for radiating and receiving said waves in coordination with said parabolic members, other ground plane means positioned in reactive relationship with said finite ground plane means for opposing radiation leakage below the bottom of said parabolic members.

2. In an antenna, reflector means for transmitting or receiving a directional high frequency beam including two parabolic members aligned in substantially a V-shape, ground plane means positioned below said parabolic members, said reflector means having finite ground plane means positioned between-said members at their bottom edges for projecting said radiated beam in a direction horizontal to said finite ground plane means and said ground plane means and reactive means positioned between said finite ground plane means and said ground plane means for stabilizing said beam in said horizontal direction.

3. The combination of claim 2, wherein said reactive means comprises a ring member electrically connected to said parabolic members and said finite ground plane means and spaced from said ground plane means giving a capacitive efiect therebetween.

4. In the combination of claim 3, wherein said ring member includes a removable section for selectively varying the elevational tilt of said beam relative to said finite ground plane means and said ground plane means, said section being slidable relative to said finite ground plane means and said ground plane means whereby said reactive efiect is variable.

5. In an antenna, reflector means for transmitting or receiving a directional high frequency beam including two parabolic members aligned in substantially a V-shape, ground plane means positioned below said parabolic members, said reflector means having finite ground plane means positioned between said members at their bottom edges for projecting said radiated beam horizontally to said finite ground plane means and conductive ring slidably positioned between said finite ground plane means and said ground plane means for selectively varying the elevational tilt of said beam, said conductive ring being electrically connected to said parabolic members and said finite ground plane means and spaced from said ground plane means permitting a capacitive effect therebetween.

6. In an antenna, reflector means for transmitting or receiving a directional high frequency beam including two parabolic members aligned in substantially a V-shape and finite ground plane means positioned between said conductive ring positioned between said finite ground plane means and said ground plane means and encircling said radiator, said conductive ring being electrically connected to said parabolic members and said finite ground plane means and spaced from said other ground plane means permitting a capacitive effect therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 1,781,046 Bethenod Jan. 23, 1934 1,944,563 Kruesi Jan. 23, 1934 2,408,373 Chu Oct. 1, 1946 2,421,988 Brown June 10, 1947 2,436,408 Tawney Feb. 24, 1948 2,534,710 Golian et a1 Dec. 19, 1950 2,567,746 Van Atta Sept. 11, 1951 2,594,871 Chu et al Apr. 29, 1952 2,600,274 Sichak June 10, 1952 2,615,132 Rumsey Oct. 21, 1952 2,836,820 Pickles et al May 27, 1958 FOREIGN PATENTS 522,682 Germany Apr. 13, 1931 OTHER REFERENCES Antennas, by Kraus, copyright 1950, page 338.

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